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Immunology Paper alert
Immunology Paper alert A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.
Current Opinion in Immunology 1998, 10:1-6 http:/Ibiomednet.com/elecrefl/0952791501000001
© Current Biology Ltd ISSN 0952-7915
Contents (chosen by) Antigen recognition (Elliott) Innate immunity (Bonneville) Lymphocyte development (Kruisbeek) Immunological techniques (Liu) Lymphocyte activation and effector functions (Ono) Immunity to infection (Bonneville) HIV (Rowland-Jones) Genetic effects on immunity (Ono) Cancer (One) Transplantation (Wood) Atopic allergy and hypersensitivity (Ono) Autoimmunity (Bonneville)
• of special interest o• of outstanding interest
Antigen recognition Selected by Tim Elliott John Radcliffe Hospital, Oxford, UK HLA-DO is a negative modulator of HLA-DM-mediated MHC class II peptide loading. VanHam SM, Tijn EPM, Lillemeier BF, Gruneberg U, Van Meijgaarden KE, Pastoors L, Verwoerd D, Tulp A, Canas B, Rahman D et a/.: Curt Biol 1997, 7:950-958. eo Significance: Expression of HLA-DO could influence the repertoire of peptides which can be presented to CD4+T cells by class II MHC molecules. The pattern of HLA-DO expression suggests that it could be important in regulating thymic tolerance to self-antigens and regulating T-cell responses in the periphery at the level of antigen presentation by B cells. Findings: HI.A-DO is a class II MHC-like molecule encoded in the MHC class II region and is expressed in B cells and thymic epithelium. This paper reports that its expression increases the cell-surface expression of class II MHC with class II-associated invariant peptide (CLIP) complexes and decreases the conversion of class II MHC molecules to the SDS-stable conformation normally associated with a functional molecule which is loaded with antigenic peptides. In support of this, VanHam et aL show that DO expression inhibits antigen presentation to T cells via the class II MHC antigen processing pathway. Both groups show that DO acts by binding to and inhibiting the function of HLA-DM - a molecular chaperone that facilitates the exchange of CLIP for antigenic peptides in the class II MHC peptide-binding groove. VanHam et aL claim that inhibition is partial. A new MHC locus that influences class I peptide presentation. Simmons WA, Roopenian DC, Summerfield SG, Jones
RC, Galocha B, Christianson G J, Maika SD, Zhou M, Gaskell S J, Bordoli RS et aL: Immunity 1997, 7:641-653. oo Significance: This careful study suggests the presence of at least one molecule, as yet undiscovered, which is functionally polymorphic and which can influence the repertoire of peptides which can be presented to cytotoxic T cells by class I MHC molecules. Findings: Having followed up on an earlier chance observation, the authors have identified a polymorphic locus (called cim2 for Class I modifier-2) in both mice and rats which influences the repertoire of peptide antigens that can be presented by MHC class I molecules. Thus dominant and recessive alleles were identified with respect to their ability to permit the presentation of an HLA-B27-restricted epitope. Reverse phase liquid chromatography analysis of peptides eluted from immunopurifled HLA-B2?, H-2Db and H-2Lq/Dq expressed on different cim2 allelic backgrounds indicates different but overlapping ligand populations. In mice, the gene maps between K and Pb in the MHC and is therefore not one of the known MHC-linked genes involved in the class I MHC antigen processing pathway. In rats, the locus (which has not been mapped) functions independently of the allelism at the TAP2 locus.
Innate immunity Selected by Marc Bonneville Institut de Biologie, Nantes, France Identification and molecular characterization of fractalkine receptor CX3CR1, which mediates both leukocyte migration and adhesion. Imai T, Hieshima K, Haskell C, Baba M, Nagira M, Nishimura M, Kakizaki M, Takagi S, Nomiyama H, Schall TJ, Yoshie O: Cell 1997, 91:521-530. • o Significance: This provides a unified model coupling cell adhesion and chemotaxis through the identification of leukocyte receptors involved in both processes. This could lead to definition of new targets for anti-inflammatory agents. Findings: A seven-transmembrane receptor for fractalkine (Fk), a CX3C chemokine inducing both adhesion and migration of leukocytes, was identified by testing the binding of an Fk-alkaline phosphatase fusion protein (Fk-SEAP) to known CC chemokine receptors. Fk-SEAP bound with high affinity (100 pM) to V28, a seven-transmembrane receptor present on most natural killer cells, monocytes and a subset of CD3+T cells. Direct involvement of Fk and V28 receptors for CX3C chemokines (herein termed CX3CR1) in both adhesion and migration was demonstrated by studying binding of CX3CRI-expressing cells to immobilized purified soluble Fk, and transendothelial migration of CX3CRl-expressing leukocytes in response to soluble Fk. The signalling machinery required for V28 receptor mediated adhesion and migration were distinct, as only the latter required pertussis toxin-sensitive G proteins. Defects in macrophage recruitment and host defence in mice lacking the CCR2 chemokine receptor. Kurihara T, Warr G, Loy J, Bravo R: J Exp Med 1997, 186:1757-1762. • Significance: This study provides the first genetic evidence for a key role of CCR2, a CC chemokine receptor for macrophage chemotattractant protein-1 in macrophage recruitment and early defense mechanisms against bacterial pathogens.
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Findings: Mice deficient for CCR2 were generated through targeted disruption of the ccr2 gene. While ccr2-/- mice had no obvious defect in hematopoietic development, they failed to recruit macrophages in an experimental peritoneal inflammation model (Le. following intraperitoneal injection of thioglycollate), and were unable to clear infection by intracellular bacteria, such as Listeria monocytogenes. Impaired mast cell-dependent natural immunity in complement C3-deficient mice. Prodeus AP, Zhou X, Maurer M, Galli S J, Carroll MC: Nature 1997, 390:172-175. • Significance: The results demonstrate an essential role of complement activation in mast-cell-dependent inflammatory responses. Findings: Acute septic peritonitis induced by caecal ligation and puncture (CLP) is known to depend primarily on mast cells and tumor necrosis factor-(z (FNF-c(). C4 and C3 complementdeficient mice showed increased sensitivity to CLP as compared to wild-type controls; sensitivity was accompanied by reductions of peritoneal mast cell degranulation, production of TNF-(~ (an important mediator in mast-cell-dependent models of natural immunity), neutrophil recruitment and clearance of bacteria. All these defects were complement-dependent since activation of mast cells, TNF-~. production and resistance to CLP were restored by treatment of C3-deficient mice with purified C3 protein. Lastly, the fact that mice deficient for CD35 (the complement C3b receptor) were highly sensitive to CLP suggests a role for this receptor in complement-dependent mast cell activation. Lymphocyte development Selected by Ada M Kruisbeek The Netherlands Cancer Institute, Amsterdam, The Netherlands Identification of clonogenic common lymphoid progenitors in mouse bone marrow. Kondo J, Weissman IL, Akashi K: Cell 1997, 91:661-672. • Significance: The existence of a common lymphoid progenitor whose developmental potential is restricted to T cells, B cells and natural killer (NK) cells is controversial. This paper provides evidence for the existence of such common lymphoid progenitors in sites of early hematopoiesis. Findings: The Lin- IL-TR + Thy-1 - Sca-11 ow c-kit low population in adult mouse bone marrow contains reconstitution capacity in vivo for T, B and NK cells, but not for cells of the myeloid lineage. Single cells from this population could generate both T and B cells. T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus. Punt JA, Havran W, Abe R, Sarin A, Singer A: J Exp Med 1997, 186:1911-1922. • Significance: Since TCR-triggered thymocyte apoptosis represents an important mechanism for negative selection among developing T cells, the mechanism(s) involved have received much attention. It has been puzzling that in vivo studies show this process to be CD28-dependent, while CD28-deficient mice have no defect in negative selection. The present paper offers a solution for this dilemma. Findings: Apoptosis of thymocytes induced by platebound antiTCR reagents is shown to be strictly dependent on co-triggering of the CD28 receptor, and no other known co-stimulatory receptors can mimic the action of CD28 engagement. Under
