The V27-580 monoclonal antibody specifically binds to GITR (Glucocorticoid-Induced Tumor necrosis factor Receptor), a member of the tumor necrosis factor receptor (TNFR) superfamily that is designated TNFRSF18. In the human, GITR is expressed at low levels in peripheral blood T cells, bone marrow, thymus, spleen, and lymph nodes and is up-regulated upon antigen stimulation or by treatment with anti-CD3 plus anti-CD28. GITR is also reported to be constitutively expressed on Treg cells. GITR's ligand (GITRL) is a member of the TNF superfamily, is designated TNFSF18, and is expressed on antigen presenting cells. The GITR cytoplasmic domain has striking homology with the cytoplasmic domains of the co-stimulatory receptors CD137 (4-1BB), CD134 (OX40) and CD27. GITR signaling is mediated by signaling adaptors, TNFR-associated factors (TRAFs), that affect signaling pathways (eg, Erk, JNK, MAPK and NF-κB) to enhance T-cell survival and cytokine production. The effects of GITR signaling upon the dynamic and interconnected roles of effector and regulatory T lymphocytes in the immune response are under investigation.