Yersinia enterocoliticaEvasion of the Host Innate Immune Response by V Antigen-Induced IL-10 Production of Macrophages Is Abrogated in IL-10-Deficient Mice

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Abstract
The virulence-associated V Ag (LcrV) of pathogenic Yersinia species is part of the translocation apparatus, required to deliver antihost effector proteins (Yersinia outer proteins) into host cells. An orthologous protein (denoted as PcrV) has also been identified in the ExoS regulon of Pseudomonas aeruginosa. Additionally, it is known that LcrV is released by yersiniae into the environment and that LcrV causes an immunosuppressive effect when injected into mice. In this study, we demonstrate for the first time that rLcrV, but not PcrV, is capable of suppressing TNF-α production in zymosan A-stimulated mouse macrophages and the human monocytic Mono-Mac-6 cell line. The underlying mechanism of TNF-α suppression could be assigned to LcrV-mediated IL (IL)-10 production, because 1) LcrV induces IL-10 release in macrophages, 2) anti-IL-10 Ab treatment completely abrogated TNF-α suppression, and 3) TNF-α suppression was absent in LcrV-treated macrophages of IL-10-deficient (IL-10−/−) mice. The relevance of LcrV-mediated immunosuppression for the pathogenicity of yersiniae became evident by experimental infection of mice; in contrast to wild-type mice, IL-10−/− mice were highly resistant against Yersinia infection, as shown by lower bacterial load in spleen and liver, absent abscess formation in these organs, and survival.