Cytosolic phospholipase A(2), increased and activated in the eosinophils of patients with hypereosinophilic syndrome in vivo, is involved in the augmented release of leukotriene C-4

Objective: Eosinophils from patients with hyper-eosinophilic syndrome (HES) showed augmented release of leukotriene C-4 (LTC4) by stimulation with A23 187. In the present study, we investigated the involvement of cytosolic pho spholipase A(2) (cPLA(2)) in this phenomenon. Methods: Eosinophils from normal and HES donors (2.5x10(6) cells/ml) were i ncubated with A23187 (0.03-3 mu M ) for 60 min in the presence or absence o f a cPLA(2) inhibitor, AACOCF(3). The LTC4 released from eosinophils was me asured by enzyme immunoassay. Distribution of cPLA(2) and 5-lipoxygenase (5 -LO) proteins within the eosinophils were detected by Western immunoblottin g. Results: The level of LTC4 released from the HES eosinophils by stimulation with A23187 was higher than that from normal eosinophils. The A23187-induc ed LTC4 release was inhibited by AACOCF(3) in a dose-dependent manner. The amounts of cPLA(2) seemed to be increased in the non-stimulated HES eosinop hils by an analysis of immunoblotting. To be noticed was that cPLA(2) was d etected as a phosphorylated and membrane-bound form in the HES eosinophils, but not in the normal eosinophils. In contrast, localization of 5-LO withi n 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 t he HES eosinophils. Conclusions: These results suggest that cPLA(2), increased and activated (p hosphorylated and membrane-translocated)in vivo, is involved in the augment ed release of LTC4 from the HES eosinophils.