The presence of Fc receptors specific for IgE (FcϵR) on human and rat eosinophils was studied using the rosette formation with sheep erythrocytes coated with IgE myeloma protein. A large proportion of both human and rat eosinophils bear FceR. The inhibition of rosette formation by aggregated IgE or IgG, together with the mixed rosette assay using IgE- and IgG-coated erythrocytes, suggested that FceR and FcγR are distinct but present on the same eosinophil population. Moreover a significant correlation was obtained between the percentage of rosettes formed with IgE-coated erythrocytes and the percentage of radioactivity specifically bound to human eosinophils after incubation with 125l-labeled human IgE. In addition, electron microscopy studies visualized the binding of human IgE to human eosinophils. The proportion of eosinophils bearing FceR was significantly higher when eosinophils were obtained from hypereosinophilic patients or from rats infected with Schistosoma mansoni, whereas the proportion of FcγR-bearing eosinophils was not increased. The same level of increase of the number of FceR was reached when normal human or rat eosinophils were preincubated with the eosinophil chemotactic factor of anaphylaxis (ECF-A). Two hypotheses were therefore considered for the modulation of FcϵR on eosinophils: either a direct inductory role of IgE, which is significantly increased in patients with hypereosinophilia and also after S. mansoni infection, or an indirect pathway involving the IgE-dependent anaphylactic release of mast cell mediators and their enhancing role on eosinophil Fc receptors. The role of eosinophil FcϵR is discussed in relation to the dual function of eosinophils in antibody-dependent cytotoxicity and in the regulation of immediate-type hypersensitivity.
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Capron et al. (1981) studied this question.