- Email: [email protected]
Immunity to protozoa
Immunity 1. H. Laboratory
of Parasitic Diseases,
Miller
to protozoa and P. Scott*
National Institute
of Allergy
and Infectious
Diseases,
National Institute of Health, Bethesda, Maryland 20892, USA, and *Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, USA Current
Opinion
in Immunology
the sequence of one of these was completely different from sequences taken from ramjomly collected isolates. In addition to the obvious problem for developing a vaccine to P. vivax, this also creates problems for the use of monoclonal antibodies to the repeats, for mosquito vector incrimination, and for linding the frequency of in fected parasites in the population. An alternative method, the use of DNA probes to 5s ribosomal RNA, has been described recently [2 ] .
Malaria IlllISt be Wih.l~ted for tYdCh Stage Ill blNTlUnit)r10 IXh-id the organism’ s life cycle as the location of the intracellular parasite dictates the range of possible immune responses and the mechanisms for immune evasion. The extracellular parasites (sporozoites and merozoites in the mam malian host and gametes and ookinetes in the mosquito midgut) present a common target to antibody-mediated mechanisms, although each has, in most cases, stage-speciftc antigens.
Pre-etythrocytic
1990, 2:368-374
NO variations have so far been found in the repeat doThe god here main of the CS protein of P. falc@arum has been to produce an antibody using the repeat (B-cell epitope) connected to a T-cell epitope derived from the native protein or from a foreign carrier. Using vari0U.S carriers as T-cell epitopes, the antibody response in humans has been poor. One explanation of the poor response of humans to (NANP), conjugated to tetanus toxoid (‘IT) was that the previous immur&ation with IT caused epitope suppression. All strains of mice tested responded to vaccination with ‘IT-(NANP), in ahtminium hydroxide [3]. Indeed, preimmunization with ‘IT reduced the anti-NANP response to subsequent immunization with However, a study in the previous year, by TI_(NANP) Lise et al. CY Infect Immun 1987, 55:2658-26611, found instead that preimmunization with IT enhanced the response to TT-(NANP)4. Despite these contradictory results in mice, the challenge remains to produce high, persistent anti-(NANP), titers in humans and to determine its protective effect against sporozoite challenge. One approach has been to develop carriers other than ?T [41, but again, the test of efficacy must be in humans, not tabbits.
stage
Infection begins in humans when sporozoites are inoc ulated by the mosquito and circulate for several minutes before they are cleared by the liver. The parasite invades hepatic parenchymal cells where it matures over 2 days in the case of rodent malarias and over 7 or more days in primate malarias. The unresolved question of whether the parasite passes through fenestrations or through endothelial or Kupffer cells will determine other potential targets. In the 197Os, Nussenzweig and her colleagues deftned antibody-mediated mechanisms of immunity to sporozoites and, in the 1980s the circumsporozoite (CS) protein which covers the sporozoite surface was defined as the target for this immunity. The protein has a number of clearly defined domains, including regions I and II which are probably involved in attachment, and the central third that consists of repeated amino-acid sequences. These central repeats are the major target for protective monoclonal antibodies. Thus, one of the aims in producing a vaccine to prevent infection was to induce antibodies to the central repeats of Phsmodium falciparum and Pkzimodium vivax. For this approach to work, the central repeat of each species must be the same. In P. vivax, this has been found not to be the case [ 1I. Mosquitoes were fed on Waxinfected humans, and the sporozoites analysed for reactivity to monoclonal antibodies against the repeat domain. Fourteen per cent did not respond;
T-cell epitopes from the native CS protein of P. fakiparum have been defined previously by Good et al. (lmmund Today 1988, 9351-355). The DNA sequences of the CS proteins from multiple clones indicate that some T-cell epitopes are in variant regions; others are invariam [ 51. Immunization with a variant region demonstrates that there is no cross-reactive response to other variants [(;I, indicating the importance of the amino-acid variation in the immune response. The value of the B-cell epitope, -I
Abbreviations CS-circumsporozoite; CT1 cytotoxlc T lymphocyte; CM-CSF--granulocyte,macrophage colony-stlmulatlng factor; Hi-A-human leukocyte antigen; IFK -interferon; Il.--- interleukin; l_P?-lipopolysaccharide; RESA-ring-Infected erythrocyte surface antigen; TN---Thelper: TNF-tumor necrosis factor: n--tetanus toxoid.
@ Current
Science
Ltd ISSN 0952-7915
immunity to protozoa Miller and Scott
combined with an invariant T-cell epitope, in boosting the response during exposure to natural infection, remains to be determined. The importance of CD8+ T cells in immunity to sporozoite challenge has previously been shown in animals that were immunized by irradiated sporozoites and CD8-depleted before challenge. The important questions include which cell expresses the epitope (probably the liver cell), which parasite protein contains the cytotoxic T lymphocyte (CTL) epitope, the variability of this epitope, the genetic restriction of response to the liver stage proteins, and the mechanism for immunizing humans. It should be remembered that CD8+ T cells are not long-lived. Irfection time may not be long enough to boost the response unless the immunization was performed immediately before exposure, or unless special mechanisms are developed to attenuate the response. A CTL epitope has been identifiti on the falciparum CS protein but, unfortunately, it is within one of the variant regions of the CS protein and the response to that epitope is restricted [7]. CD8+ (CTL) clones were made to a peptide in the CS protein that was recognized by CTL induced by immunization by irradiated sporozoites [8]. The clones transferred protection against challenge with Plasmodium bergbeisporozoites. The mechanism of parasite killing remains unknown [direct cytotoxicity or in terferon (IFN)*I] . Immunization of congenic mice with irradiated sporozoites of P. be@ei led to protection in all strains [9]. It had been shown previously in one strain of mouse that protection was both antibody-dependent and CD8+ T-cell-dependent. The question of whether the immunity in congenic mice, induced by ~mmunization with irradiated sporozoites, is CD8+ T celldependent, remains to be determined. An in vitro assay was developed to study CD8+ T cells against infected hepatocytes [lo]. The development of parasites in hepatocytes is inhibited by CD8+ T cells in a genetically restricted manner. Anti-IFNy did not inhibit the activity of CD8+ T cells against infected hepatocytes, suggesting that these cells have a direct cytotoxic effect. Asexual erythrocytic parasites
One of the recurring themes in the malarial literature is that malarial infection in some way suppresses the im mune response. Studies in Gambian children [ 111 and in Thai adults [12] found that their response to malarial antigens during acute infection was limited. However, during convalescence, the Thai adults responded but 50% of the African children did not. The inability to proliferate was not restored by the addition of interleukin (IL)1 or IL-2 to the cultures injected with malarial antigens. No IL-2 receptors appeared on the T cells as a result of acute infections during stimulation with malarial antigen. One problem in evaluating the significance of these findings in acute malaria is that any previous exposure to malaria is unknown and lymphocytes in other locations than peripheral blood (e.g., the spleen) are inaccessible. One interesting fInding in the Thai study was that circulating IL-2 receptors were present during acute infection, Intravenous injection of soluble malarial antigen into the
mouse has been shown to suppress delayed-type hypersensitivity to the antigen [ 131. The suppression was mediated by CD8+ T cells. In the 197Os, Mackaness et al (j Exp Med 1974,139:528542) found a similar suppression after intravenous injection of heterologous erythrocytes. One potential mechanism for immune evasion is antigenie diversity (variation among clones, polymorphism) and antigenic variation (variation within a clone). The polymorphisms of GP195 and the S antigens, for exam ple, have been studied previously at the antigenic and molecular level. The S antigens were found to vary be tween areas at any particular time and within an area at different times [ 141. The degree of variability of the S antigen indicates that this molecule has an important function. Its expression around the time of merozoite release suggests a role in invasion, but, like GP195, its exact function is unknown. The importance of cell-mediated immunity in some rodent malarias has been beautifully demonstrated by Grun This has been and Weidunz (Nature 1981,290:143-145). extended recently in the Pkzsmodium vincketimouse systern where solid immunity induced by repeated infection and cure has been shown to be antibody independent and to require both CD4+ T cells and an intact spleen [ 151. Naive mice that have received immune CD4+ T cells are fully susceptible to lethal P. vinckei infection, indicating that CD4+ T cells are necessary but not sulhcient for immunity and that a change in spleen is also required. It is assumed that the effector mechanism in cell mediated immunity is non-specific. However, Jarra and Brown [ 161 found that during crisis (the period of rapid decrease in parasitemia) in Plasmodium cbabaudi, the effect appeared to be strain-specific. They suggested that the effector mechanism was specific, but they did not induce crisis against the second strain or test its effect against the first strain. It is possible that one strain is more resistant to the crisis killing mechanism than the other strain. Alternatively, crisis, in some situations, has a spe cilic mechanism which has not yet been elucidated. A vaccine to the asexual erythrocytic parasite should induce protective immunity that can be boosted during natural infection. Cellular immunity and antibody-mediated immunity both require CD4+ T cells that will be boosted upon exposure to the parasite. This means that the irvariant or minimally variant regions that are encountered by a high proportion of the population who have been immunized need to be identified. Because the human leukocyte antigen (HIA) types of populations may vary, the epitopes used in an immunogen may not be identical from one area to another. It will probably be necessary to include multiple epitopes from any one protein to be sure of covering all of the epitopes encountered by the entire population. The important work of delining T-cell epitopes on two potential vaccine candidates has begun. In one approach, T-cell clones to recombinant peptides were produced from the major glycoprotein on the merozoite of P. falciparum, GP195. The epitopes on these clones were mapped to part of the Nterminal region of the protein [17]. There was minimal variation within these peptides among falciparum clones.
