Blood eosinophils from atopic donors express messenger RNA for the α, β, and γ subunits of the high-affinity IgE receptor (FcεRI) and intracellular, but not cell surface, α subunit protein

Background: Blood eosinophils from hypereosinophilic donors were previously reported to possess the functional high-affinity IgE receptor (FcεRI), so providing a potential mechanism to account for eosinophil degranulation in atopic allergic disease. Furthermore, tissue eosinophils from allergic tissue reactions were shown to be mRNA⁺ for the α, β, and γ subunits of FcεRI and gave positive immunostaining with an anti-FcεRI-α anti-body. Recent studies, however, revealed negative surface staining on peripheral blood eosinophils, but intracellular FcεRI-α protein was identified by Western blot analysis. Objective: Our purpose was to examine on peripheral blood eosinophils from atopic subjects (1) surface expression and mRNA for FcεRI-α, (2) up-regulation of FcεRI-α by allergy-associated tissue factors, and (3) FcεRI-α-dependent release of eosinophil peroxidase (EPO). Methods: We measured (1) FcεRI mRNA expression by in situ hybridization, (2) FcεRI-α by flow cytometry and immunocytochemistry (with use of nonpermeabilized and permeabilized cells), and (3) FcεRI-α-dependent release of EPO. Results: Eosinophils from atopic donors had negligible surface expression of FcεRI-α, which was not enhanced by culture with IgE, IL-3, IL-4, IL-5, GM-CSF, or fibronectin or coculture with fibroblasts. Permeabilization, however, revealed appreciable intracellular staining for FcεRI-α. The majority of eosinophils were mRNA⁺ for the α, β, and γ subunits of FcεRI. Small but significant (P = .03) increases in a chain mRNA expression were observed after coculture of eosinophils with fibroblasts but not with IgE, IL-4, or fibronectin. Cross-linking of FcεRI on the surface of eosinophils from atopic donors did not lead to detectable EPO release. Conclusion: Human blood eosinophils express negligible, non-functional membrane FcεRI-α but have intracellular FcεRI-α protein and mRNA expression for the α, β, and γ subunits.