Cross-kingdom-mediated detection of intestinal protozoa through NLRP6

Abstract

Intestinal protists are detected by the host innate immune system through mechanisms that remain poorly understood. Here, we demonstrate that Tritrichomonas protozoa induce thickening of the colonic mucus in an NLRP6-, ASC-, and caspase-11-dependent manner, consistent with the activation of sentinel goblet cells. Mucus growth is recapitulated with cecal extracts from Tritrichomonas-infected mice but not purified protozoa, suggesting that NLRP6 may detect infection-induced microbial dysbiosis. In agreement, Tritrichomonas infection causes a shift in the microbiota with the expansion of Bacteroides and Prevotella, and untargeted metabolomics reveals a dramatic increase in several classes of metabolites, including sphingolipids. Finally, using a combination of gnotobiotic mice and ex vivo mucus analysis, we demonstrate that wild-type, but not sphingolipid-deficient, B. thetaiotaomicron is sufficient to induce NLRP6-dependent sentinel goblet cell function, with the greatest effect observed in female mice. Thus, we propose that NLRP6 is a sensor of intestinal protozoa infection through monitoring microbial sphingolipids.

Keywords: Bacteroides; NLRP6; Tritrichomonas; goblet cells; inflammasomes; mucosal immunity; protozoan infection; sphingolipids.