369
370
Immunity to infection
More important, the T-cell clones proliferated on exposure to all falciparum parasites studied. We await with interest the results of the T-cell proliferation in lymphocytes from endemic populations using these epitopes. An alternative approach has been the study of the T-cell response to peptides from the Pfl55/ring-infected erythrocyte surface antigen (RESA) of P. falciparum in endemic populations [18]. This protein contains two regions of repeated amino-acid sequences. Many of the T-cell responses map to the C-terminal repeats, which are invari ant regions of the protein. The T-cell response was evauated by both lymphocyte proliferation and the produc tion of IFNy. The finding that the results of the two tests for T cells did not correlate in individual donors ma) have some, as yet undefined, significance. Further shtdies on the T-cell epitopes of PfI55/RESA demonstrate that Melanesians respond to the N-terminal repeat in the same way as African populations and that non-repeat regions also contain T-cell epitopes [ 191. Previously, Deans et al. (Mol Biocbem Parasitol 1984, 13:187-199) have shown that a monoclonal antibody to a 66 kD protein of Plasmodium knowlesi blocks invasion and that Fab fragments of the monoclonal antibody block invasion more effectively than the whole immunoglobulin. Monkeys have now been immunized with the punlied protein [ 201. Knowlesi malaria is an invariably fatal disease; one out of three immunized monkeys were able to control the infection. The other two required chemotherapy because the infections were following a virulent course. On rechallenge, however, the three monkeys were highly immune. The immunization did not select mutants that were resistant to reinfection, as parasites from the recrudescent parasitemia still expressed the target of the blocking monoclonal antibody. Cerebral malaria occurs in P. berg&$ is associated with macrophages in the cerebral vessels and can be blocked by anti-I.FNy and anti-tumor necrosis factor (TNF). Grau et al. [21] have now followed up this study by measuring TNF in children with severe malaria, including cerebral malaria. Severe malaria and high mortality were as sociated with elevated levels of TNF. It is still not known whether elevated levels of TNF are involved in the pathology or whether anti-TNF will affect survival in these chidren. Clinical trials similar to those underway in septic shock will be needed to clarify these issues. It has been observed that the course of fever following rupture of malaria-infected erythrocytes resembles the fever that follows endotoxin. Bate et al. [22] have now shown that soluble malarial antigens can induce TNF. It is important to note that there was no evidence of contamina~ tion with lipopolysaccharide (LPS) in the malarial preparation. Since TNF can cause fever, is it possible that Bate et al. have begun the isolation of the factor responsible for fever in malaria. Transmission-blocking
immunity
The epidemiology of P. uivax is influenced by the boost mg of antibodies that block transmission [ 231. Thus, if a patient is reinfected or recrudesces within 4 months of a previous attack, the infectivity to mosquitoes is reduced.
Leishmania,
Toxoplasma,
and Trypanosoma
cruzi T-cell subsets regulating protozoa1 immunity
One of the major immunological advances in protozoal immunity over the last year has been the increase in our understanding of the role of CD4+ and CD8+ cells in regulating diseases and, in particular, of the importance of CD4 + T-cell subsets Some of these results have been discussed above in the context of malaria, but advances in the field of leishmanial immunity may provide the best example of the regulatory influence of different CD4+ T-cell subsets in immunity. It is generally agreed that in leishmaniasis the primary lymphocyte regulating immunity in cutaneous leishmaniasis is the CD4 + T cell. Thus, CD4 + cells have been shown to act as either effector cells promoting resistance, or as cells that promote susceptibility. The fact that CD4+ cells could mediate both of these effects has lead to some confusion in our understanding of immunity in leishmaniasis. However, during the last year a major advance in this field has occurred, which is based upon the recent demonstration that CD4+ T-cell clones can be separated into two subsets, depending on the lym phokines they produce following stimulation (Mosmann et al., JImmunoll986,136:234%2357). One subset, designated T helper (TH)l, produces IL-2 and IFNy, while the other subset, designated Tn2, produces IL-4 and IL5. Several other lymphokines, such as IL-3 and granulocyte/macrophage colony-stimulating factor (GM-CSF), appear to be produced by both celI subsets, although in some cases in different quantities. Because of the different lymphokines that they produce, TH1 and Tn2 clones have different functions. For example, Trill cells have been shown to mediate delayed hypersensitivity reactions, while Tn2 cells act as helper cells for specific an tibody production. In leishmaniasis, a strong correlation between delayed hypersensitivity, IFNy production and healing has been shown, whereas high antibody production is associated with susceptibility. Thus, it could be that the CD4 + cells mediating resistance belong to the Tttl subset, while the cells mediating susceptibility belong to the T,2 subset. Heinzel et 61. [ 241 demonstrated clearly that a strong correlation exists between the production of lymphokines associated with Trill cells and resistance, while lymphokines associated with T,2 type cells predominated in susceptible mice. Thus, at present, the accumulated evidence suggests that two different Tcell subsets, Trill and T,2, mediate resistance and SW ceptibility in cutaneous leishmaniasis. In experimental toxoplasmosis, there are also conflicting results about the function of CD4+ cells in pathology and protection. Thus, it was shown that in vivo treatment with anti-CD4+ antisera decreased the inflammatory response to the parasite in the brains of mice infected with To.xopksmu [25]; this contrasts with a previous report that elimination of CD4+ cells exacerbates toxo plasmic encephalitis (Vollmer et al., J Immunol 1987, 138:3737-3741). Israelski et al. [ 251 argue that CD4 + depletion after infection leads to a non-random depletion
Immunity
of CD4+ cells, and that the treatment hzs an effect on the cells that mediate the inflammatory response but has little effect on the T cells mediating protection. Clearly, it would be useful if we could determine whether CD4+ T, subsets, such as Tnl and T,,Z, are involved to different degrees in these effects. Another major advance in our understanding of protozeal immunity has been the direct demonstration that CDB+ cells are important for protection. The best example may be in the field of malaria (which was discussed above). However, it has also been demonstrated that CDB+ cells are major effector cells of immunity in toxoplasmosis. Thus, it was shown by adoptive transfer experiments with cells from Toxqnlasma-immune mice, that both CD4 + and CDB+ cells mediate resistance [ 261. Depletion of CD8+ cells completely ablated the protec five effect of T-cell transfers, while depletion of CD4 $ cells partially removed the protective effects. It is not clear how CD8+ cells mediate protection. One likely mechanism is through the production of IFN?, which appears to be required for control of toxoplasmosis (discussed below). However, it has also been reported that CDB+ cells from Ta~@lasma-immunized mice are capable of direct parasiticidal activity directed against tachizoites [ 271, thus providing another potential mechanism by which CDB+ cells might provide protection. The participation of CD8+ cells in leishmaniasis has been more diEcult to define. Nevertheless, there is now convincing evidence that CDB+ cells also contribute to healing. The experiment that has been cited to demonstrate that CDB+ cells have a limited role in protection is one in which in vivo depletion of CDB+ cells in a mouse strain resistant to Letldmunia only delayed healing (Titus et al, Eur J ImmunoZl988,17:1429-1433). However, it has now been demonstrated that vaccine-induced in-munity in BALB/c mice may be more dependent upon CD8+ cells [28]. It has also been shown that anti-Ly2+ treatment completely ablates the protective immunity that is elicited in BALB/c mice by intravenous immunization with irradiated promastigotes [28]. It has also recently been suggested [29] that BALB/c mice rendered resistant by anti-WT4 treatment may require the presence of CDB+ cells to control parasite growth. Finally, in murine visceral leishmaniasis, depletion of either CD4+ or CDB+ cells inhibited protective immune responses, suggesting that both cell types are required for effective immunity 1301. These observations should generate considerable interest in the role played by CDB+ cells in promoting protection. Questions that will need to be addressed about CDS+ cells in parasite immunity include: (1) how do parasite antigens associate with class I molecules for presentation to CDB+ cells? and (2) how do CDB+ cells provide protection? Although these cells may be capable of cytotoxic activity, the production of IFNy may be a more important function.
Role of cytokines
in protozoa1
immunity
availability of recombinant lymphokines and monoclonal antibodies directed against these lymphokines has
The
to protozoa
Miller and Scott
led to a series of important experiments which help to elucidate the role of T-cell products in parasite immunity. For example, in leishmaniasis, the critical role of IFNy in protection was confirmed by the demonstration that in uivo depletion of IFNy with monoclonal antibodies leads to susceptibility to cutaneous leishmaniasis in a normally resistant mouse strain [31]. Similar experiments in which IFNy has been depleted in vivo in mice chromtally infected with Toxoplasma have also shown the importance of IFNy in controlling disease. Thus, IFNy depletion led to a significant inflammatoty response to Toxoplasma cysts in the brain [32]. The reciprocal experiment, in vivo administration of IFNy, resulted in protection against the acute phase of Typanosomu cruzzi infection [33]. In addition, Murray et al. [34] demonstrated the immunotherapeutic potential of IFNy in visceral leishmaniasis. Since Letimunia are obligate intra cellular parasites of macrophages and since macrophage activation appears to be the major effector mechanism controlling infection, these results are probably not surprising. They do not negate the fact, however, that other non-EN-I-mediated mechanisms of macrophage activation might also occur, as has been described by Wyler et al. (J Zmmunoll987,138:12461258). This group has characterized a mechanism of macrophage activation that appears not to require IFNy, but which does require contact. They recently demonstrated that this contact-medated killing was effective against a parasite strain which has previously been shown to be resistant to lymphokinemediated macrophage activation [ 351. In leishmaniasis, it has been shown that in vivo depletion of IL-4 reversed the extreme susceptibility of BALB/c mice to L, major [24]. The mechanism bywbich IL-4 promotes susceptibility is unknown. Although it has been postulated on the basis of the results of in vitro experiments, that IL-4 may down-modulate the ability of macrophages to respond to IFNy [36], it may not be the only lymphokine involved in susceptibility to leishmaniasis. It has also been clearly demonstrated that both IL-3 and GM-CSF can signikantly enhance the development of lesions in mice infected with L. major [37,38]. The mechanism by which these lymphokines augment lesion development is unclear, although it has been suggested that they may promote in&ration into lesions of macrophages in which the parasites can grow, but which are resistant to activation. Another interesting observation is the recent demonstration that L. mujor-infected BALB/c macrophages produce elevated levels of IL-1 [39]. Since it has been demonstrated that IL-1 is required for Tn2 T-cell clone proliferation, these results indicate a possible source of IL-1 in L. major-infected BALB/c mice. Vaccine development
One major area of immunological studies of protozoai infection is in the development of vaccines, One of the most important factors in defining a vaccine is the availability of experimental vaccine models. In Toxoplu.smu, a new model system for studying vaccine-induced imp munity was developed 1261 by infecting mice with a
371
372
Immunity
to infection
temperature-sensitive mutant which causes infection, but does not persist in the host. It was shown that such im munization leads to marked resistance to a challenge infection. The BALB/c mouse infected with various species of Lezkhmuniu continues to be the most commonly used vaccine model system for leishmaniasis. Several approaches have been used for defining which leishmanial antigens are responsible for inducing immunity. One approach has been to define potential vaccine candidate antigens using antibodies. Notably, within the last year, it has been demonstrated that a membrane glycoprotein of molecular weight 46kD, derived from Leisbmunia amzonensis using monoclonal antibodies, induces protective immunity in both a resistant mouse strain, and in the extremely susceptible BALB/c mouse [40]. Another approach to isolation of protective leishmanial antigens is the identification of antigens recognized by T cells. The success of this approach depends on the establishment of T-cell lines and clones that are capable of transferring protection. Such protective T-cell lines have been described in experimental visceral leishmaniasis; a T-cell line that protects against Lezlsbmunifz donozuni irktion in BALB/c mice was isolated from chronically infected animals following drug treatment [41]. These cells were WT4+ and produced IFNy, suggesting that they belonged to the TH1 subset. In contrast, a cell line that failed to produce EWy also failed to provide protection. The relationship between TH1 cells and protection, and TH2 cells and resistance, has also been directly demonstrated using T-cell lines. Thus, Scott et al. [42] demonstrated that a cell line recognizing a protective antigen derived from L major transferred protection to BALB/c mice and had the lymphokine profile of TH1 cells, while another Tcell line, which was shown to consist of TH2 cells, exacerbated subsequent infection following transfer to BALB/c mice. An interesting aspect of these studies was that certain leishmanial antigens appeared to stimulate one subset or the other preferentially. Protective T-cell clones are required for identification of particular leishmanial antigens that may be protec tive, and Muller and Louis [43] reported a T-cell clone that transfers protection against L major in the BALB/c mouse. An interesting aspect of these cells is that they could only be stimulated with live L mujor promastigotes, and that they failed to respond to killed promastigotes or any dead antigen preparation tested to date. The authors suggested that their results indicated that protec tive and non-protective T cells may respond to different antigens, as described above for T,l and TH2 cell lines. Another Lezkhnuniu T-cell clone has been described and, using T-cell immunoblotting, it was shown that the clone recognizes an antigen of molecular weight of approximately 10000 [44]. Most recently, this clone has been shown to transfer protection against L major in BALB/c mice 1441.