different conditions, however, CD28 is not required: in the presence of antigen-presenting cells, both wild-type and CD28-deficient thymocytes will undergo apoptotic death when triggered by anti-TCR antibodies. Enforced Bcl-2 expression inhibits antigen-mediated clonal elimination of peripheral B cells in an antigen dose-dependent manner and promotes receptor editing in autoreactive, immature B cells. Lang J, Arnold B, H&mmerling G, Harris AW, Korsmeyer S, Russell D, Strasser A, Nemazee D: J Exp Med 1997, 186:1513-1522. • Significance: The Bcl-2 protein is highly expressed in longlived lymphocytes and inhibits some forms of apoptosis. This study shows that enforced expression of Bcl-2 can rescue mature, but not immature, B cells from apoptotic death induced by antigen-receptor triggering. Findings: Transgenic mice with enforced Bcl-2 expression in lymphocytes were bred with mice transgenic for anti-Kk,b-specific immunoglobulin. Central and peripheral tolerance in the progeny was compared to that in mice transgenic for the antiKk,b-specific immunoglobulin receptor only. It was found that central tolerance (Le. the tolerance mechanism acting on immature B cells in the bone marrow) was not affected by Bcl-2 expression. In contrast, Bcl-2 expression protected peripheral B cells from apoptosis induced by exposure to Kb antigen. Exit of the pre-TCR from the E R / c i s - Golgi is necessary for signalling differentiation, proliferation, and allelic exclusion in immature thymocytes. O'Shea CC, Thornell AP, Rosewell IR, Hayes B, Owen MJ: Immunity 1997, 7:591-599. • Significance: The pre-TCR is essential for signalling the development of immature thymocytes. A key question is whether the low level of surface expression of the pre-TCR is essential for its signalling function, or whether signalling can occur from an intracellular form of pre-TCR. This study shows that exit of the pre-TCR from the endoplasmic reticulum (ER)/cis-Golgi compartment is required for thymocyte development. Findings: Mice were generated with a transgenic human TCR chain, with or without an ER-retention signal. Only the transgenic TCR 13 chain with an ER-retention signal was able to signal inhibition of endogenous rearrangements of TCR ~ chain genes, and to rescue the defect in thymocyte development in TCR ~ chain knockout mice. Transgenic TCR ~ chain retained in the ER was unable to perform these functions. Immunological techniques Selected by Yang Liu New York University, New York, USA CD4+T cell help impairs CD8+T cell deletion induced by cross-presentation of self-antigens and favors autoimmunity. Kurts C, Carbone FR, Barnden M, Blanas E, Allison J, Heath WR, Miller JFAP: J Exp Med 1997, 186:2057-2062. • - Significance: This is the latest of a series of elegant studies from the group on activation and tolerance of CD8 + T cells that recognize a model tissue antigen after it is taken up and presented by professional antigen-presenting cells. The current study revealed a critical role for CD4 + T cells in the survival of activated CD8 + T cells, which recognized the cross-presented antigen. Utilization of 5,6-carboxy-succinimidyl-fluoresceine-ester (CFSE)-Iabeling of transgenic T cells allows direct measurement of the kinetics and history of CD8 + T cell clonal expansion in vivo. Findings: Firstly, antigen-specific CD4 + T cells enhance in vivo pathogenicity of CD8 + T cells specific for a model tissue anti-
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gen in pancreatic islet cells; secondly, antigen-specific CD4 + T cells prevent deletion of activated CD8 + T cells; thirdly, CD4 + T cells do not enhance clonal expansion of CD8 + T cells.
Phenotypic and functional separation of memory and effector human CD8+T cells. Hamann D, Baars PA, Rep MHG, Hooibrink B, Kerkhof-Garde SR, Klein MR, Van Lier RAW: J Exp Med 1997, 186:1407-1418. • Significance: For the the first time, multiple-color flow cytometry revealed phenotypic distinctions between memory and effector CD8 + T cells. Findings: The authors reported the existence of two discrete primed subpopulations within the circulating human CD8 + T cell subset. Firstly, CD45RA" CD45R0 + cells are found, reminiscent of memory-type CD4 + T cells; secondly, a primed population of CD8 + T cells is characterized by CD45RA expression with concomitant absence of expression of the costimulatory molecules CD27 and CD28. Lymphocyte activation and effector functions Selected by Santa Ono Schepens Eye Research Institute, Cambridge Massachusetts, USA An indirect effect of Stat51 in IL-2-induced proliferation: a critical role for Stat5a in IL-2-mediated IL-2 receptor alpha chain induction. Nakajima H, Liu X-W, Wynshaw-Boris A, Rosenthal IA, Imada K, Finbloom DS, Hennighausen L, leonard WJ: Immunity 1997, 7:691-701. • . Significance: Interaction of IL-2 with the multi subunit highaffinity IL-2 receptor (IL-2R) is required for maximal responsiveness to antigenic stimuli in vivo. This group shows that the Stat5a transactivator is required for the inducible expression of the IL-2R (x chain (IL-2Rc0, and thus for antigen-mediated activation in vivo. The data demonstrate that STATs are required for the expression of both cytokines and their receptors, as might be expected for receptor-ligand pairs which operate via an autocrine mechanism. Findings: By generating Stat5a-knockout mice, the authors show that Stat5a is required for inducible expression of IL-2R(x. Splenocytes isolated from the knockout mice exhibit reduced proliferative capacity in response to IL-2, although responsiveness is nearly normal at concentrations sufficiently high to trigger intermediate affinity IL-2Rs. In v/vo, the knockout mice had defective responses to the superantigen staphylococcal enterotoxin B, as shown by impaired expansion of V~ 8+T cells. Fasmediated death was, however, normal in the knockout mice. T ceils from Jak3-deficient mice have intact TCR signaling, but increased apoptosis. Thomis DC, Lee W, Berg LJ: J Immunol 1997, 159:4708-4720. • Significance: Jak3 is required for signal transduction from the common y chain of cytokine receptors. Mice deficient in Jak3 have previously been shown to have T cells which are functionally unresponsive (as would be expected from the clinical phenotype of Jak3-deficient humans). Nevertheless, mature T cells in these mice exhibit an otherwise 'activated' phenotype, suggesting that Jak3 may not have a critical role in TCR signaling. This work clearly demonstrates that this is the case and strongly argues that the sole role of Jak3 in T cells is to mediate signaling from the common y chain. Findings: Since thymocytes and peripheral T cells from Jak3deficient mice are unresponsive, the investigators analyzed tyrosine phosphorylation and intracellular calcium levels in activated T cells from these and control mice. Upregulation of the surface
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activation markers CD44, CD69 and CD25 were unaffected. Identical patterns of tyrosine phosphorylation and elevation in intracellular calcium levels were also observed in both sets of mice. Elegant studies involving the crossing of the Jak3-deficient animals with transgenic for MHC class I-or II-restricted T-cell receptors showed that T cells are activated by antigen in vivo and cells with an activated/memory phenotype accumulate. Thus, the immune-deficient phenotype of Jak3-deficient mice and humans may be due solely to defective secondary signaling from common "y chain of the cytokine receptors. In the absence of this signal, the T cells were found to have an increased rate of apoptosis in vivo.
Alpha4betal integrin-mediated tyrosine phosphorylation in human T ceils. Hunter AJ, Shimizu Y: J Immuno! 1997, 159:4806-4814. • Significance: In addition to signaling through the TCR/CD3 complex and cytokine receptors, the 131 subfamily of integrins has been shown to enhance responses in T ceils stimulated through the TCR. However, relatively little is known about how 131 integrin stimulation leads to signal transduction. This work identifies three substrates that are tyrosine phosphorylated upon 131 integrin stimulation in human T cells. Findings: Stimulation of the H9 T cell line through O~41~1 w a s shown to result in rapid tyrosine phosphorylation of 105 kDa and 115 kDa proteins (peaking within minutes). These proteins were shown to contain Src homology (SH)2-binding motifs in precipitation experiments using glutathione s-transferase-SH2 fusion proteins. Both Crk-reactive and Fyn-reactive proteins were shown to be phosphorylated by integrin stimulation. Sequential precipitation experiments showed the Fyn-reactive protein to be 115 kDa and the Crk-reactive protein to be 105 kDa. Immunoblotting experiments further showed that the 105 and 115 kDa proteins are antigenically distinct from Cbl, focal adhesion kinase and Pyk2. Stimulation was also shown to result in the association of Crk with 105 and 115 kDa proteins. Future studies will focus on the characterization and functional dissection of these two signaling proteins. Characterization of CD40 signaling determinants regulating nuclear factor-~B activation in B lymphocytes. Hsing Y, Hostager BS, Bishop GA: J Immuno11997, 159:4898-4906. • Significance: Activation of B lymphocytes requires CD40-mediated signaling. One consequence of CD40-mediated signaling is the nuclear translocation of NFKB. Using NF}~B translocation as an endpoint, the authors have made fundamental progress toward our understanding of CD40-mediated signaling by dissecting regions of the CD40 molecule required for this phenomenon. Most interestingly, the data implicate a pathway which is distinct from the Jak3, TRAF3 or TRAF5 signalling pathways. A second intriguing result was that nuclear translocation of NFKB in this system occurred via a mechanism that is apparently independent of tyrosine phosphorylation, yet dependent on I~B degradation. Findings: A panel of stable transfectants expressing mutant CD40 molecules was generated in the M12.4.1 and CH12.LX cell lines. The 22 carboxy-terminal amino acids were shown to be required for NF-~B activation. However, residues T242, S249 and $252 (in single-letter code for amino-acids) were not solely responsible for signal transduction, as mutagenesis of these residues did not inhibit activation of NF~B. The transmembrane domain was shown to be nonessential for CD40-mediated NFKB translocation, which contrasts with the hypothesis that CD40 interaction with p23 protein is required for this signal transduction process. All Rel family proteins except for RelB and
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p52 were shown to be translocated to the nucleus upon CD40 ligation.
