TNFR1 belongs to the TNFR superfamily of transmembrane proteins, and is expressed in most cell types. Binding of either TNF-α or TNF-β to TNFR1 initiates a signal transduction pathway that results in the activation of the transduction factor NFkB, whose target genes are involved in the regulation of inflammatory responses, and, in certain cells induce apoptosis. Soluble TNF Receptor I (sTNFR1) is capable of inhibiting TNF-α and TNF-β activities by acting as a decoy receptor that serves as a sink for the TNF ligands. Recombinant human sTNFR1 is an 18.3 kDa protein (162 amino acid residues) comprising the cysteine rich ligand binding portion of the extracellular domain of the TNFR1 protein.