Characterization and affinity crosslinking of receptors for tumor necrosis factor on human cells

Receptors for tumor necrosis factor (TNF) were characterized in the U-937 human histiocytic lymphoma cell line with the aid of highly purified recombinant human TNF, radiolabeled with 125I. Saturation binding to specific cell surface receptors occurred with less than 15% nonspecific binding. Analysis of the equilibrium binding data obtained at 4 °C revealed a single class of noninteracting binding sites. The mean number of binding sites per cell was calculated to be 12,000, and the apparent dissociation constant ( K d ) was 2 × 10 −10 m. Crosslinking of 125I-TNF to the cell surface receptor with disuccinimidyl suberate, followed by NaDodSO 4-polyacrylamide gel electrophoresis of the cell lysate, revealed a TNF-receptor complex with a molecular weight of approximately 100,000. Binding to concanavalin A-Sepharose suggested that the TNF receptor is a glycoprotein.