GITR ligand (GITRL) is a member of the TNF sperfamily, also known as TNFSF18 or TL6. It is expressed on B cells, macrophages, dendritic cells and endothelial cells. The expression of GITRL on dendritic cell surface can be transiently up-regulated and then rapidly down-regulated by LPS stimulation. GITRL binds to its receptor, GITR, to co-stimulate T cell activation, proliferation, and cytokine production, and inhibit the suppressive functions of CD4+CD25+ Treg cells, as well as induce macrophages activation. GITR-GITRL interaction has been implicated as an essential regulator of immune response to self antigens and phathogens.