Immunity to infection Selected by Marc Bonneville Institut de Biologie, Nantes, France
CD4 + responses, but the authors find vigorous proliferative responses to the p24 and gp120 antigens of HIV, associated with the production of IFN-~' and the HIV-suppressing CC chemokines, in a cohort of long-term nonprogressors. Furthermore, there is an inverse correlation with the extent of the proliferative response to p24 and the plasma viral load.
Protection against invasive amebiasis by a single monoclonal antibody directed against a lipophosphoglycan antigen localized on the surface of Entamoeba histolytica. Marinets A, Zhang T, Guillen N, Gounon P, Bohle B, Vollmann U, Scheiner O, Wiedermann, Stanley SL, Duch~ne M: J Exp Med 1997, 186:1557-1565. • Significance: The first report demonstrating protective capacities of a monoclonal antibody reactive against Entamoeba histolytica, the agent of invasive amebiasis in humans. Findings: Monoclonal antibodies (mAbs) were raised against membrane preparations from E. histolytica. One mAb (EH5) reacted much better against E. histolytica than against nonpathogenic Entamoeba strains, and was shown to recognize a lipophosphoglycan on the basis of several indirect biochemical results. Protective capacities of EH5 mAb were studied in severe combined immunodeficiency mice challenged with E. histolytica: while 6/6 control mice developed amebic liver abscesses 7 days after challenge, only 1/12 mice treated with a single dose of EH5 mAb 24 hours before challenge developed amebic abscesses (p<0.0005).
Recovery of replication-competent HIV despite prolonged suppression of plasma viraemia. Wong JK, Hezareh M, Gunthard HF, Havlir DV, Ignacio CC, Spina CA, Richman DD: Science 1997, 278:1291-1295. AND Identification of a reservoir for HIV-1 in patients on highly active antiretroviral therapy. Finzi D, Hermankova M, Pierson T, Carruth LM, Buck C, Chaisson RE, euinn TC, Chadwick K, Margolick J, Brookmeyer R et al.: Science 1997, 278:1295-1300. • Significance: Despite the initial optimism that effective combination antiretroviral therapy might result in long-term suppression and even elimination of replicating HIV, these studies show that an active viral reservoir remains. Findings: These two studies examine patients who had experienced prolonged periods (more than one year) of undetectable plasma viraemia on combination antiretroviral therapy. Replicating virus could readily be isolated from resting CD4 + T cells taken from their peripheral blood. There was little evidence of viral acquisition of drug-resistance mutations, implying that the problem is viral latency rather than drug failure.
A crucial role for B cells in neuroinvasive scrapie. Klein MA, Frigg R, Flechsig E, Raeber AJ, Kalinke U, Bluethmann H, Bootz F, Suter M, Zinkernagel RM, Aguzzi A: Nature 1997, 390:687690. • e Significance: This study demonstrates a central role of mature B cells in peripherally acquired scrapie, a finding with important public health implications. Findings: Development of scrapie following peripheral inoculation of prion proteins (PrPsc) depends on PrPsc expansion within cells of the lymph•reticular system. Cells responsible for prion propagation were identified by studying incidence of neuroinvasive scrapie following intraperitoneal inoculation of PrPsc in mice with defects in development of either T cells, follicular dendritic cells (FDCs) or B cells. While mutations affecting T cells or FDCs had no effect on development of the disease, all mutations disrupting differentiation of B cells prevented deveF opment of clinical scrapie. The fact that scrapie developed unaffected in mice carrying exclusively IgM, with a limited repertoire not directed against PrP, suggests a role for prions in propagation of mature B cells regardless of the specificity of their receptors.
Genetic effects on immunity
HIV Selected by Sarah Rowland-Jones Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK Vigorous HIV-l-specific CD4+T-cell responses associated with control of viraemia. Rosenberg ES, Billingsley JM, Caliendo A, Boswell SL, Sax PE, Kalams SA, Walker BD: Science 1997, 278:1447-1450. ee Significance: The key to a successful immune response to HIV may be the ability to generate and maintain virus-specific CD4 + T-cell responses. Findings: It has previously been difficult to identify immune responses which reliably correlate with the outcome of HIV infection. Most HIV-infected De•pie lack detectable HIV-specific
Selected by Santa Ono Schepens Eye Research Institute, Cambridge Massachusetts, USA IL-4 prevents insulitis and insulin-dependent diabetes mellitus in nonobese diabetic mice by potentiation of regulatory T helper-2 cell function. Cameron MJ, Arreaza GA, Zucker P, Chensue SW, Strieter RM, Chakrabarti S, Delovitch TL: J Immuno/1997, 159:4686-4693. • Significance: Immune deviation in both rodent and human insulin-dependent diabetes mellitus (IDDM) has been documented with respect to the ratio of Thl/Th2 cytokines produced upon T-cell activation. Indeed, IDDM can be prevented in nonobese diabetic (NOD) mice by repeated injections of IL-4, and by transgenic expression of IL-4 from pancreatic islets. It has been assumed, but not directly demonstrated, that the protective mechanism utilized by IL-4 is the correction of immune deviation toward the Thl phenotype in disease-prone subjects. This report shows that treatment with IL-4 does indeed potentiate Th2 responses in protected mice, and that inflammatory responses in the pancreas and other sites of infiltration are decreased as a result of this correction in cytokine balance. Findings: As shown previously, a structured regimen of IL-4 treatment prevents IDDM in female NOD mice. Lymphocytic infiltration of the pancreas, thyroid and salivary glands is markedly inhibited by treatment with IL-4. Treated animals exhibit enhanced IL-4 production (among thymocytes, splenic T cells and islet infiltrating cells), without a marked increase in IgE levels. Adoptive transfer of T cells from the IL-4 treated mice was able to delay the onset of IDDM in NOD.scid recipients. These data indicate that hyporesponsiveness of endogenous Th2 cells can be rescued by exogenous IL-4 administration and that the regulatory Th2 cells can efficiently suppress onset of diabetes. Autoantigen recognition by human CD8 T cell clones. Enhanced agonist response induced by altered peptide lig-
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ands. Dressel A, Chin JL, Sette A, Gausling R, Hollsberg P, Hafler DA: J Immuno/1997, 159:4941-4951. • Significance: This study supports the hypothesis that molecular mimics on pathogens may drive the clonal expansion of CD8 + auto-reactive T cells during the onset of multiple sclerosis. Findings: Using a computer algorithm, PLP- and MBP- derived peptides were identified and tested for their ability to bind to HLMA-A2.1. Twenty-seven peptide-reactive T cell lines were generated from both normal and MS patients. All cell lines were CD8 +. Analogue peptide ligands were then generated by replacement of sequential amino acids in the defined epitopes. Critical MHC contact and TCR contact residues were determined by in vitro assays. Somewhat surprisingly, the Tcell clones were remarkably unaffected by substitutions in the peptide sequence, and different T cell clones were sensitive to distinct amino acid changes. Certain analogues behaved as superagonists compared with the native peptide epitope, with greater affinities for HLA-A2 and consequent reductions in the concentration of peptides required for a half maximal activation response. Recombinant T cell receptor molecules can prevent and reverse experimental autoimmune encephalomyelitis. Kumar V, Coulsell E, • b e t B, Hubbard G, Sercarz E, Ward ES: J/mmunol 1997, 159:5150-5156. • Significance: Many autoimmune diseases undergo spontaneous remission. Recent evidence has suggested that this is achieved through the action of regulatory T cells which recognize antigenic determinants within the TCRs of pathogenic T cell clones. The authors show that disease-susceptible animals can be protected from the development of EAE by pre-priming with soluble single chains of TCRs (scTCRs) of the same clonality as the predominant autoaggressive T cells. Moreover, they show that ongoing disease can be reversed with an optimized dose of the scTCRs. These data indicate that multiple sclerosis and other autoimmune diseases may potentially be treated by activating regulatory T cells directed against predominant TCR sequences encoded by autoreactive T cells. Findings: The investigators identified a single epitope (B5) within the V~8.2 chain which induced strong proliferation in cells from mice susceptible to EAE. Mice primed with scTCR harboring the same B5 epitope were protected from major basic protein-induced EAE. Treatment of diseased mice with low levels of the scTCR reversed the disease, while those treated with high levels exhibited exacerbation of disease symptoms. The degree of protection from disease was shown to correlate with the level of priming of regulatory CD4 + T cells. Despite this, both CD4 + and CD8 + T cells appear to be required for scTCR-mediated control of EAE. Spontaneous autoimmune diabetes in monoclonal T cell nonobese diabetic mice. Verdaguer J, Schmidt D, Amrani A, Anderson B, Averill N, Santamaria P: J Exp Med 1997, 186:1663-1676. 0- Significance: Long-standing experiments from a multiplicity of laboratories have implicated both CD4 + and CD8 + T cells in the path•genesis of type I diabetes, and this work clearly shows that the two subsets of cells co-operate in diabetogenesis. The elegant work involves the crossing of TCR-transgenic mice with mice deficient in recombination activating gene (RAG)-2. Findings: TCR-transgenic mice restricted against Kd or I-Ag7 were generated and crossed with RAG-2 deficient nonobese diabetic mice. CD8 + Kd-restricted TCR-transgenic mice re-
