PDCD1 and diabetes mellitus: NOD mice carrying deficiency in programmed cell death 1 (PD-1)—an adhesion molecule with costimulatory function—develop diabetes with increased severity [108], while PD-1-deficient NOD mice, carrying the anti-diabetogenic major histocompatibility complex (MHC) haplotype H-2b, are protected from diabetes but develop spontaneous peripheral neuritis [109, 110].