CD4+CD25+Foxp3+ regulatory T cells induce cytokine deprivation–mediated apoptosis of effector CD4+ T cells

A key issue in mammalian immunology is how CD4+CD25+Foxp3+ regulatory T cells (Treg cells) suppress immune responses. Here we show that Treg cells induced apoptosis of effector CD4+ T cells in vitro and in vivo in a mouse model of inflammatory bowel disease. Treg cells did not affect the early activation or proliferation of effector CD4+ T cells. Cytokines that signal through the common γ-chain suppressed Treg cell–induced apoptosis. Treg cell–induced effector CD4+ T cell death required the proapoptotic protein Bim, and effector CD4+ T cells incubated with Treg cells showed less activation of the prosurvival kinase Akt and less phosphorylation of the proapoptotic protein Bad. Thus, cytokine deprivation–induced apoptosis is a prominent mechanism by which Treg cells inhibit effector T cell responses.