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quired the presence of CD4 + transgenic T cells for efficient homing into the pancreatic Cancer Selected by Santa On• Schepens Eye Research Institute, Cambridge Massachusetts, USA TCR vaccines for active immunotherapy of T cell malignancies. Okada CY, Wong CP, Denney DW, Levy R: J Immunol 159:5516-5528. • Significance: An elegant study which demonstrates the feasibility and efficacy of vaccination against clonotypic T-cell tumors using soluble TCRs cloned from the T cell tumor. High levels of soluble TCR were expressed by replacing the transmembrane portions of the TCR cDNAs with sequences encoding phosphatidylinositol linkages. Following cleavage with phospholipase and affinity chromatography, the soluble ed~ TCR protein was used as a vaccine in conjunction with the keyhole limpet haemocyanin adjuvant. Findings: Specific anti-TCR humoral and T-cell responses were generated following immunization. TCR repertoire was unaffected in immunized mice. The mice were protected from subsequent lethal doses of the T cell tumor line. The requirement for both B cells and CD8 + cells in the anti tumor response was demonstrated using lineage-deficient animals. Transplantation Selected by Kathryn Wood John Radcliffe Hospital, Oxford, UK Complementation of dominant suppression implicates CD98 in integrin activation. Fenczik C, Sethi T, Ramos J, Hughes P, Ginsberg M: Nature 1997, 390:81-85. o• Significance: Integrin activation is required for cell adhesion and for infiltration of recipient leukocytes into transplanted organs and tissues. Regulators of integrin-mediated cell adhesion, such as CD98, identified in this paper, may provide novel targets for preventing inflammation and rejection. Findings: CD98, an early marker of T-cell activation that associates with functional integrins, was found to regulate integrin activation. Cross-linking of CD98 by monoclonal antibody binding stimulated ~l-integrin-dependent cell adhesion. Randomised trial of basiliximab versus placebo for control of acute cellular rejection in renal all•grafts. Hashan R, Moore R, Amlot P, Schmidt A-G, Abeywickrama K, Soulillou J-P, and for the CHIB 201 study group.: Lancet 1997, 350:11931198. • Significance: A chimeric monoclonal antibody to IL-2 receptor (CD25), basiliximab, reduced the incidence of acute renal rejection significantly. It is possible that basiliximab could be used routinely to control transplant rejection. Findings: Evidence that CD25 is an effective target for prevention of rejection. The incidence of acute rejection was reduced significantly; 29.8o/0 in patients treated with the monoclonal antibody versus 44% in the placebo group. Atopic allergy and hypersensitivity Selected by Santa On• Schepens Eye Research Institute, Cambridge Massachusetts, USA Functional properties of human intestinal mast cells cultured in a new culture system: enhancement of igE receptor-dependent mediator release and response to
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stem cell factor. Bischoff SC, Schwengberg S, Raab R, Manns MP: J/mmuno/159:5560-5568. • Significance: The study of human allergic diseases has been complicated by the difficulty of obtaining highly enriched populations of mast cells and basophils. While high-level purification has been achieved for human basophils using the method of Lichtenstein, the high-level purification of human mast cells to has been difficult. This study describes a cell culture system which results in nearly 1000/0 pure mast cells from human intestinal tissue. This method should greatly accelerate studies on the cell biology of mast cell responses to allergen, and aid in the screening of pharmaceuticals. Findings: Using a four-step enzymatic process intestinal mast cells were purified from both large and small bowel. Mast cells were further enriched on discontinuous Percoll gradients and using immunomagnetic beads. From this point, preparations of mast cells at 6.60/0 purity were cultured in the presence of recombinant stem cell factor and IL-3. After approximately 100 days, nearly 100°/0 of surviving cells were mast cells. Studies of histamine and leukotriene release showed that the cultured human mast cells mimicked more closely the functional status of mast cells in vivo compared to freshly isolated mast cells. This provides a further reason to employ this method of generating highly purified human mast cell populations.
Autoimmunity Marc Bonneville Institut de Biologie, Nantes, France Spontaneous autoimmune diabetes in monoclonal T cell nonobese diabetic mice. Verdaguer .I, Schmidt D, Amrani A, Anderson B, Averill N, Santamaria P: J Exp Med 1997, 186:1663-1676. • Significance: Unlike widely accepted models, this study suggests an early diabetogenic role of CD4 + T cells in diabetesprone nonobese diabetic (NOD) mice followed by a late implication of both CD4 + and CD8 + subsets in diabetes progression. Findings: Incidence of spontaneous diabetes was studied in NOD mice transgenic for TCRs derived from either CD4 + or CD8 + diabetogenic T-cell clones (named 4.1 and 8.3 TCR respectively) and in corresponding recombinase-deflcient (RAG-) TCR-transgenic mice (which thus bear a monoclonal T-cell repertoire). While diabetes frequency and severity were comparable in RAG + and RAG- mice transgenic for the 4.1 TCR, they were both reduced in RAG- mice transgenic for the 8.3 TCR as compared to RAG + counterparts. Delayed diabetes onset
in RAG- 8.3 NOD mice was due to inefficient accumulation of 8.3 TCR-bearing CD8 + T cells in pancreatic islets, and was restored by passive administration of CD4 + splenic cells from nontransgenic NOD mice. These results suggest that efficient recruitment of CD8 + cells in pancreatic islets requires a CD4dependent signal and therefore is preceded, or accompanied, by recruitment of autoreactive CD4 + T cells. Regulation of experimental autoimmune encephelomyeliUs by Natural Killer (NK) cells. Zhang BN, Yamamura T, Kondo T, Fujiwara M, Tabira T: .I Exp Med 1997, 186:1677-1687. • Significance: Demonstrates a regulatory role of NK cells during initiation and effector phases of experimental encephalomyelitis (EAE), a classical model of autoimmune disease. Findings: B6-strain mice depleted of NK cells by antibody treatment develop an aggravated form of EAE induced by sensitization with myelin oligodendrocyte glycoprotein (MOG)-derived peptides. NK depletion also leads to enhancement of EAE passively induced by MOG-specific T cells, in a manner independent of T, B or NK cells since this regulatory effect was observed in ~2 microglobulin- and recombinase-deficient mice. A direct regulatory role of NK cells on the effector phase of the disease is suggested by in vitro experiments showing inhibition of antigen-dependent proliferation of spleen cells by NK cells, through yet undefined mechanisms. Association of human herpes virus 6 (HHV-6) with multiple sclerosis : increased IgM response to HHV-6 early antigen and detection of serum HHV-6 DNA. Soldan SS, Berti R, Salem N, Secchiero P, Flamand L, Calabresi PA, Brennan MB, Maloni HW, McFarland HF, Lin HC et al.: Nat Med 1997, 3:1394-1397. • Significance: Provides indirect evidence involving a ~-herpes virus (HHV-6) in the etiology of multiple sclerosis (MS). Findings: Increased IgM serum responses to an HHV-6 early antigen (p41138) were detected in patients with the relapsingremitting form of MS (RRMS) (n=22), compared with patients with chronic progressive MS (n=l 4), other neurologic diseases( n=31), other inflammatory diseases (n=21) or normal controis (n=14). HHV-6 DNA was detected by nested PCR, using primers to an HHV-6 capsid protein, in sera from 15/50 MS patients (14 RRMS) but in none of the other samples (from healthy controls or from patients with other neurologic or inflammatory diseases), thus suggesting occurrence of active HHV-6 infection in a large fraction of RRMS patients.
