Unusual distribution of a non-classical MHC I restricted CD8+ T population

Abstract

Abstract A broad repertoire of peptides is constitutively presented through the MHC I molecules on the cell surface. ER aminopeptidase associated with Ag processing (ERAAP), a critical molecule in the antigen processing and presentation pathway, has profound effects on the generation of this peptide repertoire. Interestingly, the ERAAP deficient cells can be effectively detected by a unique population of the cytotoxic CD8+ T cell, named QFL-T cells which are specific for the ligand presented by the non-classical MHC Ib molecule, Qa-1b. The QFL-T cells showed similar characteristics with the other non-classical MHC Ib restricted unconventional T cells, such as the NKT or MAIT cells in their semi-invariant αβ TCRs, but their function(s) remains unknown. To study the potential function of the QFL-T cells, we assessed a variety of tissues for the ligand expression and the presence of the QFL-T cells. We observed high expression of this ERAAP dependent Qa-1b restricted ligand and relatively high frequency of the QFL-T cells in the small intestine. Remarkably, the number and the frequency of QFL-T cells among the intraepithelial lymphocytes (IELs) was tightly associated with the age and the gut microbiota of the mice. These findings suggest a role for gut microbiota in the homing/maintenance of the QFL-T cells in the small intestine.