In vitro effects of platelet factor 4 on normal human neutrophil functions

Platelet factor (PF4) prepared from human outdated platelets by heparinagarose affinity chromatography was confirmed to be chemotactic for human neutrophils and in a concentration-dependent fashion caused significant release of lysosomal enzymes (myeloperoxidase, lysozyme, beta-glucuronidase) from human neutrophils treated with cytochalasin B. Lysosomal enzyme release from PF4-stimulated neutrophils was rapid and reached a plateau by 1-3 min. PF4 did not cause release of the cytoplasmic enzyme lactate dehydrogenase which indicates that exocytosis of granule-containing lysosomal enzymes did not result from cytolysis. In contrast, superoxide anion generation from human neutrophils stimulated with PF4 was undetectable even at the highest PF4 concentration tested (2 X 10(-5) M). Pretreatment of neutrophils with PF4 caused significant increased adherence of neutrophils to plastic surfaces and cultured pulmonary artery endothelial cells. The concentration of PF4 that elicited neutrophil chemotaxis, lysosomal enzyme release and increased adherence is slightly higher than those concentrations found in normal human sera. However, the results suggest that PF4 may be an important mediator in neutrophil-platelet interactions and the induction of acute inflammation especially at sites of platelet microthrombi where the concentration of PF4 would be elevated.