4B). Moreover, we did not detect a significant change in the frequency, absolute

number or phenotype of B cells during colitis development (Supporting Information Fig. 1). While these observations do not exclude a possible role for B cells in this process, IDH activation they also do not exclude a potential contribution for resident γδ T cells during T-cell-induced immune pathology in the gut. Flow cytometric analysis of draining mesLN of colitic mice showed a two-fold increase in accumulation of donor CD4+ TEFF cells in TCR-β−/− compared with RAG2−/− recipient mice; however, CD4+ TEFF cells accumulated at a similar rate in the LP of either recipients (Fig. 4C). Interestingly, when we examined frequencies of IFN-γ- and IL-17-secreting donor CD4+ T cells, we observed that RAG2−/− recipient mice harbored significantly fewer IL-17+ TEFF cells compared with TCR-β−/− mice, despite a slightly more elevated frequency in IFN-γ-secreting

TEFF cells. Over 50% of donor CD4+ T cells isolated from mesLN and LP of RAG2−/− recipients secreted IFN-γ, and only 10% were positive for IL-17, which is three times less compared with TCR-β−/− recipient Ibrutinib order mice (Fig. 4D and E). Thus, γδ T cells resident in mesenteric sites of TCR-β−/− mice fuel Th17 responses and actively participate in intestinal inflammation. Our results show that TREG cells potently inhibit the expansion and accumulation of pro-inflammatory cytokine secreting donor CD4+ TEFF and host γδ T cells in T-cell-induced intestinal inflammation in TCR-β−/− mice. Interestingly, by 21 days post CD4+ TEFF cell transfer, co-transfer of TREG cells resulted in a two-fold reduction in the proportion of γδ T cells in mesLN compared with colitic mice receiving only TEFF cells (Fig. 5A and B). Furthermore, this decrease was more profound in the LP and reached an eight-fold reduction in the proportion of γδ T cells (Fig. 5B), suggesting that TREG cells impair the

accumulation of γδ T cells in the inflamed gut. To examine the proliferation of donor and host T cells in the presence and absence of TREG cells, the proportion of cycling Glycogen branching enzyme cells was determined by intracellular Ki-67 expression. Co-transfer of TREG cells significantly decreased the frequency and absolute numbers of cycling donor CD4+ TEFF and resident γδ T-cell populations in lymphoid organs as well as in the LP in recipient TCR-β−/− mice (Fig. 5C and D). Thus, TREG-cell transfer suppresses the expansion and accumulation of resident γδ T cells in the inflamed colon during development of T-cell-induced colitis. In order to show a direct inhibitory effect of TREG cells on γδ T cells, we performed an in vitro suppression assay where anti-CD3 pre-activated FACS sorted responder populations were co-cultured with titrated numbers of freshly isolated CD4+CD25+ TREG cells. At the highest 1:1 TREG to T responder ratio, TREG cells inhibited γδ T-cell proliferation by 75%, with a similar effect on control CD4+CD25− T responder cells (Fig. 6A).