Pascal Launois

IL-4 instructs TH1 responses and resistance to Leishmania major in susceptible BALB/c mice.

Immunity to infection with intracellular pathogens is regulated by interleukin 12 (IL-12), which mediates protective T helper type 1 (TH1) responses, or IL-4, which induces TH2 cells and susceptibility. Paradoxically, we show here that when present during the initial activation of dendritic cells (DCs) by infectious agents, IL-4 instructed DCs to produce IL-12 and promote TH1 development. This TH1 response established resistance to Leishmania major in susceptible BALB/c mice. When present later, during the period of T cell priming, IL-4 induced TH2 differentiation and progressive leishmaniasis in resistant mice. Because immune responses developed via the consecutive activation of DCs and then T cells, the contrasting effects of IL-4 on DC development and T cell differentiation led to immune responses that had opposing functional phenotypes.

Neutrophil-Derived CCL3 Is Essential for the Rapid Recruitment of Dendritic Cells to the Site of Leishmania major Inoculation in Resistant Mice

Neutrophils are rapidly and massively recruited to sites of microbial infection, where they can influence the recruitment of dendritic cells. Here, we have analyzed the role of neutrophil released chemokines in the early recruitment of dendritic cells (DCs) in an experimental model of Leishmania major infection. We show in vitro, as well as during infection, that the parasite induced the expression of CCL3 selectively in neutrophils from L. major resistant mice. Neutrophil-secreted CCL3 was critical in chemotaxis of immature DCs, an effect lost upon CCL3 neutralisation. Depletion of neutrophils prior to infection, as well as pharmacological or genetic inhibition of CCL3, resulted in a significant decrease in DC recruitment at the site of parasite inoculation. Decreased DC recruitment in CCL3−/− mice was corrected by the transfer of wild type neutrophils at the time of infection. The early release of CCL3 by neutrophils was further shown to have a transient impact on the development of a protective immune response. Altogether, we identified a novel role for neutrophil-secreted CCL3 in the first wave of DC recruitment to the site of infection with L. major, suggesting that the selective release of neutrophil-secreted chemokines may regulate the development of immune response to pathogens.

Leishmania major induces distinct neutrophil phenotypes in mice that are resistant or susceptible to infection

Polymorphonuclear neutrophils (PMN) are key components of the inflammatory response contributing to the development of pathogen‐specific immune responses. Following infection with Leishmania major, neutrophils are recruited within hours to the site of parasite inoculation. C57BL/6 mice are resistant to infection, and BALB/c mice are susceptible to infection, developing unhealing, inflammatory lesions. In this report, we investigated the expression of cell surface integrins, TLRs, and the secretion of immunomodulatory cytokines by PMN of both strains of mice, in response to infection with L. major. The parasite was shown to induce CD49d expression in BALB/c‐inflammatory PMN, and expression of CD49d remained at basal levels in C57BL/6 PMN. Equally high levels of CD11b were expressed on PMN from both strains. In response to L. major infection, the levels of TLR2, TLR7, and TLR9 mRNA were significantly higher in C57BL/6 than in BALB/c PMN. C57BL/6 PMN secreted biologically active IL‐12p70 and IL‐10. In contrast, L. major‐infected BALB/c PMN transcribed and secreted high levels of IL‐12p40 but did not secrete biologically active IL‐12p70. Furthermore, IL‐12p40 was shown not to associate with IL‐23 p19 but formed IL‐12p40 homodimers with inhibitory activity. No IL‐10 was secreted by BALB/c PMN. Thus, following infection with L. major, in C57BL/6 mice, PMN could constitute one of the earliest sources of IL‐12, and in BALB/c mice, secretion of IL‐12p40 could contribute to impaired, early IL‐12 signaling. These distinct PMN phenotypes may thus influence the development of L. major‐specific immune response.

