The MABTNFR1-A1 antibody reacts with the extracellular domain of the 55 kDa receptor for the human cytokines: TNF (aka tumor necrosis factor-alpha , TNF-α) and lymphotoxin-alpha (LT-α3, aka, lymphotoxin or TNF-β). This receptor is referred to as the p55 or Type I Tumor Necrosis Factor Receptor (TNFRI) or CD120a. TNFRI are expressed by a variety of cell lines, tumor cells, and normal cell types including T cells, monocytes, macrophages, neutrophils, endothelial cells, hepatocytes, chondrocytes, and fibroblasts. Naive B cells express very low or undetectable levels of TNFRI whereas mature erythrocytes and platelets are uniformly negative for TNFRI expression. For the generation of the MABTNFRI-B1 hybridoma, BALB/c mice were immunized with purified, full-length human TNFRI protein. MABTNFRI-A1 specifically binds to natural and recombinant truncated forms of TNFRI.