SUMMARY Aryl hydrocarbon receptor (Ahr) is crucial for the maintenance and function of group 3 innate lymphoid cells (ILCs), which are important in gut immunity. Because Ahr promotes T helper 17 (Th17) cell differentiation in vitro, it is reasonable to expect that Ahr would enhance Th17 cells in vivo. Instead, we show that Ahr deficiency caused increased intestinal Th17 cells, raising the possibility that group 3 ILCs could negatively regulate Th17 cells. Reduced innate interleukin-22 (IL-22) in Ahr-deficient mice allowed expansion of commensal segmented filamentous bacteria (SFB), known to promote Th17 cells. Compared to Rorc+/+Ahr−/− mice, Rorcgfp/+Ahr−/− mice had further reduced group 3 ILCs and were prone to spontaneous colitis with increased SFB and Th17 cells. Innate expression of Ahr played a protective role in T-cell-mediated experimental colitis by suppressing pathogenic Th17 cells. Our data reveal an intricate balance between ILCs and Th17 cells regulated by Ahr and commensal flora.

BackgroundThe current knowledge of immunological responses to schistosomiasis, a major tropical helminthic disease, is insufficient, and a better understanding of these responses would support vaccine development or therapies to control granuloma-associated immunopathology. CD4+ T cells play critical roles in both host immune responses against parasitic infection and immunopathology in schistosomiasis. The induction of T helper (Th)1, Th2 and T regulatory (Treg) cells and their roles in schistosome infections are well-illustrated. However, little in vivo data are available on the dynamics of Th17 cells, another important CD4+ T cell subset, after Schistosoma japonicum infection or whether these cells and their defining IL-17 cytokine mediate host protective responses early in infection.MethodologyLevels of Th17 and the other three CD4+ T cell subpopulations and the cytokines related to induction or repression of Th17 cell generation in different stages of S. japonicum infection were observed. Contrary to reported in vitro studies, our results showed that the Th17 cells were induced along with the Th1, Th2, Treg cells and the IFN-γ and IL-4 cytokines in S. japonicum infected mice. The results also suggested that S. japonicum egg antigens but not adult worm antigens preferentially induced Th17 cell generation. Furthermore, decreasing IL-17 with a neutralizing anti-IL-17 monoclonal antibody (mAb) increased schistosome-specific antibody levels and partial protection against S. japonicum infection in mice.ConclusionsOur study is the first to report the dynamics of Th17 cells during S. japonicum infection and indicate that Th17 cell differentiation results from the integrated impact of inducing and suppressive factors promoted by the parasite. Importantly, our findings suggest that lower IL-17 levels may result in favorable host protective responses. This study significantly contributes to the understanding of immunity to schistosomiasis and may aid in developing interventions to protect hosts from infection or restrain immunopathology.

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Recent studies show that colonic vitamin D receptor (VDR) signaling protects the mucosal epithelial barrier and suppresses colonic inflammation, but the underlying molecular mechanism remains to be fully understood. To investigate the implication of colonic VDR downregulation seen in patients with inflammatory bowel disease, we assessed the effect of gut epithelial VDR deletion on colonic inflammatory responses in an experimental colitis model. In a 2,4,6-trinitrobenzenesulfonic acid-induced colitis model, mice carrying VDR deletion in gut epithelial cells [VDRflox/flox (VDRf/f);Villin-Cre or VDRΔIEC] or in colonic epithelial cells (VDRf/f;CDX2-Cre or VDRΔCEC) developed more severe clinical colitis than VDRf/f control mice, characterized by more robust T-helper (TH)1 and TH17 responses, with greater increases in mucosal interferon (IFN)-γ+, interleukin (IL)-17+, and IFN-γ+IL-17+ T cells. Accompanying the severe mucosal inflammation was more profound colonic epithelial cell apoptosis in the mutant mice. Treatment with caspase inhibitor Q-VD-OPh dramatically reduced colitis severity and attenuated TH1 and TH17 responses in VDRΔCEC mice. The blockade of cell apoptosis also prevented the increase in mucosal CD11b+CD103+ dendritic cells (DCs), known to be critical for TH17-cell activation. Moreover, depletion of gut commensal bacteria with antibiotics eliminated the robust TH1 and TH17 responses and CD11b+CD103+ DC induction. Taken together, these observations demonstrate that gut epithelial VDR deletion aggravates epithelial cell apoptosis, resulting in increases in mucosal barrier permeability. Consequently, invading luminal bacteria activate CD11b+CD103+ DCs, which promote mucosal TH1 and TH17 responses. Therefore, gut epithelial VDR signaling controls mucosal inflammation by suppressing epithelial cell apoptosis.

Chronic schistosome infection results in the suppression of host immune responses, allowing long-term schistosome survival and restricting pathology. Current theories suggest that Treg play an important role in this regulation. However, the mechanism of Treg induction during schistosome infection is still unknown. The aim of this study was to determine the mechanism behind the induction of CD4 1 CD25 1 T cells by Schistosoma japonicum HSP60 (SjHSP60)-derived peptide SJMHE1 as well as to elucidate the cellular and molecular basis for the induction of CD4 1 CD25 1 T cells during S. japonicum infection. Mice immunized with SJMHE1 or spleen and LN cells from naïve mice pretreated with SJMHE1 in vitro all displayed an increase in CD4 1 CD25 1 T-cell populations. Release of IL-10 and TGF-b by SJMHE1 stimulation may contribute to suppression. Adoptively transferred SJMHE1-induced CD4 1 CD25 1 T cells inhibited delayed-type hypersensitivity in BALB/c mice. Additionally, SJMHE1-treated APC were tolerogenic and induced CD4 1 cells to differentiate into suppressive CD4 1 CD25 1 Treg. Furthermore, our data support a role for TLR2 in SJMHE1-mediated CD4 1 CD25 1 Treg induction. These findings provide the basis for a more complete understanding of the S. japonicum-host interactions that contribute to host homeostatic mechanisms, preventing an excessive immune response.Key words: CD4 1 CD25 1 Treg . Immunomodulation . Schistosomes . SJMHE1 . TLR2 Supporting Information available online IntroductionImmune regulation associated with protective immunity is intricate and entails the effective elimination of the pathogen without causing serious damage to the host. Conversely, effective pathogens have developed multiple mechanisms for modulating or suppressing host immunity as survival and dissemination strategies. Therefore, during the course of an infection, a struggle between host defense mechanisms and the pathogen's immunomodulatory processes results in a complex interplay that may result in pathogen eradication or damage to the host (and persistence of the pathogen). One of the survival strategies used by pathogens involves the induction of immunosuppressive cell populations, e.g. Treg [1,2]. 3052The first observations suggesting that Treg induction occurs during infections with certain pathogens were made in mice infected with Bordetella pertussis [3] and in humans infected with HCV [4] or the nematode Onchocerca volvulus [5]. More recently, Treg induction has been described in chronic infections caused by Candida albicans [6], Mycobacterium tuberculosis [7], HIV [8], Leishmania major [9], Litomosoides sigmodontis [10], and Helicobacter pylori [11]. Treg induction has also been associated with Schistosome infection. Schistosomiasis is a major human disease primarily caused by one of the three species of Schistosome endemic to parts of Asia, South America, and Africa, i.e. S. mansoni, S. haematobium, and S. japonicum. Mortality rates resulting from these types of parasitic infections are second only to malaria. Chronic schis...