Role of endogenous LTs and their receptors in AM killing of opsonized K pneumoniae. (A) AMs from WT or 5-LO KO mice were infected with 50:1 K pneumoniae for 30 minutes, incubated without or with LT mixture (LTB₄, 1 nM; LTC₄ and LTD₄, 100 nM each), and bacterial killing was then assessed. (B) Rat AMs were pretreated with vehicle control, the 5-LO inhibitor AA-861 (10 μM), or the FLAP inhibitor MK-886 (1 μM) for 15 minutes before the addition of opsonized K pneumoniae. Thirty minutes after infection, drugs were added back with or without LT mixture, and bacterial killing was assessed. (C) Rat AMs were treated with the LTB₄ receptor antagonist CP105696 (10 μM) or the cysLT receptor antagonist MK571 (10 μM) or vehicle control for 15 minutes before the addition of opsonized K pneumoniae. Thirty minutes after infection, the antagonists were added back with or without 1 nM LTB₄ or LTC₄ plus LTD₄ (100 nM each). Microbicidal activity was assessed. Data are expressed as mean ± SE percentage of survival of ingested bacteria of quadruplicate values from 1 of 4 representative experiments. ^*P < .05 compared with untreated control by ANOVA. #P < .05 versus AA-861, MK 886, or 5-LO KO group by ANOVA.