Disease resistant, NOD-related strains reveal checkpoints of immunoregulation in the pancreas

The autoimmune diabetic NOD mouse serves as a model for human type 1 diabet es. Disease development is due to islet beta cell destruction in the contex t of immune cell infiltration of islets and inflammatory changes throughout the pancreas. In the present study we tried to identify immune reactivity patterns in the pancreas associated with diabetes resistance in NOD-related mouse strains. The pancreata of diabetes-prone female NOD/LtJ, NOD/Bom and of genetically related but diabetes-resistant strains; NOR, NON, NON.NOD-H 2(g7), NOD.NON-H-2(nbl) were obtained at the age of 70 days for semiquantit ative analysis of insulitis and of mRNA expression by reverse transcriptase PCR, In addition, the response to a single dose of cyclophosphamide for sy nchronizing and accelerating the progression of insulitis was determined. T he progression of insulitis and immune gene expression in response to cyclo phosphamide revealed characteristic differences between the six strains. NO D/LtJ and NOD/Bom mice were found significantly to upregulate pancreatic IL -12p40 and IL-18 expression after cyclophosphamide treatment, followed by a n increase in IFN-gamma mRNA levels. In contrast, the two MHC-haplotype H-2 (nbl) expressing strains either upregulated neither IL-12/IL-18 nor IFN-gam ma gene expression. The two strains sharing MHC haplotype H-2(g7) expressio n with NOD did respond to cyclophosphamide with IL-12p40/IL-18 gene express ion. However, NON,NOD H-2(g7) mice failed to progress to IFN-gamma gene exp ression. NOR mice progressed to IFN-gamma expression but exhibited sustaine d IL-4 gene expression. Only severe intra-insulitis was associated with the expression of inducible NO synthase, The comparison of diabetes-prone and diabetes-resistant strains revealed three checkpoints of;immune regulation in the pancreas. The earliest checkpoint is the induction of an IL-12p40/IL -18 response in innate immune or antigen-presenting;no cells. The next leve l of control is at the induction of IFN-gamma gene expression, and a third checkpoint is the maintenance or loss of antagonistic Th2 type reactions.