Annotated
references
and recommended
reading 0 a*
Of interest Of outstanding interest
1.
ROSENBERG R, WIRTZRA, L&NAR DE, SA’IXEIONGKOT J, HALLT,
??o
WATERSAP, PRASITI’ISUK C: Circumsporozoite
protein hetero-
geneity in the human malaria parasite Plasmodium vivax. Science 1989, 245973-976. Field isolates of vivax malaria had variations in the repeat region of the CS protein causing non-reactivity with the antiCS protein antibodies. WATERSAP, MCCLITCHAN TF: Rapid, sensitive diagnosis of malaria based on ribrosomal RNA Lancer 1989, 3:X%4%1345. The development of DNA probes to unique regions of the ribosomal genes that differentiate the 4 human malarias. 2.
.a
ETLINGER HM, HEIMEREP, TRZECMK A, FELIXAM, GIIBSEN D: Assessment in mice of a synthetic peptide-based vaccine against the sporozoite stage of the human malaria parasite, P.faldpanrm. Immundogy 1988, 64:551-558. Preimmunization with Tf suppressed the response to NANP after boosting with m-NANP. 3. 0
QUE JU, CRYZ SJ JR, BALUXJ R, FERRER E, GROSSM, YOUNG J, WASSERMAN GF, LOOMJSL4, SADOFFJC: Effect of carrier selection on immunogenicity of protein conjugate vaccines circnmsporozoites. Infect against Plasmodium farciparum Immun 1988, 10:264>2649. Carriers other than lT are explored in this paper.
4. 0
M, CARPERS P, TAKACSB, TR~XUK A, GIIIESSEN D, PINK JR, SINIGAGLIA F: Human T cells recognize polymorphic and non-polymorphic regions of the Plasmodium faktparum circnmsporozoite protein. EMBO / 1988, 7:2555-2558. The epitope in the CS protein of P. falc@apanrmwhich is recognized by human T-cell clones were mapped.
5.
GUTITNGER
0
6.
DE IA CRUZ
a
MCC~TCHANTF: Lack of cross-reactivity between variant T
VP,
MAlL3Y WI,
h&lER
m,
hl.
AA,
GOoD
MP,
cell determinan ts from malaria circumsporozoite protein. J Immunoll988, 141:245&2460. Mice immunized with 1 T-cell epitope of the CS protein of P. falciparum did not react with variants of that epitope. GOOD MF, M!HJZR LH, KUMAR S, QUAKYI I& KEISITR D, ADM JH, Moss B, BERZOFSKY J& CARTER R: Limited immunological recognition of critical malaria vaccine candidate antigens. Science 1988, 242~574-576. Congenic mice immunized with parasites showed restriction in the cy totoxic response to the CS protein and in antibody to gamete surface antigens. The implications for vaccine development are discussed.
7. .a
8. 00
ROMERO P, MARYANSKI Jb CORRADIN G, NUSSENZVEIG RS, ZAVALA F: Cloned cytotoxic T cells recognize an epitope in the circnmsporozoite
protein and protect against malaria [letter].
Nature 1989, 341:323-325. CD8+ T-cell clones to the P. be@ei CS protein transferred protection to sporozoite challenge. Interestingly, these clones reacted with an epitope in the region designated Th2R in P. falczparum that is polymorphic in P. fak$kwum. 9. 0
HOFFMAN SL, BERZOFSW JA, ISENBARGER D, ZELTSER E, MAJARL~N GROSSM, BAUI~UWR: Immune response gene regulation of immunity to Plasmodium bergbef sporozoites and
WR,
circumsporozoite protein vaccines. Overcoming genetic restriction with whole organism and subunit vaccines. J Im-
mund 1989, 142:3581-3584.
Immunity to protozoa Miller
Au congenic mice strains immunized with irradiated sporozoites &q&i were protected against challenge with live sporozoites.
of Y
HOFFMAN SL, ISENGAHGER D, LONG GW, SEDEGAHM, SZARFMAN A, WA?ERS 1 HOLLINGDALEMR, VAN DER MEIDE PH, FIN~LOOM DS, BALUXJ WR: Sporozoite vaccine induces genetically restricted T cell elimination of malaria From hepatocytes. Sci em% 1989, 244:107!31080. This is the first in vitro assay of the killing of the stages of the life cycle occurring in the liver by CD8+ T ceils. Importandy, anti-IFNy did not block killing. 10.
. .
RU!ZY EM, ANDER%ON G, Oreo LN, JEPSEN S, GREENWOOD BM: Cellular immune responses to Plasmodium falciparum antigens in Gambian children during and after an acute attack of falciparum malaria. Clin Exp Immunoll988, 7317-22. T cells From Gambian children with acute malaria did not respond to malarial antigens; 50% responded during convalescence. 11. 0
12. ??
HO M, WEB5TERHK, GKEEN B, L~xIAKEESI~XA\S, KONGCIUK~UX S, WHITE NJ: Defective production of a response to IL-
2 in acute human FaIciparum malaria. J Immunol 1988, 141:27552759. This study characterized the suppression of reactivity to malarial antis gens during acute malaria Defects were identified, but the cause of suppression remains unknown. Russo DM, WE~DANZWP: Activation of antigen-specific suppressor T cells by the intravenous injection of soluble blood-stage malarial antigen. Cell Immunol 1988, 115:437-446. Malarial antigens injected intravenously suppressed the delayed-type hypersensitivity response to the antigen, The suppression was ClX+ T-cell-mediated. 13. 0
FORSYI’HKP, ANLIERSRF, CA~TANI JA, AlPERS MP: Small area in prevalence of an S-antigen serotype Of Plasmedium falciparum in villages of Madang, Papua New Guinea. Am J Trap Med Hx 1989, 40:344-350. ‘Ihe S antigen type within and between areas is constantly changing. 14.
0
variation
JM, MllLER t.H: InKUMARS, tiD MF, DONTFRAID F, Vwm terdependence of CD4+ T cells and malarial spleen in immunity to Plasmodium uinckei vinckei. J Immunol 1989, 143:2017-2023. CD4+ T cells alone transferred immunity to immune CD4depleted mice but not to naive mice. Immunity also requires a modified spleen. 15. 0
immunity to malaria: studies with cloned lines of rodent malaria in CBA/Ca mice. IV. The specificity of mechanisms resulting in crisis and resolution of the primary acute phase parasitaemia of P~Xmodium cbabaudi cbabaudi and P. yoelii yoelii. Parasite Immund 1989, ll:l-14. Mice undergoing crisis due to 1 strain of P. chabaudi were not pro tected against another strain. The authors argue that crisis is specific; other explanations of the data are possible.
16. *
JARRAW, BROWN KN: Protective
CRETANSA, M~JUER H-M, HIIBICH C, SIN~GAGIU F, MATU H, MCKAYM, SCAIFEJ, BEYREUIHERK, BUJARJIH: Epitopes recognized by human T cells map within the conserved part of the GPl9O of p. falcipanrm. Science 1988, 240:1324-1325. Human T-cell clones to the major glycoprotein of P. fak@umm reacted Importantly, they reacted with with a region of minimal polymorphism. a number of field isolates. 17. ??*
KABILANL, TROYE-BLOMBERGM. PEIUIANN H, ANDERSSONG, HOGH B, PETERSENE, BJORKMANA, PERUIANN P: T-cell epitapes in Pf155/RESA a major candidate for a Plusmodium farciparum malaria vaccine (correction). PVX Nat1 Acad Sci USA 1988, 85:8648. The reactivity of T cells from Africans was mapped to the non-variant repeat epitop in Pfl55/RESA Reactivity was measured by T cell proliferation. or by production of IFNy. 18. aa
and Scott
19.
