Influence of interleukin-4 and platelet-activating factor on the Fc epsilon RII/CD23 expression on human monocytes

Human recombinant interleukin-4 (IL-4) induces the expression of the low-affinity receptor for IgE (Fc epsilon RII/CD23) on human normal monocytes as assessed by flow cytometry. Also, platelet-activating factor (PAF) induces a time- and dose-dependent increase in Fc epsilon RII/CD23 expression, which is maximal with 1 microM PAF and after a 24-h incubation period. Under similar experimental conditions, lyso-PAF (1 microM) has no effect on Fc epsilon RII/CD23 expression. The PAF-induced Fc epsilon RII/CD23 expression on human monocytes is inhibited by two unrelated antagonists of the mediator, namely BN 52021 and BN 50730, but is not significantly affected when the cells are incubated in the presence of a rabbit anti-IL-4 antiserum. The IL-4-induced Fc epsilon RII/CD23 is abolished in the presence of the anti-IL-4 antiserum and slightly (not significantly) reduced when BN 52021 or BN 50730 is added to the incubation medium. These results suggest that PAF regulates Fc epsilon RII/CD23 expression and may indicate a new role for this autacoid in allergic diseases.