An endogenous aryl hydrocarbon receptor ligand enhances de novo generation of regulatory T cells in humans.

The aromatic hydrocarbons receptor (AhR) is a ligand-dependent transcription factor that plays a role in mediating toxicity to xenobiotics. Its key role in immune regulation has been recently demonstrated. Recent data pointed to the efficacy of ITE (2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester), a nontoxic ligand of AhR, in experimental models of inflammatory diseases. Such effect was mainly through the expansion of regulatory T cells (Tregs). Similarly, TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), a toxic ligand of AhR, has been shown to exert comparable effects on Tregs in mice. Herein, we showed that ITE has no effects on natural Tregs. However, it supports the de novo generation of Tregs in humans while promoting their suppressive functions. Our data bring new elements supporting the use of ITE in human therapy of inflammatory diseases.

Human cellular immune response to the saliva of Phlebotomus papatasi is mediated by IL-10-producing CD8+ T cells and Th1-polarized CD4+ lymphocytes.

BACKGROUND: The saliva of sand flies strongly enhances the infectivity of Leishmania in mice. Additionally, pre-exposure to saliva can protect mice from disease progression probably through the induction of a cellular immune response. METHODOLOGY/PRINCIPAL FINDINGS: We analysed the cellular immune response against the saliva of Phlebotomus papatasi in humans and defined the phenotypic characteristics and cytokine production pattern of specific lymphocytes by flow cytometry. Additionally, proliferation and IFN-γ production of activated cells were analysed in magnetically separated CD4+ and CD8+ T cells. A proliferative response of peripheral blood mononuclear cells against the saliva of Phlebotomus papatasi was demonstrated in nearly 30% of naturally exposed individuals. Salivary extracts did not induce any secretion of IFN-γ but triggered the production of IL-10 primarily by CD8+ lymphocytes. In magnetically separated lymphocytes, the saliva induced the proliferation of both CD4+ and CD8+ T cells which was further enhanced after IL-10 blockage. Interestingly, when activated CD4+ lymphocytes were separated from CD8+ cells, they produced high amounts of IFN-γ. CONCLUSION: Herein, we demonstrated that the overall effect of Phlebotomus papatasi saliva was dominated by the activation of IL-10-producing CD8+ cells suggesting a possible detrimental effect of pre-exposure to saliva on human leishmaniasis outcome. However, the activation of Th1 lymphocytes by the saliva provides the rationale to better define the nature of the salivary antigens that could be used for vaccine development.

Resistance to exogenous TGF-ß effects in patients with systemic lupus erythematosus.

BACKGROUND: The mechanisms underlying the loss of self-tolerance in systemic lupus erythematosus (SLE) are incompletely deciphered. TGF-ß plays a key role in self-tolerance demonstrated by the onset of a fatal autoimmune syndrome associated with lupus autoantibodies in mice lacking a functional TGF-ß receptor. The present work aims to define whether resistance to TGF-ß might contribute to the pathogenesis of SLE. METHODS: Twenty-two patients with active SLE, 16 with other connective tissue diseases, and 10 healthy controls were prospectively included in this study. The effects of exogenous TGF-ß1 on IL-2-dependent T-cell proliferation, IFN-γ secretion, and target gene transcription were analyzed on peripheral blood mononuclear cells. RESULTS: Our results showed that 75% of patients with SLE or other connective tissue diseases were totally or partially resistant to the effects of TGF-ß1. The responses to the anti-proliferative and transcriptional effects of TGF-ß were, however, discordant in a high proportion of our patients. Hence, we distinguish three distinct profiles of resistance to TGF-ß1 and suggest that patients may exhibit different defects affecting distinct points of TGF-ß1 signaling pathways. CONCLUSION: Our data demonstrate the presence of an impaired response of peripheral cells to TGF-ß1 in patients with active SLE that may participate to the pathogenesis of the disease. Further studies will be necessary to delineate the mechanisms underlying the lymphocyte resistance to TGF-ß1 in SLE.

IL-15 renders conventional lymphocytes resistant to suppressive functions of regulatory T cells through activation of the phosphatidylinositol 3-kinase pathway.

IL-15 drives chronic inflammation in several human diseases. We have recently shown that IL-15 inhibits the immunosuppressive effects of TGF-beta through blockage of the Smad3-signaling pathway. Data pointing to reciprocal interactions between TGF-beta and CD4(+) regulatory T cells led us to investigate the impact of IL-15 on the de novo generation and function of regulatory T cells in humans. Our data indicate that IL-15 does not counteract, but rather promotes the effect of TGF-beta on the de novo generation of regulatory T cells (Treg). Thus, in the presence of TGF-beta, IL-15 enhanced the acquisition of regulatory functions by CD4(+)CD25(-) T cells stimulated by anti-CD3 and anti-CD28 Abs. In contrast, IL-15 impaired the functions of Tregs by acting on effector CD4 and CD8 T cells. Accordingly, in the presence of IL-15, proliferation and IFN-gamma production by peripheral CD4 and CD8 T cells could not be efficiently inhibited by Tregs. IL-15-induced resistance of effector T cells to Tregs resulted from activation of the PI3K signaling pathway but did not involve the rescue of effector T cells from apoptosis. Altogether, these data point to the ambiguous role of IL-15 in the control of Treg functions. This dual role may be instrumental to mount rapid but transient proinflammatory immune responses against pathogens but may become deleterious in situations associated with protracted IL-15 over-expression.