Regulation of Surface FcεRI Expression on Human Eosinophils by IL-4 and IgE

Background: Recent studies have demonstrated that eosinophils from allergic patients express low levels of FcΕRI on their surface, but the regulatory mechanisms of eosinophil surface FcΕRI expression are not fully understood. We investigated whether IL-4 and IgE, which are reported to regulate surface FcΕRI expression on human mast cells, are able to affect surface FcΕRI 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 FcΕRI expression was analyzed by flow cytometry using an anti-FcΕRI mAb, CRA-1. Results: Apparent FcΕRI expression (∼1% of mast cell FcΕRI levels) was observed in eosinophils cultured with both IL-4 and IgE. A combination of IL-4 (≧1 ng/ml) and IgE (≧ 0.5 µg/ml) was necessary for the maximal induction of surface FcΕRI expression. In the presence of IL-4 and IgE, eosinophils cultured for 2 days demonstrated low but statistically significant levels of surface FcΕRI, which reached a plateau after 7 days of culture. However, cross-linkage of surface FcΕRI molecules by CRA-1 or anti-IgE did not induce any eosinophil activation. Conclusions: IL-4 and IgE can affect the levels of surface FcΕRI on normal human eosinophils. FcΕRI expression on eosinophils may be regulated by a mechanism similar to that in mast cells.