Peroxisome Proliferator-Activated Receptor γ Is Required for Regulatory CD4+ T Cell-Mediated Protection against Colitis

Abstract

Peroxisome proliferator-activated receptor (PPAR) γ activation has been implicated in the prevention of immunoinflammatory disorders; however, the mechanisms of regulation of effector and regulatory CD4+ T cell functions by endogenously activated PPAR-γ remain unclear. We have used PPAR-γ-deficient CD4+ T cells obtained from tissue-specific PPAR-γ null mice (i.e., PPAR-γ fl/fl; MMTV-Cre+) to investigate the role of endogenous PPAR-γ on regulatory T cell (Treg) and effector CD4+ T cell function. Overall, we show that the loss of PPAR-γ results in enhanced Ag-specific proliferation and overproduction of IFN-γ in response to IL-12. These findings correlate in vivo with enhanced susceptibility of tissue-specific PPAR-γ null mice to trinitrobenzene sulfonic acid-induced colitis. Furthermore, the transfer of purified PPAR-γ null CD4+ T cells into SCID recipients results in enteric disease. To test the assertion that the deficiency of PPAR-γ in Treg impairs their ability to prevent effector T cell-induced colitis, we performed cotransfer studies. These studies demonstrate that PPAR-γ-expressing, but not PPAR-γ null Treg, prevent colitis induced by transfer of naive CD4+ T cells into SCID recipients. In line with these findings, the production of IFN-γ by spleen and mesenteric lymph node-derived CD4+ T cells was down-regulated following transfer of PPAR-γ-expressing, but not PPAR-γ null, Treg. In conclusion, our data suggest that endogenous PPAR-γ activation represents a Treg intrinsic mechanism of down-regulation of effector CD4+ T cell function and prevention of colitis.