Chemokines in host–protozoan-parasite interactions

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Chemokines in host–protozoan-parasite interactions Marie-Pierre Brenier-Pinchart, Hervé Pelloux, Dorra Derouich-Guergour and Pierre Ambroise-Thomas Here, we review the interactions between parasites and chemokines and chemokine receptors in toxoplasmosis, trypanosomiasis, leishmaniasis, malaria and other diseases caused by protozoan parasites. The potential roles of chemokines after infection by these intracellular pathogens include host defence functions such as leukocyte recruitment, participation in cell-mediated immunity and antiprotozoal activity. However, these interactions can also help the parasite in, for example, the penetration of host cells.

Marie-Pierre BrenierPinchart Hervé Pelloux* Dorra Derouich-Guergour Pierre Ambroise-Thomas Interactions Cellulaires Parasite–Hôte, CNRSER2014, Faculté de Médecine, Université J. Fourier, Domaine de la Merci, 38706 La Tronche, France. *e-mail: hpelloux@ chu-grenoble.fr

In recent years, chemokines and chemokine receptors have become a focus of interest in immunology and microbiology. About 50 chemokines, expressed in a wide range of cell types and tissues, have been identified in humans1,2. These small cytokines (8–10 kDa) have been subdivided into two major subfamilies on the basis of the arrangement of the two N-terminal cysteine residues: CXC and CC chemokines1,2. In the CXC chemokines, the first two cysteines are separated by an amino acid; they are adjacent in CC chemokines1,2. Two other, less well characterized, classes have also been described: the C chemokine (lymphotactin) and CX3C chemokine (fractalkine)1,2. These structural distinctions are associated with the ability to act on particular leukocyte subsets. For example, interleukin 8 (IL-8), a CXC chemokine, acts predominantly on neutrophils, whereas monocyte chemotactic protein-1 (MCP-1), a CC chemokine, attracts predominantly lymphocytes and monocytes (Table 1). Their actions are mediated via specific cell-surface receptors, which are members of the seventransmembrane domain, G-protein-coupled receptor family1. The chemokine–receptor interaction is characterized by considerable promiscuity: one receptor interacts with several chemokines and one chemokine binds to several receptors3. Chemokines are key molecules in recruiting immune cells by chemotaxis, but also act in leukocyte activation, angiogenesis, haematopoiesis, inflammatory diseases and antimicrobial mechanisms1,2. Moreover, chemokines can be secreted in response to bacterial, viral, parasitic, fungal and mycobacterial pathogens4. Protozoan parasites can also induce these cell mediators, and they play various roles in the parasite–host relationship. Toxoplasmosis

The CCR5 receptor interacts with the CC chemokines RANTES (regulated on activation normal T-cell expressed and secreted) and macrophage inflammatory proteins 1α and 1β (MIP-1α and

MIP-1β). However, it is also an essential co-receptor for human immunodeficiency virus (HIV) entry into CD4 cells5. A 32 base pair deletion (∆32) in the CCR5 gene confers marked resistance to HIV infection in CCR5-∆32 homozygotes, and heterozygotes progress less rapidly to AIDS (Ref. 5). Interestingly, the CCR5-∆32 deletion has also been shown to delay the progression of some opportunistic infections, such as toxoplasmosis, in AIDS patients6. CCR5 is preferentially expressed by Th1 cells compared with Th2, and Th1 are attracted by CC chemokines more than Th2 cells are7. This protective effect of the ∆32 deletion does not seem to be due to an increased resistance to Toxoplasma gondii, but the defect in CCR5 protein expression could lead to dysregulation of CC chemokines and Th1 cell recruitment6. In a mouse model, T. gondii is a potent inducer of the chemokines Mig [monokine induced by interferon γ (IFN-γ)] and Crg-2 [human IFN-γinducible protein 10 (IP-10)], which are both induced by IFN-γ (Ref. 8). IFN-γ knockout mice do not activate the Mig and Crg2 genes, which could explain the modification in cell population of inflammatory exudate in the peritoneal cavity of knockout mice after T. gondii infection9. Moreover, the neutralization of IP-10 in T. gondii-infected mice inhibits the T-cell influx into tissues and modifies the function of T cells at sites of Th1 inflammation10. In vitro, T. gondii increases the secretion of several CC and CXC chemokines in different cell types11–13. Infection of HeLa cells and fibroblasts with live tachyzoites led to increased IL-8 (requiring host-cell invasion and lysis), growth-related oncogen α (GROα) and MCP-1 secretion. Il-1α seemed to be the principal mediator of T. gondii-induced IL-8 secretion11. A separate study showed that penetration of live tachyzoites (strain RH) induced increased MCP-1 secretion and expression by human fibroblasts12. Neutrophils also seem to be involved in the early cytokine response to T. gondii because their stimulation by T. gondii antigens leads to an upregulation of other chemokines such as MIP-1α and MIP-1β. This increase seems to be due partly to autocrine stimulation through tumour necrosis factor α (TNFα)13. The role of these chemokines could be to recruit cells such as monocytes, natural killer (NK) cells and dendritic cells during infection but could also be to attract Th1 cells13. They could be implicated in the inflammatory reaction observed

