Project Summary/Abstract Bacterial pathogens use type III secretion systems to translocate effectors into host cells to promote virulence. Type III secretion can also activate compensatory innate immune responses that are host protective. For example, type III secretion can trigger inflammasome assembly in host cells, resulting in release of the cytokine IL-1b. Virulent pathogens can inhibit compensatory protective immune responses triggered by type III secretion but how this is achieved at the cellular and molecular levels in vivo remains poorly understood. To address this knowledge gap, this project seeks to determine at the cellular and molecular levels how type III secretion effectors in virulent Yersinia species inhibit a protective inflammasome pathway in vivo. Yersinia uses two effectors, YopM and YopJ, to inhibit the pyrin inflammasome. It is not known if YopM and YopJ promote virulence by inhibiting the pyrin inflammasome in a cell specific manner. During invasive infections of lymphoid tissues Yersinia grow as extracellular microcolonies in direct contact with neutrophils within an organize immune structure known as a pyogranuloma. Pyogranulomas can be considered battlefields where Yersinia virulence factors combat protective immune responses in neutrophils acting as foot soldiers. Yersinia mutants lacking YopM and YopJ have a significant survival defect in lymphoid tissues suggesting that these effectors inhibit the pyrin inflammasome in pyogranuloma neutrophils. Additionally, IL-1b is important for host protection against infection by Yersinia lacking YopM and YopJ. Based on these published data and preliminary results we hypothesize that YopM and YopJ promote Yersinia virulence by inhibiting the pyrin inflammasome in neutrophils to prevent release of IL-1b in pyogranulomas. This hypothesis will be tested in Aim 1. YopM binds to pyrin in infected host cells and in purified form, but the molecular basis of this interaction is undefined. Based on published and preliminary we hypothesize that YopM targets the pyrin domain to inhibit the inflammasome in vivo and promote Yersinia virulence. This hypothesis will be tested in Aim 2. Completion of these aims will fill important knowledge gaps, move Yersinia pathogenesis research forward, have a broad impact on the field of neutrophil inflammasomes and inform new therapeutic strategies aimed at augmenting protective neutrophil inflammasome responses to bacterial pathogens.

Project Narrative The results of this study will provide new mechanistic insights into how bacterial virulence factors inhibit protective immune responses during infection. Completion of the aims will fill important knowledge gaps and inform new therapeutic strategies aimed at augmenting protective immune responses to bacterial pathogens.