GITR (glucocorticoid-induced TNF receptor family-regulated gene) is a 25 kD TNF receptor superfamily member (also known as AITR and TNFRSF18). GITR is expressed on activated lymphocytes and is upregulated by T cell receptor engagement. The cytoplasmic domain of GITR is homologous to CD40, 4-1BB and CD27 and has been shown to interact with TRAF 1-3, but not TRAF 5 or 6. GITR signaling has been shown to regulate T cell proliferation and TCR-mediated apoptosis, and to break immunological self-tolerance. GITR binds GITRL and is involved in the development of regulatory T cells and to regulate the activity of Th1 subsets.