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Table 1. Chemokines studied in protozoan infectionsa,b Chemokines CXC chemokines IL-8 GRO-α MIG IP-10 CC chemokines MCP-1 RANTES

Target cellsc Neutrophils; T cells; NK cell; keratinocytes; basophils; endothelial cells Neutrophils; endothelial cells Monocytes; activated T cells; NK cells T cells; NK cells; endothelial cells

MIP-1β I309

Monocytes; T cells; mast cells; basophils Monocytes; T cells; NK cells; eosinophils; basophils; dendritic cells Monocytes; T cells; B cells; NK cells; mast cells; eosinophils; basophils; dendritic cells Monocytes; T cells Monocytes

C chemokine Lymphotactin

T cells

CX3C chemokine Fractalkine

T cells; monocytes

MIP-1α

aAbbreviations:

IP-10, interferon-γ inducible protein 10; IL-8, interleukin 8; GRO-α, growth-related oncogen α; MIP-1α, macrophage inflammatory protein 1α; MIP-1β, macrophage inflammatory protein 1β; MCP-1, monocyte chemotactic protein 1; MIG, monocyte induced by interferon γ; RANTES, regulated on activation normal T cells expressed and secreted; NK cells, natural killer cells. bData from Refs 1,2. cMain targets in bold type.

during acute invasion, which is characterized by a mononuclear-cell inflammatory reaction in necrotic areas9, and during reactivation of latent infection during immunodepression14. Chemokines have been shown to have a direct antiprotozoal activity for three protozoans: T. gondii15, Leishmania donovani15 and Trypanosoma cruzi16–18. Pretreatment of human monocyte-derived macrophages with MCP-1 induces the inhibition of T. gondii and L. donovani replication15. Furthermore, MCP-1 pretreatment might activate effector mononuclear phagocytes because, after pretreatment of human MRC5 fibroblasts by MCP-1, we have not observed the inhibition of multiplication of tachyzoites of T. gondii RH (H. Pelloux, unpublished). This antiprotozoal activity seems to depend on the cell types infected, with the chemokines activating the recruited cells. Trypanosomiasis

The activity of CC chemokines seems to be particularly beneficial for the host during infection with T. cruzi. RANTES, MIP-1α and MIP-1β increase the uptake and cause intracellular destruction of trypomastigotes by human macrophages in vitro and in mouse inflammatory macrophages both in vivo and in vitro16,18. Chemokines appear to induce macrophage trypanocidal activity via the NO pathway17,18. Moreover, T. cruzi stimulates the synthesis of MIP-1α, MIP-1β, RANTES and MCP-1 by macrophages18. These results indicate that these CC chemokines released by macrophages after infection by T. cruzi participate in the control of parasite replication and might play a role in the acute phase of infection. http://parasites.trends.com

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During African trypanosomiasis, parasites invade the central nervous system and cause a diffuse infiltration of inflammatory cells19. The CC chemokines MIP-1α, MIP-2 and RANTES are increased early in infections of brains of rats infected with Trypanosoma brucei brucei19. This increase in CC chemokines occurs before brain lesions develop, leading to accumulation of inflammatory cells and amplifying the formation of lesions19. Thus, chemokines appear to be detrimental to the host during African trypanosomiasis. Moreover, CC chemokines are also upregulated in splenocytes (via the sympathetic nervous system)20. Leishmaniasis Cutaneous leishmaniasis

