Platelet-activating factor augments tumor necrosis factor and procoagulant activity

Abstract

Infusion of platelet activating factor (PAF) reproduces the host physiologic response to endotoxemia and sepsis. Tumor necrosis factor (TNF) and procoagulant activity (PCA) are two other potentially deleterious central inflammatory mediators produced in large quantities by tissue-fixed macrophages (Mφ). The relationship, if any, between PAF and TNF or PCA production is unknown. Rabbit alveolar Mφ were treated in vitro with PAF alone and prior to endotoxin (LPS). PAF alone had no effect on Mφ PCA or TNF. PAF (10 −9−10 −6 M) cotreatment enhanced Mφ PCA and TNF levels in a dose response from two- to sixfold above that of LPS treatment alone. PAF (10 −6 M) pretreatment of Mφ at T -4 to -6 hr produces an eight- to ninefold enhancement in both TNF and PCA levels. Thus, both coincubation and pretreatment or “priming” of the Mφ with PAF prior to LPS stimulation greatly increase Mφ production of PCA and TNF. The ability to augment the production of these two potent inflammatory mediators may explain in part the mechanism of action of PAF in vivo.