Current Opinion in Immunology 1998, 10:1-6 http:/Ibiomednet.com/elecrefl/0952791501000001
© Current Biology Ltd ISSN 0952-7915
Contents (chosen by) Antigen recognition (Elliott) Innate immunity (Bonneville) Lymphocyte development (Kruisbeek) Immunological techniques (Liu) Lymphocyte activation and effector functions (Ono) Immunity to infection (Bonneville) HIV (Rowland-Jones) Genetic effects on immunity (Ono) Cancer (One) Transplantation (Wood) Atopic allergy and hypersensitivity (Ono) Autoimmunity (Bonneville)
• of special interest o• of outstanding interest
Antigen recognition Selected by Tim Elliott John Radcliffe Hospital, Oxford, UK HLA-DO is a negative modulator of HLA-DM-mediated MHC class II peptide loading. VanHam SM, Tijn EPM, Lillemeier BF, Gruneberg U, Van Meijgaarden KE, Pastoors L, Verwoerd D, Tulp A, Canas B, Rahman D et a/.: Curt Biol 1997, 7:950-958. eo Significance: Expression of HLA-DO could influence the repertoire of peptides which can be presented to CD4+T cells by class II MHC molecules. The pattern of HLA-DO expression suggests that it could be important in regulating thymic tolerance to self-antigens and regulating T-cell responses in the periphery at the level of antigen presentation by B cells. Findings: HI.A-DO is a class II MHC-like molecule encoded in the MHC class II region and is expressed in B cells and thymic epithelium. This paper reports that its expression increases the cell-surface expression of class II MHC with class II-associated invariant peptide (CLIP) complexes and decreases the conversion of class II MHC molecules to the SDS-stable conformation normally associated with a functional molecule which is loaded with antigenic peptides. In support of this, VanHam et aL show that DO expression inhibits antigen presentation to T cells via the class II MHC antigen processing pathway. Both groups show that DO acts by binding to and inhibiting the function of HLA-DM - a molecular chaperone that facilitates the exchange of CLIP for antigenic peptides in the class II MHC peptide-binding groove. VanHam et aL claim that inhibition is partial. A new MHC locus that influences class I peptide presentation. Simmons WA, Roopenian DC, Summerfield SG, Jones
RC, Galocha B, Christianson G J, Maika SD, Zhou M, Gaskell S J, Bordoli RS et aL: Immunity 1997, 7:641-653. oo Significance: This careful study suggests the presence of at least one molecule, as yet undiscovered, which is functionally polymorphic and which can influence the repertoire of peptides which can be presented to cytotoxic T cells by class I MHC molecules. Findings: Having followed up on an earlier chance observation, the authors have identified a polymorphic locus (called cim2 for Class I modifier-2) in both mice and rats which influences the repertoire of peptide antigens that can be presented by MHC class I molecules. Thus dominant and recessive alleles were identified with respect to their ability to permit the presentation of an HLA-B27-restricted epitope. Reverse phase liquid chromatography analysis of peptides eluted from immunopurifled HLA-B2?, H-2Db and H-2Lq/Dq expressed on different cim2 allelic backgrounds indicates different but overlapping ligand populations. In mice, the gene maps between K and Pb in the MHC and is therefore not one of the known MHC-linked genes involved in the class I MHC antigen processing pathway. In rats, the locus (which has not been mapped) functions independently of the allelism at the TAP2 locus.
Innate immunity Selected by Marc Bonneville Institut de Biologie, Nantes, France Identification and molecular characterization of fractalkine receptor CX3CR1, which mediates both leukocyte migration and adhesion. Imai T, Hieshima K, Haskell C, Baba M, Nagira M, Nishimura M, Kakizaki M, Takagi S, Nomiyama H, Schall TJ, Yoshie O: Cell 1997, 91:521-530. • o Significance: This provides a unified model coupling cell adhesion and chemotaxis through the identification of leukocyte receptors involved in both processes. This could lead to definition of new targets for anti-inflammatory agents. Findings: A seven-transmembrane receptor for fractalkine (Fk), a CX3C chemokine inducing both adhesion and migration of leukocytes, was identified by testing the binding of an Fk-alkaline phosphatase fusion protein (Fk-SEAP) to known CC chemokine receptors. Fk-SEAP bound with high affinity (100 pM) to V28, a seven-transmembrane receptor present on most natural killer cells, monocytes and a subset of CD3+T cells. Direct involvement of Fk and V28 receptors for CX3C chemokines (herein termed CX3CR1) in both adhesion and migration was demonstrated by studying binding of CX3CRI-expressing cells to immobilized purified soluble Fk, and transendothelial migration of CX3CRl-expressing leukocytes in response to soluble Fk. The signalling machinery required for V28 receptor mediated adhesion and migration were distinct, as only the latter required pertussis toxin-sensitive G proteins. Defects in macrophage recruitment and host defence in mice lacking the CCR2 chemokine receptor. Kurihara T, Warr G, Loy J, Bravo R: J Exp Med 1997, 186:1757-1762. • Significance: This study provides the first genetic evidence for a key role of CCR2, a CC chemokine receptor for macrophage chemotattractant protein-1 in macrophage recruitment and early defense mechanisms against bacterial pathogens.
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Findings: Mice deficient for CCR2 were generated through targeted disruption of the ccr2 gene. While ccr2-/- mice had no obvious defect in hematopoietic development, they failed to recruit macrophages in an experimental peritoneal inflammation model (Le. following intraperitoneal injection of thioglycollate), and were unable to clear infection by intracellular bacteria, such as Listeria monocytogenes. Impaired mast cell-dependent natural immunity in complement C3-deficient mice. Prodeus AP, Zhou X, Maurer M, Galli S J, Carroll MC: Nature 1997, 390:172-175. • Significance: The results demonstrate an essential role of complement activation in mast-cell-dependent inflammatory responses. Findings: Acute septic peritonitis induced by caecal ligation and puncture (CLP) is known to depend primarily on mast cells and tumor necrosis factor-(z (FNF-c(). C4 and C3 complementdeficient mice showed increased sensitivity to CLP as compared to wild-type controls; sensitivity was accompanied by reductions of peritoneal mast cell degranulation, production of TNF-(~ (an important mediator in mast-cell-dependent models of natural immunity), neutrophil recruitment and clearance of bacteria. All these defects were complement-dependent since activation of mast cells, TNF-~. production and resistance to CLP were restored by treatment of C3-deficient mice with purified C3 protein. Lastly, the fact that mice deficient for CD35 (the complement C3b receptor) were highly sensitive to CLP suggests a role for this receptor in complement-dependent mast cell activation. Lymphocyte development Selected by Ada M Kruisbeek The Netherlands Cancer Institute, Amsterdam, The Netherlands Identification of clonogenic common lymphoid progenitors in mouse bone marrow. Kondo J, Weissman IL, Akashi K: Cell 1997, 91:661-672. • Significance: The existence of a common lymphoid progenitor whose developmental potential is restricted to T cells, B cells and natural killer (NK) cells is controversial. This paper provides evidence for the existence of such common lymphoid progenitors in sites of early hematopoiesis. Findings: The Lin- IL-TR + Thy-1 - Sca-11 ow c-kit low population in adult mouse bone marrow contains reconstitution capacity in vivo for T, B and NK cells, but not for cells of the myeloid lineage. Single cells from this population could generate both T and B cells. T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus. Punt JA, Havran W, Abe R, Sarin A, Singer A: J Exp Med 1997, 186:1911-1922. • Significance: Since TCR-triggered thymocyte apoptosis represents an important mechanism for negative selection among developing T cells, the mechanism(s) involved have received much attention. It has been puzzling that in vivo studies show this process to be CD28-dependent, while CD28-deficient mice have no defect in negative selection. The present paper offers a solution for this dilemma. Findings: Apoptosis of thymocytes induced by platebound antiTCR reagents is shown to be strictly dependent on co-triggering of the CD28 receptor, and no other known co-stimulatory receptors can mimic the action of CD28 engagement. Under
