Activation of cytosolic phospholipase A₂α in resident peritoneal macrophages by Listeria monocytogenes involves listeriolysin O and TLR2

Eicosanoid production by macrophages is an early response to microbial infection that promotes acute inflammation. The intracellular pathogen Listeria monocytogenes stimulates arachidonic acid release and eicosanoid production from resident mouse peritoneal macrophages through activation of group IVA cytosolic phospholipase A₂ (cPLA₂α). The ability of wild type L. monocytogenes (WTLM) to stimulate arachidonic acid release is partially dependent on the virulence factor listeriolysin O; however, WTLM and L. monocytogenes lacking listeriolysin O (ΔhlyLM) induce similar levels of cyclooxygenase 2. Arachidonic acid release requires activation of MAPKs by WTLM and ΔhlyLM. The attenuated release of arachidonic acid that is observed in TLR2^-/- and MyD88^-/- macrophages infected with WTLM and ΔhlyLM correlates with diminished MAPK activation. WTLM but not ΔhlyLM increases intracellular calcium, which is implicated in regulation of cPLA₂α. Prostaglandin E₂, prostaglandin I ₂, and leukotriene C₄ are produced by cPLA ₂α^+/+ but not cPLA₂α^-/- macrophages in response to WTLM and ΔhlyLM. Tumor necrosis factor (TNF)-α production is significantly lower in cPLA₂α ^+/+ than in cPLA₂α^-/- macrophages infected with WTLM and ΔhlyLM. Treatment of infected cPLA ₂α^+/+ macrophages with the cyclooxygenase inhibitor indomethacin increases TNFα production to the level produced by cPLA ₂α^-/- macrophages implicating prostaglandins in TNFα down-regulation. Therefore activation of cPLA₂α in macrophages may impact immune responses to L. monocytogenes.