Susanna Lopez Kostka

Uptake of Leishmania major by dendritic cells is mediated by Fcγ 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 (MΦ) 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 FcγRI and FcγRIII. 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 Fcγ−/− mice contained fewer parasite-infected DCs in vivo. Infected B cell–deficient mice as well as Fcγ−/− 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-γ production, and these deficits were normalized by infection with IgG-opsonized parasites. These data demonstrate that DC and MΦ use different receptors to recognize and ingest L. major with different outcomes, and indicate that B cell–derived, parasite-reactive IgG and DC FcγRI and FcγRIII are essential for optimal development of protective immunity.

IL-17 promotes progression of cutaneous leishmaniasis in susceptible mice

Resistance to leishmaniasis in C57BL/6 mice depends on Th1/Tc1 cells. BALB/c mice preferentially develop Th2 immunity and succumb to infection. We now assessed the role of IL-17 in cutaneous leishmaniasis. During the course of Leishmania major infection, BALB/c CD4 cells and neutrophils produced increased amounts of IL-17 as compared with cells from C57BL/6 mice. This increase was associated with significantly increased IL-23 release from L. major-infected BALB/c dendritic cells (DC), whereas IL-6 and TGF-β1 production by BALB/c and C57BL/6 DC were comparable. Interestingly, lesion sizes in infected IL-17-deficient BALB/c mice were dramatically smaller and failed to progress as compared with those in control mice. Similar amounts of IL-4, IL-10, and IFN-γ were produced by T cells from IL-17-deficient mice and control mice consistent with development of Th2-predominant immunity in all animals. Improved disease outcome was associated with decreased CXCL2-accumulation in lesion sites and decreased neutrophil immigration into lesions of infected IL-17-deficient mice confirming prior observations that enhanced neutrophil recruitment contributes to disease susceptibility in BALB/c mice. This study excludes an important facilitating role for IL-17 in Th1/Th2 development in L. major-infected BALB/c mice, and suggests that IL-23 production by L. major-infected DC maintains IL-17+ cells that influence disease progression via regulation of neutrophil recruitment.

Interleukin 1α 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-1α in response to lipopolysaccharide/interferon γ or L. major when expanded from BALB/c as compared with C57BL/6 mice. In addition, IL-1α mRNA accumulation in lymph nodes of L. major–infected BALB/c mice was ∼3-fold lower than that in C57BL/6 mice. Local injections of IL-1α during the first 3 d after infection led to dramatic, persistent reductions in lesion sizes. In L. major–infected BALB/c mice, IL-1α administration resulted in increased Th1- and strikingly decreased Th2-cytokine production. IL-1α and IL-12 treatments were similarly effective, and IL-1α efficacy was strictly IL-12 dependent. These data indicate that transient local administration of IL-1α 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.

Skin mast cells control T cell-dependent host defense in Leishmania major infections

Mast cells (MCs) initiate protective im‐ munity against bacteria. Here we demonstrate that MCs also contribute to the control of parasitic skin infections by Leishmania major. L. major‐infected MC‐defi‐cient KitW/KitW‐v mice developed markedly larger skin lesions than did normal Kit+/+ mice (>2‐fold), and cutaneous reconstitution with MCs resulted in normalization of lesion development. KitW/KitW‐v lesions contained significantly more parasites, and infections resulted in enhanced spreading of parasites to the spleens as compared to controls. In addition, recruitment of proinflammatory neutrophils, macrophages, and dendritic cells (DCs) in infected mice was MC dependent. In the absence of MCs, reduced numbers of lesional DCs were associated with decreased production of Th1‐promoting interleukin (IL)‐12. Antigen‐specific T cell priming was delayed in KitW/KitW‐v mice and cytokine responses were skewed towards Th2. Notably, local skin MC reconstitution at sites of infection was sufficient for the induction of systemic protection. Thus, MC‐mediated control of L. major infections is not limited to the induction of local inflammation. Instead, MCs contribute significantly to local DC recruitment, which mediates protective immunity. These findings extend the view of MCs as salient sentinels of innate immunity to complex host defense reactions against intracellular pathogens.—Maurer, M., Lopez Kostka, S., Siebenhaar, F., Moelle, K., Metz, M., Knop, J., von Stebut, E. Skin mast cells control T cell‐dependent host defense in Leishmania major infections. FASEB J. 20, 2460–2467 (2006)