different conditions, however, CD28 is not required: in the presence of antigen-presenting cells, both wild-type and CD28-deficient thymocytes will undergo apoptotic death when triggered by anti-TCR antibodies. Enforced Bcl-2 expression inhibits antigen-mediated clonal elimination of peripheral B cells in an antigen dose-dependent manner and promotes receptor editing in autoreactive, immature B cells. Lang J, Arnold B, H&mmerling G, Harris AW, Korsmeyer S, Russell D, Strasser A, Nemazee D: J Exp Med 1997, 186:1513-1522. • Significance: The Bcl-2 protein is highly expressed in longlived lymphocytes and inhibits some forms of apoptosis. This study shows that enforced expression of Bcl-2 can rescue mature, but not immature, B cells from apoptotic death induced by antigen-receptor triggering. Findings: Transgenic mice with enforced Bcl-2 expression in lymphocytes were bred with mice transgenic for anti-Kk,b-specific immunoglobulin. Central and peripheral tolerance in the progeny was compared to that in mice transgenic for the antiKk,b-specific immunoglobulin receptor only. It was found that central tolerance (Le. the tolerance mechanism acting on immature B cells in the bone marrow) was not affected by Bcl-2 expression. In contrast, Bcl-2 expression protected peripheral B cells from apoptosis induced by exposure to Kb antigen. Exit of the pre-TCR from the E R / c i s - Golgi is necessary for signalling differentiation, proliferation, and allelic exclusion in immature thymocytes. O'Shea CC, Thornell AP, Rosewell IR, Hayes B, Owen MJ: Immunity 1997, 7:591-599. • Significance: The pre-TCR is essential for signalling the development of immature thymocytes. A key question is whether the low level of surface expression of the pre-TCR is essential for its signalling function, or whether signalling can occur from an intracellular form of pre-TCR. This study shows that exit of the pre-TCR from the endoplasmic reticulum (ER)/cis-Golgi compartment is required for thymocyte development. Findings: Mice were generated with a transgenic human TCR chain, with or without an ER-retention signal. Only the transgenic TCR 13 chain with an ER-retention signal was able to signal inhibition of endogenous rearrangements of TCR ~ chain genes, and to rescue the defect in thymocyte development in TCR ~ chain knockout mice. Transgenic TCR ~ chain retained in the ER was unable to perform these functions. Immunological techniques Selected by Yang Liu New York University, New York, USA CD4+T cell help impairs CD8+T cell deletion induced by cross-presentation of self-antigens and favors autoimmunity. Kurts C, Carbone FR, Barnden M, Blanas E, Allison J, Heath WR, Miller JFAP: J Exp Med 1997, 186:2057-2062. • - Significance: This is the latest of a series of elegant studies from the group on activation and tolerance of CD8 + T cells that recognize a model tissue antigen after it is taken up and presented by professional antigen-presenting cells. The current study revealed a critical role for CD4 + T cells in the survival of activated CD8 + T cells, which recognized the cross-presented antigen. Utilization of 5,6-carboxy-succinimidyl-fluoresceine-ester (CFSE)-Iabeling of transgenic T cells allows direct measurement of the kinetics and history of CD8 + T cell clonal expansion in vivo. Findings: Firstly, antigen-specific CD4 + T cells enhance in vivo pathogenicity of CD8 + T cells specific for a model tissue anti-
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gen in pancreatic islet cells; secondly, antigen-specific CD4 + T cells prevent deletion of activated CD8 + T cells; thirdly, CD4 + T cells do not enhance clonal expansion of CD8 + T cells.
Phenotypic and functional separation of memory and effector human CD8+T cells. Hamann D, Baars PA, Rep MHG, Hooibrink B, Kerkhof-Garde SR, Klein MR, Van Lier RAW: J Exp Med 1997, 186:1407-1418. • Significance: For the the first time, multiple-color flow cytometry revealed phenotypic distinctions between memory and effector CD8 + T cells. Findings: The authors reported the existence of two discrete primed subpopulations within the circulating human CD8 + T cell subset. Firstly, CD45RA" CD45R0 + cells are found, reminiscent of memory-type CD4 + T cells; secondly, a primed population of CD8 + T cells is characterized by CD45RA expression with concomitant absence of expression of the costimulatory molecules CD27 and CD28. Lymphocyte activation and effector functions Selected by Santa Ono Schepens Eye Research Institute, Cambridge Massachusetts, USA An indirect effect of Stat51 in IL-2-induced proliferation: a critical role for Stat5a in IL-2-mediated IL-2 receptor alpha chain induction. Nakajima H, Liu X-W, Wynshaw-Boris A, Rosenthal IA, Imada K, Finbloom DS, Hennighausen L, leonard WJ: Immunity 1997, 7:691-701. • . Significance: Interaction of IL-2 with the multi subunit highaffinity IL-2 receptor (IL-2R) is required for maximal responsiveness to antigenic stimuli in vivo. This group shows that the Stat5a transactivator is required for the inducible expression of the IL-2R (x chain (IL-2Rc0, and thus for antigen-mediated activation in vivo. The data demonstrate that STATs are required for the expression of both cytokines and their receptors, as might be expected for receptor-ligand pairs which operate via an autocrine mechanism. Findings: By generating Stat5a-knockout mice, the authors show that Stat5a is required for inducible expression of IL-2R(x. Splenocytes isolated from the knockout mice exhibit reduced proliferative capacity in response to IL-2, although responsiveness is nearly normal at concentrations sufficiently high to trigger intermediate affinity IL-2Rs. In v/vo, the knockout mice had defective responses to the superantigen staphylococcal enterotoxin B, as shown by impaired expansion of V~ 8+T cells. Fasmediated death was, however, normal in the knockout mice. T ceils from Jak3-deficient mice have intact TCR signaling, but increased apoptosis. Thomis DC, Lee W, Berg LJ: J Immunol 1997, 159:4708-4720. • Significance: Jak3 is required for signal transduction from the common y chain of cytokine receptors. Mice deficient in Jak3 have previously been shown to have T cells which are functionally unresponsive (as would be expected from the clinical phenotype of Jak3-deficient humans). Nevertheless, mature T cells in these mice exhibit an otherwise 'activated' phenotype, suggesting that Jak3 may not have a critical role in TCR signaling. This work clearly demonstrates that this is the case and strongly argues that the sole role of Jak3 in T cells is to mediate signaling from the common y chain. Findings: Since thymocytes and peripheral T cells from Jak3deficient mice are unresponsive, the investigators analyzed tyrosine phosphorylation and intracellular calcium levels in activated T cells from these and control mice. Upregulation of the surface
3
activation markers CD44, CD69 and CD25 were unaffected. Identical patterns of tyrosine phosphorylation and elevation in intracellular calcium levels were also observed in both sets of mice. Elegant studies involving the crossing of the Jak3-deficient animals with transgenic for MHC class I-or II-restricted T-cell receptors showed that T cells are activated by antigen in vivo and cells with an activated/memory phenotype accumulate. Thus, the immune-deficient phenotype of Jak3-deficient mice and humans may be due solely to defective secondary signaling from common "y chain of the cytokine receptors. In the absence of this signal, the T cells were found to have an increased rate of apoptosis in vivo.
Alpha4betal integrin-mediated tyrosine phosphorylation in human T ceils. Hunter AJ, Shimizu Y: J Immuno! 1997, 159:4806-4814. • Significance: In addition to signaling through the TCR/CD3 complex and cytokine receptors, the 131 subfamily of integrins has been shown to enhance responses in T ceils stimulated through the TCR. However, relatively little is known about how 131 integrin stimulation leads to signal transduction. This work identifies three substrates that are tyrosine phosphorylated upon 131 integrin stimulation in human T cells. Findings: Stimulation of the H9 T cell line through O~41~1 w a s shown to result in rapid tyrosine phosphorylation of 105 kDa and 115 kDa proteins (peaking within minutes). These proteins were shown to contain Src homology (SH)2-binding motifs in precipitation experiments using glutathione s-transferase-SH2 fusion proteins. Both Crk-reactive and Fyn-reactive proteins were shown to be phosphorylated by integrin stimulation. Sequential precipitation experiments showed the Fyn-reactive protein to be 115 kDa and the Crk-reactive protein to be 105 kDa. Immunoblotting experiments further showed that the 105 and 115 kDa proteins are antigenically distinct from Cbl, focal adhesion kinase and Pyk2. Stimulation was also shown to result in the association of Crk with 105 and 115 kDa proteins. Future studies will focus on the characterization and functional dissection of these two signaling proteins. Characterization of CD40 signaling determinants regulating nuclear factor-~B activation in B lymphocytes. Hsing Y, Hostager BS, Bishop GA: J Immuno11997, 159:4898-4906. • Significance: Activation of B lymphocytes requires CD40-mediated signaling. One consequence of CD40-mediated signaling is the nuclear translocation of NFKB. Using NF}~B translocation as an endpoint, the authors have made fundamental progress toward our understanding of CD40-mediated signaling by dissecting regions of the CD40 molecule required for this phenomenon. Most interestingly, the data implicate a pathway which is distinct from the Jak3, TRAF3 or TRAF5 signalling pathways. A second intriguing result was that nuclear translocation of NFKB in this system occurred via a mechanism that is apparently independent of tyrosine phosphorylation, yet dependent on I~B degradation. Findings: A panel of stable transfectants expressing mutant CD40 molecules was generated in the M12.4.1 and CH12.LX cell lines. The 22 carboxy-terminal amino acids were shown to be required for NF-~B activation. However, residues T242, S249 and $252 (in single-letter code for amino-acids) were not solely responsible for signal transduction, as mutagenesis of these residues did not inhibit activation of NF~B. The transmembrane domain was shown to be nonessential for CD40-mediated NFKB translocation, which contrasts with the hypothesis that CD40 interaction with p23 protein is required for this signal transduction process. All Rel family proteins except for RelB and
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p52 were shown to be translocated to the nucleus upon CD40 ligation.
