EFFECTS OF PAF, FMLP AND OPSONIZED ZYMOSAN ON THE RELEASE OF ECP, ELASTASE AND SUPEROXIDE FROM HUMAN GRANULOCYTES

Platelet-activating factor (PAF) is a potent chemoattractant for human eosinophils and neutrophils and causes eosinophil and neutrophil recr uitment into animal airways. Since eosinophils and eosinophil cationic proteins are thought to play an important role in the pathophysiology of asthma, we have examined the hypothesis that PAF may also stimulat e eosinophil cationic protein (ECP) release from human granulocytes. G ranulocytes (93% neutrophils, 3% eosinophils) were isolated from the b lood of normal volunteers, using metrizamide density gradients, and st imulated in vitro with PAF, L-formyl-L-methionyl-L-leucyl-L-phenylalan ine (FMLP) or opsonized zymosan (OPZ). Superoxide generation was measu red colorimetrically, granulocyte degranulation by a fluorimetric assa y for elastase, and eosinophil activation by specific radioimmunoassay (RTA) for ECP. Granulocyte chemotaxis was also measured. Whilst both PAF and FMLP were potent chemoattractants for human mixed granulocytes (concentrations producing half the maximal effect (EC(50)s) ca 10 nM) , PAF at concentrations below 10 mu M was a poor stimulus to superoxid e generation, elastase release or ECP release from the same cell popul ation. In contrast, FMLP was a potent stimulus to both superoxide gene ration (EC(50) 48 nM) and ECP (EC(50) ca 100 nM) and elastase release (EC(50) ca 1 mu M). OPZ was a potent stimulus to superoxide generation , but was a poor stimulus to ECP or elastase release. Thus, although P AF is a potent chemoattractant for human granulocytes, our results sug gest that it alone may not stimulate their subsequent activation and r elease of cytotoxic products.