The possible involvement of chemokines in leishmaniasis was initially investigated in localized cutaneous leishmaniasis (LCL) and diffuse cutaneous leishmaniasis (DCL). The skin lesions caused by Leishmania infections are hallmarked by a massive lymphohistiocytic infiltrate (an infiltrate containing lymphocytes and macrophages)21. The CC chemokines MCP-1 and MIP-1α attract monocytes and certain T-cell subsets21. They are preferentially expressed in different forms of cutaneous infection by Leishmania mexicana. The concentration of MCP-1 in lesions of patients with self-healing LCL was high, whereas that of MIP-1α was moderate. By contrast, MIP-1α expression predominated in lesions of patients suffering from DCL, whereas the MCP-1 concentration was much lower21,22. MCP-1 contributes to reduced parasite load in self-healing LCL and this predominance in LCL must be regarded as beneficial21,22. Indeed, MCP-1, but not MIP-1α, stimulates the oxidative burst in macrophages. These differences in chemokine profiles explain the different compositions of the lymphocyte subsets in the two forms of disease. MCP-1 and MIP-1α are responsible not only for the recruitment of macrophages and T cells in cutaneous leishmaniasis but also for displaying different stimulatory activities (e.g. the effector functions of macrophages and lymphocytes)22. The participation of chemokines in cellular activation during leishmaniasis has been observed in other studies. In an experimental mouse cutaneous infection with Leishmania major, the fatal disease in some strains of mice is associated with an insufficient NK-cell-mediated innate immune response23. In an analysis of the expression of NK-cell-activating chemokines, MCP-1, IP-10 and lymphotactin were found to be expressed in lymph nodes early after infection of resistant mice23. Although, in susceptible mice, the recruitment of NK cells is normal, the lack of early production of chemokines (IP-10) might contribute to insufficient NK cell activation. The migration of Langerhans cells also appears to be regulated by cytokines and chemokines such as MIP-1α (Ref. 24). In vitro,

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infection of human monocytes with L. major induces IL-8 and MCP-1 secretion25. Furthermore, expression of JE (human MCP-1) and KC (human GRO) in mouse bone-marrow-derived macrophages rises shortly after infection and returns to uninduced levels by 4–24 h. On average, the magnitude of chemokine expressions was higher with avirulent than with virulent strains. It has been suggested that the parasite lipophosphoglycan (a major surface molecule whose expression varies with the strain) is involved in modulating the signal for chemokine induction26. Visceral leishmaniasis

During experimental visceral leishmaniasis caused by L. donovani in immunocompetent mice, the acquisition of resistance is associated with hepatic inflammation and granuloma formation27. Immunodeficient mice that lacked T and B cells did not generate a detectable inflammatory response and resistance. A rapid hepatic rise in MIP-1α, MCP-1 and IP-10 was observed after infection but only the kinetics of IP-10 was different in immunodeficient mice. The presence of both CD8+ and CD4+ cells is necessary for the maintenance of maximal tissue IP-10 mRNA levels, following an initial T-cellindependent response by Kuppfer cells. T cells are implicated in the regulation of these chemokines, both to amplify the chemokine response and to control the inflammatory responses and granuloma formation27. The secretion of IP-10 amplified by T cells is essential to allow granuloma formation and inflammatory response. This function is positive for the host defence. The immune response mediated by Th1 cells or IFN-γ is important for the control of leishmaniasis. In CCR5-, CCR2- and MIP-1α-deficient mice, the antigen-specific IFN-γ response was lower during the early phase of infection, but this was overcome during chronic infection28. During the late phase of infection, an enhanced IFN-γ response was found in CCR-5- and MIP-1α-deficient mice, and this correlated with a lower parasite burden. These data suggest that CCR5, MIP-1α and CCR2 have a role in the generation of IFN-γ, and that CCR5 and MIP-1α might play a deleterious role in the outcome of chronic L. donovani infection. They also suggest that there might be cross-talk between T-cell-receptor (TCR) and chemokine-receptor signalling pathways28. These chemokines and chemokine receptors have a role in Th-1 cell response, because their deletion modifies the profile of IFN-γ secretion. However, in this model, they are not essential for containment of murine infection. Furthermore, in CCR2-null mice, which are susceptible to L. major infection, the migration of dendritic cells (DCs) to the draining lymph nodes and spleen was impaired, especially for the CD8α+-Th1-cell-inducing subsets of DCs29. These CCR2-null mice had a dominant Th2 phenotype29 but the implication of CCR2 in a Th1 http://parasites.trends.com

