Regulatory Cells that Control Intestinal Inflammation

It is now clear that functionally specialized regulatory T (Treg) cells exist as part of the normal immune repertoire, preventing the development of pathogenic responses to both selfand intestinal antigens. Here, we report that the Treg cells that control intestinal inflammation express the same phenotype (CD25 1 CD45RB low CD4 1 ) as those that control autoimmunity. Previous studies have failed to identify how CD25 1 Treg cells function in vivo. Our studies reveal that the immune-suppressive function of these cells in vivo is dependent on signaling via the negative regulator of T cell activation cytotoxic T lymphocyte–associated antigen 4 (CTLA-4), as well as secretion of the immune-suppressive cytokine transforming growth factor b . Strikingly, constitutive expression of CTLA-4 among CD4 1 cells was restricted primarily to Treg cells, suggesting that CTLA-4 expression by these cells is involved in their immune-suppressive function. These findings raise the possibility that Treg cell function contributes to the immune suppression characteristic of CTLA-4 signaling. Identification of costimulatory molecules involved in the function of Treg cells may facilitate further characterization of these cells and development of new therapeutic strategies for the treatment of inflammatory diseases.