Compensatory roles of CD8+ T cells and plasmacytoid dendritic cells in gut immune regulation for reduced function of CD4+ Tregs.

CD4+ Tregs need to migrate from the mucosal periphery into the draining lymph node via CCR7 to exert their suppressive effects. In this study, we investigated whether CCR7 deficiency resulted in failure of immune suppression in 2% dextran sulfate sodium-induced colitis. Unexpectedly, intestinal inflammation was not exacerbated in the absence of CCR7. Expression of IL-10, a representative suppressive cytokine, was enhanced in CCR7KO CD8+ T cells. Colon CCR7KO CD8+ T cells reduced the activation of CD4+ T cells. Depletion of CD8+ T cells using anti-CD8 antibody exacerbated colitis in CCR7KO mice. Plasmacytoid dendritic cell numbers were also slightly increased during intestinal inflammation in the absence of CCR7, and the depletion of those cells exacerbated DSS-induced colitis in CCR7KO mice. These results suggest that CD8+ T cells and plasmacytoid dendritic cells have compensatory roles in immune regulation in the gut for impaired function of CD4+ Tregs.