INDUCTION OF THE HIGH-AFFINITY IGE RECEPTOR (FC-EPSILON-RI) ON HUMAN MAST-CELLS BY IL-4

The high-affinity IgE receptor (Fc epsilon RI) is necessary for the in duction of IgE-mediated allergic reactions, Cross-linking of Fc epsilo n RI expressed on mast cells causes the release of various inflammator y mediators, which trigger allergic reactions, Recently, mast cells la cking Fc epsilon RI have been observed in vivo and in vitro, suggestin g the presence of regulational mechanisms in the induction of Fc epsil on RI, In this report, we demonstrate that IL-4 up-regulates Fc epsilo n RI in cultured human mast cells, which are grown from cord blood mon onuclear cells in the presence of stem cell factor and IL-6, and usual ly lack Fc epsilon RI expression, At the protein level, the induction of Fc epsilon RI was observed by flow cytometric analysis and the indu ced Fc epsilon RI expression was stable for at least 23 days in the pr esence of IL-4, Consistently, Northern blot analysis demonstrated the increase of alpha chain mRNA of Fc epsilon RI and revealed that the up -regulation of Fc epsilon RI occurred at the transcriptional level, Fc epsilon RI induced by IL-4 was functional and caused histamine and be ta-hexosaminidase release from mast cells upon cross-linking, Taken to gether, these results indicate a new role of IL-4 in allergic reaction s, besides the stimulation of IgE production.