RZEPCZYKCM, RAMASAMVR, Ho PC-L, MUTCH DA ANDERSONKL,
??b
DUGGLEBY RG, DORAN TJ, MLJRRAVBJ, IRVING DO, WOODROW of TGC, PARKINSOND, BRABINBJ, ALPER~MP: Identification
epitopes within a potential Plasmodium fahparum vaccine antigen: a study of human lvmohocvte resnonses to repeat and nonrepeat regions of Pfl55IRESA. J Immunoi 1988, 141:3197-3202. This paper also mapped T-cell epitopes in Pfl55/RESA s.
,
DEANS JA, KNIGHT AM, JEAN WC, WATERS Al’, COHEN S. M~TCHEU.GH: Vaccination trials in rhesus monkeys with a minor, invariant, Plasmodium knowlesi 66 kD merozoite antigen. Parasite Immunol 1988, 10:53%552. Rhesus monkeys were immunized with the 66 kD protein of P. k!nouhzsi, Only 1 out of 3 were immune after challenge. On rechal lenge, all 3 were immune, showing the importance of infection after immunization to the development of high immunity
20. ??*
21 00
GRAL GE, TA~L~R TE, MOLYNEUX ME, WIRE&%JJ, VASSALUP, HOMMELM, LAMBERTP-H: Tumor necrosis factor and disease
severity in children with falciparum malaria. N Engf ,I Med 1989, 320:15861591. Humans with severe malaria had high levels of Serum TNF. It is still not known whether this plays a role in the pathogenesis of severe malaria. By analogy with Gram-negative sepsis, it may be important. 22. ??o
BATE CAW, TAVERNEJ, P~AYFAIR JHL: Soluble malarial antigens are toxic and induce the production of turnour necrosis factor in vivo. Immun&gy 1989, 66-5. This paper identities the soluble malarial proteins that stimulated the release of TNP. These molecules may play a role in induction of fever and may cause disease. RANAWAKAMB, MUNESINGHE YD, DE SILVA MR, CARTER R, MENDIS KN: Boosting of transmission-blocking immunity during natural Plasmodium vivax infections in humans depends upon frequent reinfection. Infect Immun 1988, 56:182@1824. Natural infection with P. vivax boosts transmission-blocking immunity, an effect that has consequences for the epidemiology of vivax malaria. 23. 0
HEINZELFP, SADICKMD, HOUDAY BJ, COFFMANRL, IQCKSLEY RM: Reciprocal expression of interferon y or interleukin 4 during the resolution or progression of murine leishmaniasis. Evidence for expansion of distinct helper T cell subsets. J hp Med 1989, X$9:5+72. The authors demonstrated a correlation between the presence of messenger RNA for iymphokines associated with TH1 cells and resistance, and those associated with TH2 cells and susceptibility. In addition, they demonstrate that in oivo II-4 depletion reverses the susceptibility of BALB/c mice. 24. ??e
&AELXI DM, k4UJO FG, CONLEV FK, SUZUKI Y, SHAR~~AS, REMINGTONJS: Treatment with anti-L3T4 (CD4) monoclonal antibody reduces the inllammatory response in toxoplasmic encephalitis. J Immund 1989, 142:954--958. ~,_. ,_-. It is demonstrated that in uiuo treatment with anti-CD4+ antisera decreases the -tory response in the brain of mice chronicalty infected with Taqhima 25. 0
SUZUKIY, REMINGTONJS: Dual regulation of resistance against Toxoplasma gondii infection by lyt-2+ and Iyt-l+, L3T4+ T cells in mice. J Immunol 1988, 140:394+3946. It was shown that a temperature-sensit mutant would immunize mice against fatal infection. Adoptive transfer experiments demonstrated that both CD4+ and CD8+ cells were involved in protection. 26. 00
KHAN IA, SMITH KA, KA~PER LH: Induction of antigen-specific parasiticidal cytotoxic T cell splenocytes by a major membrane protein (P30) of Toxoplasma gondii. J Immunol 1988, 141:360&3605. The authors demonstrated the direct parasiticidal activity by CD8+ cell5 directed against tachizoites 27. 0
28.
FARRELLJP, M~UER I, LKNIS JA: A role
00
resistance to cutaneous leishmaniastis .I Immunol 1989, 142:2052-2056.
for LYT-2+ T cells in in immunized mice.
373
374
Immunity
to infection
It is shown that CD8+ cells are required for vaccine-induced in BALB/c mice immunized with irradiated promastigotes.
resistance
Hlu. JO, APCWAD M, NORTHRJ: Bhmination of CD4+ suppressor T cells from susceptible BALB/c mice releases CDS+ T lymphocytes to mediate protective immunity against Leishmania. J &II Med 1989, 169:18191828. These authors demonstrated that, in BALB/c mice rendered resistant by anti-I3T4 treatment, CD8+ ceiis are required for control of parasite growth. 29. a*
STERNJJ, OCA MJ, RUBIN BY, ANDERSON SL, MURRAYHW: Role of L3T4+ and Lyt-2+ cells in experimental visceral ieishmaniasis. J Immunol 1988, 140:3971-3977. A demonstration that both CD4+ and CD@ cells may be important in controlling visceral leishmaniasis. 30.
??e
31. ??e
BEUXWIC M, -LOOM DS, VAN DER MEIDEPH, SWTER MV, NACV CA: Administration of monoclonal anti-IPN-y antibod ies in viva abrogates natural resistance of C3H/HeN mice
to infection with Lefshmania major. J Immunol 1989, 143:266-274. In this paper, the investigators clearly demonstrate the importance of LFNy in controlling the development of lesions in cutaneous leishma~ n&is. of endogeIPN-y for prevention of toxoplasmic encephalitis in J fmmunol 1989, 143~2045-2050. IFNy led to a signiiicant intlammatory response to toxoin the brain.
32. ??e
SUZUKIY,CONLF( FK, REMINGTON JS: Importance
33.
IPNy induces macrophage activation and prevents acute disease, immune suppression and death in experimental Ttypanosoma cruzi infections. J Immunol 1988,
nous mice. Depletion of plasma cysts ??
REED SG:
In
viuo administration of recombinant
140:43424347. The experiments
demonstrate
that IFNy reverses murine susceptibility
to 7: cruzi. MURRAYHW, BERMANJD, WRIGHT SD: Immunotherapy for intraceIhtlar Lefsbmanfu donovani infection: y interferon plus pentavalent antimony. J InfeCr Db 1988, 157:973-978. The experiments presented provide a rational basis for treatment with anti-leishmaniaidrugs in conjunction with IFNy
34. ??
35.
SVPEKJP, &YLER DJ: Susceptibility of lymphokine-resistant
Leisbmanfa to cell contact-mediated macrophage activation. J Infect LXs 1988, 158:392-397. The authors further characterize a mechanism of macrophage activation that requires ceil contact. ??
H: DEW FY, Mtuo-rr S, LI Y, IEKH~JKR, CHAN WL, ZILTENER Macrophage activation by interferon-gamma from host-protective T-cells is inhibited by interleukin (IL)3 and IL4 produced by disease-promoting T-cells in leishmaniasis. Eur J lmmunof 1989, 19:1227-1232. In this paper, experiments are presented which demonstrate that both IL-4 and IL-~ can inhibit macrophage activation. These data provide a potential mechanism by which these iymphokines may act in viva.
36.
me
37. ??e
FENGZY, LOUISJ, KINDLER V, PEDRAZI~W T, EUASONJF, BEHIN R, VASSALLI P: Aggravation of experimental cutaneous leish-
maniasis in mice by administration of interleukin-3. Eur J Immunol 1988, la:12451253. The data presented in this paper cleariy demonstrate that IL-3 can augument susceptibility to leishmaniasis. GREILJ, BODEND~RFER B, ROUNGHOFFM, SOIBACHW: Apphcation of recombinant granulocyte-macrophage colonystimulating factor has a detrimental effect in experimental murine leishmaniasis. Eur J Immunol 1988, 18:1527-1534. The data presented here show clearly that GM-CSF can augument sus~ ceptibihty to leishmaniasis.
38. ??e
39.
CILLW E, DLEUM, MALTESE E, MUNO S, SALERNO A, LIEWFY
Enhancement of macrophage IL-1 production by Lefsbmanfa major infection in vfttv and its inhibition by IPN-y. ./ Immunol 1989, 143:200-2005. it is shown that Infection of BALB/c macrophages leads to enhanced IL-1 production by these ceils, and that IFNy could down-modulate this IL-I production. ??
CHAMPSIJ, MCMOHAN-PRATTD: Membrane glycoprotein M-2 protects against Leishmanfa amuronesfs infection. Infect Immun 1988, 56~3272-3278. It is demonstrated that a put&d Ieishmanial antigen can protect both resistant mouse strains and the susceptible BALB/c mouse. Moreover, protection could be obtained by either systemic immunization or subcutanous immunization. 40. ??e
41. ??e
HOLADAYB, SADICKMD, PEARSONRD: Isolation
of protective T cells from BALB/c mice chronically infected with
Leisbmania donovani. J Immunof 1988, 141:2132-2137. This paper is the hrst demonstrating transfer of protection against viscerai leishmaniasis by a T-cell line Scorr P, NATOVITZP, COFFMANRL, PEARCEE, SHERA hnmunoregulation of cutaneous leishmaniasis. T cell lines that transfer protective immunity or exacerbation belong to different T helper subsets and respond to distinct parasite antigens. J E~J Med 1988, 168:167~1684. This paper demonstrates that Tul and TB2 celi lines function in oioo to either protect against or exacerbate leishmanial infection. 42. ??e
43. ??e
MLJUER 1, LOUISJA: Immunity to experimental
infection with
Leisbmania major: generation of protective L3T4+ T-cell
clones recognizing antigen(s) associated with live parasites. Eur J Immund 1989, 19865872. The investigators have established a T-cell clone that provides protee tion against L major. Their most interesting obsetvation is that this clone will oniy respond to living promastigotes. 44. ??
