The diabetogenic mouse MHC class II molecule I-Ag7 is endowed with a switch that modulates TCR affinity.

The epitope is a mimotope of the peptide recognized by I-Ag7-restricted T cell receptor BDC-2.5. BDC-2.5 was derived from a diabetic female NOD mouse and was shown to greatly accelerate disease when transferred to young animals. The nature of the presented antigen is still unknown, although it has been shown to be associated with the membrane fraction of beta granules. Epitope/Ag7 tetramer positive CD4+ T cells were present in the thymus and expand in the periphery (pancreatic lymph nodes) from age 3 to 20 weeks, at which time NOD mice are diabetic.