Cytokine that binds to TNFRSF18/AITR/GITR (PubMed:14521928, PubMed:14647196). Regulates T-cell responses (PubMed:14647196). Can function as costimulator and lower the threshold for T-cell activation and T-cell proliferation (PubMed:14608036, PubMed:15128759). Important for interactions between activated T-lymphocytes and endothelial cells. Mediates activation of NF-kappa-B (PubMed:14521928, PubMed:14647196, PubMed:18178614). Triggers increased phosphorylation of STAT1 and up-regulates expression of VCAM1 and ICAM1 (By similarity). Promotes leukocyte adhesion to endothelial cells (PubMed:23892569). Regulates migration of monocytes from the splenic reservoir to sites of inflammation (PubMed:24107315). Homotrimer. Homodimer. Detected in immature and mature dendritic cells and in macrophages (at protein level). Detected in spleen, lung, heart, thymus, monocytes, macrophages, B-cells and dendritic cells. Up-regulated by exposure to bacterial lipopolysaccharide (LPS). N-glycosylated. Reduced levels of pro-inflammatory macrophages in the peritoneal cavity following injection with thioglycollate broth to induce peritonitis and reduced AGTR1 levels in spleen macrophages. Belongs to the tumor necrosis factor family.