phenotype is not so clear. Indeed, mice lacking MCP-1 (which is a major ligand of CCR-2) cannot generate a Th2 response but secrete normal amounts of INF-γ and are resistant to L. major infection30. In summary, it is clear that the CCR-2–MCP-1 axis participates in innate immunity to Leishmania infection (e.g. cell recruitment) but also takes part in adaptive immunity through control of T helper cell polarization (Th1–Th2 balance). However, the direction of preferential polarization is not yet known for certain. Malaria

It is now well known that Duffy-negative human erythrocytes are resistant to invasion by Plasmodium vivax and the related monkey malaria Plasmodium knowlesi, but not to infection by other Plasmodium species. The Duffy blood antigen is an erythrocyte chemokine receptor (DARC) that binds IL-8, melanoma growth-stimulating activity (MGSA), MCP-1 and RANTES but not MIP-1α and MIP-β (Ref. 31). Although the exact physiological role of DARC is not yet known31, the finding that the erythrocyte chemokine receptor is also a receptor for P. vivax suggests that receptor blockade therapy could be useful therapeutically31. In time-course studies of MIP-1α and IL-8 secretion in patients with Plasmodium falciparum malaria, the IL-8 concentration correlates with parasite count and with the severity of disease32,33. The significance of the IL-8 and MIP-1α increase during malaria is not known, although MIP-1α is a potent inhibitor of haematopoietic cell proliferation and might be one of the agents responsible for prolonged anaemia in malaria32. However, it is still possible that the IL-8 increase is an incidental event. Amoebiasis

The chemokines produced by intestinal epithelial cells in response to microbial infection might be essential for the initiation and maintenance of the mucosal inflammatory response. During intestinal amoebiasis, invasion of the intestinal mucosa might be accompanied by an inflammatory infiltrate composed primarily of neutrophils. An in vitro study showed that culturing Entamoeba histolytica with different cell lines induced secretion and expression of IL-8 and GRO-α, which are known to be potent chemoattractants and activators of polymorphonuclear leukocytes34 (PMNs). In another study, it was shown that live E. histolytica without cell–cell contact can increase the secretion and expression of IL-8 by human colonic epithelial cells35, which was confirmed using severe combined immunodeficiency (SCID) mice with a human intestinal xenograft36. The local release of these cytokines might play a role in the PMN infiltration in acute experimental E. histolytica infection and in the pathogenesis of amoebic infection. Moreover, chemokines can activate PMN functions, such as the release of microbicidal enzymes.

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Role in leukocyte recruitment and cell activation

Toxoplasma gondii Trypanosoma brucei brucei Leishmania major Entamoeba histolytica Cryptosporidium parvum Trichomonas vaginalis

Direct anti-protozoal effects

Toxoplasma gondii Leishmania donovani Trypanosoma cruzi

Chemokines

Participation in cell-mediated immunity and in regulation of Th differentiation

Role in penetration (chemokine as receptor for protozoan)

Toxoplasma gondii Leishmania donovani

Plasmodium vivax

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Fig. 1. Potential roles of chemokines in infection by protozoan parasites.

