IRF8 directs stress-induced autophagy in macrophages and promotes clearance of Listeria monocytogenes

Autophagy, activated by many stresses, plays a critical role in innate immune responses. Here we show that interferon regulatory factor 8 (IRF8) is required for the expression of autophagy-related genes in dendritic cells. Furthermore in macrophages, IRF8 is induced by multiple autophagy-inducing stresses, including IFNγ and Toll-like receptor stimulation, bacterial infection, starvation and by macrophage colony-stimulating factor. IRF8 directly activates many genes involved in various steps of autophagy, promoting autophagosome formation and lysosomal fusion. Consequently, Irf8−/− macrophages are deficient in autophagic activity, and excessively accumulate SQSTM1 and ubiquitin-bound proteins. We show that clearance of Listeria monocytogenes in macrophages requires IRF8-dependent activation of autophagy genes and subsequent autophagic capturing and degradation of Listeria antigens. These processes are defective in Irf8−/− macrophages where uninhibited bacterial growth ensues. Together these data suggest that IRF8 is a major autophagy regulator in macrophages, essential for macrophage maturation, survival and innate immune responses. Autophagy is critical for pathogen clearance by innate immune cells. Here the authors show that IRF8 is activated in response to autophagy-inducing stimuli, promotes autophagic progression by driving transcription of autophagy genes and is critical for clearance of intracellular bacteria.

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