Immunity to infection Selected by Marc Bonneville Institut de Biologie, Nantes, France
CD4 + responses, but the authors find vigorous proliferative responses to the p24 and gp120 antigens of HIV, associated with the production of IFN-~' and the HIV-suppressing CC chemokines, in a cohort of long-term nonprogressors. Furthermore, there is an inverse correlation with the extent of the proliferative response to p24 and the plasma viral load.
Protection against invasive amebiasis by a single monoclonal antibody directed against a lipophosphoglycan antigen localized on the surface of Entamoeba histolytica. Marinets A, Zhang T, Guillen N, Gounon P, Bohle B, Vollmann U, Scheiner O, Wiedermann, Stanley SL, Duch~ne M: J Exp Med 1997, 186:1557-1565. • Significance: The first report demonstrating protective capacities of a monoclonal antibody reactive against Entamoeba histolytica, the agent of invasive amebiasis in humans. Findings: Monoclonal antibodies (mAbs) were raised against membrane preparations from E. histolytica. One mAb (EH5) reacted much better against E. histolytica than against nonpathogenic Entamoeba strains, and was shown to recognize a lipophosphoglycan on the basis of several indirect biochemical results. Protective capacities of EH5 mAb were studied in severe combined immunodeficiency mice challenged with E. histolytica: while 6/6 control mice developed amebic liver abscesses 7 days after challenge, only 1/12 mice treated with a single dose of EH5 mAb 24 hours before challenge developed amebic abscesses (p<0.0005).
Recovery of replication-competent HIV despite prolonged suppression of plasma viraemia. Wong JK, Hezareh M, Gunthard HF, Havlir DV, Ignacio CC, Spina CA, Richman DD: Science 1997, 278:1291-1295. AND Identification of a reservoir for HIV-1 in patients on highly active antiretroviral therapy. Finzi D, Hermankova M, Pierson T, Carruth LM, Buck C, Chaisson RE, euinn TC, Chadwick K, Margolick J, Brookmeyer R et al.: Science 1997, 278:1295-1300. • Significance: Despite the initial optimism that effective combination antiretroviral therapy might result in long-term suppression and even elimination of replicating HIV, these studies show that an active viral reservoir remains. Findings: These two studies examine patients who had experienced prolonged periods (more than one year) of undetectable plasma viraemia on combination antiretroviral therapy. Replicating virus could readily be isolated from resting CD4 + T cells taken from their peripheral blood. There was little evidence of viral acquisition of drug-resistance mutations, implying that the problem is viral latency rather than drug failure.
A crucial role for B cells in neuroinvasive scrapie. Klein MA, Frigg R, Flechsig E, Raeber AJ, Kalinke U, Bluethmann H, Bootz F, Suter M, Zinkernagel RM, Aguzzi A: Nature 1997, 390:687690. • e Significance: This study demonstrates a central role of mature B cells in peripherally acquired scrapie, a finding with important public health implications. Findings: Development of scrapie following peripheral inoculation of prion proteins (PrPsc) depends on PrPsc expansion within cells of the lymph•reticular system. Cells responsible for prion propagation were identified by studying incidence of neuroinvasive scrapie following intraperitoneal inoculation of PrPsc in mice with defects in development of either T cells, follicular dendritic cells (FDCs) or B cells. While mutations affecting T cells or FDCs had no effect on development of the disease, all mutations disrupting differentiation of B cells prevented deveF opment of clinical scrapie. The fact that scrapie developed unaffected in mice carrying exclusively IgM, with a limited repertoire not directed against PrP, suggests a role for prions in propagation of mature B cells regardless of the specificity of their receptors.
Genetic effects on immunity
HIV Selected by Sarah Rowland-Jones Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK Vigorous HIV-l-specific CD4+T-cell responses associated with control of viraemia. Rosenberg ES, Billingsley JM, Caliendo A, Boswell SL, Sax PE, Kalams SA, Walker BD: Science 1997, 278:1447-1450. ee Significance: The key to a successful immune response to HIV may be the ability to generate and maintain virus-specific CD4 + T-cell responses. Findings: It has previously been difficult to identify immune responses which reliably correlate with the outcome of HIV infection. Most HIV-infected De•pie lack detectable HIV-specific
Selected by Santa Ono Schepens Eye Research Institute, Cambridge Massachusetts, USA IL-4 prevents insulitis and insulin-dependent diabetes mellitus in nonobese diabetic mice by potentiation of regulatory T helper-2 cell function. Cameron MJ, Arreaza GA, Zucker P, Chensue SW, Strieter RM, Chakrabarti S, Delovitch TL: J Immuno/1997, 159:4686-4693. • Significance: Immune deviation in both rodent and human insulin-dependent diabetes mellitus (IDDM) has been documented with respect to the ratio of Thl/Th2 cytokines produced upon T-cell activation. Indeed, IDDM can be prevented in nonobese diabetic (NOD) mice by repeated injections of IL-4, and by transgenic expression of IL-4 from pancreatic islets. It has been assumed, but not directly demonstrated, that the protective mechanism utilized by IL-4 is the correction of immune deviation toward the Thl phenotype in disease-prone subjects. This report shows that treatment with IL-4 does indeed potentiate Th2 responses in protected mice, and that inflammatory responses in the pancreas and other sites of infiltration are decreased as a result of this correction in cytokine balance. Findings: As shown previously, a structured regimen of IL-4 treatment prevents IDDM in female NOD mice. Lymphocytic infiltration of the pancreas, thyroid and salivary glands is markedly inhibited by treatment with IL-4. Treated animals exhibit enhanced IL-4 production (among thymocytes, splenic T cells and islet infiltrating cells), without a marked increase in IgE levels. Adoptive transfer of T cells from the IL-4 treated mice was able to delay the onset of IDDM in NOD.scid recipients. These data indicate that hyporesponsiveness of endogenous Th2 cells can be rescued by exogenous IL-4 administration and that the regulatory Th2 cells can efficiently suppress onset of diabetes. Autoantigen recognition by human CD8 T cell clones. Enhanced agonist response induced by altered peptide lig-
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ands. Dressel A, Chin JL, Sette A, Gausling R, Hollsberg P, Hafler DA: J Immuno/1997, 159:4941-4951. • Significance: This study supports the hypothesis that molecular mimics on pathogens may drive the clonal expansion of CD8 + auto-reactive T cells during the onset of multiple sclerosis. Findings: Using a computer algorithm, PLP- and MBP- derived peptides were identified and tested for their ability to bind to HLMA-A2.1. Twenty-seven peptide-reactive T cell lines were generated from both normal and MS patients. All cell lines were CD8 +. Analogue peptide ligands were then generated by replacement of sequential amino acids in the defined epitopes. Critical MHC contact and TCR contact residues were determined by in vitro assays. Somewhat surprisingly, the Tcell clones were remarkably unaffected by substitutions in the peptide sequence, and different T cell clones were sensitive to distinct amino acid changes. Certain analogues behaved as superagonists compared with the native peptide epitope, with greater affinities for HLA-A2 and consequent reductions in the concentration of peptides required for a half maximal activation response. Recombinant T cell receptor molecules can prevent and reverse experimental autoimmune encephalomyelitis. Kumar V, Coulsell E, • b e t B, Hubbard G, Sercarz E, Ward ES: J/mmunol 1997, 159:5150-5156. • Significance: Many autoimmune diseases undergo spontaneous remission. Recent evidence has suggested that this is achieved through the action of regulatory T cells which recognize antigenic determinants within the TCRs of pathogenic T cell clones. The authors show that disease-susceptible animals can be protected from the development of EAE by pre-priming with soluble single chains of TCRs (scTCRs) of the same clonality as the predominant autoaggressive T cells. Moreover, they show that ongoing disease can be reversed with an optimized dose of the scTCRs. These data indicate that multiple sclerosis and other autoimmune diseases may potentially be treated by activating regulatory T cells directed against predominant TCR sequences encoded by autoreactive T cells. Findings: The investigators identified a single epitope (B5) within the V~8.2 chain which induced strong proliferation in cells from mice susceptible to EAE. Mice primed with scTCR harboring the same B5 epitope were protected from major basic protein-induced EAE. Treatment of diseased mice with low levels of the scTCR reversed the disease, while those treated with high levels exhibited exacerbation of disease symptoms. The degree of protection from disease was shown to correlate with the level of priming of regulatory CD4 + T cells. Despite this, both CD4 + and CD8 + T cells appear to be required for scTCR-mediated control of EAE. Spontaneous autoimmune diabetes in monoclonal T cell nonobese diabetic mice. Verdaguer J, Schmidt D, Amrani A, Anderson B, Averill N, Santamaria P: J Exp Med 1997, 186:1663-1676. 0- Significance: Long-standing experiments from a multiplicity of laboratories have implicated both CD4 + and CD8 + T cells in the path•genesis of type I diabetes, and this work clearly shows that the two subsets of cells co-operate in diabetogenesis. The elegant work involves the crossing of TCR-transgenic mice with mice deficient in recombination activating gene (RAG)-2. Findings: TCR-transgenic mice restricted against Kd or I-Ag7 were generated and crossed with RAG-2 deficient nonobese diabetic mice. CD8 + Kd-restricted TCR-transgenic mice re-
