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NLRP1B and NLRP3 Control the Host Response following Colonization with the Commensal Protist Tritrichomonas musculis

Commensal intestinal protozoa, unlike their pathogenic relatives, are neglected members of the mammalian microbiome. These microbes have a significant impact on the host’s intestinal immune homeostasis, typically by elevating anti-microbial host defense. Tritrichomonas musculis, a protozoan gut commensal, strengthens the intestinal host defense against enteric Salmonella infections through Asc- and Il1r1-dependent Th1 and Th17 cell activation. However, the underlying inflammasomes mediating this effect remain unknown. In this study, we report that colonization with T. musculis results in an increase in luminal extracellular ATP that is followed by increased caspase activity, higher cell death, elevated levels of IL-1β, and increased numbers of IL-18 receptor–expressing Th1 and Th17 cells in the colon. Mice deficient in either Nlrp1b or Nlrp3 failed to display these protozoan-driven immune changes and lost resistance to enteric Salmonella infections even in the presence of T. musculis. These findings demonstrate that T. musculis–mediated host protection requires sensors of extracellular and intracellular ATP to confer resistance to enteric Salmonella infections. Key Points The gut commensal Tritrichomonas musculis elevates luminal extracellular ATP levels. NLRP1B and NLRP3 direct the Tritrichomonas musculis–driven Th cell response.