Cytosolic phospholipase A2, increased and activated in the eosinophils of patients with hypereosinophilic syndrome in vivo, is involved in the augmented release of leukotriene C4

Abstract.

Objective: Eosinophils from patients with hypereosinophilic syndrome (HES) showed augmented release of leukotriene C₄ (LTC₄) by stimulation with A23187. In the present study, we investigated the involvement of cytosolic phospholipase A₂ (cPLA₂) in this phenomenon.¶Methods: Eosinophils from normal and HES donors (2.5 × 10⁶ cells/ml) were incubated with A23187 (0.03–3 μM) for 60 min in the presence or absence of a cPLA₂ inhibitor, AACOCF₃. The LTC₄ released from eosinophils was measured by enzyme immunoassay. Distribution of cPLA₂ and 5-lipoxygenase (5-LO) proteins within the eosinophils were detected by Western immunoblotting.¶Results: The level of LTC₄ released from the HES eosinophils by stimulation with A23187 was higher than that from normal eosinophils. The A23187-induced LTC₄ release was inhibited by AACOCF₃ in a dose-dependent manner. The amounts of cPLA₂ seemed to be increased in the non-stimulated HES eosinophils by an analysis of immunoblotting. To be noticed was that cPLA₂ was detected as a phosphorylated and membrane-bound form in the HES eosinophils, but not in the normal eosinophils. In contrast, localization of 5-LO within the eosinophils under A23187 stimulation was not different between normal and HES donors, while the amounts of 5-LO also seemed to be increased in the HES eosinophils.¶Conclusions: These results suggest that cPLA₂, increased and activated (phosphorylated and membrane-translocated) in vivo, is involved in the augmented release of LTC₄ from the HES eosinophils.