T cell receptors for antigen on intraepithelial cytolytic T lymphocytes in celiac disease engage enterocyte HLA-E and HLA-B.

We compared duodenal biopsies showing active celiac disease (CeD) to normal controls using single-cell RNA sequencing, cyclic immunofluorescence, RNAScope, and proximity ligation assays. There is increased infiltration of villous but not crypt epithelium T cells bearing either αβ or γδ T cell receptors (TCRs) in CeD. Both T cell subsets are activated cytotoxic T lymphocytes (CTLs) and are the predominant mucosal source of IFNγ. In response to this IFNγ, villous but not crypt enterocytes show an IFNγ signature, including nuclear phospho-STAT1 protein, class II HLA molecules and IFNγ-inducible chemokines known to recruit CTLs (e.g., CCL3, CCL4, CXCL10, and CXCL11) and receptors for these chemokines are expressed on the infiltrating CTLs. Villous enterocytes also display increased HLA-E and HLA-B mRNAs and proteins. Bioinformatic analyses (NICHES) and proximity ligation assays show frequent binding of both αβ and γδ TCRs with enterocyte HLA-E or HLA-B, but not HLA-DR. In contrast, NKG2C, proposed as an alternative trigger of CTL activation, is infrequently expressed and shows few interactions with HLA-E. Our data suggest that activated intraepithelial CTLs produce IFNγ which recruits additional CTLs and increases antigen-dependent killing of villous epithelium using either conventional or HLA-E antigen presentation.