Mast cells promote Th1 and Th17 responses by modulating dendritic cell maturation and function

Mast cells (MCs) play an important role in the regulation of protective adaptive immune responses against pathogens. However, it is still unclear whether MCs promote such host defense responses via direct effects on T cells or rather by modifying the functions of antigen‐presenting cells. To identify the underlying mechanisms of the immunoregulatory capacity of MCs, we investigated the impact of MCs on dendritic cell (DC) maturation and function. We found that murine peritoneal MCs underwent direct crosstalk with immature DCs that induced DC maturation as evidenced by enhanced expression of costimulatory molecules. Furthermore, the MC/DC interaction resulted in the release of the T‐cell modulating cytokines IFN‐γ, IL‐2, IL‐6 and TGF‐β into coculture supernatants and increased the IL‐12p70, IFN‐γ, IL‐6 and TGF‐β secretion of LPS‐matured DCs. Such MC‐“primed” DCs subsequently induced efficient CD4+ T‐cell proliferation. Surprisingly, we observed that MC‐primed DCs stimulated CD4+ T cells to release high levels of IFN‐γ and IL‐17, demonstrating that MCs promote Th1 and Th17 responses. Confirming our in vitro findings, we found that the enhanced disease progression of MC‐deficient mice in Leishmania major infection is correlated with impaired induction of both Th1 and Th17 cells.

IL-1 signalling is dispensable for protective immunity in Leishmania-resistant mice.

Abstract:  Leishmaniasis is a parasitic disease affecting ∼12 million people. Control of infection (e.g. in C57BL/6 mice) results from IL‐12‐dependent production of IFNγ by Th1/Tc1 cells. In contrast, BALB/c mice succumb to infection because of preferential Th2‐type cytokine induction. Infected dendritic cells (DC) represent important sources of IL‐12. Genetically determined differences in DC IL‐1α/β production contribute to disease outcome. Whereas the course of disease was not dramatically altered in IL‐1RI−/− mice, local administration of IL‐1α to infected C57BL/6 mice improved disease outcome. To definitively elucidate the involvement of IL‐1 in immunity against leishmaniasis, we now utilized IL‐1α/β‐double‐deficient C57BL/6 mice. C57BL/6 mice are believed to be a good surrogate model for human, self limited cutaneous leishmaniasis (CL). Leishmania major‐infected IL‐1α/β−/− mice were resistant to experimental CL comparable to controls. In addition, DC‐based vaccination against leishmaniasis in C57BL/6 mice was independent of IL‐1. Thus, in Leishmania‐resistant C57BL/6 mice, IL‐1 signalling is dispensable for protection.

Blue light irradiation suppresses dendritic cells activation in vitro.

Blue light is a UV‐free irradiation suitable for treating chronic skin inflammation, for example, atopic dermatitis, psoriasis, and hand‐ and foot eczema. However, a better understanding of the mode of action is still missing. For this reason, we investigated whether dendritic cells (DC) are directly affected by blue light irradiation in vitro. Here, we report that irradiation neither induced apoptosis nor maturation of monocyte‐derived and myeloid DC. However, subsequent DC maturation upon LPS/IFNγ stimulation was impaired in a dose‐dependent manner as assessed by maturation markers and cytokine release. Moreover, the potential of this DC to induce cytokine secretion from allogeneic CD4 T cells was reduced. In conclusion, unlike UV irradiation, blue light irradiation at high and low doses only resulted in impaired DC maturation upon activation and a reduced subsequent stimulatory capacity in allogeneic MLRs with strongest effects at higher doses.

