Neonatal islet-specific expression of IL-10 in nonobese diabetic (NOD) mice accelerates the onset of diabetes, whereas systemic treatment of young NOD mice with IL-10 prevents diabetes. The mechanism for acceleration of diabetes in IL-10-NOD mice is not known. Here we show, by adoptive transfers, that prediabetic or diabetic NOD splenocytes upon encountering IL-10 in the pancreatic islets readily promoted diabetes. This outcome suggests that the compartment of exposure, not the timing, confers proinflammatory effects on this molecule. Moreover, injection of IL-10-deficient NOD splenocytes into transgenic IL-10-NOD.scid/scid mice elicited accelerated disease, demonstrating that pancreatic IL-10 but not endogenous IL-10 is sufficient for the acceleration of diabetes. Immunohistochemical analysis revealed hyperexpression of ICAM-1 on the vascular endothelium of IL-10-NOD mice. The finding suggests that IL-10 may promote diabetes via an ICAM-1-dependent pathway. We found that introduction of ICAM-1 deficiency into IL-10-NOD mice as well as into NOD mice prevented accelerated insulitis and diabetes. Failure to develop insulitis and diabetes was preceded by the absence of GAD65-specific T cell responses. The data suggest that ICAM-1 plays a role in the formation of the “immunological synapse”, thereby affecting the generation and/or expansion of islet-specific T cells. In addition, ICAM-1 also played a role in the effector phase of autoimmune diabetes because adoptive transfer of diabetogenic BDC2.5 T cells failed to elicit clinical disease in ICAM-1-deficient IL-10-NOD and NOD mice. These findings provide evidence that pancreatic IL-10 is sufficient to drive pathogenic autoimmune responses and accelerates diabetes via an ICAM-1-dependent pathway.

Granulocyte macrophage-colony stimulating factor (GM-CSF) is one of the most widely used growth factors for enhancing immune responses and is known to recruit and activate antigen-presenting cells (APCs). This study hypothesized that overexpression of this cytokine within the pancreatic beta-cells would recruit, expand, and activate APCs. The question was whether this would lead to tolerance or autoimmunity to pancreatic antigens. This possibility was tested by preparing transgenic mice (ins-GM-CSF) whose islets expressed murine GM-CSF. By 6-8 weeks of age, these mice developed a profound mononuclear cell infiltration that often overwhelmed the exocrine pancreas, although no changes in enzyme or hormone function were apparent. The majority of the mononuclear infiltrate within the pancreas was identified as F4/80+ macrophages. Transgenic ins-GM-CSF mice had splenomegaly due to a massive increase in the macrophage population. Additionally, mononuclear cells were found within the livers of transgenic mice, with F4/80+ cells also identified within the infiltrate, indicating that GM-CSF-activated mononuclear cells circulated to organs other than the pancreas. To assess the disease potential, this study tested whether macrophage recruitment to the pancreas might accelerate or protect the islets from diabetes. It was found that the induction of diabetes by low-dose streptozotocin (STZ) was delayed and reduced within ins-GM-CSF transgenic mice, in comparison with negative littermates. Together, these data highlight the role of GM-CSF in recruiting APCs such as macrophages. Advanced cellular infiltration does not overtly harm, and may even protect, pancreatic function, as seen with the delay in chemically induced diabetes.

In developmental terms, the endocrine system of neither the gut nor the pancreatic islets has been characterized fully. Little is known about the involvement of cholecystokinin (CCK), a gut hormone, involved in regulating the secretion of pancreatic hormones, and pancreatic growth. Here, we tracked CCK-expressing cells in the intestines and pancreata of normal mice (BALB/c), Non Obese Diabetic (NOD) mice and interferon (IFN)-transgenic mice, which exhibit pancreatic regeneration, during embryonic development, the postnatal period and adulthood. We also questioned whether IFN-influences the expression of CCK. The results from embryonic day 16 showed that all three strains had CCK in the acinar region of pancreata, and specifically in cells that also expressed glucagon. However, in adulthood only BALB/c and NOD mice continued this pattern. By contrast, in IFNtransgenic mice, CCK expression was suppressed from birth to 3 months of age in the pancreata but not intestines. However, by 5 months of age, CCK expression appeared in the regenerating pancreatic ductal region of IFNtransgenic mice. In the intestine, CCK expression persisted from fetus to adulthood and was not influenced by IFN-. Intestinal cells expressing CCK did not co-express glucagon, suggesting that these cells are phenotypically distinct from CCK-expressing cells in the pancreatic islets, and the effect of IFN-on CCK varies depending upon the cytokine's specific microenvironment.

In the presence of interferon-gamma (IFN-gamma), pancreatic ductal epithelial cells grow continuously, and islets undergo neogenesis. To determine whether these new islets are derived from conventional precursors, we tested whether IFN-gamma can complement the loss of transcription factors known to regulate pancreatic development. We analyzed the effect of a transgene on lethality in mice lacking the transcription factors Pax4, Pax6, or Pdx-1, by intercrossing such mice with transgenic mice whose pancreatic cells make IFN-gamma (ins-IFN-gamma mice). However, IFN-gamma expression did not rescue these mice from the lethal mutations, because no homozygous knockout mice carrying the IFN-gamma transgene survived, despite the survival of all other hemizygous gene combinations. This outcome demonstrates that the pathway for IFN-gamma regeneration requires the participation of Pax4, Pax6, and Pdx-1. We conclude that the striking islet regeneration observed in the ins-IFN-gamma NOD strain is regulated by the same transcription factors that control initial pancreatic development.