Differential Production of Systemic and Intralesional Gamma Interferon and Interleukin-10 in Nodular and Ulcerative Forms of Buruli Disease

ABSTRACT Buruli disease, caused by Mycobacterium ulcerans, is the third most important mycobacterial disease in humans besides tuberculosis and leprosy. We have compared systemic and intralesional cytokine production in patients presenting with a nodular form and a necrotizing, ulcerative form of the disease. Gamma interferon (IFN-γ) levels in response to whole M. ulcerans and Mycobacterium bovis BCG bacilli and in response to purified Ag85 protein from BCG were lower in peripheral blood mononuclear cells (PBMC) cultures from Buruli disease patients than in PBMC from healthy purified protein derivative-positive contacts. Interleukin-4 (IL-4) and IL-13 content was below the detection threshold in these PBMC cultures. IFN-γ production after stimulation with M. ulcerans was significantly lower (P < 0.05) in PBMC cultures from patients with ulcers than in those from patients with nodules. On the other hand, PBMC from Buruli disease patients produced significant levels of IL-10 in response to M. ulcerans (but not to M. bovis BCG) and production was highest in patients with the ulcerative form. Third, semiquantitative reverse transcription-PCR analysis demonstrated a similar difference in the local, intralesional cytokine profile for the two forms of the disease: high IFN-γ but low IL-10 mRNA levels in nodular lesions and high IL-10 but low IFN-γ mRNA levels in ulcerative lesions. Intralesional IL-4 and IL-13 mRNA levels were low and only detected in patients with the ulcerative form. Our results indicate, although they do not formally prove, that production of IL-10 rather than production of IL-4 or IL-13 by Th2-type T cells may be involved in the low M. ulcerans-specific IFN-γ response in Buruli disease patients.

High Intralesional Interleukin-10 Messenger RNA Expression in Localized Cutaneous Leishmaniasis Is Associated with Unresponsiveness to Treatment

The intralesional expression of cytokines (interleukin [IL]-4, IL-13, IL-10, and interferon-gamma) was analyzed in 65 patients with localized cutaneous leishmaniasis due to Leishmania guyanensis before specific treatment with pentamidine isethionate. The local expression of IL-10 was significantly higher in patients who responded poorly to treatment than in patients whose lesions were regressing. When an IL-10 level >10 (ratio of the concentration of IL-10 [pg/microL] to that of beta-actin [pg/microL]) was used as an indicator of treatment failure, the sensitivity of this test was 78.6, and the specificity was 72.5. Thus, high intralesional expression of IL-10 might predict a poor response to conventional treatment.

Interleukin (IL)-13 is the predominant Th2 cytokine in localized cutaneous leishmaniasis lesions and renders specific CD4+ T cells unresponsive to IL-12

Semiquantitative reverse transcription-polymerase chain reaction analysis of leishmania lesion cytokine profile showed a Th2 cytokine expression pattern, as reflected by interleukin (IL)-4 and IL-13 mRNA expression. There was a predominance of IL-13 in most lesions from patients with American localized cutaneous leishmaniasis caused by Leishmania guyanensis. IL-13 production by peripheral blood mononuclear cells in response to specific leishmania antigens was confirmed in these patients. The absence of the second chain of the IL-12 receptor (IL-12Rbeta2) mRNA expression in lesions and the presence of specific IgE and IgG4 in some serum samples demonstrated the functional role of these Th2 cytokines. IL-13, unlike IL-4, rendered specific T cells unresponsive to IL-12 by inhibiting the expression of the IL-12Rbeta2 chain. These data establish the crucial role of IL-13 in human cutaneous leishmaniasis.

American Cutaneous Leishmaniasis, Lepromatous Leprosy, and Pulmonary Tuberculosis Coinfection with Downregulation of the T-helper 1 Cell Response

Cutaneous leishmaniasis, leprosy, and tuberculosis are caused by intracellular pathogens whose development depends on impaired cell-mediated immunity. We report an exceptional triple association of American cutaneous leishmaniasis, lepromatous leprosy, and pulmonary tuberculosis in a man with no recognized immunodeficiency. Normal immunological assessment of the interferon-gamma pathway does not support the hypothesis of a genetic defect in any of the genes involved in the T helper (Th)-1 cytokine cascade in this patient. Unresponsiveness to interleukin (IL)-12 of his T cells after stimulation with Leishmania guyanensis, Mycobacterium bovis bacille Calmette-Guérin, and Mycobacterium leprae antigens suggested the inability to mount an appropriate Th cell response to upregulate the IL-12 receptor expression.

