Platelet activating factor amplifies human neutrophil adherence to bovine endothelial cells: evidence for a lipoxygenase dependent mechanism.

Platelet activating factor (PAF) is a potent lipid mediator that induces the release of leukotrienes and prostaglandins from various cells and tissues. We examined the capacity of PAF alone and in combination with soluble stimuli to enhance eicosanoid synthesis and adherence of human neutrophils. Neutrophils were preincubated with PAF and washed before exposure to the soluble stimuli F-Met-Leu-Phe (FMLP), calcium ionophore A23187, and phorbol myristate acetate. Preincubation of neutrophils with 1 microM PAF enhanced the release of both LTB4 and LTC4 in response to each of the three agonists, in contrast with the unprimed neutrophils. Priming was specific for PAF since lyso-PAF was inactive. Priming concentrations of PAF also augmented the adherence of neutrophils to endothelium in the presence of the soluble agonists A23187, phorbol myristate acetate, and FMLP. The priming effect of PAF on eicosanoid release and neutrophil adherence was shown to have similar time- and dose-dependent effects. Further, the priming effects of PAF on adherence could be reversed by preincubation of neutrophils with the lipoxygenase inhibitors nordihydroguiaretic acid and 5,8,11,14-ETYA but not by preincubation with the cyclooxygenase inhibitor indomethacin. These data demonstrate that PAF amplifies neutrophil adherence to endothelium through a lipoxygenase dependent mechanism.