Cytokine that binds to TNFRSF18/AITR/GITR. Regulates T-cell responses. Can function as costimulator and lower the threshold for T-cell activation and T-cell proliferation. Important for interactions between activated T-lymphocytes and endothelial cells. Mediates activation of NF-kappa-B. Triggers increased phosphorylation of STAT1 and up-regulates expression of VCAM1 and ICAM1 (PubMed:23892569). Promotes leukocyte adhesion to endothelial cells (PubMed:23892569). Regulates migration of monocytes from the splenic reservoir to sites of inflammation (By similarity). Homodimer (By similarity). Homotrimer. Expressed at high levels in the small intestine, ovary, testis, kidney and endothelial cells. Up-regulated after stimulation by bacterial lipopolysaccharides (LPS). Belongs to the tumor necrosis factor family.