Cryptosporidiosis

Cryptosporidium parvum infects intestinal epithelial cells and can cause mucosal inflammation with prominent neutrophils, mononuclear infiltrates in the lamina propria and numerous intraepithelial neutrophils37. Human intestinal epithelial cells secrete and express IL-8 and GRO-α (Refs 37,38). Interestingly, the CXC chemokine response to C. parvum infection occurs later than the response to infection with E. histolytica34,35,37. This difference could be explained by different mechanisms occurring at the origin of secretion: the amplification of secretion by IL-1 released from lysed cells for E. histolytica; and the production of infected cells without amplification by other mediators for C. parvum. Trichomoniasis

An infiltration of leukocytes, particularly neutrophils, is observed in the vaginal discharges of patients with Trichomonas vaginalis infection. T. vaginalis induces human monocytes to produce IL-8 in a dose- and time-dependent manner39. The secretion is induced by parasitic membrane components and is partially dependent on TNFα. This IL-8 production might play a role in local neutrophil infiltrate and in resistance to T. vaginalis. Conclusion

The secretion of chemokines induced by the interaction between protozoan parasites and host cells might help to determine the parasite–host relationship because these cytokines can play different roles after infection by protozoan parasites (Fig. 1), the most obvious one being the attraction of immune cells such as macrophages. Chemokines can http://parasites.trends.com

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contribute to the inflammatory responses observed in E. histolytica, C. parvum and T. vaginalis infections34–39. They can also activate cellular functions and have a beneficial effect. For example, in intestinal amoebiasis, IL-8 activates PMNs and so might participate in reducing the initial trophozoite load by the release of microbicidal enzymes. However, the accumulation of non-specific inflammatory cells attracted by chemokines can have a detrimental effect and amplify lesion formation, as observed in experimental African trypanosomiasis19. Interestingly, some differences in chemokine profiles are observed in different forms of diseases and participate in their evolution (e.g. cutaneous leishmaniasis)21,22. Chemokines have a much wider range of biological activity, such as participation in cell-mediated immunity and involvement in Th1–Th2 differentiation40, which is of greatest importance in the control of infection by intracellular protozoa41. The involvement of chemokines (and chemokine receptors) in these functions is most obvious in visceral leishmaniasis28–30. Furthermore, some chemokines can stimulate cytokine production associated with Th1–Th2 polarization. For example, MCP-1 can stimulate IL-4 production, indicating that it might be involved in Th2 differentiation and contribute to a detrimental effect in disease for which the Th1 profile is associated with resistance to the disease (e.g. toxoplasmosis)42. This chemotactic factor is increased after in vitro infection with virulent strains of T. gondii. By favouring Th2 differentiation, this chemokine could be involved in the determination of virulence (H. Pelloux, unpublished). If chemokines have a role in protozoan virulence, these immune mediators will be more important in the parasite–host equilibrium than is currently believed. Chemokines also have direct antiprotozoal effects on T. gondii15, L. donovani15 and T. cruzi16–18, although these functions might be secondary to their capacities of cell activation. Strikingly, infection of macrophages with T. cruzi led to chemokine secretion, and the same chemokines induce a trypanocidal activity via the effect of NO on macrophages17,18. Chemokines participate in antimicrobial defence but, paradoxically and perversely, these cytokines and their receptors can also be direct promicrobial factors. Indeed, it is now clear that certain chemokine receptors, such as CCR5 and CXCR4, act as essential co-receptors for HIV infection5. Also, P. vivax penetrates the host via a chemokine receptor, the IL-8 receptor31. The diversity of chemokines’ roles in the course of infectious diseases probably reflects some characteristics of this family: redundancy in their action on targets cells, promiscuity in receptor use and polyspeirism (multiple chemokines produced in a redundant way by a single cell)3. Nevertheless, two effects of the roles of these molecules on the

