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The objective of this investigation was to determine the role of secretory and cytosolic isoforms of phospholipase A 2 (PLA 2) in the induction of arachidonic acid (AA) and leukotriene synthesis in human eosinophils and the mechanism of PLA 2 activation by mitogen-activated protein kinase (MAPK) isoforms in this process. Pharmacological activation of eosinophils with fMLP caused increased AA release in a concentration (EC 50= 8.5 nM)-and time-dependent (t 1/2= 3.5 min) manner. Both fMLP-induced AA release and leukotriene C 4 (LTC 4) secretion were inhibited concentration dependently by arachidonic trifluoromethyl ketone, a cytosolic PLA 2 (cPLA 2) inhibitor; however, inhibition of neither the 14-kDa secretory phospholipase A 2 by 3-(3-acetamide-1-benzyl-2-ethylindolyl-5-oxy) propanephosphonic acid nor cytosolic Ca 2+-independent phospholipase A 2 inhibition by bromoenol lactone blocked hydrolysis …