BACKGROUND & AIMS: Intestinal epithelial cells (IECs) provide a barrier that separates the mucosal immune system from the luminal microbiota. IECs constitutively express low levels of major histocompatibility complex (MHC) class II proteins, which are upregulated upon exposure to interferon gamma. We investigated the effects of deleting MHCII proteins specifically in mice with infectious, dextran sodium sulfate (DSS)-, and T-cell-induced colitis.
METHODS: We disrupted the histocompatibility 2, class II antigen A, beta 1 gene (H2-Ab1) in IECs of C57BL/6 mice (I-Ab) or Rag1 mice (Rag1I-Ab); we used I-Ab mice as controls. Colitis was induced by administration of DSS, transfer of CD4CD45RB T cells, or infection with Citrobacter rodentium. Colon tissues were collected and analyzed by histology, immunofluorescence, xMAP, and reverse-transcription polymerase chain reaction and organoids were generated. Microbiota (total and immunoglobulin [Ig]A-coated) in intestinal samples were analyzed by16S amplicon profiling. IgACD138 plasma cells from Peyer’s patches and lamina propria were analyzed by flow cytometry and IgA repertoire was determined by next-generation sequencing.
RESULTS: Mice with IEC-specific loss of MHCII (I-Ab mice) developed less severe DSS- or T-cell transfer-induced colitis than control mice. Intestinal tissues from I-Ab mice had a lower proportion of IgA-coated bacteria compared with control mice, and a reduced luminal concentration of secretory IgA (SIgA) following infection with C rodentium. There was no significant difference in the mucosal IgA repertoire of I-Ab vs control mice, but opsonization of cultured C rodentium by SIgA isolated from I-Ab mice was 50% lower than that of SIgA from mAb mice. Fifty percent of I-Ab mice died after infection with C rodentium, compared with none of the control mice. We observed a transient but significant expansion of the pathogen in the feces of I-Ab mice compared with I-Ab mice.
CONCLUSIONS: In mice with DSS or T-cell-induced colitis, loss of MHCII from IECs reduces but does not eliminate mucosal inflammation. However, in mice with C rodentium-induced colitis, loss of MHCII reduces bacterial clearance by decreasing binding of IgA to commensal and pathogenic bacteria.