Tyk2 negatively regulates adaptive Th1 immunity by mediating IL-10 signaling and promoting IFN-gamma-dependent IL-10 reactivation

The Jak, Tyk2, is activated in response to IL-12 and IFN-alphabeta and promotes IFN-gamma production by Th1-type CD4 cells. Mice deficient in Tyk2 function have been previously shown to be resistant to autoimmune arthritis and septic shock but are acutely susceptible to opportunistic pathogens such as Toxoplasma gondii. In this study, we show that Tyk2, in addition to mediating the biological effects of IL-12 and IFN-alphabeta, is an important regulator for the signaling and expression of the immunosuppressive cytokine IL-10. In the absence of Tyk2, Ag-reactive CD4 cells exhibit impaired IL-10 synthesis following rechallenge of T. gondii vaccine-primed mice. The impaired IL-10 reactivation leads to unopposed antimicrobial effector mechanisms which results in a paradoxically superior protection of immune Tyk2(-/-) mice against virulent T. gondii challenge. We further demonstrate that Tyk2 indirectly controls CD4 IL-10 reactivation by signaling for maximal IFN-gamma secretion. The unexpected role of IFN-gamma in mediating IL-10 reactivation by Th1 cells provides compelling evidence that conditions driving Th1 responses establish a negative feedback loop, which will ultimately lead to its autoregulation. Thus, Tyk2 can be viewed as a dual-function Jak, mediating both pro and anti-inflammatory cytokine responses.

CD4+CD25+ T cells in skin lesions of patients with cutaneous leishmaniasis exhibit phenotypic and functional characteristics of natural regulatory T cells

Endogenous regulatory T (Treg) cells are involved in the control of infections, including Leishmania infection in mice. Leishmania viannia braziliensis is the main etiologic agent of cutaneous leishmaniasis (CL) in Brazil, and it is also responsible for the more severe mucocutaneous form. Here, we investigated the possible involvement of Treg cells in the control of the immune response in human skin lesions caused by L. viannia braziliensis infection. We show that functional Treg cells can be found in skin lesions of patients with CL. These cells express phenotypic markers of Treg cells--such as CD25, cytotoxic T lymphocyte-associated antigen 4, Foxp3, and glucocorticoid-induced tumor necrosis factor receptor--and are able to produce large amounts of interleukin-10 and transforming growth factor- beta . Furthermore, CD4+CD25+ T cells derived from the skin lesions of 4 of 6 patients with CL significantly suppressed in vitro the phytohemagglutinin-induced proliferative T cell responses of allogeneic peripheral-blood mononuclear cells (PBMCs) from healthy control subjects at a ratio of 1 Treg cell to 10 allogeneic PBMCs. These findings suggest that functional Treg cells accumulate at sites of Leishmania infection in humans and possibly contribute to the local control of effector T cell functions.

Infected site-restricted Foxp3+ natural regulatory T cells are specific for microbial antigens

Natural regulatory T (T reg) cells are involved in control of the immune response, including response to pathogens. Previous work has demonstrated that the repertoire of natural T reg cells may be biased toward self-antigen recognition. Whether they also recognize foreign antigens and how this recognition contributes to their function remain unknown. Our studies addressed the antigenic specificity of natural T reg cells that accumulate at sites of chronic infection with Leishmania major in mice. Our results support the idea that natural T reg cells are able to respond specifically to foreign antigens in that they strongly proliferate in response to Leishmania-infected dendritic cells, they maintain Foxp3 expression, and Leishmania-specific T reg cell lines can be generated from infected mice. Surprisingly, the majority of natural T reg cells at the infected site are Leishmania specific. Further, we showed that parasite-specific natural T reg cells are restricted to sites of infection and that their survival is strictly dependent on parasite persistence.

