NO-mediated cytotoxicity contributes to multiple low-dose streptozotocin-induced diabetes but not to NOD diabetes.

Type 1 diabetes (T1D) is caused mostly by autoimmune destruction of pancreatic beta-cells, the precise mechanism of which remains unclear. Two major effector mechanisms have been proposed: direct cell-mediated and indirect cytokine-mediated cytotoxicity. Cytokine-mediated beta-cell destruction is presumed mainly caused by NO production. To evaluate the role of iNOS expression in T1D, this study used a novel iNOS inhibitor ONO-1714. ONO-1714 significantly reduced cytokine-mediated cytotoxicity and NO production in both MIN6N9a cells and C57BL/6 islets in the presence of IL-1beta, TNF-alpha, and IFN-gamma. To evaluate whether NO contributes to diabetes progression in vivo, ONO-1714 was administered to four different mouse models of autoimmune diabetes: multiple low-dose STZ (MLDS)-induced C57BL/6, CY-induced, adoptive transfer and spontaneous NOD diabetes. Exposure to STZ in vitro induced NO production in MIN6N9a cells and C57BL/6 islets, and in vivo injection of ONO-1714 to MLDS-treated mice significantly reduced hyperglycemia and interestingly, led to complete suppression of cellular infiltration of pancreatic islets. In contrast, when ONO-1714 was injected into spontaneous NOD mice and CY-induced and adoptive transfer models of NOD diabetes, overt diabetes could not be inhibited in these models. These findings suggest that NO-mediated cytotoxicity significantly contributes to MLDS-induced diabetes but not to NOD diabetes.

Detection of GAD65-reactive T-Cells in type 1 diabetes by immunoglobulin-free ELISPOT assays.

OBJECTIVE: To investigate the prevalence of beta-cell autoantigen-reactive peripheral T-cells in type 1 diabetes, we developed an immunoglobulin-free enzyme-linked immunospot (ELISPOT) assay and assessed its usefulness for diagnosing this disease. RESEARCH DESIGN AND METHODS: Cellular immune responses to beta -cell autoantigens were studied both by immunoglobulin-free proliferation assays and ELISPOT assays in 33 patients with type 1 diabetes and 15 patients with type 2 diabetes, compared with 23 healthy control subjects. Autoantibodies against GAD65 and IA-2 were measured by radioimmunoassay. RESULTS: Significant proliferative responses to GAD65 were observed in 10 of 31 (32.3%) type 1 diabetic patients (P < 0.05), whereas GAD65-reactive gamma-interferon (IFN-gamma)-secreting cells were detected in 22 of 33 patients (66.7%) by ELISPOT assay (P < 0.001). Of patients negative for both GAD65 and IA-2, five of six (83.3%) showed IFN-gamma positivity in ELISPOT and two of five (40.0%) showed significant proliferation against GAD65. CONCLUSIONS: Using a newly developed ELISPOT assay, GAD-reactive T-helper 1 cells in PBMC of type 1 diabetic patients could be identified at a higher frequency than by the proliferation assay. Therefore, the immunoglobulin-free ELISPOT assay is an excellent tool for detecting T-cell reactivity to autoantigens with greater specificity and, in combination with beta-cell autoantibody determination, will improve the diagnosis of type 1 diabetes.

Tolerance mechanisms in murine autoimmune diabetes induced by anti-ICAM-1/LFA-1 mAb and anti-CD8 mAb.

A short-term administration of antibodies against ICAM-1/LFA-1 or CD8 molecules during a critical period of younger age resulted in complete protection of autoimmune diabetes in NOD mice. In this study, we attempted to elucidate the tolerance mechanisms. Transfer of splenocytes from both antibody-treated NOD mice to NOD-SCID mice failed to develop diabetes. On the other hand, when splenocytes from diabetic mice were transferred to the antibody-treated mice, 40% of both mAb-treated recipients became diabetic. In vitro response of T cells from these protected mice exhibited strong proliferation against syngeneic islet cells or ConA. Furthermore, semiquantitative RT-PCR analysis of cytokines showed that T cells from anti-CD8-treated mice could express IFN-gamma, IL-4, IL-10 and TGF-beta1 in response to islet antigen. In contrast, T cells from anti-ICAM-1/LFA-1-treated mice expressed IFN-gamma, IL-10 and TGF-beta1 but not IL-4. These results suggest that tolerance mechanisms like clonal deletion, anergy, immunoregulatory T cells or Th1 to Th2/Th3 cytokine shifting are not responsible for the tolerance induction, indicating the presence of other unrevealed mechanism responsible for the loss of capability of autoreactive T cells to infiltrate and destroy the pancreatic beta-cells in vivo.