SCOT-~P, CASPARP, SHERA: Protection
against Lefsbmanfa major in BAIB/c mice by adoptive transfer of a T cell
clone recognixing a low molecular weight antigen released by promastigotes. J Immund 1990, 144:107%1079. This paper identRies and partially characterizes an antigen recognized by a T-cell clone capable of transferring protection against L. major infection.
of Parasitic Diseases,
Miller
to protozoa and P. Scott*
National Institute
of Allergy
and Infectious
Diseases,
National Institute of Health, Bethesda, Maryland 20892, USA, and *Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, USA Current
Opinion
in Immunology
the sequence of one of these was completely different from sequences taken from ramjomly collected isolates. In addition to the obvious problem for developing a vaccine to P. vivax, this also creates problems for the use of monoclonal antibodies to the repeats, for mosquito vector incrimination, and for linding the frequency of in fected parasites in the population. An alternative method, the use of DNA probes to 5s ribosomal RNA, has been described recently [2 ] .
Malaria IlllISt be Wih.l~ted for tYdCh Stage Ill blNTlUnit)r10 IXh-id the organism’ s life cycle as the location of the intracellular parasite dictates the range of possible immune responses and the mechanisms for immune evasion. The extracellular parasites (sporozoites and merozoites in the mam malian host and gametes and ookinetes in the mosquito midgut) present a common target to antibody-mediated mechanisms, although each has, in most cases, stage-speciftc antigens.
Pre-etythrocytic
1990, 2:368-374
NO variations have so far been found in the repeat doThe god here main of the CS protein of P. falc@arum has been to produce an antibody using the repeat (B-cell epitope) connected to a T-cell epitope derived from the native protein or from a foreign carrier. Using vari0U.S carriers as T-cell epitopes, the antibody response in humans has been poor. One explanation of the poor response of humans to (NANP), conjugated to tetanus toxoid (‘IT) was that the previous immur&ation with IT caused epitope suppression. All strains of mice tested responded to vaccination with ‘IT-(NANP), in ahtminium hydroxide [3]. Indeed, preimmunization with ‘IT reduced the anti-NANP response to subsequent immunization with However, a study in the previous year, by TI_(NANP) Lise et al. CY Infect Immun 1987, 55:2658-26611, found instead that preimmunization with IT enhanced the response to TT-(NANP)4. Despite these contradictory results in mice, the challenge remains to produce high, persistent anti-(NANP), titers in humans and to determine its protective effect against sporozoite challenge. One approach has been to develop carriers other than ?T [41, but again, the test of efficacy must be in humans, not tabbits.
stage
Infection begins in humans when sporozoites are inoc ulated by the mosquito and circulate for several minutes before they are cleared by the liver. The parasite invades hepatic parenchymal cells where it matures over 2 days in the case of rodent malarias and over 7 or more days in primate malarias. The unresolved question of whether the parasite passes through fenestrations or through endothelial or Kupffer cells will determine other potential targets. In the 197Os, Nussenzweig and her colleagues deftned antibody-mediated mechanisms of immunity to sporozoites and, in the 1980s the circumsporozoite (CS) protein which covers the sporozoite surface was defined as the target for this immunity. The protein has a number of clearly defined domains, including regions I and II which are probably involved in attachment, and the central third that consists of repeated amino-acid sequences. These central repeats are the major target for protective monoclonal antibodies. Thus, one of the aims in producing a vaccine to prevent infection was to induce antibodies to the central repeats of Phsmodium falciparum and Pkzimodium vivax. For this approach to work, the central repeat of each species must be the same. In P. vivax, this has been found not to be the case [ 1I. Mosquitoes were fed on Waxinfected humans, and the sporozoites analysed for reactivity to monoclonal antibodies against the repeat domain. Fourteen per cent did not respond;
T-cell epitopes from the native CS protein of P. fakiparum have been defined previously by Good et al. (lmmund Today 1988, 9351-355). The DNA sequences of the CS proteins from multiple clones indicate that some T-cell epitopes are in variant regions; others are invariam [ 51. Immunization with a variant region demonstrates that there is no cross-reactive response to other variants [(;I, indicating the importance of the amino-acid variation in the immune response. The value of the B-cell epitope, -I
Abbreviations CS-circumsporozoite; CT1 cytotoxlc T lymphocyte; CM-CSF--granulocyte,macrophage colony-stlmulatlng factor; Hi-A-human leukocyte antigen; IFK -interferon; Il.--- interleukin; l_P?-lipopolysaccharide; RESA-ring-Infected erythrocyte surface antigen; TN---Thelper: TNF-tumor necrosis factor: n--tetanus toxoid.
@ Current
Science
Ltd ISSN 0952-7915
immunity to protozoa Miller and Scott
combined with an invariant T-cell epitope, in boosting the response during exposure to natural infection, remains to be determined. The importance of CD8+ T cells in immunity to sporozoite challenge has previously been shown in animals that were immunized by irradiated sporozoites and CD8-depleted before challenge. The important questions include which cell expresses the epitope (probably the liver cell), which parasite protein contains the cytotoxic T lymphocyte (CTL) epitope, the variability of this epitope, the genetic restriction of response to the liver stage proteins, and the mechanism for immunizing humans. It should be remembered that CD8+ T cells are not long-lived. Irfection time may not be long enough to boost the response unless the immunization was performed immediately before exposure, or unless special mechanisms are developed to attenuate the response. A CTL epitope has been identifiti on the falciparum CS protein but, unfortunately, it is within one of the variant regions of the CS protein and the response to that epitope is restricted [7]. CD8+ (CTL) clones were made to a peptide in the CS protein that was recognized by CTL induced by immunization by irradiated sporozoites [8]. The clones transferred protection against challenge with Plasmodium bergbeisporozoites. The mechanism of parasite killing remains unknown [direct cytotoxicity or in terferon (IFN)*I] . Immunization of congenic mice with irradiated sporozoites of P. be@ei led to protection in all strains [9]. It had been shown previously in one strain of mouse that protection was both antibody-dependent and CD8+ T-cell-dependent. The question of whether the immunity in congenic mice, induced by ~mmunization with irradiated sporozoites, is CD8+ T celldependent, remains to be determined. An in vitro assay was developed to study CD8+ T cells against infected hepatocytes [lo]. The development of parasites in hepatocytes is inhibited by CD8+ T cells in a genetically restricted manner. Anti-IFNy did not inhibit the activity of CD8+ T cells against infected hepatocytes, suggesting that these cells have a direct cytotoxic effect. Asexual erythrocytic parasites
One of the recurring themes in the malarial literature is that malarial infection in some way suppresses the im mune response. Studies in Gambian children [ 111 and in Thai adults [12] found that their response to malarial antigens during acute infection was limited. However, during convalescence, the Thai adults responded but 50% of the African children did not. The inability to proliferate was not restored by the addition of interleukin (IL)1 or IL-2 to the cultures injected with malarial antigens. No IL-2 receptors appeared on the T cells as a result of acute infections during stimulation with malarial antigen. One problem in evaluating the significance of these findings in acute malaria is that any previous exposure to malaria is unknown and lymphocytes in other locations than peripheral blood (e.g., the spleen) are inaccessible. One interesting fInding in the Thai study was that circulating IL-2 receptors were present during acute infection, Intravenous injection of soluble malarial antigen into the
mouse has been shown to suppress delayed-type hypersensitivity to the antigen [ 131. The suppression was mediated by CD8+ T cells. In the 197Os, Mackaness et al (j Exp Med 1974,139:528542) found a similar suppression after intravenous injection of heterologous erythrocytes. One potential mechanism for immune evasion is antigenie diversity (variation among clones, polymorphism) and antigenic variation (variation within a clone). The polymorphisms of GP195 and the S antigens, for exam ple, have been studied previously at the antigenic and molecular level. The S antigens were found to vary be tween areas at any particular time and within an area at different times [ 141. The degree of variability of the S antigen indicates that this molecule has an important function. Its expression around the time of merozoite release suggests a role in invasion, but, like GP195, its exact function is unknown. The importance of cell-mediated immunity in some rodent malarias has been beautifully demonstrated by Grun This has been and Weidunz (Nature 1981,290:143-145). extended recently in the Pkzsmodium vincketimouse systern where solid immunity induced by repeated infection and cure has been shown to be antibody independent and to require both CD4+ T cells and an intact spleen [ 151. Naive mice that have received immune CD4+ T cells are fully susceptible to lethal P. vinckei infection, indicating that CD4+ T cells are necessary but not sulhcient for immunity and that a change in spleen is also required. It is assumed that the effector mechanism in cell mediated immunity is non-specific. However, Jarra and Brown [ 161 found that during crisis (the period of rapid decrease in parasitemia) in Plasmodium cbabaudi, the effect appeared to be strain-specific. They suggested that the effector mechanism was specific, but they did not induce crisis against the second strain or test its effect against the first strain. It is possible that one strain is more resistant to the crisis killing mechanism than the other strain. Alternatively, crisis, in some situations, has a spe cilic mechanism which has not yet been elucidated. A vaccine to the asexual erythrocytic parasite should induce protective immunity that can be boosted during natural infection. Cellular immunity and antibody-mediated immunity both require CD4+ T cells that will be boosted upon exposure to the parasite. This means that the irvariant or minimally variant regions that are encountered by a high proportion of the population who have been immunized need to be identified. Because the human leukocyte antigen (HIA) types of populations may vary, the epitopes used in an immunogen may not be identical from one area to another. It will probably be necessary to include multiple epitopes from any one protein to be sure of covering all of the epitopes encountered by the entire population. The important work of delining T-cell epitopes on two potential vaccine candidates has begun. In one approach, T-cell clones to recombinant peptides were produced from the major glycoprotein on the merozoite of P. falciparum, GP195. The epitopes on these clones were mapped to part of the Nterminal region of the protein [17]. There was minimal variation within these peptides among falciparum clones.
