Bacterial Lipopolysaccharides prime human neutrophils for enhanced production of leukotriene B4

Production of leukotriene B4 (LTB4) by human neutrophils (PMN) in response to different stimuli is increased after pre-treatment with lipopolysaccharides (LPS). We have analyzed the steps in arachidonic acid (AA) metabolism affected by LPS by examining release of AA and its metabolites from [3HIAA prelabeled PMN. Pretreatment ofPMN for 60 min with up to 1 yg/ml of LPS alone had no effect, but release of 13HIAA was stimulated up to fivefold during subsequent stimulation with a second agent. In the absence of LPS-binding protein (LBP), priming was maximal after pretreatment ofPMN with 10 ng of LPS/ml for 60 min; in the presence of LBP maximal priming occurred within 45 min at 0.1 ng of LPS/ml and within 15 mi at 100 ng of LPS/ml. Treatment ofPMN with 10 ng of LPS/ ml also increased uptake of opsonized zymosan by up to 60%. Phospholipids are the source of released 13HIAA. No release was observed from I'4CIoleic acid (OA)-labeled PMN sug-gesting that phospholipolysis may be specific for 13HIAA-labeled phospholipid pools. Cytosol from PMN primed with LPS contains two to three times the phospholipase A2 (PLA2) activity of control PMN, against 1-palmitoyl-12-14C1-arachidonoyl-phosphatidylcholine. This activity is Ca2+ depen-dent and dithiothreitol resistant. LPS priming is accompanied by reduced migration during SDS-PAGE of an 85-kD protein, identified as a cytosolic PLA2. The extent and kinetics of this effect ofLPS on cPLA2 parallel the priming of13HIAA release, both depending on LPS concentration either with or without LBP. These findings suggest that priming byLPS ofAA metab-olism by PMN includes phosphorylation of an AA-phospho-lipid-selective cytosolic PLA2 that is dissociated from activa-tion until a second stimulus is applied. (J. Clin. Invest. 1994