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physiopathology of protozoan diseases can be envisaged. Most intracellular protozoan parasites can invade many types of cells. Chemokines attract immune cells, a source of possible cells to infect, and might participate in the virulence of parasites. The recruitment of these immune cells such as macrophages – which are major contributors to defence, mediating innate resistance to References 1 Rollins, B.J. (1997) Chemokines. Blood 90, 909–938 2 Luster, A.D. (1998) Chemokines – chemotactic cytokines that mediate inflammation. New Engl. J. Med. 338, 436–445 3 Mantovani, A. (1999) The chemokine system: redundancy for robust outputs. Immunol. Today 20, 254–257 4 Schluger, N.W. and Rom, W.N. (1997) Early responses to infection: chemokines as mediators of inflammation. Curr. Opin. Immunol. 9, 504–508 5 Stewart, G. (1998) Chemokine genes – beating the odds. Nat. Med. 4, 275–277 6 Meyer, L. et al. (1999) CCR5 ∆32 deletion and reduced risk of toxoplasmosis in persons infected with human immunodeficiency virus type 1. J. Infect. Dis. 180, 920–924 7 Bonnechi, R. et al. (1998) Differential expression of chemokine receptors and chemotactic responsiveness of type 1 T helper cells (Th1s) and Th2s. J. Exp. Med. 187, 129–134 8 Amichay, D. et al. (1996) Genes for chemokines MuMig and Crg-2 are induced in protozoan and viral infection in response to IFN-γ with patterns of tissue expression that suggest nonredundant roles in vivo. J. Immunol. 157, 4511–4520 9 Gazzinelli, R. et al. (1996) Role of macrophagederived cytokines in the induction and regulation of cell-mediated immunity to Toxoplasma gondii. In Toxoplasma gondii (Gross, U., ed.), pp. 127–139, Springer-Verlag 10 Khan, I.A. et al. (2000) IP-10 is critical for effector T cell trafficking and host survival in Toxoplasma gondii infection. Immunity 12, 483–494 11 Denney, C.F. et al. (1999) Chemokine secretion of human cells in response to Toxoplasma gondii infection. Infect. Immun. 67, 1547–1552 12 Brenier-Pinchart, M.P. et al. (2000) Toxoplasma gondii induces the secretion of monocyte chemotactic protein 1 in human fibroblasts in vitro. Mol. Cell. Biochem. 209,79–87 13 Bliss, S.K. et al. (1999) Human polymorphonuclear leukocytes produce IL-12, TNFα, and chemokines macrophage inflammatory protein-1α and -1β in response to Toxoplasma gondii antigens. J. Immunol. 162, 7369–7375 14 Hunter, A.A. and Remington, J.S. (1994) Immunopathogenesis of toxoplasmic encephalitis. J. Infect. Dis. 170, 1057–1067 15 Mannheimer, S.B. et al. (1996) Induction of macrophage antiprotozoal activity by monocyte chemotactic and activating factor. FEMS Immunol. Med. Microbiol. 14, 59–61 16 Lima, M.F. et al. (1997) β-Chemokines that inhibit HIV-1 infection of macrophages stimulate uptake and promote destruction of Trypanosoma cruzi by human macrophages. Cell. Mol. Biol. 43, 1067–1076

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intracellular pathogens – can participate in the regulation of their own number and ensure both host and parasite survival. However, even if our knowledge about involvement of chemokines in protozoan diseases is more limited than in viral diseases43, chemokines appear to be of paramount importance in the pathophysiology of protozoan infection in humans.

