DM Peptide-Editing Function Leads to Immunodominance in CD4 T Cell Responses In Vivo

Abstract

DM functions as a peptide editor for MHC class II-bound peptides. We examined the hypothesis that DM peptide editing plays a key role in focusing the in vivo CD4 T cell responses against complex pathogens and protein Ags to only one, or at most a few, immunodominant peptides. Most CD4 T cells elicited in the wild-type BALB/c (H-2d) mice infected with Leishmania major predominantly recognize a single epitope 158–173 within Leishmania homologue of activated receptor for c-kinase (LACK), as is the case when these mice are immunized with rLACK. Using DM-deficient (DM−/−) H-2d mice, we now show that in the absence of DM, the in vivo CD4 T cell responses to rLACK are skewed away from the immunodominant epitopes and are diversified to include two novel epitopes (LACK 33–48 and 261–276). DM−/− B10.BR (H-2k) mice showed similar results. These results constitute the first demonstration of the role of DM peptide editing in sculpting the specificity and immunodominance in in vivo CD4 T cell responses.