Leukotriene C₄ production from human eosinophils in vitro. Role of eosinophil chemotactic factors on eosinophil activation

We studied the role of naturally occurring eosinophil chemotactic factors on leukotriene (LT)C₄ production from highly purified (87.1 ± 2.4%) normodense eosinophils. Platelet activating factor (PAF) directly induced LTC₄ production from eosinophils in a dose (10^-9 to 10^-5 M) and a time-dependent manner. PAF (10^-5 M) induced 0.74 ± 0.08 ng of LTC₄ production/10⁶ eosinophils. However, lyso-PAF, eosinophil chemotactic factor of anaphylaxis, and LTB₄ failed to induce LTC₄ production within the tested range. Furthermore, the pre-incubation of eosinophils with 5 μg/ml of cytochalasin B did not alter the chemotactic factor-induced LTC₄ production. When eosinophils were stimulated by the submaximal concentration (1 μg/ml) of calcium ionophore A23187, the pre-incubation of eosinophils with 10^-6 M or 10^-5 M of PAF, or 10^-5 M of eosinophil chemotactic factor of anaphylaxis significantly enhanced LTC₄ production up to 163.9 ± 17.5% (p <0.05), 279.2 ± 32.9% (p <0.01) and 165.2 ± 21.2% (p <0.05) of the control, respectively. However, the pre-incubation with lyso-PAF or LTB₄ failed to enhance A23187-induced LTC₄ production. The preincubation of eosinophils with phosphatidyl serine also failed to enhance A23187-induced LTC₄ production. However, the direct stimulation of protein kinase C by PMA enhanced the submaximal concentration of A23187-induced LTC₄ production from eosinophils up to 179.5 ± 20.9% (p <0.05) of the control. Our findings indicate that PAF and ECF-A work not only as chemotactic factors but also induce a functionally active state of eosinophils probably through their post-receptor mechanisms, and contribute to the inflammatory processes.