In the T1D NOD mouse model, I-Ag7-B:9-23 (R3) refers to a pathogenic complex wherein the MHC class II molecule I-Ag7in register 3 (R3) binds to the B:9-23 peptide which is a primary initiating epitope located between residues 9 and 23 of the insulin B chain, and a monoclonal antibody named mAb287 that can selectively bind to this complex was generated. Here, INS is linked to type 1 diabetes mellitus.