Immune Modulating Effects of NKT Cells in a Physiologically Low Dose Leishmania major Infection Model after αGalCer Analog PBS57 Stimulation

Leishmaniasis is a parasitic infection affecting ∼12 million people worldwide, mostly in developing countries. Treatment options are limited and no effective vaccines exist to date. Natural Killer T (NKT) cells are a conserved innate-like lymphocyte population with immunomodulating effects in various settings. A number of reports state a role of NKT cells in different models of Leishmania infection. Here, we investigated the effect of NKT cells in a physiologically relevant, intradermal low dose infection model. After inoculation of 103 infectious-stage L. major, comparable numbers of skin-immigrating NKT cells in both susceptible BALB/c mice and resistant C57BL/6 mice were noted. Compared to their wild type counterparts, NKT cell-deficient mice on a C57BL/6 background were better able to contain infection with L. major and showed decreased IL-4 production in cytokine analysis performed 5 and 8 weeks after infection. Low doses of the NKT cell stimulating αGalCer analog PBS57 applied at the time of infection led to disease exacerbation in C57BL/6 wild-type, but not NKT-deficient mice. The effect was dependent both on the timing and amount of PBS57 administered. The effect of NKT cell stimulation by PBS57 proved to be IL-4 dependent, as it was neutralized in IL-4-deficient C57BL/6 or anti-IL-4 antibody-treated wild-type mice. In contrast to C57BL/6 mice, administration of PBS57 in susceptible BALB/c mice resulted in an improved course of disease. Our results reveal a strain- and cytokine-dependent regulatory role of NKT cells in the development of immunity to low dose L. major infections. These effects, probably masked in previous studies using higher parasite inocula, should be considered in future therapy and immunization approaches.

Disease control in cutaneous leishmaniasis is independent of IL-22.

University Hospital, Sousse, Tunisia; Department of Dermatology and Venerology, Nabeul Regional Hospital, Nabeul, Tunisia; Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA; École Pratique des Hautes Études, heSam University and Institut du Cerveau et de la Moelle Epinière, Sorbonne University, PitiéSalpêtrière Hospital, Paris, France; Department of Pathological Anatomy and Cytology, Farhat Hached University Hospital, Sousse, Tunisia and Department of Paediatrics, National University of Singapore, Singapore, Singapore E-mail: ali.saad@rns.tn or bruno@reversade.com

A Role for Leukocyte-Derived IL-1RA in DC Homeostasis Revealed by Increased Susceptibility of IL-1RA-Deficient Mice to Cutaneous Leishmaniasis

Dendritic cell (DC)-derived IL-1α/β plays a critical role in the induction of T helper type 1 (Th1)-dependent immunity against Leishmania. DCs from susceptible BALB/c mice produce less IL-1α/β when compared with resistant C57BL/6 mice, contributing to aberrant Th2 development and ultimate death of infected mice. We have extended our studies of the role of IL-1 in leishmaniasis using IL-1RA(-/-) BALB/c mice that are characterized by upregulated IL-1 receptor signaling. Unexpectedly, infection of IL-1RA(-/-) mice led to significantly worsened disease outcome with larger lesions, dramatically higher parasite burdens, and decreased IFN-γ production by antigen-specific T cells. We determined that IL-1RA(-/-) DCs were more mature already in the steady state, exhibited less phagocytotic capacity, and IL-12 production in response to various stimuli was impaired. Our data suggest that in addition to effects on Th education, IL-1α/β signaling also modulates DC homeostasis with increased signaling, leading to downmodulation of IL-12 synthesis and worsened disease outcome after infection with Leishmania major. Thus, the complex regulation of various members of the IL-1 cytokine family mediated through effects on both DCs and T cells critically contributes to disease outcome against this important human pathogen.