Abstract
Type 1 Diabetes (T1D) is an autoimmune disease characterized by the destruction of insulin-producing beta cells in the pancreas. Amelioration of T1D and the prevention of its detrimental complications are possible through islet transplantation, wherein hormone-producing clusters of cells, islets of Langerhans (islets), are separated from the pancreas and transplanted into a diabetic patient. However, alterations due to the effects of organ recovery, cold ischemia time (CIT), and islet isolation may increase the inflammatory and immunogenic properties of these islets, thereby predisposing them to functional impairment and rejection in a transplant. Understanding the inflammatory properties of islets will allow for the development of strategies that decrease early islet loss and effectively enhance engraftment and long-term function. Therefore, the aims of this study were to 1) identify and characterize populations of antigen presenting cells (APC) and other immune cells in nonhuman primate (NHP) islets in situ and after isolation; and 2) characterize the expression and functional role of CD40 and the IFN alpha receptor in NHP islets, including their effects on islet immunogenicity. A surprising result of these studies was that half of the APC present in isolated NHP islets were B lymphocytes. We observed that the number of islet-resident immune cells increased with islet size, and described the localization pattern of these cells within islets. We characterized CD40 expression in NHP islets, demonstrating that multiple CD40 isoforms are expressed, and made the novel finding that functional CD40 is expressed on the somatostatin-producing δ cells. When CD40 was stimulated with its ligand, it induced downstream signaling changes, increased proinflammatory cytokine release, and increased islet immunogenicity. Based on our results, we have hypothesized a model of CD40 signaling in islet δ cells. Microarray analysis revealed expression changes in many inflammatory molecules integral to inflammation, the immune response, and apoptosis in islets that had endured increased CIT, demonstrating the unfavorable conditions created within islets following organ recovery, CIT, and islet isolation. Furthermore, we demonstrated that the IFN alpha receptor is present on isolated NHP islets, and that stimulation with IFN alpha leads to increased proinflammatory cytokine release, surface receptor upregulation, and a decrease in immunogenicity. In summary, in NHP islets we have defined the type and quantity of immune cells, the inflammatory molecules expressed, including CD40 and the IFN alpha receptor, and their downstream functional roles in an immune response.