Leukotriene C4 formation by purified human eosinophils can be induced by arachidonic acid in the absence of calcium-inophore A23187

Addition of arachidonic acid (50 μM) to purified human eosinophils leads to the formation of considerable amounts of LTC₄ ((11.3±1.3)×10⁶ molecules/cell, mean±SEM, n=10), 15-HETE ((412±142)×10⁶ molecules/cell, mean±SEM, n=3) and 15-series leukotrienes ((35±15)×10⁶ molecules/cell, mean±SEM, n=3). The ratio of the amounts of LTC₄ and 15-lipoxygenase products was found to be strongly dependent on the arachidonic acid concentration, being relatively large at low arachidonic acid concentrations and very small at high arachidonic acid concentrations. Platelet activating factor (1 μM) was able to enhance significantly the production of LTC₄ but not that of 15-lipoxygenase products. As arachidonic acid was found to be capable of inducing a fast, transient rise in the cytosolic free Ca²⁺ concentration, this explains, at least partly, its ability to induce the Ca²⁺-dependent formation of LTC₄.