Innate γδT17 cells play a protective role in DSS-induced colitis via recruitment of Gr-1+CD11b+ myeloid suppressor cells

Innate γδ T cells play critical roles in mucosal immunity such as regulating intestinal epithelial homeostasis. In addition, γδ T cells are significantly increased in the inflamed mucosa of patients with ulcerative colitis. However, γδ T cells are a heterogeneous population. IL-17-producing versus IFNγ-producing γδ T cells play differential roles in different disease settings. Therefore, dissecting the exact role of different subsets of γδ T cells in colitis is essential for understanding colitis immunopathogenesis. In the current study, we found that TCR δ-deficient mice had a more severe dextran sodium sulfate (DSS)-induced colitis that was reduced upon reconstitution of γδT17 cells but not IFNγ-producing γδ T cells. Immunophenotyping of the cellular infiltrate upon DSS-induced colitis showed a reduced infiltration of Gr-1⁺CD11b⁺ myeloid cells into the sites of inflammation in mice lacking γδT17 cells. Further experiments demonstrated that IL-17, IL-18, and chemokine CXCL5 were critical in Gr-1⁺CD11b⁺ myeloid cell recruitment. In vitro T cell suppressive assay indicated that this Gr-1⁺CD11b⁺ population was immunosuppressive. Depletion of Gr-1⁺CD11b⁺ myeloid cells resulted in an increase severity of DSS-induced colitis. Our study elucidates a new immune pathway involving γδT17-dependent recruitment of Gr-1⁺CD11b⁺ myeloid cells to the site of colitis inflammation important in the protection of colitis initiation and progression.