Uptake of Leishmania major by dendritic cells is mediated by Fcgamma receptors and facilitates acquisition of protective immunity

Uptake of Leishmania major by dendritic cells (DCs) results in activation and interleukin (IL)-12 release. Infected DCs efficiently stimulate CD4- and CD8- T cells and vaccinate against leishmaniasis. In contrast, complement receptor 3-dependent phagocytosis of L. major by macrophages (MPhi) leads exclusively to MHC class II-restricted antigen presentation to primed, but not naive, T cells, and no IL-12 production. Herein, we demonstrate that uptake of L. major by DCs required parasite-reactive immunoglobulin (Ig)G and involved FcgammaRI and FcgammaRIII. In vivo, DC infiltration of L. major-infected skin lesions coincided with the appearance of antibodies in sera. Skin of infected B cell-deficient mice and Fcgamma-/- mice contained fewer parasite-infected DCs in vivo. Infected B cell-deficient mice as well as Fcgamma-/- mice (all on the C57BL/6 background) showed similarly increased disease susceptibility as assessed by lesion volumes and parasite burdens. The B cell-deficient mice displayed impaired T cell priming and dramatically reduced IFN-gamma production, and these deficits were normalized by infection with IgG-opsonized parasites. These data demonstrate that DC and MPhi use different receptors to recognize and ingest L. major with different outcomes, and indicate that B cell-derived, parasite-reactive IgG and DC FcgammaRI and FcgammaRIII are essential for optimal development of protective immunity.

Inhibition of TLR-4/MD-2 signaling by RP105/MD-1

Activation of Toll-like receptor (TLR) signaling by microbial and host molecular signatures is critical to the induction of immune responses. Such signaling is, perforce, kept under tight control. We recently discovered a novel endogenous inhibitor of TLR-4 - RP105. Initially identified as a B-cell-specific molecule with a role in B-cell proliferation in response to RP105 mAb and LPS, RP105 is a TLR-4 homologue. Further, like TLR-4 whose surface expression and signaling depends upon co-expression of the secreted protein MD-2, surface expression of RP105 is dependent upon co-expression of the MD2 homologue, MD-1. Unlike the TLRs, however, RP105 lacks a signaling domain, having the apparent structure of a TLR inhibitor. Further, RP105 is not B-cell-specific; its expression directly mirrors that of TLR-4 on dendritic cells and macrophages. These considerations suggested a role for RP105 as a physiological inhibitor of TLR-4 signaling. Indeed, we have recently found that: (i) RP105 is a specific inhibitor of TLR-4 signaling in HEK293 cells; (ii) RP105/MD-1 interacts directly with TLR-4/MD-2, inhibiting the ability of this signaling complex to bind LPS; (iii) RP105 regulates TLR-4 signaling in dendritic cells and macrophages; and (iv) RP105 regulates in vivo responses to LPS.

Inhibition of TLR-4/MD-2 signaling by RP105/MD-1

Activation of Toll-like receptor (TLR) signaling by microbial and host molecular signatures is critical to the induction of immune responses. Such signaling is, perforce, kept under tight control. We recently discovered a novel endogenous inhibitor of TLR-4 - RP105. Initially identified as a B-cell-specific molecule with a role in B-cell proliferation in response to RP105 mAb and LPS, RP105 is a TLR-4 homologue. Further, like TLR-4 whose surface expression and signaling depends upon co-expression of the secreted protein MD-2, surface expression of RP105 is dependent upon co-expression of the MD2 homologue, MD-1. Unlike the TLRs, however, RP105 lacks a signaling domain, having the apparent structure of a TLR inhibitor. Further, RP105 is not B-cell-specific; its expression directly mirrors that of TLR-4 on dendritic cells and macrophages. These considerations suggested a role for RP105 as a physiological inhibitor of TLR-4 signaling. Indeed, we have recently found that: (i) RP105 is a specific inhibitor of TLR-4 signaling in HEK293 cells; (ii) RP105/MD-1 interacts directly with TLR-4/MD-2, inhibiting the ability of this signaling complex to bind LPS; (iii) RP105 regulates TLR-4 signaling in dendritic cells and macrophages; and (iv) RP105 regulates in vivo responses to LPS.

