Lymphotoxin-alpha, also known as LT-alpha, TNF-beta, Tumor necrosis factor ligand superfamily member 1, LTA TNFSF1, and TNFB, is a secreted protein that belongs to the tumor necrosis factor family. TNF-beta/TNFSF1/Lymphotoxin alpha is highly inducible, secreted, and exists as a homotrimeric molecule. It is a cytokine that in its homotrimeric form binds to TNFRSF1A / TNFR1, TNFRSF1B / TNFBR, and TNFRSF14 / HVEM. In its heterotrimeric form with LTB, TNF-beta/TNFSF1/Lymphotoxin alpha binds to TNFRSF3 / LTBR. Lymphotoxin is produced by lymphocytes and cytotoxic for a wide range of tumor cells. TNF-beta/TNFSF1/Lymphotoxin alpha forms heterotrimers with lymphotoxin-beta which anchors lymphotoxin-alpha to the cell surface. It mediates a large variety of inflammatory, immunostimulatory, and antiviral responses. TNF-beta/TNFSF1/Lymphotoxin alpha is also involved in the formation of secondary lymphoid organs during development and plays a role in apoptosis. Genetic variations in TNF-beta/TNFSF1/Lymphotoxin alpha are a cause of susceptibility psoriatic arthritis which is an inflammatory, seronegative arthritis associated with psoriasis. It is a heterogeneous disorder ranging from a mild, non-destructive disease to a severe, progressive, erosive arthropathy.