Paneth Cell-Dependent Intestinal Homeostasis During T. Gondii Infection

The intestinal epithelial barrier faces the arduous task of constantly monitoring and controlling the diverse bacteria which colonize the gut. Key for this balance are the Paneth cells, highly specialized secretory epithelial cells in the intestinal crypts which secrete anti-microbial peptides to regulate the microbiota. Breakdown of the symbiotic host-microbe relationship, possibly due to Paneth cell dysfunction, leads to intestinal pathologies such as inflammatory bowel disease (IBD) and infection. The protozoan parasite Toxoplasma gondii triggers severe small intestinal immunopathology that recapitulates many characteristics of IBD such as elevated IFN-g and microbiota-mediated inflammation, along with disappearance of Paneth cells. However, little is known about what happens to these Paneth cells and if their loss exacerbates inflammation. In this study, we have generated a number of fluorescent Paneth cell-specific reporter mice to demonstrate that acute T. gondii infection leads to Paneth cell death by an IFN-g-dependent pathway. Our results also revealed that constitutive elimination of Paneth cells does not enhance susceptibility to T. gondii infection, enhance inflammation, or increase damage to the intestinal epithelium, suggesting that Paneth cell retention at the peak of inflammation may be detrimental and these cells may be targeted for controlled elimination early during T. gondii infection. We also demonstrate that the microbiota triggers basal Paneth cell-specific autophagy via induction of IFN-g. Deletion of Atg5 in Paneth cells resulted in exaggerated intestinal inflammation characterized by the complete destruction of the intestinal crypts seen in pan-epithelial Atg5 deficient mice. An evaluation of Atg5 in intestinal organoids and in T. gondii-infected mice revealed that lack of functional autophagy in Paneth cells resulted in increased sensitivity to TNF, leading to exaggerated microbiota and IFN-g-dependent intestinal immunopathology. Our results reveal that Paneth cell expression of Atg5 is essential for tissue protection against cytokine-mediated immunopathology during acute gastrointestinal infection. Together, these findings have broad implications for the role of Paneth cells during both acute infection and chronic intestinal inflammation.