Expression and rodulation of FcεRIα and FcεRIβ in human blood basophils

Background: The IgE receptor (FcεRI) may exist as a tetramer (αβγ2) or a trimer (αγ2) because FcεRIβ is dispensable for membrane expression of FcεRIα. FcεRIβ amplifies Signaling of FcεRI so that regulation of FcεRIα:β stoichiometry would affect cellular responsiveness. Objective: We examined basophils from a variety of donors for differences in their expression of FcεRIα and FcεRIβ protein. Methods: Enriched blood basophils were assessed at baseline and after IL-3 culture for FcεRIα and FcεRIβ protein by Western blotting, surface FcεRIα by flow cytometry, and FcεRIβ mRNA by real-time PCR. Basophil functional response was measured by allergen-triggered histamine release. Results: For the FcεRIα 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 FcεRIα detected by flow cytometry (Spearman R = 0.78, P < .01). Surface FcεRIα also correlated with FcεRIβ protein (Spearman R = 0.92, P < .01). FcεRIβ protein levels increased disproportionately with higher surface FcεRIα expression. The ratio of FcεRIβ to FcεRIα varied 10-fold among donors and correlated With surface FcεRIα. Basophil 50-kd α protein levels were similar despite a 10-fold range in surface FcεRIα 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 β protein and mRNA were enhancedby IL-3 culture, whereas FcεRIα expression (by flow cytometry and 60 kd) was not. Conclusion: These findings demonstrate variable stoichiometry of FcεRIα:β in whole cells and that this stoichiometry can be altered by IL-3 culture. With the assumption that all detected β protein is surface expressed, these findings suggest a variable stoichiometry for FcεRIα:β that is also related to FcεRIα surface expression.