Isolation and characterization of ige receptors from rat intestinal mucosal mast cells

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Abstract
High‐(FcϵRI) and low‐(FcϵRII) affinity IgE receptors were isolated from surface radioiodinated, Nonidet‐P40‐solubilized rat intestinal mucosal mast cells (IMMC) and compared with those on rat peritoneal mast cells (PMC) and rat basophilic leukemia (RBL) cells. FcϵRII were isolated by affinity chromatography using IgE‐Sepharose or by anti‐FcϵRII antisera and protein A‐Sepharose. The surface‐exposed, IgE‐binding α subunits of FcϵRI [FcϵRIα] were isolated by affinity chromatography using IgE and anti‐IgE‐Sepharose. FcϵRIα on IMMC had an apparent molecular mass of 59 kDa, somewhat larger than that of PMC (51 kDa), RBL‐2H3 cells (51 kDa) or RBL‐CA10.7 cells (46 kDa). Brief (45 s) incubation of IMMC or PMC in glycine‐HCl, pH 3, prior to iodination removed much of the surface‐bound IgE. This permitted more thorough labeling of the receptors, but had no affect on the estimate of receptor size. Surprisingly and in contrast to acid‐treated PMC, upon anti‐IgE‐Sepharose isolation acid‐treated IMMC yielded an intensely radioactive FcϵRIα band in the absence of added IgE. Such a finding suggests that IMMC, more so than PMC, may have an intracellular store of IgE, as has been suggested by many others. IMMC also differed from PMC in the number of forms of FcϵRII isolated; 50‐kDa and 58‐kDa forms of FcϵRII were obtained from IMMC, whereas PMC yielded most often a single 56‐kDa FcϵRII band. These results were mimicked by the two RBL cell sublines: RBL‐2H3 cells yielded two FcϵRII (46 kDa and 55 kDa), but only one form of FcϵRII (54‐kDa) was obtained from RBL‐CA10.7 cells. Thus, the two subtypes of rat mast cells, which have previously been shown to differ in mediator profile and responsiveness to secretagogues and antiallergic drugs, are also distinguished by differences in IgER profile.