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Background The coinhibitory receptor T cell immunoglobulin and ITIM domain (TIGIT) is widely expressed by immune cells, including CD4+ T cells. Previously, we showed that circulating gut homing CD38+ (CD62LnegCD4+) effector T cells are enriched for TIGIT+ cells with an immunoregulatory phenotype. In newly diagnosed inflammatory bowel disease (IBD) patients, low frequencies of regulatory TIGIT+ cells in circulating gut homing CD38+CD62LnegCD4+ effector T cells associate with more severe disease. IBD is a chronic disease characterized by aberrant CD4+ T cell responses to intestinal microbiota. Together, this led us to hypothesize that TIGIT+CD4+ T cells regulate immune responses to intestinal bacteria thereby maintaining intestinal homeostasis. Methods We studied TIGIT expression in subpopulations of murine and human intestinal CD4+ T cells. In addition, we assessed the signals required for the induction of TIGIT expression in vitro using CD4+ T cells isolated from human healthy donor peripheral blood. Results TIGIT was expressed by more than 50% of memory, but not naïve, CD4+ T cells in the intestinal lamina propria of both mouse and human. Both Foxp3+ and Foxp3neg intestinal CD4+ T cells expressed TIGIT. Intestinal TIGIT expression depended on the presence of microbial antigens, as conventionalization of germ-free mice with specific-pathogen free (SPF) microbiota dramatically increased TIGIT expression in both small intestine and colon. T cell receptor (TCR) ligation mimicked by anti-CD3 stimulation was essential to induce TIGIT expression on CD4+ T cells isolated from human peripheral blood, but CD28 co-stimulation led to reduced TIGIT expression. TIGIT expression could only be induced on antigen-experienced CD4+ memory T cells, but not naïve CD4+ T cells. Using the calcium ionophore ionomycin and the calcineurin inhibitor tacrolimus, we demonstrated that the induction of TIGIT expression upon TCR ligation depended on downstream calcium-dependent signaling. We next assessed whether retinoic acid (RA), a metabolite produced by intestinal antigen-presenting cells (APCs), can further enhance TIGIT expression. RA plays an important role in mucosal immune responses, as it promotes the development of Foxp3+ regulatory T cells and induces the expression of the gut-homing markers CD38 and α4β7. We showed that co-stimulation with RA also significantly enhanced TCR-induced TIGIT expression, as it increased both the mean fluorescence intensity (MFI) and frequencies of TIGIT+ cells in CD4+ memory T cells. Conclusion In conclusion, these data argue that TCR ligation and retinoic acid production by intestinal APCs induces TIGIT expression on CD4+ memory T cells, which in turn may contribute to regulation of immune responses against microbial antigens.

journal of crohn's and colitis

P063 Expression of the coinhibitory receptor TIGIT on memory CD4+ T cells is induced by TCR ligation and retinoic acid co-stimulation and is elicited during microbial colonization of the intestine