TL‐1A belongs to the TNF superfamily of ligands. It is expressed predominantly in endothelial cells, and to a lesser extent in the placenta, lung, kidney, skeletal muscle, pancreas, small intestine and colon. TL‐1A inhibits endothelial cell proliferation and angiogenesis, and has been shown to induce NF‐kappaB activation, caspase activity, and apoptosis in responding cell lines. TL‐1A interacts with TNFRSF25/DR3 receptor, but can also bind to a decoy receptor TNFRSF21/DR6. Recombinant Human TL‐1A is a 22.1 kDa polypeptide of 195 amino acid residues.