Antigen requirements for efficient priming of CD8+ T cells by Leishmania major-infected dendritic cells

CD4(+) and CD8(+) T-cell responses have been shown to be critical for the development and maintenance of acquired resistance to infections with the protozoan parasite Leishmania major. Monitoring the development of immunodominant or clonally restricted T-cell subsets in response to infection has been difficult, however, due to the paucity of known epitopes. We have analyzed the potential of L. major transgenic parasites, expressing the model antigen ovalbumin (OVA), to be presented by antigen-presenting cells to OVA-specific OT-II CD4(+) or OT-I CD8(+) T cells. Truncated OVA was expressed in L. major as part of a secreted or nonsecreted chimeric protein with L. donovani 3' nucleotidase (NT-OVA). Dendritic cells (DC) but not macrophages infected with L. major that secreted NT-OVA could prime OT-I T cells to proliferate and release gamma interferon. A diminished T-cell response was observed when DC were infected with parasites expressing nonsecreted NT-OVA or with heat-killed parasites. Inoculation of mice with transgenic parasites elicited the proliferation of adoptively transferred OT-I T cells and their recruitment to the site of infection in the skin. Together, these results demonstrate the possibility of targeting heterologous antigens to specific cellular compartments in L. major and suggest that proteins secreted or released by L. major in infected DC are a major source of peptides for the generation of parasite-specific CD8(+) T cells. The ability of L. major transgenic parasites to activate OT-I CD8(+) T cells in vivo will permit the analysis of parasite-driven T-cell expansion, differentiation, and recruitment at the clonal level.

CD4+CD25+ T cells protect against experimentally induced asthma and alter pulmonary dendritic cell phenotype and function

The role of natural CD4+CD25+ regulatory T (T reg) cells in the control of allergic asthma remains poorly understood. We explore the impact of T reg cell depletion on the allergic response in mice susceptible (A/J) or comparatively resistant (C3H) to the development of allergen-induced airway hyperresponsiveness (AHR). In C3H mice, anti-CD25-mediated T reg cell depletion before house dust mite treatment increased several features of the allergic diathesis (AHR, eosinophilia, and IgE), which was concomitant with elevated T helper type 2 (Th2) cytokine production. In similarly T reg cell-depleted A/J mice, we observed a moderate increase in airway eosinophilia but no effects on AHR, IgE levels, or Th2 cytokine synthesis. As our experiments suggested that T reg cell depletion in C3H mice before sensitization was sufficient to enhance the allergic phenotype, we characterized dendritic cells (DCs) in T reg cell-depleted C3H mice. T reg cell-depleted mice had increased numbers of pulmonary myeloid DCs with elevated expression of major histocompatibility complex class II, CD80, and CD86. Moreover, DCs from T reg cell-depleted mice demonstrated an increased capacity to stimulate T cell proliferation and Th2 cytokine production, which was concomitant with reduced IL-12 expression. These data suggest that resistance to allergen-driven AHR is mediated in part by CD4+CD25+ T reg cell suppression of DC activation and that the absence of this regulatory pathway contributes to susceptibility.

Association of CTLA4 polymorphism with regulatory T cell frequency

A common single nucleotide polymorphism in CTLA4 has been linked with susceptibility and outcome in autoimmune and infectious diseases, respectively. Here, we show that this polymorphism is associated with the frequency of CD4(+)CD25(+) regulatory T cells in healthy human volunteers. We further show that, on a per cell basis, such regulatory T cells appear to be functionally indistinguishable across CTLA4 genotypes. These data implicate CTLA4 in regulatory T cell development, and provide a mechanism to account for the link between polymorphisms at this locus and the biological outcome of adaptive immune responses to self and to pathogens.

Conditions influencing the efficacy of vaccination with live organisms against Leishmania major infection

