Tumor necrosis factor-like ligand 1A (TL1A), also known as TNFSF15, is a member of the TNF superfamily. It is a homologous trimer factor consisting of 251 amino acids expressed by the TNFSF15 gene at locus 9q32 on chromosome 9. The expression of this protein is induced by TNF and IL-1α, and it is expressed in large quantities in endothelial cells, but not in B or T cells. This cytokine is a ligand for the TNFRSF25 receptor and the TNFRSF21/DR6 trap receptor. It can activate NF-kappaB and MAP kinase, and can induce apoptosis of vascular endothelial cells as an autocrine factor. This cytokine also inhibits endothelial cell proliferation and thus may act as an angiogenesis inhibitor.