Leukotriene formation by peripheral monocytes in contact-activated human blood

Contact activation of the intrinsic coagulation cascade in whole human blood in vitro has previously been demonstrated to trigger release of leukotrienes (LT) into serum samples. In our present study we intended to identify the cellular origin of the activated 5-lipoxygenase pathway leading to LT formation under these experimental conditions. Therefore, whole human blood samples incubated for 60 min in vitro were supplemented with Percoll-isolated, 5-lipoxygenase-carrying, autologous blood cells. Surprisingly, exogenously added polymorphonuclear neutrophils (PMN, 5 x 10(6) or 15 x 10(6)/ml) capable of producing cysteinyl-LT in response to ionophore A23187 (1 microM) stimulation, had no effect neither on immunoreactive cysteinyl-LT nor on thromboxane (TX) B2 formation. However, exogenously added mononuclear cells (MNC, 5 x 10(6) or 15 x 10(6)/ml) led to a cell number-dependent increase in cysteinyl-LT generation as did supplementation with peripheral monocytes (PM, 5 x 10(5) or 15 x 10(5)/ml). While MNC enhanced the TXB2 production, PM had no such effect. Incubation of PM (5 x 10(5) or 15 x 10(5)/ml) in recalcified platelet-rich plasma (PRP) induced a cysteinyl-LT formation comparable to that in whole human blood. In contrast to the TXB2 generation, the cysteinyl-LT formation appears to be largely independent from thrombin, since recombinant hirudin (HBW 023, 2 microM), a specific thrombin inhibitor, had no significant effect on the cysteinyl-LT production but nearly completely abolished the TXB2 formation. By reverse phase HPLC the immunoreactive cysteinyl-LT were shown to consist of a mixture of LTC4, LTD4 and LTE4, with LTC4 being the predominant metabolite in all samples studied.(ABSTRACT TRUNCATED AT 250 WORDS)