Binding of conserved islet peptides by human and murine MHC class II molecules associated with susceptibility to type I diabetes

The major histocompatibility complex (MHC) is the most important susceptibility locus for type I diabetes in humans and NOD mice. NOD mice express a single MHC class II molecule (I-A(g7)) which carries a unique beta chain sequence. In humans, DQ alleles that encode DQ8 and DQ2 confer the highest risk for the disease. Soluble DQ8 and I-A(g7) were used to directly compare the binding specificity of these MHC molecules. Peptides from three islet antigens - insulin, GAD 65 and HSP 60 - bound to both CQ8 and I-A(g7). These peptides included epitopes that are immunodominant in NOD mice, namely insulin (9-23), GAD (206-220) and HSP 60 (441-460). All of these peptide sequences are highly conserved between the human and murine antigens. The binding specificity of DQ8 and I-A(g7) was similar, but not identical, since two peptides eluted from splenocytes of NOD mice did not bind to DQ8. DQ8 formed long-lived complexes with the majority of these peptides, indicating that DQ8 is not a poor peptide binder. These results demonstrate functional similarities between human and murine MHC class II molecules that confer susceptibility to type I diabetes.