Tumor necrosis factor receptor superfamily member 10A (TNFRSF10A) is also known as TNF-related apoptosis-inducing ligand receptor 1 (TRAIL-R1), Death receptor 4 (DR4), CD261 and APO2, which belongs to TNF superfamily. TNFRSF10A / DR4 is widely expressed and high levels are found in spleen, peripheral blood leukocytes, small intestine and thymus, but also in K-562 erythroleukemia cells, MCF-7 breast carcinoma cells and activated T-cells. APO2 / TNFRSF10A is receptor for the cytotoxic ligand TNFSF10 / TRAIL. This receptor is activated by tumor necrosis factor-related apoptosis inducing ligand (TNFSF1/TRAIL), and thus transduces cell death signal and induces cell apoptosis. TRAIL R1 can promote the activation of NF-kappa-B. TRAIL R1/CD261/TNFRSF1A induces apoptosis of many transformed cell lines but not of normal tissues, even though its death domain-containing receptor, DR4, is expressed on both cell types.