The presence of two kinds of receptors for IgE on rat mast cells.

Receptors for IgE from peritoneal mast cells (RMC) of six strains of rats were studied and compared with those of rat basophilic leukemia cells (RBL). Receptors were isolated from surface iodinated and detergent solubilized cells by means of IgE-Sepharose, IgE and anti-IgE, and a rabbit antiserum specific for the receptors of RBL cells (RAR). Like RBL cells, RMC from all rate strains were shown to be associated with two receptor molecules H and R, having apparent m.w. of about 55,000 and 45,000, respectively. THe presence of both molecules could be clearly demonstrated with RAR. When IgE-Sepharose was used, the presence of H could only be unequivocally shown if large numbers of IgE molecules were bound to the RMC.