Listeria monocytogenes exploits efferocytosis to promote cell-to-cell spread

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Efferocytosis, the process by which dying or dead cells are removed by phagocytosis, has an important role in development, tissue homeostasis and innate immunity1. Efferocytosis is mediated, in part, by receptors that bind to exofacial phosphatidylserine (PS) on cells or cellular debris after loss of plasma membrane asymmetry. Here we show that a bacterial pathogen,Listeria monocytogenes, can exploit efferocytosis to promote cell-to-cell spread during infection. These bacteria can escape the phagosome in host cells by using the pore-forming toxin listeriolysin O (LLO) and two phospholipase C enzymes2. Expression of the cell surface protein ActA allowsL. monocytogenesto activate host actin regulatory factors and undergo actin-based motility in the cytosol, eventually leading to formation of actin-rich protrusions at the cell surface. Here we show that protrusion formation is associated with plasma membrane damage due to LLO’s pore-forming activity. LLO also promotes the release of bacteria-containing protrusions from the host cell, generating membrane-derived vesicles with exofacial PS. The PS-binding receptor TIM-4 (encoded by theTimd4gene) contributes to efficient cell-to-cell spread byL. monocytogenesin macrophagesin vitroand growth of these bacteria is impaired inTimd4−/−mice. Thus,L. monocytogenespromotes its dissemination in a host by exploiting efferocytosis. Our results indicate that PS-targeted therapeutics may be useful in the fight against infections byL. monocytogenesand other bacteria that use similar strategies of cell-to-cell spread during infection.

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