369
370
Immunity to infection
More important, the T-cell clones proliferated on exposure to all falciparum parasites studied. We await with interest the results of the T-cell proliferation in lymphocytes from endemic populations using these epitopes. An alternative approach has been the study of the T-cell response to peptides from the Pfl55/ring-infected erythrocyte surface antigen (RESA) of P. falciparum in endemic populations [18]. This protein contains two regions of repeated amino-acid sequences. Many of the T-cell responses map to the C-terminal repeats, which are invari ant regions of the protein. The T-cell response was evauated by both lymphocyte proliferation and the produc tion of IFNy. The finding that the results of the two tests for T cells did not correlate in individual donors ma) have some, as yet undefined, significance. Further shtdies on the T-cell epitopes of PfI55/RESA demonstrate that Melanesians respond to the N-terminal repeat in the same way as African populations and that non-repeat regions also contain T-cell epitopes [ 191. Previously, Deans et al. (Mol Biocbem Parasitol 1984, 13:187-199) have shown that a monoclonal antibody to a 66 kD protein of Plasmodium knowlesi blocks invasion and that Fab fragments of the monoclonal antibody block invasion more effectively than the whole immunoglobulin. Monkeys have now been immunized with the punlied protein [ 201. Knowlesi malaria is an invariably fatal disease; one out of three immunized monkeys were able to control the infection. The other two required chemotherapy because the infections were following a virulent course. On rechallenge, however, the three monkeys were highly immune. The immunization did not select mutants that were resistant to reinfection, as parasites from the recrudescent parasitemia still expressed the target of the blocking monoclonal antibody. Cerebral malaria occurs in P. berg&$ is associated with macrophages in the cerebral vessels and can be blocked by anti-I.FNy and anti-tumor necrosis factor (TNF). Grau et al. [21] have now followed up this study by measuring TNF in children with severe malaria, including cerebral malaria. Severe malaria and high mortality were as sociated with elevated levels of TNF. It is still not known whether elevated levels of TNF are involved in the pathology or whether anti-TNF will affect survival in these chidren. Clinical trials similar to those underway in septic shock will be needed to clarify these issues. It has been observed that the course of fever following rupture of malaria-infected erythrocytes resembles the fever that follows endotoxin. Bate et al. [22] have now shown that soluble malarial antigens can induce TNF. It is important to note that there was no evidence of contamina~ tion with lipopolysaccharide (LPS) in the malarial preparation. Since TNF can cause fever, is it possible that Bate et al. have begun the isolation of the factor responsible for fever in malaria. Transmission-blocking
immunity
The epidemiology of P. uivax is influenced by the boost mg of antibodies that block transmission [ 231. Thus, if a patient is reinfected or recrudesces within 4 months of a previous attack, the infectivity to mosquitoes is reduced.
Leishmania,
Toxoplasma,
and Trypanosoma
cruzi T-cell subsets regulating protozoa1 immunity
One of the major immunological advances in protozoal immunity over the last year has been the increase in our understanding of the role of CD4+ and CD8+ cells in regulating diseases and, in particular, of the importance of CD4 + T-cell subsets Some of these results have been discussed above in the context of malaria, but advances in the field of leishmanial immunity may provide the best example of the regulatory influence of different CD4+ T-cell subsets in immunity. It is generally agreed that in leishmaniasis the primary lymphocyte regulating immunity in cutaneous leishmaniasis is the CD4 + T cell. Thus, CD4 + cells have been shown to act as either effector cells promoting resistance, or as cells that promote susceptibility. The fact that CD4+ cells could mediate both of these effects has lead to some confusion in our understanding of immunity in leishmaniasis. However, during the last year a major advance in this field has occurred, which is based upon the recent demonstration that CD4+ T-cell clones can be separated into two subsets, depending on the lym phokines they produce following stimulation (Mosmann et al., JImmunoll986,136:234%2357). One subset, designated T helper (TH)l, produces IL-2 and IFNy, while the other subset, designated Tn2, produces IL-4 and IL5. Several other lymphokines, such as IL-3 and granulocyte/macrophage colony-stimulating factor (GM-CSF), appear to be produced by both celI subsets, although in some cases in different quantities. Because of the different lymphokines that they produce, TH1 and Tn2 clones have different functions. For example, Trill cells have been shown to mediate delayed hypersensitivity reactions, while Tn2 cells act as helper cells for specific an tibody production. In leishmaniasis, a strong correlation between delayed hypersensitivity, IFNy production and healing has been shown, whereas high antibody production is associated with susceptibility. Thus, it could be that the CD4 + cells mediating resistance belong to the Tttl subset, while the cells mediating susceptibility belong to the T,2 subset. Heinzel et 61. [ 241 demonstrated clearly that a strong correlation exists between the production of lymphokines associated with Trill cells and resistance, while lymphokines associated with T,2 type cells predominated in susceptible mice. Thus, at present, the accumulated evidence suggests that two different Tcell subsets, Trill and T,2, mediate resistance and SW ceptibility in cutaneous leishmaniasis. In experimental toxoplasmosis, there are also conflicting results about the function of CD4+ cells in pathology and protection. Thus, it was shown that in vivo treatment with anti-CD4+ antisera decreased the inflammatory response to the parasite in the brains of mice infected with To.xopksmu [25]; this contrasts with a previous report that elimination of CD4+ cells exacerbates toxo plasmic encephalitis (Vollmer et al., J Immunol 1987, 138:3737-3741). Israelski et al. [ 251 argue that CD4 + depletion after infection leads to a non-random depletion
Immunity
of CD4+ cells, and that the treatment hzs an effect on the cells that mediate the inflammatory response but has little effect on the T cells mediating protection. Clearly, it would be useful if we could determine whether CD4+ T, subsets, such as Tnl and T,,Z, are involved to different degrees in these effects. Another major advance in our understanding of protozeal immunity has been the direct demonstration that CDB+ cells are important for protection. The best example may be in the field of malaria (which was discussed above). However, it has also been demonstrated that CDB+ cells are major effector cells of immunity in toxoplasmosis. Thus, it was shown by adoptive transfer experiments with cells from Toxqnlasma-immune mice, that both CD4 + and CDB+ cells mediate resistance [ 261. Depletion of CD8+ cells completely ablated the protec five effect of T-cell transfers, while depletion of CD4 $ cells partially removed the protective effects. It is not clear how CD8+ cells mediate protection. One likely mechanism is through the production of IFN?, which appears to be required for control of toxoplasmosis (discussed below). However, it has also been reported that CDB+ cells from Ta~@lasma-immunized mice are capable of direct parasiticidal activity directed against tachizoites [ 271, thus providing another potential mechanism by which CDB+ cells might provide protection. The participation of CD8+ cells in leishmaniasis has been more diEcult to define. Nevertheless, there is now convincing evidence that CDB+ cells also contribute to healing. The experiment that has been cited to demonstrate that CDB+ cells have a limited role in protection is one in which in vivo depletion of CDB+ cells in a mouse strain resistant to Letldmunia only delayed healing (Titus et al, Eur J ImmunoZl988,17:1429-1433). However, it has now been demonstrated that vaccine-induced in-munity in BALB/c mice may be more dependent upon CD8+ cells [28]. It has also been shown that anti-Ly2+ treatment completely ablates the protective immunity that is elicited in BALB/c mice by intravenous immunization with irradiated promastigotes [28]. It has also recently been suggested [29] that BALB/c mice rendered resistant by anti-WT4 treatment may require the presence of CDB+ cells to control parasite growth. Finally, in murine visceral leishmaniasis, depletion of either CD4+ or CDB+ cells inhibited protective immune responses, suggesting that both cell types are required for effective immunity 1301. These observations should generate considerable interest in the role played by CDB+ cells in promoting protection. Questions that will need to be addressed about CDS+ cells in parasite immunity include: (1) how do parasite antigens associate with class I molecules for presentation to CDB+ cells? and (2) how do CDB+ cells provide protection? Although these cells may be capable of cytotoxic activity, the production of IFNy may be a more important function.
Role of cytokines
in protozoa1
immunity
availability of recombinant lymphokines and monoclonal antibodies directed against these lymphokines has
The
to protozoa
Miller and Scott
led to a series of important experiments which help to elucidate the role of T-cell products in parasite immunity. For example, in leishmaniasis, the critical role of IFNy in protection was confirmed by the demonstration that in uivo depletion of IFNy with monoclonal antibodies leads to susceptibility to cutaneous leishmaniasis in a normally resistant mouse strain [31]. Similar experiments in which IFNy has been depleted in vivo in mice chromtally infected with Toxoplasma have also shown the importance of IFNy in controlling disease. Thus, IFNy depletion led to a significant inflammatoty response to Toxoplasma cysts in the brain [32]. The reciprocal experiment, in vivo administration of IFNy, resulted in protection against the acute phase of Typanosomu cruzzi infection [33]. In addition, Murray et al. [34] demonstrated the immunotherapeutic potential of IFNy in visceral leishmaniasis. Since Letimunia are obligate intra cellular parasites of macrophages and since macrophage activation appears to be the major effector mechanism controlling infection, these results are probably not surprising. They do not negate the fact, however, that other non-EN-I-mediated mechanisms of macrophage activation might also occur, as has been described by Wyler et al. (J Zmmunoll987,138:12461258). This group has characterized a mechanism of macrophage activation that appears not to require IFNy, but which does require contact. They recently demonstrated that this contact-medated killing was effective against a parasite strain which has previously been shown to be resistant to lymphokinemediated macrophage activation [ 351. In leishmaniasis, it has been shown that in vivo depletion of IL-4 reversed the extreme susceptibility of BALB/c mice to L, major [24]. The mechanism bywbich IL-4 promotes susceptibility is unknown. Although it has been postulated on the basis of the results of in vitro experiments, that IL-4 may down-modulate the ability of macrophages to respond to IFNy [36], it may not be the only lymphokine involved in susceptibility to leishmaniasis. It has also been clearly demonstrated that both IL-3 and GM-CSF can signikantly enhance the development of lesions in mice infected with L. major [37,38]. The mechanism by which these lymphokines augment lesion development is unclear, although it has been suggested that they may promote in&ration into lesions of macrophages in which the parasites can grow, but which are resistant to activation. Another interesting observation is the recent demonstration that L. mujor-infected BALB/c macrophages produce elevated levels of IL-1 [39]. Since it has been demonstrated that IL-1 is required for Tn2 T-cell clone proliferation, these results indicate a possible source of IL-1 in L. major-infected BALB/c mice. Vaccine development
One major area of immunological studies of protozoai infection is in the development of vaccines, One of the most important factors in defining a vaccine is the availability of experimental vaccine models. In Toxoplu.smu, a new model system for studying vaccine-induced imp munity was developed 1261 by infecting mice with a
371
372
Immunity
to infection
temperature-sensitive mutant which causes infection, but does not persist in the host. It was shown that such im munization leads to marked resistance to a challenge infection. The BALB/c mouse infected with various species of Lezkhmuniu continues to be the most commonly used vaccine model system for leishmaniasis. Several approaches have been used for defining which leishmanial antigens are responsible for inducing immunity. One approach has been to define potential vaccine candidate antigens using antibodies. Notably, within the last year, it has been demonstrated that a membrane glycoprotein of molecular weight 46kD, derived from Leisbmunia amzonensis using monoclonal antibodies, induces protective immunity in both a resistant mouse strain, and in the extremely susceptible BALB/c mouse [40]. Another approach to isolation of protective leishmanial antigens is the identification of antigens recognized by T cells. The success of this approach depends on the establishment of T-cell lines and clones that are capable of transferring protection. Such protective T-cell lines have been described in experimental visceral leishmaniasis; a T-cell line that protects against Lezlsbmunifz donozuni irktion in BALB/c mice was isolated from chronically infected animals following drug treatment [41]. These cells were WT4+ and produced IFNy, suggesting that they belonged to the TH1 subset. In contrast, a cell line that failed to produce EWy also failed to provide protection. The relationship between TH1 cells and protection, and TH2 cells and resistance, has also been directly demonstrated using T-cell lines. Thus, Scott et al. [42] demonstrated that a cell line recognizing a protective antigen derived from L major transferred protection to BALB/c mice and had the lymphokine profile of TH1 cells, while another Tcell line, which was shown to consist of TH2 cells, exacerbated subsequent infection following transfer to BALB/c mice. An interesting aspect of these studies was that certain leishmanial antigens appeared to stimulate one subset or the other preferentially. Protective T-cell clones are required for identification of particular leishmanial antigens that may be protec tive, and Muller and Louis [43] reported a T-cell clone that transfers protection against L major in the BALB/c mouse. An interesting aspect of these cells is that they could only be stimulated with live L mujor promastigotes, and that they failed to respond to killed promastigotes or any dead antigen preparation tested to date. The authors suggested that their results indicated that protec tive and non-protective T cells may respond to different antigens, as described above for T,l and TH2 cell lines. Another Lezkhnuniu T-cell clone has been described and, using T-cell immunoblotting, it was shown that the clone recognizes an antigen of molecular weight of approximately 10000 [44]. Most recently, this clone has been shown to transfer protection against L major in BALB/c mice 1441.