Numerous experimental vaccines have been developed with the goal of generating long-term cell-mediated immunity to the obligate intracellular parasite Leishmania major, yet inoculation with live, wild-type L. major remains the only successful vaccine in humans. We examined the expression of immunity at the site of secondary, low-dose challenge in the ear dermis to determine the kinetics of parasite clearance and the early events associated with the protection conferred by vaccination with live L. major organisms in C57BL/6 mice. Particular attention was given to the route of vaccination. We observed that the rapidity, strength, and durability of the memory response following subcutaneous vaccination with live parasites in the footpad are even greater than previously appreciated. Antigen-specific gamma interferon (IFN-gamma)-producing T cells infiltrate the secondary site by 1.5 weeks, and viable parasites are cleared as early as 2.5 weeks following rechallenge, followed by a rapid drop in IFN-gamma(+) CD4(+) cell numbers in the site. In comparison, intradermal vaccination with live parasites in the ear generates immunity that is delayed in effector cell recruitment to the rechallenge site and in the clearance of parasites from the site. This compromised immunity was associated with a rapid recruitment of interleukin-10 (IL-10)-producing CD4(+) T cells to the rechallenge site. Treatment with anti-IL-10-receptor or anti-CD25 antibody enhanced early parasite clearance in ear-vaccinated mice, indicating that chronic infection in the skin generates a population of regulatory cells capable of influencing the level of resistance to reinfection. A delicate balance of effector and regulatory T cells may be required to optimize the potency and durability of vaccines against Leishmaniasis and other intracellular pathogens.

A role for CD103 in the retention of CD4+CD25+ Treg and control of Leishmania major infection

Endogenous regulatory T cells (T(reg)) play a central role in the control of excessive or misdirected immune responses against self or foreign Ags. To date, virtually no data are available on the nature of the molecules and signals involved in the trafficking and retention of T(reg) in tissues where regulation is required. Here, we show that expression of alpha(E)beta(7) integrin is necessary for the homing of T(reg) at site of Leishmania major infection. The vast majority of T(reg) present in the dermis at steady-state conditions or during L. major infection express the alpha(E) chain (CD103) of alpha(E)beta(7). Genetically susceptible BALB/c mice that lack CD103 become resistant to infection, a phenotype that is associated with a poor capacity of T(reg) to be retained in the infected site. Such susceptible phenotype can be restored when T(reg) from wild-type mice were transferred in CD103(-/-) mice. The central role of CD103 in T(reg) retention was further demonstrated by usage of blocking Abs against CD103 and the transfer of T(reg) purified from CD103(-/-) mice. Our results strongly suggest that this molecule is induced and maintained on T(reg) following or just prior to their arrival in tissues. Furthermore, the expression of CD103 and the subsequent retention of T(reg) in tissues is highly regulated by their exposure to Leishmania Ag and the level of activation of the APCs they encounter. Thus, CD103, by controlling T(reg) retention, can contribute to the outcome of chronic infection by Leishmania.

C5a negatively regulates toll-like receptor 4-induced immune responses

The complement system and the Toll-like receptors (TLRs) are two central arms of innate immunity that are critical to host defense as well as the development of adaptive immunity. Most pathogens activate both complement and TLRs, suggesting the potential for crosstalk between the two systems. We show here that the complement-derived C5a anaphylatoxin negatively regulates TLR4- and CD40-induced synthesis of IL-12 family cytokines (IL-12, IL-23, and IL-27) from inflammatory macrophages (M phi s) by extracellular signal-regulated kinase- and phosphoinositide 3 kinase-dependent pathways. This decreased cytokine response translates into a decreased T helper type 1 (Th1) response in vitro and in vivo. Accordingly, we found enhanced Th1 immunity in C5a receptor-deficient mice, something that conferred protection from Leishmania major infection. Our findings identify the negative impact of C5a on IL-12 family cytokines as an important mechanism for regulating Th1 polarization in response to innate and adaptive immune network activation.

Negative regulation of Toll-like receptor 4 signaling by the Toll-like receptor homolog RP105

Activation of Toll-like receptor (TLR) signaling by microbial signatures is critical to the induction of immune responses. Such responses demand tight regulation. RP105 is a TLR homolog thought to be mostly B cell specific, lacking a signaling domain. We report here that RP105 expression was wide, directly mirroring that of TLR4 on antigen-presenting cells. Moreover, RP105 was a specific inhibitor of TLR4 signaling in HEK 293 cells, a function conferred by its extracellular domain. Notably, RP105 and its helper molecule, MD-1, interacted directly with the TLR4 signaling complex, inhibiting its ability to bind microbial ligand. Finally, RP105 regulated TLR4 signaling in dendritic cells as well as endotoxin responses in vivo. Thus, our results identify RP105 as a physiological negative regulator of TLR4 responses.

