Pathogenic Yersinia injects virulent Yersinia outer proteins (Yops) into the host cell through a type three secretion system (T3SS) to express its pathogenicity. Through inactivation of small GTPases by YopT protease, YopE GTPase-activating protein, and YpkA/YopO sequestration of GDP-bound small GTPases, Yersinia prevents its uptake by phagocytic cells and disrupts the actin cytoskeleton. YopH phosphatase shuts down phagocytosis by dephosphorylating key host proteins as well as suppresses T cell activation. Yersinia induces macrophage pyroptosis via YopB/YopD activation of canonical and noncanonical inflammasomes and YopT/YopE-mediated activation of pyrin. These effects are counteracted by YopK and YopM. YopP/J is a member of an ubiquitin-like protein cysteine protease family and simultaneously targets signaling components of the MAPK and NF-kappaB signaling pathways following activation of Toll-like receptor4 to inhibit production of proinflammatory cytokines.