Annotated
references
and recommended
reading 0 a*
Of interest Of outstanding interest
1.
ROSENBERG R, WIRTZRA, L&NAR DE, SA’IXEIONGKOT J, HALLT,
??o
WATERSAP, PRASITI’ISUK C: Circumsporozoite
protein hetero-
geneity in the human malaria parasite Plasmodium vivax. Science 1989, 245973-976. Field isolates of vivax malaria had variations in the repeat region of the CS protein causing non-reactivity with the antiCS protein antibodies. WATERSAP, MCCLITCHAN TF: Rapid, sensitive diagnosis of malaria based on ribrosomal RNA Lancer 1989, 3:X%4%1345. The development of DNA probes to unique regions of the ribosomal genes that differentiate the 4 human malarias. 2.
.a
ETLINGER HM, HEIMEREP, TRZECMK A, FELIXAM, GIIBSEN D: Assessment in mice of a synthetic peptide-based vaccine against the sporozoite stage of the human malaria parasite, P.faldpanrm. Immundogy 1988, 64:551-558. Preimmunization with Tf suppressed the response to NANP after boosting with m-NANP. 3. 0
QUE JU, CRYZ SJ JR, BALUXJ R, FERRER E, GROSSM, YOUNG J, WASSERMAN GF, LOOMJSL4, SADOFFJC: Effect of carrier selection on immunogenicity of protein conjugate vaccines circnmsporozoites. Infect against Plasmodium farciparum Immun 1988, 10:264>2649. Carriers other than lT are explored in this paper.
4. 0
M, CARPERS P, TAKACSB, TR~XUK A, GIIIESSEN D, PINK JR, SINIGAGLIA F: Human T cells recognize polymorphic and non-polymorphic regions of the Plasmodium faktparum circnmsporozoite protein. EMBO / 1988, 7:2555-2558. The epitope in the CS protein of P. falc@apanrmwhich is recognized by human T-cell clones were mapped.
5.
GUTITNGER
0
6.
DE IA CRUZ
a
MCC~TCHANTF: Lack of cross-reactivity between variant T
VP,
MAlL3Y WI,
h&lER
m,
hl.
AA,
GOoD
MP,
cell determinan ts from malaria circumsporozoite protein. J Immunoll988, 141:245&2460. Mice immunized with 1 T-cell epitope of the CS protein of P. falciparum did not react with variants of that epitope. GOOD MF, M!HJZR LH, KUMAR S, QUAKYI I& KEISITR D, ADM JH, Moss B, BERZOFSKY J& CARTER R: Limited immunological recognition of critical malaria vaccine candidate antigens. Science 1988, 242~574-576. Congenic mice immunized with parasites showed restriction in the cy totoxic response to the CS protein and in antibody to gamete surface antigens. The implications for vaccine development are discussed.
7. .a
8. 00
ROMERO P, MARYANSKI Jb CORRADIN G, NUSSENZVEIG RS, ZAVALA F: Cloned cytotoxic T cells recognize an epitope in the circnmsporozoite
protein and protect against malaria [letter].
Nature 1989, 341:323-325. CD8+ T-cell clones to the P. be@ei CS protein transferred protection to sporozoite challenge. Interestingly, these clones reacted with an epitope in the region designated Th2R in P. falczparum that is polymorphic in P. fak$kwum. 9. 0
HOFFMAN SL, BERZOFSW JA, ISENBARGER D, ZELTSER E, MAJARL~N GROSSM, BAUI~UWR: Immune response gene regulation of immunity to Plasmodium bergbef sporozoites and
WR,
circumsporozoite protein vaccines. Overcoming genetic restriction with whole organism and subunit vaccines. J Im-
mund 1989, 142:3581-3584.
Immunity to protozoa Miller
Au congenic mice strains immunized with irradiated sporozoites &q&i were protected against challenge with live sporozoites.
of Y
HOFFMAN SL, ISENGAHGER D, LONG GW, SEDEGAHM, SZARFMAN A, WA?ERS 1 HOLLINGDALEMR, VAN DER MEIDE PH, FIN~LOOM DS, BALUXJ WR: Sporozoite vaccine induces genetically restricted T cell elimination of malaria From hepatocytes. Sci em% 1989, 244:107!31080. This is the first in vitro assay of the killing of the stages of the life cycle occurring in the liver by CD8+ T ceils. Importandy, anti-IFNy did not block killing. 10.
. .
RU!ZY EM, ANDER%ON G, Oreo LN, JEPSEN S, GREENWOOD BM: Cellular immune responses to Plasmodium falciparum antigens in Gambian children during and after an acute attack of falciparum malaria. Clin Exp Immunoll988, 7317-22. T cells From Gambian children with acute malaria did not respond to malarial antigens; 50% responded during convalescence. 11. 0
12. ??
HO M, WEB5TERHK, GKEEN B, L~xIAKEESI~XA\S, KONGCIUK~UX S, WHITE NJ: Defective production of a response to IL-
2 in acute human FaIciparum malaria. J Immunol 1988, 141:27552759. This study characterized the suppression of reactivity to malarial antis gens during acute malaria Defects were identified, but the cause of suppression remains unknown. Russo DM, WE~DANZWP: Activation of antigen-specific suppressor T cells by the intravenous injection of soluble blood-stage malarial antigen. Cell Immunol 1988, 115:437-446. Malarial antigens injected intravenously suppressed the delayed-type hypersensitivity response to the antigen, The suppression was ClX+ T-cell-mediated. 13. 0
FORSYI’HKP, ANLIERSRF, CA~TANI JA, AlPERS MP: Small area in prevalence of an S-antigen serotype Of Plasmedium falciparum in villages of Madang, Papua New Guinea. Am J Trap Med Hx 1989, 40:344-350. ‘Ihe S antigen type within and between areas is constantly changing. 14.
0
variation
JM, MllLER t.H: InKUMARS, tiD MF, DONTFRAID F, Vwm terdependence of CD4+ T cells and malarial spleen in immunity to Plasmodium uinckei vinckei. J Immunol 1989, 143:2017-2023. CD4+ T cells alone transferred immunity to immune CD4depleted mice but not to naive mice. Immunity also requires a modified spleen. 15. 0
immunity to malaria: studies with cloned lines of rodent malaria in CBA/Ca mice. IV. The specificity of mechanisms resulting in crisis and resolution of the primary acute phase parasitaemia of P~Xmodium cbabaudi cbabaudi and P. yoelii yoelii. Parasite Immund 1989, ll:l-14. Mice undergoing crisis due to 1 strain of P. chabaudi were not pro tected against another strain. The authors argue that crisis is specific; other explanations of the data are possible.
16. *
JARRAW, BROWN KN: Protective
CRETANSA, M~JUER H-M, HIIBICH C, SIN~GAGIU F, MATU H, MCKAYM, SCAIFEJ, BEYREUIHERK, BUJARJIH: Epitopes recognized by human T cells map within the conserved part of the GPl9O of p. falcipanrm. Science 1988, 240:1324-1325. Human T-cell clones to the major glycoprotein of P. fak@umm reacted Importantly, they reacted with with a region of minimal polymorphism. a number of field isolates. 17. ??*
KABILANL, TROYE-BLOMBERGM. PEIUIANN H, ANDERSSONG, HOGH B, PETERSENE, BJORKMANA, PERUIANN P: T-cell epitapes in Pf155/RESA a major candidate for a Plusmodium farciparum malaria vaccine (correction). PVX Nat1 Acad Sci USA 1988, 85:8648. The reactivity of T cells from Africans was mapped to the non-variant repeat epitop in Pfl55/RESA Reactivity was measured by T cell proliferation. or by production of IFNy. 18. aa
and Scott
19.
