Expression and modulation of FcεRIα and FcεRIβ in human blood basophils

Background: The IgE receptor (Fc epsilon RI) may exist as a tetramer (alpha beta gamma2) or a trimer (alpha gamma2) because Fc epsilon RI beta is dispensable for membrane expression of Fc epsilon RI alpha. Fc epsilon RI beta amplifies signaling of FceRI so that regulation of FceRIa: P stoichiometry would affect cellular responsiveness. Objective: We examined basophils from a variety of donors fur differences in their expression of Fc epsilon RI alpha and Fc epsilon RI beta protein. Methods: Enriched blood basophils were assessed at baseline and after IL-3 culture for Fc epsilon RI alpha and Fc epsilon RI beta protein by Western blotting, surface Fc epsilon RI alpha by flow cytometry, and Fc epsilon RI beta mRNA by real-time PCR, Basophil functional response was measured by allergen-triggered histamine release. Results: For the FceRIa subunit, 2 protein bands with molecular weights of 50 kd and 60 kd were identified by Western blots. The 60-kd band correlated to surface-expressed Fc epsilon RI alpha detected by flow cytometry (Spearman R = 0.78, P < .01). Surface FceRIa also correlated with Fc epsilon RI beta protein (Spearman R = 0.92, P < .01), Fc epsilon RI beta protein levels increased disproportionately with higher surface Fc epsilon RI alpha expression, The ratio of Fc epsilon RI beta to FceRIa varied 10-fold among donors and correlated with surface FceRIa. Basophil 50-kd a protein levels were similar despite a 10-fold range in surface Fc epsilon RI alpha expression, implying stores of this protein such as those found in eosinophils, Unlike eosinophils, the basophil 50-kd protein was lost with culture and was absent from supernatants. Levels of p protein and mRNA were enhanced by IL-3 culture, whereas Fc epsilon RI alpha expression (by now cytometry and 60 kd) was not. Conclusion: These findings demonstrate variable stoichiometry of FceRIa:P in whole cells and that this stoichiometry can be altered by IL-3 culture. With the assumption that all detected p protein is surface expressed, these findings suggest a variable stoichiometry for FceRIa:P that is also related to FceRIa surface expression.