17 Villalta, F. et al. (1998) The cysteine–cysteine family of chemokines RANTES, MIP-1α, and MIP-1β induce trypanocidal activity in human macrophages via nitric oxide. Infect. Immun. 66, 4690–4695 18 Aliberti, J.C.S. et al. (1999) β-Chemokines enhance parasite uptake and promote nitric oxide-dependent microbiostatic activity in murine inflammatory macrophage infected with Trypanosoma cruzi. Infect. Immun. 67, 4819–4826 19 Sharafeldin, A. et al. (2000) Chemokines are produced in the brain early during the course of experimental African trypanosomiasis. J. Neuroimmunol. 103, 167–170 20 Liu, Y. et al. (1999) Upregulation of the chemokines RANTES, MCP-1, MIP-1α and MIP-2 in early infection with Trypanosoma brucei and inhibition by sympathetic denervation of the spleen. Trop. Med. Int. Health 4, 85–92 21 Ritter, U. et al. (1996) Differential expression of chemokines in patients with localized and diffuse cutaneous American leishmaniasis. J. Infect. Dis. 173, 699–709 22 Moll, H. (1997) The role of chemokines and accessory cells in the immunoregulation of cutaneous leishmaniasis. Behring Inst. Mitt. 99, 73–78 23 Vester, B. et al. (1999) Early gene expression of NK cell-activating chemokines in mice resistant to Leishmania major. Infect. Immun. 67, 3155–3159 24 Arnoldi, J. and Moll, H. (1998) Langerhans cell migration in murine cutaneous leishmaniasis: regulation by tumor necrosis factor α, interleukin1β, and macrophage inflammatory protein-1α. Dev. Immunol. 6, 3–11 25 Badolato, R. et al. (1996) Leishmania major: infection of human monocytes induces expression of IL-8 and MCAF. Exp. Parasitol. 82, 21–26 26 Racoosin, E.L. and Beverley, S.M. (1997) Leishmania major: promastigotes induce expression of a subset of chemokine genes in murine macrophages. Exp. Parasitol. 85, 283–295 27 Cotterell, S.E. et al. (1999) Leishmania donovani infection initiates T cell-independent chemokine responses, which are subsequently amplified in a T cell-dependent manner. Eur. J. Immunol. 29, 203–214 28 Sato, N. et al. (1999) Defects in the generation of INF-γ are overcome to control infection with Leishmania donovani in CC chemokine receptor (CCR) 5-, macrophage inflammatory protein-1α, or CCR 2-deficient mice. J. Immunol. 163, 5519–5525 29 Sato, N. et al. (2000) CC chemokine receptor (CCR)2 is required for Langerhans cell migration and localization of T helper cell type 1 (Th1)inducing dendritic cells: absence of CCR2 shifts the Leishmania major-resistant phenotype to a susceptible state dominated by Th2 cytokines, B cell outgrowth and sustained neutrophilic inflammation. J. Exp. Med. 192, 205–218

30 Gu, L. et al. (2000) Control of TH2 polarization by the chemokine monocyte chemoattractant protein-1. Nature 404, 407–411 31 Horuk, R. et al. (1993) A receptor for the malarial parasite Plasmodium vivax: the erythrocyte chemokine receptor. Science 261, 1182–1184 32 Burgmann, H. et al. (1995) Serum concentrations of MIP-1α and interleukin-8 in patients suffering from acute Plasmodium falciparum malaria. Clin. Immunol. Immunopathol. 76, 32–36 33 Friedland, J.S. et al. (1993) Interleukin-8 and Plasmodium falciparum malaria in Thailand. Trans. R. Soc. Trop. Med. Hyg. 87, 54–55 34 Eckmann, L. et al. (1995) Entamoeba histolytica trophozoites induce an inflammatory cytokine response by cultured human cells through the paracrine action of cytolytically released interleukin-1α. J. Clin. Invest. 96, 1269–1279 35 Yu, Y. and Chadee, K. (1997) Entamoeba histolytica stimulates interleukin 8 from human colonic epithelial cells without parasite–enterocyte contact. Gastroenterology 112, 1536–1547 36 Seydel, K.B. et al. (1997) Human intestinal epithelial cells produce proinflammatory cytokines in response to infection in a SCID mouse–human intestinal xenograft model of amebiasis. Infect. Immun. 65, 1631–1639 37 Laurent, F. et al. (1997) Cryptosporidium parvum infection of human intestinal epithelial cells induces the polarized secretion of C–X–C chemokines. Infect. Immun. 65, 5067–5073 38 Seydel, K.B. et al. (1998) Cryptosporidium parvum infection of human intestinal xenografts in SCID mice induces production of human tumor necrosis factor alpha and interleukin-8. Infect. Immun. 66, 2379–2382 39 Shaio, M.F. et al. (1995) Generation of interleukin8 from human monocytes in response to Trichomonas vaginalis stimulation. Infect. Immun. 63, 3864–3870 40 Kim, C.H. and Broxmeyer, H.E. (1999) Chemokines: signal lamps for trafficking of T and B cells for development and effector function. J. Leukocyte Biol. 65, 6–15 41 Gazzinelli, R.T. et al. (1998) Induction of cellmediated immunity during early stage of infection with intracellular protozoa. Braz. J. Med. Biol. Res. 31, 89–104 42 Karpus, W.J. et al. (1997) Differential CC chemokine-induced enhancement of T helper cell cytokine production. J. Immunol. 158, 4129–4136 43 Lalami, A.S. et al. (2000) Modulating chemokines: more lessons from viruses. Immunol. Today 21, 100–106