The cyclooxygenase and lipoxygenase activities of platelet-depleted human monocytes

The significant numbers of platelet contaminants bound to the surface of freshly isolated human monocytes can be removed during incubations in fresh human serum. We used cells purified by these means to examine the cyclooxygenase and lipoxygenase metabolites of arachidonic acid synthesized in response to various stimuli. Thromboxane is the single major product synthesized by human monocytes in response to inflammatory particles (opsonized zymosan or immunoglobulin G complex-coated beads). The molar amounts produced were equivalent to those by platelets stimulated with thrombin. In contrast, exposure to calcium ionophore A23187 led to greatly enhanced lipoxygenase metabolite synthesis. Under these conditions, levels of leukotriene B4 (30 to 70 pmol/10(6) cells) and leukotriene C4 (up to 20 pmol/10(6) cells) production were five- to tenfold higher than those observed with particulate stimuli. The circulating human monocyte is a source of a variety of vasoactive mediators derived from arachidonic acid.