HUMAN POLYMORPHONUCLEAR LEUKOCYTE ACTIVATION INDUCED BY PLATELET ACTIVATING FACTOR (PAF).

Human polymorphonuclear leukocytes (PMNs) loaded with the photoprotein Aequorin, were exposed to PAF in the presence of extracellular Ca2+ (1 mM). PMNs aggregation measured In the “Platelet Ionized Calcium Aggregometer” (P.I.C.A.) was dependent on the concentration of the stimulus. Ca2+ cytoplasmatic increase was monitored in parallel at concentrations of PAF which did not modify cellular integrity (10-7-10-5M). The intracellular Ca2+ flux (up to 19±3 µM) triggered by PAF was also concentration-dependent. In order to establish the role played by this intracellular messenger, we studied some cellular responses possibly related to Ca2+ mobilization: enzymatic release, oxygen radicals production, and arachidonic acid metabolism. PAF induced release of both lysozyme , and β-glucuronldase (15% to 20% of the total enzyme content at the maximal concentration). However PAF (10-712-10“Vl) stimulated the production of only small amounts of oxygen radicals as compared to Phorbol Myristate Acetate (PMA). Leukotriene B4 (LTB4), the main arachidonic acid metabolite in PMNs and the products of its catabolism (20-OH and 20-C00H LTBO were assayed by two different technics (HPLC and RIA) in the same cellular suspensions. PAF (10-4 M)-stimulated PMNs (0.5-2xl07 cells/ml) did not produce any detectable amount of these arachidonic acid metabolites. In contrast, calcium ionophore A 23187 (2 μM)-stimulated PMNs (in the same range of cellular concentration) produce up to 170 ng/ml of LTB4. In conclusion, cytoplasmatic Ca2+ increase in PAF-stimulated PMNs was not accompanied either by oxygen radicals production or by activation of arachidonic acid metabolism catalyzed by 5-1 ipoxygenase.