Nlrp6 inflammasome and colonic inner mucus layer function. The Nlrp6 inflammasome is not required for baseline colonic inner mucus layer formation or function

The inner mucus layer (IML) is an innate defensive barrier that protects the colonic epithelium from luminal threats and prevents inflammatory bowel disease. Innate immune signalling is thought to regulate IML formation via epithelial Nlrp6 inflammasome-mediated secretion of the core mucus structural component Muc2 from colonic goblet cells. Here we report that isolated colonic goblet cells express components of several inflammasomes; however, extensive analysis of IML properties in multiple inflammasome deficient mice, including littermate controlled Nlrp6-/-, detected a functional IML barrier in all strains. Analysis of mice lacking inflammasome substrate cytokines did identify a defective IML in Il18-/- mice; but this phenotype was ultimately traced to a microbiota driven, genotype-independent effect. Together our results demonstrate that baseline IML formation and function is independent of inflammasome activity and serves to highlight the critical importance of microbiota-controlled experimental design in order to reduce the risk of false-positive results in this field.