Natural regulatory T cells in infectious disease

This review discusses the control exerted by natural CD4(+) CD25(+) regulatory T cells (natural T(reg) cells) during infectious processes. Natural T(reg) cells may limit the magnitude of effector responses, which may result in failure to adequately control infection. However, natural T(reg) cells also help limit collateral tissue damage caused by vigorous antimicrobial immune responses. We describe here various situations in which the balance between natural T(reg) cells and effector immune functions influences the outcome of infection and discuss how manipulating this equilibrium might be exploited therapeutically.

Role for CD4(+) CD25(+) regulatory T cells in reactivation of persistent leishmaniasis and control of concomitant immunity

Reactivation of dormant infections causes an immense burden of morbidity and mortality in the world at large. Reactivation can occur as a result of immunosuppression, environmental insult, or aging; however, the cause of reactivation of such infections is often not clear. We have previously shown that persistence of the parasite Leishmania major is controlled by endogenous CD4(+) CD25(+) regulatory T (T reg) cells. In this report, we show that despite efficient parasite clearance at secondary sites of infection, Leishmania superinfection can cause disease reactivation at the primary site. Our results strongly suggest that T reg cells, whose numbers increase in sites of reactivation, are directly responsible for such reactivation. Depletion of CD25(+) cells at the time of secondary challenge prevented disease reactivation at the site of persistent infection while strengthening the expression of immunity at the site of secondary challenge. Finally, transfer of T reg cells purified from infected mice into chronically infected mice was sufficient to trigger disease reactivation and prevent the expression of an effector memory response. Our results demonstrate that after persistence is achieved, an equilibrium between T reg cells and effector lymphocytes, which can be disturbed by superinfection, controls the efficiency of recall immune responses and disease reactivation.

The pathogenesis of schistosomiasis is controlled by cooperating IL-10-producing innate effector and regulatory T cells

IL-10 reduces immunopathology in many persistent infections, yet the contribution of IL-10 from distinct cellular sources remains poorly defined. We generated IL-10/recombination-activating gene (RAG)2-deficient mice and dissected the role of T cell- and non-T cell-derived IL-10 in schistosomiasis by performing adoptive transfers. In this study, we show that IL-10 is generated by both the innate and adaptive immune response following infection, with both sources regulating the development of type-2 immunity, immune-mediated pathology, and survival of the infected host. Importantly, most of the CD4(+) T cell-produced IL-10 was confined to a subset of T cells expressing CD25. These cells were isolated from egg-induced granulomas and exhibited potent suppressive activity in vitro. Nevertheless, when naive, naturally occurring CD4(+)CD25(+) cells were depleted in adoptive transfers, recipient IL-10/RAG2-deficient animals were more susceptible than RAG2-deficient mice, confirming an additional host-protective role for non-T cell-derived IL-10. Thus, innate effectors and regulatory T cells producing IL-10 cooperate to reduce morbidity and prolong survival in schistosomiasis.

Mice deficient in LRG-47 display increased susceptibility to mycobacterial infection associated with the induction of lymphopenia

Although IFN-gamma is essential for host control of mycobacterial infection, the mechanisms by which the cytokine restricts pathogen growth are only partially understood. LRG-47 is an IFN-inducible GTP-binding protein previously shown to be required for IFN-gamma-dependent host resistance to acute Listeria monocytogenes and Toxoplasma gondii infections. To examine the role of LRG-47 in control of mycobacterial infection, LRG-47(-/-) and wild-type mice were infected with Mycobacterium avium, and host responses were analyzed. LRG-47 protein was strongly induced in livers of infected wild-type animals in an IFN-gamma-dependent manner. LRG-47(-/-) mice were unable to control bacterial replication, but survived the acute phase, succumbing 11-16 wk postinfection. IFN-gamma-primed, bone marrow-derived macrophages from LRG-47(-/-) and wild-type animals produced equivalent levels of TNF and NO upon M. avium infection in vitro and developed similar intracellular bacterial loads. In addition, priming for IFN-gamma production was observed in T cells isolated from infected LRG-47(-/-) mice. Importantly, however, mycobacterial granulomas in LRG-47(-/-) mice showed a marked lymphocyte deficiency. Further examination of these animals revealed a profound systemic lymphopenia and anemia triggered by infection. As LRG47(-/-) T lymphocytes were found to both survive and confer resistance to M. avium in recipient recombinase-activating gene-2(-/-) mice, the defect in cellular response and bacterial control in LRG-47(-/-) mice may also depend on a factor(s) expressed in a nonlymphocyte compartment. These findings establish a role for LRG-47 in host control of mycobacteria and demonstrate that in the context of the IFN-gamma response to persistent infection, LRG-47 can have downstream regulatory effects on lymphocyte survival.

