A nuclear-localized Gasdermin D fragment licenses MHCII induction to maintain food tolerance in small intestine

The intestinal immune system is continually exposed to diverse foreign antigens from commensals, pathogens, and even food, so animals must have a way to induce immune responses against pathogens while retaining immune tolerance towards commensals and food. Here, we found that genetic knockout of the pyroptosis executioner protein Gasdermin D in intestinal epithelial cells disrupts immune tolerance to food in the small intestine, and we discovered that IECs accumulate a previously unknown 13kD fragment of GSDMD that is cleaved by CASPASE3 and CASPASE7 in response to dietary antigens. Unlike the 30kD GSDMD cleavage fragment that executes pyroptosis by translocating from the cytosol and rupturing cell membranes, we demonstrate that the 13kD N-terminal GSDMD cleavage fragment translocates to the nucleus, where it induces the transcription of CIITA and MHCII molecules in IECs, which in turn induces the Type 1 regulatory T cells in upper small intestine to regulate food tolerance. Mice given amino acid diet devoid of proteins, mice treated with a CASP3 7 inhibitor AcDEVDCHO, and a small intestinal cleavage resistant variant GsdmdSICR mutant mice all displayed both impaired MHCII expression and a dysregulated food tolerance phenotype. Viewed alongside GSDMDs pyroptosis executioner function, our study supports that the differential cleavage of GSDMD can be understood as a regulatory hub controlling immunity versus tolerance in the small intestine.