Self peptides isolated from MHC glycoproteins of non-obese diabetic mice.

The non-obese diabetic (NOD) mouse spontaneously develops an insulin-dependent diabetes mellitus that resembles human type I diabetes. This disease can be transferred by purified T cells or cloned T cell lines, implicating an autoimmune T cell attack on the pancreatic beta cells of the islets of Langerhans. As all T cell responses involve recognition of peptides bound to MHC molecules displayed at the cell surface, we have examined self peptides binding to the MHC molecules on spleen cells of the NOD mouse. Peptides eluted from the MHC class I molecule Kd have sequences that conform to known motifs for peptides binding this molecule in other strains of mice. The NOD mouse expresses the unique MHC class II molecule I-Ag7. Peptides eluted from I-Ag7 have sequences that implicate an acidic residue in the C terminus of the peptide as important for binding. The role of this residue in binding has been confirmed by direct peptide-binding analysis. This C-terminal acidic amino acid may interact with an arginine residue in the MHC class II alpha-chain that is exposed when beta-chain residue 57 is mutated to serine, or to the unique beta-chain residue histidine 56. These data may provide valuable insights into the nature of autoantigenic peptides presented by NOD mouse MHC molecules by defining the nature of I-Ag7-peptide binding.