Defective lipoxin-mediated anti-inflammatory activity in the cystic fibrosis airway

In cystic fibrosis, dysregulated neutrophilic inflammation and chronic infection lead to progressive destruction of the airways. The underlying mechanisms have remained unclear. Lipoxins are anti-inflammatory lipid mediators that modulate neutrophilic inflammation. We report here that lipoxin concentrations in airway fluid were significantly suppressed in patients with cystic fibrosis compared to patients with other inflammatory lung conditions. We also show that administration of a metabolically stable lipoxin analog in a mouse model of the chronic airway inflammation and infection associated with cystic fibrosis suppressed neutrophilic inflammation, decreased pulmonary bacterial burden and attenuated disease severity. These findings suggest that there is a pathophysiologically important defect in lipoxin-mediated anti-inflammatory activity in the cystic fibrosis lung and that lipoxins have therapeutic potential in this lethal autosomal disease.

Coinjection with CpG-containing immunostimulatory oligodeoxynucleotides reduces the pathogenicity of a live vaccine against cutaneous Leishmaniasis but maintains its potency and durability

The inoculation of live, nonattenuated Leishmania major to produce a lesion in a selected site that heals, referred to as leishmanization, is to date the only vaccine against leishmaniasis that has proven to be effective in humans. Its use has been restricted or abandoned entirely, however, due to safety concerns. In an attempt to develop a leishmanization protocol that minimizes pathology while maintaining long-term protection, live parasites were coinjected with CpG-containing immunostimulatory oligodeoxynucleotides (CpG ODNs) alone or in combination with whole-cell lysates of heat-killed L. major promastigotes bound to alum (ALM). C57BL/6 mice infected intradermally by using L. major plus CpG ODN with or without ALM developed few or no dermal lesions and showed an early containment of parasite growth, while mice infected with L. major with or without ALM developed sizable dermal lesions that required up to 10 weeks to heal. The CpG ODNs provoked a transient inflammation that included an early recruitment and accumulation of gamma interferon-producing CD4(+) lymphocytes in the site. Attenuation of the live vaccine did not compromise its ability to confer long-term immunity, as mice receiving L. major and CpG ODN plus ALM were totally protected against reinfection with L. major for up to 6 months. By comparison, the immunity elicited by two efficient nonlive vaccines began to wane by 6 months. Our results suggest that immune modulation using CpG ODNs might be a practical approach to improving the safety of a highly effective live vaccine that has already been widely applied.

The role of CD4(+)CD25(+) regulatory T cells in Leishmania infection

There is growing evidence that regulatory T cells and, in particular, the endogenous CD4(+)CD25(+) T cells (T(reg)) are playing a fundamental role in the infectious process due to the protozoan parasite Leishmania. Endogenous CD4(+)CD25(+) T cells are a population of regulatory T cells, recently described for their capacity to control excessive or misdirected immune response. During human or murine Leishmaniasis, many features characteristic of T(reg )function, such as high levels of IL-10, transforming growth factor-beta (TGF-beta) or immunosuppression, have been extensively described. Recent reports formally involved T(reg) in the control of Leishmania major infection. Such control occurs by modulation of the effector immune response; in susceptible mouse strains, CD4(+)CD25(+) T cells suppress excessive T helper (Th)2 response, while in genetically resistant mouse strains, they control protective Th1 responses, allowing for parasite survival and maintenance of memory response. The mechanisms and consequences of such control in both susceptible or resistant mouse strains are discussed.