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quired the presence of CD4 + transgenic T cells for efficient homing into the pancreatic Cancer Selected by Santa On• Schepens Eye Research Institute, Cambridge Massachusetts, USA TCR vaccines for active immunotherapy of T cell malignancies. Okada CY, Wong CP, Denney DW, Levy R: J Immunol 159:5516-5528. • Significance: An elegant study which demonstrates the feasibility and efficacy of vaccination against clonotypic T-cell tumors using soluble TCRs cloned from the T cell tumor. High levels of soluble TCR were expressed by replacing the transmembrane portions of the TCR cDNAs with sequences encoding phosphatidylinositol linkages. Following cleavage with phospholipase and affinity chromatography, the soluble ed~ TCR protein was used as a vaccine in conjunction with the keyhole limpet haemocyanin adjuvant. Findings: Specific anti-TCR humoral and T-cell responses were generated following immunization. TCR repertoire was unaffected in immunized mice. The mice were protected from subsequent lethal doses of the T cell tumor line. The requirement for both B cells and CD8 + cells in the anti tumor response was demonstrated using lineage-deficient animals. Transplantation Selected by Kathryn Wood John Radcliffe Hospital, Oxford, UK Complementation of dominant suppression implicates CD98 in integrin activation. Fenczik C, Sethi T, Ramos J, Hughes P, Ginsberg M: Nature 1997, 390:81-85. o• Significance: Integrin activation is required for cell adhesion and for infiltration of recipient leukocytes into transplanted organs and tissues. Regulators of integrin-mediated cell adhesion, such as CD98, identified in this paper, may provide novel targets for preventing inflammation and rejection. Findings: CD98, an early marker of T-cell activation that associates with functional integrins, was found to regulate integrin activation. Cross-linking of CD98 by monoclonal antibody binding stimulated ~l-integrin-dependent cell adhesion. Randomised trial of basiliximab versus placebo for control of acute cellular rejection in renal all•grafts. Hashan R, Moore R, Amlot P, Schmidt A-G, Abeywickrama K, Soulillou J-P, and for the CHIB 201 study group.: Lancet 1997, 350:11931198. • Significance: A chimeric monoclonal antibody to IL-2 receptor (CD25), basiliximab, reduced the incidence of acute renal rejection significantly. It is possible that basiliximab could be used routinely to control transplant rejection. Findings: Evidence that CD25 is an effective target for prevention of rejection. The incidence of acute rejection was reduced significantly; 29.8o/0 in patients treated with the monoclonal antibody versus 44% in the placebo group. Atopic allergy and hypersensitivity Selected by Santa On• Schepens Eye Research Institute, Cambridge Massachusetts, USA Functional properties of human intestinal mast cells cultured in a new culture system: enhancement of igE receptor-dependent mediator release and response to
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stem cell factor. Bischoff SC, Schwengberg S, Raab R, Manns MP: J/mmuno/159:5560-5568. • Significance: The study of human allergic diseases has been complicated by the difficulty of obtaining highly enriched populations of mast cells and basophils. While high-level purification has been achieved for human basophils using the method of Lichtenstein, the high-level purification of human mast cells to has been difficult. This study describes a cell culture system which results in nearly 1000/0 pure mast cells from human intestinal tissue. This method should greatly accelerate studies on the cell biology of mast cell responses to allergen, and aid in the screening of pharmaceuticals. Findings: Using a four-step enzymatic process intestinal mast cells were purified from both large and small bowel. Mast cells were further enriched on discontinuous Percoll gradients and using immunomagnetic beads. From this point, preparations of mast cells at 6.60/0 purity were cultured in the presence of recombinant stem cell factor and IL-3. After approximately 100 days, nearly 100°/0 of surviving cells were mast cells. Studies of histamine and leukotriene release showed that the cultured human mast cells mimicked more closely the functional status of mast cells in vivo compared to freshly isolated mast cells. This provides a further reason to employ this method of generating highly purified human mast cell populations.
Autoimmunity Marc Bonneville Institut de Biologie, Nantes, France Spontaneous autoimmune diabetes in monoclonal T cell nonobese diabetic mice. Verdaguer .I, Schmidt D, Amrani A, Anderson B, Averill N, Santamaria P: J Exp Med 1997, 186:1663-1676. • Significance: Unlike widely accepted models, this study suggests an early diabetogenic role of CD4 + T cells in diabetesprone nonobese diabetic (NOD) mice followed by a late implication of both CD4 + and CD8 + subsets in diabetes progression. Findings: Incidence of spontaneous diabetes was studied in NOD mice transgenic for TCRs derived from either CD4 + or CD8 + diabetogenic T-cell clones (named 4.1 and 8.3 TCR respectively) and in corresponding recombinase-deflcient (RAG-) TCR-transgenic mice (which thus bear a monoclonal T-cell repertoire). While diabetes frequency and severity were comparable in RAG + and RAG- mice transgenic for the 4.1 TCR, they were both reduced in RAG- mice transgenic for the 8.3 TCR as compared to RAG + counterparts. Delayed diabetes onset
in RAG- 8.3 NOD mice was due to inefficient accumulation of 8.3 TCR-bearing CD8 + T cells in pancreatic islets, and was restored by passive administration of CD4 + splenic cells from nontransgenic NOD mice. These results suggest that efficient recruitment of CD8 + cells in pancreatic islets requires a CD4dependent signal and therefore is preceded, or accompanied, by recruitment of autoreactive CD4 + T cells. Regulation of experimental autoimmune encephelomyeliUs by Natural Killer (NK) cells. Zhang BN, Yamamura T, Kondo T, Fujiwara M, Tabira T: .I Exp Med 1997, 186:1677-1687. • Significance: Demonstrates a regulatory role of NK cells during initiation and effector phases of experimental encephalomyelitis (EAE), a classical model of autoimmune disease. Findings: B6-strain mice depleted of NK cells by antibody treatment develop an aggravated form of EAE induced by sensitization with myelin oligodendrocyte glycoprotein (MOG)-derived peptides. NK depletion also leads to enhancement of EAE passively induced by MOG-specific T cells, in a manner independent of T, B or NK cells since this regulatory effect was observed in ~2 microglobulin- and recombinase-deficient mice. A direct regulatory role of NK cells on the effector phase of the disease is suggested by in vitro experiments showing inhibition of antigen-dependent proliferation of spleen cells by NK cells, through yet undefined mechanisms. Association of human herpes virus 6 (HHV-6) with multiple sclerosis : increased IgM response to HHV-6 early antigen and detection of serum HHV-6 DNA. Soldan SS, Berti R, Salem N, Secchiero P, Flamand L, Calabresi PA, Brennan MB, Maloni HW, McFarland HF, Lin HC et al.: Nat Med 1997, 3:1394-1397. • Significance: Provides indirect evidence involving a ~-herpes virus (HHV-6) in the etiology of multiple sclerosis (MS). Findings: Increased IgM serum responses to an HHV-6 early antigen (p41138) were detected in patients with the relapsingremitting form of MS (RRMS) (n=22), compared with patients with chronic progressive MS (n=l 4), other neurologic diseases( n=31), other inflammatory diseases (n=21) or normal controis (n=14). HHV-6 DNA was detected by nested PCR, using primers to an HHV-6 capsid protein, in sera from 15/50 MS patients (14 RRMS) but in none of the other samples (from healthy controls or from patients with other neurologic or inflammatory diseases), thus suggesting occurrence of active HHV-6 infection in a large fraction of RRMS patients.