IFN‐γ‐producing CD45RA+ CD8+ and IL‐10‐producing CD45RA– CD4+ T cells generated in response to LACK in naive subjects never exposed to Leishmania

Leishmania guyanensis (L.u2009g.)‐specific CD8+ T cells can be isolated from PBMC of subjects who have never been previously exposed to Leishmania. Cells that produce IFN‐γ in response to live L.u2009g. are generated from naive CD45RA+ CD8+ T cells. The generation of L.u2009g.‐specific CD8+ T cells requires the presence of whole L.u2009g. or UV‐irradiated parasite but not the soluble antigens from L.u2009g. promastigotes. The IFN‐γ‐producing T cells recognize a specific antigen, the Leishmania homologue of receptors of activated C kinases (LACK) and this antigen but not live L.u2009g. can produce a strong IL‐10 response in CD45RA– CD4+ memory T cells from naive subjects. A single epitope (amino acid 156u2009–u2009173) is found to induce the IL‐10 synthesis. While the IFN‐γ‐producing cells are present among CD45RA+ CD8+ T cells that are CD62L– CDR7– and CLA–, the LACK‐reactive IL‐10‐producing cells are CD4+ T cells that are CD62L+ CCR7– and CLA–.

LACK-Specific CD4+ T Cells That Induce Gamma Interferon Production in Patients with Localized Cutaneous Leishmaniasis during an Early Stage of Infection

ABSTRACT The profile of cytokines induced by soluble leishmania antigen (SLA) and the Leishmania homologue of the mammalian receptor for activated C kinase (LACK), a candidate vaccine against leishmaniasis, and the cellular source of the cytokines produced in response to these antigens were analyzed in patients infected with Leishmania guyanensis. Gamma interferon (IFN-γ) and interleukin-10 (IL-10) were produced in response to LACK. Although LACK-specific CD4+ cells producing IFN-γ were isolated only during the early phase of infection (less than 30 days following the onset of infection), cells producing IL-10 in response to LACK were detected in all patients. CD4+ T cells producing IFN-γ and IL-13 were produced in response to SLA in all patients. SLA- and LACK-specific T cells are effector memory cells, as they are CD45RA− CCR7− CD4+ T cells. CD4+ T cells producing IFN-γ are CD62L−, and CD4+ T cells producing IL-10 are CD62L+, indicating that these cells have different tissue-homing capacities. These findings show that SLA and LACK induce both type 1 (IFN-γ) and type 2 (IL-10 or IL-13) cell responses.

T cell response to purified filtrate antigen 85 from Mycobacterium bovis Bacilli Calmette-Guerin (BCG) in leprosy patients

T cell proliferation and IFN‐γ production of peripheral blood mononuclear cells from 25 healthy controls and 39 leprosy patients were tested against BCG‐bacilli and culture filtrate, Mycobacterium leprae and purified antigen 85 (the major secreted 30–32 kD protein antigen) from M. bovis strain BCG. In lepromin negative healthy controls, blastogenesis was low to M. leprae and completely negative to antigen 85. IFN‐γ levels were very low, close to detection limits. In all lepromin positive controls, significant proliferation and IFN‐γ secretion was found in response to M. leprae and antigen 85. In the group of lepromatous leprosy (LL) patients, 25/29 of patients (with either positive (13) or negative (12) lymphoproliferative response to BCG) were unreactive to M. leprae or to antigen 85. Four LL patients with positive T cell response to BCG responded with detectable lymphoproliferative response and IFN‐γ secretion to antigen 85. All tuberculoid (TT) leprosy patients responded to BCG, M. teprae and antigen 85. Hence, T cells from leprosy patients and controls demonstrate a marked parallelism of responsiveness towards whole M. leprae and purified antigen 85 from M. bovis BCG, suggesting strong eross‐reactivity between the two species and underlining the biological importance of such secreted antigens.