The interaction between macrophages and bacterial pathogens plays a crucial role in the pathogenesis of infectious diseases. Pathogenic species of the gram-negative bacterium Yersinia deploy complex strategies to disarm macrophages and to disrupt their response to infection. For this purpose, Yersinia spp. engage a type III protein secretion system that mediates polarized translocation of Yersinia virulence factors, the so-called Yops, into the host cell cytoplasm. There, the Yops act on different cellular levels to neutralize a sequence of programmed phagocyte effector functions. Yersiniae initially impair the phagocytic machinery and block the generation of the bactericidal oxidative burst. Furthermore, yersiniae uncouple an array of fine-tuned signals of innate immunity, which leads to suppression of the macrophage TNF- production and to macrophage apoptosis. The impairment of cellular functions results in a scenario, by which Yersinia efficiently resist the attack of the macrophage and finally kills the macrophage by activating its intrinsic cell suicide mechanism. This review highlights the aspects of Yersinia-macrophage interaction that determine the fate of the infected cell.
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