GITR (glucocorticoid-induced tumor necrosis factor receptor) is a surface receptor molecule that has been shown to be involved in inhibiting the suppressive activity of T-regulatory cells and extending the survival of T-effector cells. In mouse models, GITR was initially noted to be selectively enriched on the surface of regulatory T cells, making this an attractive potential surface marker for these rare cells. However, subsequent studies revealed GITR to also be up-regulated on any activated T cells in humans, thus undermining its utility as a regulatory T cell marker.Members of the tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies, such as TNFRSF18, regulate diverse biologic functions, including cell proliferation, differentiation, and survival. For further background information on the TNF and TNFR superfamilies.