Interleukin 1alpha promotes Th1 differentiation and inhibits disease progression in Leishmania major-susceptible BALB/c mice

Protective immunity against pathogens such as Leishmania major is mediated by interleukin (IL)-12-dependent Th1-immunity. We have shown previously that skin-dendritic cells (DCs) from both resistant C57BL/6 and susceptible BALB/c mice release IL-12 when infected with L. major, and infected BALB/c DCs effectively vaccinate against leishmaniasis. To determine if cytokines other than IL-12 might influence disease outcome, we surveyed DCs from both strains for production of a variety of cytokines. Skin-DCs produced significantly less IL-1alpha in response to lipopolysaccharide/interferon gamma or L. major when expanded from BALB/c as compared with C57BL/6 mice. In addition, IL-1alpha mRNA accumulation in lymph nodes of L. major-infected BALB/c mice was approximately 3-fold lower than that in C57BL/6 mice. Local injections of IL-1alpha during the first 3 d after infection led to dramatic, persistent reductions in lesion sizes. In L. major-infected BALB/c mice, IL-1alpha administration resulted in increased Th1- and strikingly decreased Th2-cytokine production. IL-1alpha and IL-12 treatments were similarly effective, and IL-1alpha efficacy was strictly IL-12 dependent. These data indicate that transient local administration of IL-1alpha acts in conjunction with IL-12 to influence Th-development in cutaneous leishmaniasis and prevents disease progression in susceptible BALB/c mice, perhaps by enhancing DC-induced Th1-education. Differential production of IL-1 by C57BL/6 and BALB/c mice may provide a partial explanation for the disparate outcomes of infection in these mouse strains.

CD4+CD25+ regulatory T cells control Leishmania major persistence and immunity

The long-term persistence of pathogens in a host that is also able to maintain strong resistance to reinfection, referred to as concomitant immunity, is a hallmark of certain infectious diseases, including tuberculosis and leishmaniasis. The ability of pathogens to establish latency in immune individuals often has severe consequences for disease reactivation. Here we show that the persistence of Leishmania major in the skin after healing in resistant C57BL/6 mice is controlled by an endogenous population of CD4+CD25+ regulatory T cells. These cells constitute 5-10% of peripheral CD4+ T cells in naive mice and humans, and suppress several potentially pathogenic responses in vivo, particularly T-cell responses directed against self-antigens. During infection by L. major, CD4+CD25+ T cells accumulate in the dermis, where they suppress-by both interleukin-10-dependent and interleukin-10-independent mechanisms-the ability of CD4+CD25- effector T cells to eliminate the parasite from the site. The sterilizing immunity achieved in mice with impaired IL-10 activity is followed by the loss of immunity to reinfection, indicating that the equilibrium established between effector and regulatory T cells in sites of chronic infection might reflect both parasite and host survival strategies.

Optimization of DNA vaccination against cutaneous leishmaniasis

The present studies were designed to examine the requirements of dose, route of inoculation and constituent antigens for the maintenance of complete and long lasting protection against cutaneous leishmaniasis due to Leishmania major conferred by a cocktail DNA vaccine encoding the Leishmania antigens LACK, LmST11 and TSA. Vaccination of C57Bl/6 mice with LACK DNA alone resulted in partial protection, whereas the combination of LmST11 and TSA provided stronger, though still incomplete protection compared to the combination of all three Ag DNAs. When intradermal (i.d), intramuscular (i.m.), and subcutaneous (s.c.) vaccination routes were compared, i.d. immunization reduced by five-fold the dose necessary to maintain complete protection. In vivo depletion of CD4+ or CD8+ T cells provided direct evidence that both populations are necessary to mediate complete protection. These results establish intradermal vaccination using DNA encoding multiple Leishmania antigens as a way to optimize priming of CD4+ and CD8+ T cells necessary for potent and durable protection against cutaneous leishmaniasis.