Cytosolic Phospholipase A sub(2)-alpha Is Necessary for Platelet-activating Factor Biosynthesis, Efficient Neutrophil-mediated Bacterial Killing, and the Innate Immune Response to Pulmonary Infection: cPLA sub(2)-alpha does not regulate meutrophil NADPH oxidase activity

The role of a cytosolic phospholipase A sub(2)-alpha (cPLA sub(2)-alpha) in neutrophil arachidonic acid release, platelet-activating factor (PAF) biosynthesis, NADPH oxidase activation, and bacterial killing in vitro, and the innate immune response to bacterial infection in vivo was examined. cPLA sub(2)- alpha activity was blocked with the specific cPLA sub(2)-alpha inhibitor, Pyrrolidine-1 (human cells), or by cPLA sub(2) -alpha gene disruption (mice). cPLA sub(2)-alpha inhibition or gene disruption led to complete suppression of neutrophil arachidonate release and PAF biosynthesis but had no effect on neutrophil NADPH oxidase activation, Fcgamma II/ III or CD11b surface expression, primary or secondary granule secretion, or phagocytosis of Escherichia coli in vitro. In contrast, cPLA sub(2)-alpha inhibition or gene disruption diminished neutrophil-mediated E. coli killing in vitro, which was partially rescued by exogenous arachidonic acid or PAF but not leukotriene B sub(4). Following intratracheal inoculation with live E. coli in vivo, pulmonary PAF biosynthesis, inflammatory cell infiltration, and clearance of E. coli were attenuated in cPLA sub(2)-alpha(-/-) mice compared with wild type littermates. These studies identify a novel role for cPLA sub(2)-alpha in the regulation of neutrophil-mediated bacterial killing and the innate immune response to bacterial infection.