IgE receptors on human lymphocytes. I. Identification of the molecules binding to monoclonal anti-Fc epsilon receptor antibodies.

The present study indicates that the surface molecules from Fc epsilon receptor-bearing human lymphoblastoid cells binding to monoclonal antibodies to Fc epsilon receptor (mAbER) are identical to those binding to IgE. mAbER identify three components in the Nonidet-P40 cell lysate of surface-iodinated RPMI 8866 cells with approximately 65-95 kDa, 45 kDa and 37 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions and autoradiography. The same pattern is observed under nonreducing conditions, except for the low mol. wt component which displays an apparent molecular mass 31 kDa. When the labeled and solubilized membranes are adsorbed on IgE-Sepharose the 45-kDa component is always found in the eluate, whereas the 65-95-kDa component is occasionally detected and the low mol. wt component is rarely found. The binding of these molecules to IgE-Sepharose is inhibited by soluble IgE, mAbER but not by an unrelated mAb; reciprocally, the binding to mAbER-Sepharose is prevented by mAbER and to some extent by IgE. To improve the stability of IgE-Fc epsilon R complexes, biotinylated IgE was cross-linked on surface iodinated intact cells, which were then solubilized and adsorbed on avidin-Sepharose. Under these conditions, it was clearly shown that IgE binds to the same three surface molecules as mAbER. The isoelectric point of the high mol. wt component ranged from 4.2 to 4.4 as compared to 5.1-5.2 for the 45-kDa and the 37-kDa components. The observation in the Western blot assay that both the 65-95-kDa and the 45-kDa molecules react with 9 different mAbER indicates that these molecules have a polypeptide sequence in common.