Cytokine that binds to TNFRSF3/LTBR. Binding to the decoy receptor TNFRSF6B modulates its effects. Acts as a ligand for TNFRSF14/HVEM (PubMed:9462508, PubMed:10754304). Upon binding to TNFRSF14/HVEM, delivers costimulatory signals to T cells, leading to T cell proliferation and IFNG production (PubMed:10754304). Homotrimer. Interacts with TNFRSF14. Predominantly expressed in the spleen but also found in the brain. Weakly expressed in peripheral lymphoid tissues and in heart, placenta, liver, lung, appendix, and kidney, and no expression seen in fetal tissues, endocrine glands, or nonhematopoietic tumor lines. Up-regulated after T-cell activation. N-glycosylated. The soluble form of isoform 1 derives from the membrane form by proteolytic processing. Belongs to the tumor necrosis factor family.