RZEPCZYKCM, RAMASAMVR, Ho PC-L, MUTCH DA ANDERSONKL,
??b
DUGGLEBY RG, DORAN TJ, MLJRRAVBJ, IRVING DO, WOODROW of TGC, PARKINSOND, BRABINBJ, ALPER~MP: Identification
epitopes within a potential Plasmodium fahparum vaccine antigen: a study of human lvmohocvte resnonses to repeat and nonrepeat regions of Pfl55IRESA. J Immunoi 1988, 141:3197-3202. This paper also mapped T-cell epitopes in Pfl55/RESA s.
,
DEANS JA, KNIGHT AM, JEAN WC, WATERS Al’, COHEN S. M~TCHEU.GH: Vaccination trials in rhesus monkeys with a minor, invariant, Plasmodium knowlesi 66 kD merozoite antigen. Parasite Immunol 1988, 10:53%552. Rhesus monkeys were immunized with the 66 kD protein of P. k!nouhzsi, Only 1 out of 3 were immune after challenge. On rechal lenge, all 3 were immune, showing the importance of infection after immunization to the development of high immunity
20. ??*
21 00
GRAL GE, TA~L~R TE, MOLYNEUX ME, WIRE&%JJ, VASSALUP, HOMMELM, LAMBERTP-H: Tumor necrosis factor and disease
severity in children with falciparum malaria. N Engf ,I Med 1989, 320:15861591. Humans with severe malaria had high levels of Serum TNF. It is still not known whether this plays a role in the pathogenesis of severe malaria. By analogy with Gram-negative sepsis, it may be important. 22. ??o
BATE CAW, TAVERNEJ, P~AYFAIR JHL: Soluble malarial antigens are toxic and induce the production of turnour necrosis factor in vivo. Immun&gy 1989, 66-5. This paper identities the soluble malarial proteins that stimulated the release of TNP. These molecules may play a role in induction of fever and may cause disease. RANAWAKAMB, MUNESINGHE YD, DE SILVA MR, CARTER R, MENDIS KN: Boosting of transmission-blocking immunity during natural Plasmodium vivax infections in humans depends upon frequent reinfection. Infect Immun 1988, 56:182@1824. Natural infection with P. vivax boosts transmission-blocking immunity, an effect that has consequences for the epidemiology of vivax malaria. 23. 0
HEINZELFP, SADICKMD, HOUDAY BJ, COFFMANRL, IQCKSLEY RM: Reciprocal expression of interferon y or interleukin 4 during the resolution or progression of murine leishmaniasis. Evidence for expansion of distinct helper T cell subsets. J hp Med 1989, X$9:5+72. The authors demonstrated a correlation between the presence of messenger RNA for iymphokines associated with TH1 cells and resistance, and those associated with TH2 cells and susceptibility. In addition, they demonstrate that in oivo II-4 depletion reverses the susceptibility of BALB/c mice. 24. ??e
&AELXI DM, k4UJO FG, CONLEV FK, SUZUKI Y, SHAR~~AS, REMINGTONJS: Treatment with anti-L3T4 (CD4) monoclonal antibody reduces the inllammatory response in toxoplasmic encephalitis. J Immund 1989, 142:954--958. ~,_. ,_-. It is demonstrated that in uiuo treatment with anti-CD4+ antisera decreases the -tory response in the brain of mice chronicalty infected with Taqhima 25. 0
SUZUKIY, REMINGTONJS: Dual regulation of resistance against Toxoplasma gondii infection by lyt-2+ and Iyt-l+, L3T4+ T cells in mice. J Immunol 1988, 140:394+3946. It was shown that a temperature-sensit mutant would immunize mice against fatal infection. Adoptive transfer experiments demonstrated that both CD4+ and CD8+ cells were involved in protection. 26. 00
KHAN IA, SMITH KA, KA~PER LH: Induction of antigen-specific parasiticidal cytotoxic T cell splenocytes by a major membrane protein (P30) of Toxoplasma gondii. J Immunol 1988, 141:360&3605. The authors demonstrated the direct parasiticidal activity by CD8+ cell5 directed against tachizoites 27. 0
28.
FARRELLJP, M~UER I, LKNIS JA: A role
00
resistance to cutaneous leishmaniastis .I Immunol 1989, 142:2052-2056.
for LYT-2+ T cells in in immunized mice.
373
374
Immunity
to infection
It is shown that CD8+ cells are required for vaccine-induced in BALB/c mice immunized with irradiated promastigotes.
resistance
Hlu. JO, APCWAD M, NORTHRJ: Bhmination of CD4+ suppressor T cells from susceptible BALB/c mice releases CDS+ T lymphocytes to mediate protective immunity against Leishmania. J &II Med 1989, 169:18191828. These authors demonstrated that, in BALB/c mice rendered resistant by anti-I3T4 treatment, CD8+ ceiis are required for control of parasite growth. 29. a*
STERNJJ, OCA MJ, RUBIN BY, ANDERSON SL, MURRAYHW: Role of L3T4+ and Lyt-2+ cells in experimental visceral ieishmaniasis. J Immunol 1988, 140:3971-3977. A demonstration that both CD4+ and CD@ cells may be important in controlling visceral leishmaniasis. 30.
??e
31. ??e
BEUXWIC M, -LOOM DS, VAN DER MEIDEPH, SWTER MV, NACV CA: Administration of monoclonal anti-IPN-y antibod ies in viva abrogates natural resistance of C3H/HeN mice
to infection with Lefshmania major. J Immunol 1989, 143:266-274. In this paper, the investigators clearly demonstrate the importance of LFNy in controlling the development of lesions in cutaneous leishma~ n&is. of endogeIPN-y for prevention of toxoplasmic encephalitis in J fmmunol 1989, 143~2045-2050. IFNy led to a signiiicant intlammatory response to toxoin the brain.
32. ??e
SUZUKIY,CONLF( FK, REMINGTON JS: Importance
33.
IPNy induces macrophage activation and prevents acute disease, immune suppression and death in experimental Ttypanosoma cruzi infections. J Immunol 1988,
nous mice. Depletion of plasma cysts ??
REED SG:
In
viuo administration of recombinant
140:43424347. The experiments
demonstrate
that IFNy reverses murine susceptibility
to 7: cruzi. MURRAYHW, BERMANJD, WRIGHT SD: Immunotherapy for intraceIhtlar Lefsbmanfu donovani infection: y interferon plus pentavalent antimony. J InfeCr Db 1988, 157:973-978. The experiments presented provide a rational basis for treatment with anti-leishmaniaidrugs in conjunction with IFNy
34. ??
35.
SVPEKJP, &YLER DJ: Susceptibility of lymphokine-resistant
Leisbmanfa to cell contact-mediated macrophage activation. J Infect LXs 1988, 158:392-397. The authors further characterize a mechanism of macrophage activation that requires ceil contact. ??
H: DEW FY, Mtuo-rr S, LI Y, IEKH~JKR, CHAN WL, ZILTENER Macrophage activation by interferon-gamma from host-protective T-cells is inhibited by interleukin (IL)3 and IL4 produced by disease-promoting T-cells in leishmaniasis. Eur J lmmunof 1989, 19:1227-1232. In this paper, experiments are presented which demonstrate that both IL-4 and IL-~ can inhibit macrophage activation. These data provide a potential mechanism by which these iymphokines may act in viva.
36.
me
37. ??e
FENGZY, LOUISJ, KINDLER V, PEDRAZI~W T, EUASONJF, BEHIN R, VASSALLI P: Aggravation of experimental cutaneous leish-
maniasis in mice by administration of interleukin-3. Eur J Immunol 1988, la:12451253. The data presented in this paper cleariy demonstrate that IL-3 can augument susceptibility to leishmaniasis. GREILJ, BODEND~RFER B, ROUNGHOFFM, SOIBACHW: Apphcation of recombinant granulocyte-macrophage colonystimulating factor has a detrimental effect in experimental murine leishmaniasis. Eur J Immunol 1988, 18:1527-1534. The data presented here show clearly that GM-CSF can augument sus~ ceptibihty to leishmaniasis.
38. ??e
39.
CILLW E, DLEUM, MALTESE E, MUNO S, SALERNO A, LIEWFY
Enhancement of macrophage IL-1 production by Lefsbmanfa major infection in vfttv and its inhibition by IPN-y. ./ Immunol 1989, 143:200-2005. it is shown that Infection of BALB/c macrophages leads to enhanced IL-1 production by these ceils, and that IFNy could down-modulate this IL-I production. ??
CHAMPSIJ, MCMOHAN-PRATTD: Membrane glycoprotein M-2 protects against Leishmanfa amuronesfs infection. Infect Immun 1988, 56~3272-3278. It is demonstrated that a put&d Ieishmanial antigen can protect both resistant mouse strains and the susceptible BALB/c mouse. Moreover, protection could be obtained by either systemic immunization or subcutanous immunization. 40. ??e
41. ??e
HOLADAYB, SADICKMD, PEARSONRD: Isolation
of protective T cells from BALB/c mice chronically infected with
Leisbmania donovani. J Immunof 1988, 141:2132-2137. This paper is the hrst demonstrating transfer of protection against viscerai leishmaniasis by a T-cell line Scorr P, NATOVITZP, COFFMANRL, PEARCEE, SHERA hnmunoregulation of cutaneous leishmaniasis. T cell lines that transfer protective immunity or exacerbation belong to different T helper subsets and respond to distinct parasite antigens. J E~J Med 1988, 168:167~1684. This paper demonstrates that Tul and TB2 celi lines function in oioo to either protect against or exacerbate leishmanial infection. 42. ??e
43. ??e
MLJUER 1, LOUISJA: Immunity to experimental
infection with
Leisbmania major: generation of protective L3T4+ T-cell
clones recognizing antigen(s) associated with live parasites. Eur J Immund 1989, 19865872. The investigators have established a T-cell clone that provides protee tion against L major. Their most interesting obsetvation is that this clone will oniy respond to living promastigotes. 44. ??
SCOT-~P, CASPARP, SHERA: Protection
against Lefsbmanfa major in BAIB/c mice by adoptive transfer of a T cell
clone recognixing a low molecular weight antigen released by promastigotes. J Immund 1990, 144:107%1079. This paper identRies and partially characterizes an antigen recognized by a T-cell clone capable of transferring protection against L. major infection.