[Analysis of the TNF receptor in KYM cells by affinity cross-linking]

We investigated the identity of the TNF receptor on the KYM cell membrane by cross-linking 125I-TNF and the presumed receptor site with DSS, and subjecting the TNF-receptor complex to electrophoresis. Four specific bands were observed at 145 K, 50 K, 35 K, and 17 K, and those at 50 K, 35 K and 17 K being consistent with trimers, dimers and monomers of TNF, respectively. The 145 K band disappeared after addition of excess unlabelled TNF or anti-human recombinant TNF monoclonal antibody (IV3-E), which quenched the cytotoxic activity of TNF and inhibited the TNF binding to the receptor. The molecular weight of native TNF as estimated by gel filtration was 45 K and this observation showed that native TNF existed only as the TNF trimer. These results confirmed that 95K, i.e., the difference between 145 K and 50 K, is the molecular size of the TNF receptor.