METABOLIC, MEMBRANE, AND FUNCTIONAL-RESPONSES OF HUMAN POLYMORPHONUCLEAR LEUKOCYTES TO PLATELET-ACTIVATING FACTOR

Abstract

A phospholipid mediator of anaphylaxis, platelet-activating factor (PAF) is chemotactic for polymorphonuclear leukocytes (PMN). This agent''s effects on several other PMN functions were examined. Human PMN were prepared from heparinized venous blood by Ficoll gradient. Metabolic burst was examined by measurement of O2 use and .**GRAPHIC**. production in the presence or absence of PAF (10-6-10-9 M). Unless cells were treated with cytochalasin-B (5 .mu.g/ml), no significant respiratory burst was demonstrated. Pretreatment with PAF (10-7 M) enhanced .apprx. 3-fold the O2 utilization found when cells were subsequently stimulated with 10-7 M FMLP [N-fMet-Leu-Phe]. PAF also stimulated arachidonic acid metabolism in 14C-arachidonic acid-labeled PMN. TLC analysis of chloroform-methanol extracts showed substances that comigrated with authentic 5-hydroxyeicosatetraenoic acid had a marked increase in radioactivity following PAF stimulation at 10-7 M. PAF failed to stimulate release of granule enzymes, B-glucuronidase, lysozyme or myeloperoxidase unless cytochalasin-B was added. PAF from 10-6-10-10 M affected PMN surface responses. PMN labeled with the fluorescent dye chlorotetracycline showed decreased fluorescence upon addition of PAF, suggesting translocation of membrane-bound cations. The rate of migration of PMN in an electric field was decreased following PAF exposure, a change consistent with reduced cell surface charge. PMN self-aggregation and adherence to endothelial cells were both influenced by PAF (10-6-10-9 M). Aggregation was markedly stimulated by the compound and the percent PMN adhering to endothelial cell monolayers increased almost 2-fold in the presence of 10-8 M PAF. PAF promotes a variety of PMN responses: enhances respiratory burst, stimulates arachidonic acid turnover, alters cell membrane cation content and surface charge and promotes PMN self-aggregation as well as adherence to endothelial cells.