Degranulation of human eosinophilic granulocytes by the platelet activating factor

Incubation of purified human eosinophil granulocytes (greater than 93%) with the platelet activating factor (PAF), led at concentrations of 1 pM to 10 microM, to a non-cytotoxic and dose-dependent liberation of proteins both from the "small" and the "specific" granules. The mean EC50 for this PAF-induced effect was 1.47 nM (n = 9), with a maximum at 100 nM PAF. The degranulating effect of PAF can be inhibited competitively by the specific PAF-receptor antagonist, WEB 2086 (KB between 12 and 13 nM), and is Ca2(+)-dependent.