Regulation of surface FcepsilonRI expression on human eosinophils by IL-4 and IgE

BACKGROUND: Recent studies have demonstrated that eosinophils from allergic patients express low levels of FcepsilonRI on their surface, but the regulatory mechanisms of eosinophil surface FcepsilonRI expression are not fully understood. We investigated whether IL-4 and IgE, which are reported to regulate surface FcepsilonRI expression on human mast cells, are able to affect surface FcepsilonRI expression in normal human eosinophils. METHODS: Eosinophils purified from peripheral blood were cultured with IL-5 and with or without IL-4 and/or IgE, and surface FcepsilonRI expression was analyzed by flow cytometry using an anti-FcepsilonRI mAb, CRA-1. RESULTS: Apparent FcepsilonRI expression (approximately 1% of mast cell FcepsilonRI levels) was observed in eosinophils cultured with both IL-4 and IgE. A combination of IL-4 (>or=1 ng/ml) and IgE (>or= 0.5 microg/ml) was necessary for the maximal induction of surface FcepsilonRI expression. In the presence of IL-4 and IgE, eosinophils cultured for 2 days demonstrated low but statistically significant levels of surface FcepsilonRI, which reached a plateau after 7 days of culture. However, cross-linkage of surface FcepsilonRI molecules by CRA-1 or anti-IgE did not induce any eosinophil activation. CONCLUSIONS: IL-4 and IgE can affect the levels of surface FcepsilonRI on normal human eosinophils. FcepsilonRI expression on eosinophils may be regulated by a mechanism similar to that in mast cells.