Clearance of invading pathogens is essential to preventing overwhelming inflammation and sepsis that are symptomatic of bacterial peritonitis. Macrophages participate in this innate immune response by engulfing and digesting pathogens, a process called phagocytosis. Oxidized phospholipids (OxPL) are danger-associated molecular patterns (DAMPs) generated in response to infection that can prevent the phagocytic clearance of bacteria. We investigated the mechanism underlying OxPL action in macrophages. Exposure to OxPL induced alterations in actin polymerization, resulting in spreading of peritoneal macrophages and diminished uptake of E. coli. Pharmacological and cell-based studies showed that an anchored pool of PKA mediates the effects of OxPL. Gene silencing approaches identified the A-kinase anchoring protein (AKAP) WAVE1 as an effector of OxPL action in vitro. Chimeric Wave1(-/-) mice survived significantly longer after infection with E. coli and OxPL treatment in vivo. Moreover, we found that endogenously generated OxPL in human peritoneal dialysis fluid from end-stage renal failure patients inhibited phagocytosis via WAVE1. Collectively, these data uncover an unanticipated role for WAVE1 as a critical modulator of the innate immune response to severe bacterial infections.
The pore-forming toxin Panton-Valentine leukocidin (PVL) is carried by community-acquired methicillin-resistant Staphylococcus aureus and associated with necrotizing pneumonia together with poor prognosis of infected patients. Although the cell-death-inducing properties of PVL have previously been examined, the pulmonary immune response to PVL is largely unknown. Using an unbiased transcriptional profiling approach, we show that PVL induces only 29 genes in mouse alveolar macrophages, which are associated with TLR signaling. Further studies indicate that PVL directly binds to TLR2 and induces immune responses via NF-?B in a TLR2, CD14, MyD88, IL-1R-associated kinase 1, and TNFR-associated factor 6-dependent manner. PVL-mediated inflammation is independent of pore formation but strongly depends on the LukS subunit and is suppressed in CD14/TLR2(-/-) cells. In vivo PVL or LukS induced a robust inflammatory response in lungs, which was diminished in CD14/TLR2(-/-) mice. These results highlight the proinflammatory properties of PVL and identify CD14/TLR2 as an essential receptor complex for PVL-induced lung inflammation.
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