| Abstract: | An eosinophil chemotactic factor (ECF) can be released from human polymorphonuclear neutrophils (PMN), rat mononuclear and rat mast cells by the calcium ionophore (A23187), during phagocytosis, by arachidonic acid and phospholipase A2. It has been suggested that stimuli such as the ionophore and the phagocytic event lead to phospholipid turnover with the generation of arachidonic acid which is subsequently transformed by a lipoxygenase-like enzyme into ECF. Addition of phospholipids such as phosphatidylethanolamine and phosphatidylinositol during ionophore stimulation of various cells increased the ECF release significantly. ECF activity is also enhanced in the presence of indomethacin at concentrations which inhibit prostaglandin synthesis. With bromphenylacylbromide and eicosatetraynoic acid, ECF generation as well as the chemotaxis of eosinophils is inhibited suggesting that the phospholipase A2-arachidonic acid pathway represents a common link for ECF release as well as for the chemotaxis of eosinophils. From the cytosol of human PMN an ECF-containing enzyme was obtained. Incubation of phospholipase A2 and phospholipids with the ECF-converting enzyme led to potent ECF indicating that addition of phospholipids provides the soluble ECF-generating system with an additional source of arachidonic acid. The data represent a molecular approach to analyze the mechanisms of ECF release from soluble components after immunological triggering of the cells. |
