CD120a is a 55 kD Type I transmembrane protein, also known as Tumor Necrosis Factor Receptor Type I (TNFRI) or p55. It is expressed on a variety of cells at low levels. Resting T cells and erythrocytes express very little to no CD120a. This receptor binds both TNF-alpha and LT-alpha (also known as TNF-beta). In association with TRADD and RIP, the receptor crosslinking induced by TNF-alpha or LT-alpha trimers is critical for signal transduction, leading to apoptosis, NF-kB activation, increased expression of proinflammatory genes, tumor necrosis, and cell differentiation depending on cell type and differentiation state. The 55R-593 antibody has been shown to block ligand-induced receptor signaling.