Macrophage Innate Immune Responses Delineate Between Defective Translocon Assemblies Produced by YopD Mutants

Translocon pores formed in the eukaryotic cell membrane by a type III secretion system facilitate the translocation of immune-modulatory effector proteins into the host cell interior. The YopB and YopD proteins produced and secreted by pathogenic spp. harboring a virulence plasmid-encoded type III secretion system perform this pore-forming translocator function. We had previously characterized T3SS function and pathogenicity of a number of strains encoding sited-directed point mutations in . This resulted in the classification of mutants into three different classes based upon the severity of the phenotypic defects. To investigate the molecular and functional basis for these defects, we explored the effectiveness of RAW 264.7 cell line to respond to infection by representative YopD mutants of all three classes. Signature cytokine profiles could separate the different YopD mutants into distinct categories. The activation and suppression of certain cytokines that function as central innate immune response modulators correlated well with the ability of mutant bacteria to alter anti-phagocytosis and programmed cell death pathways. These analyses demonstrated that sub-optimal translocon pores impact the extent and magnitude of host cell responsiveness, and this limits the capacity of pathogenic spp. to fortify against attack by both early and late arms of the host innate immune response.