Experimental immunoprevention of type I diabetes mellitus

Clinical review 103: T helper type 1 and 2 cytokines mediate the onset and progression of type I (insulin-dependent) diabetes

Type I (insulin-dependent) diabetes mellitus (IDDM) is an autoimmune disease that results from the destruction of insulin-secreting pancreatic islet beta-cells by autoreactive cells and their mediators. Although its exact cause is not completely understood, it is well established that IDDM is associated with dysregulated humoral and cellular immunity, exemplified by altered production of and response to macrophage- and T cell-derived cytokines and a shift in T helper (Th) cell differentiation in favor of a pathogenic Th1 pathway. Th1 cytokines, including interleukin-2 and interferon-gamma, induced islet beta-cell destruction directly by accelerating activation-induced cell death (apoptosis) and by up-regulating the expression of select adhesion molecules, Th1 cytokines facilitated the pancreatic homing of autoreactive leukocytes, hence enhancing beta-cell destruction. More recently, a role for Th2 cytokines in IDDM pathogenesis was described. Accordingly, local production of Th2 cytokines, in particular interleukin-10, accelerated beta-cell destruction by enhancing autoreactive cell infiltration of the pancreas (insulitis) through modulation of the release of other cytokines and by modulating the microvasculature. Whereas both Th1 and Th2 cytokines are present in peripheral T cells and in the pancreas in IDDM, the mechanism of action and the kinetics of a cell damage induced by Th1 and Th2 cytokines appeared to be distinct. Collectively, this supports the idea that IDDM is not an exclusive Th1-mediated disorder as was suggested, and that both Th1 and Th2 cells and their respective mediators participate and cooperate in inducing and sustaining pancreatic islet beta-cell destruction in IDDM.

Immunotherapy for insulin-dependent diabetes mellitus in the "BB" rat

We have previously reported that weekly administration of the adenosine deaminase inhibitor, 2'-deoxycoformycin (dCF), reduces the incidence of insulin-dependent diabetes mellitus (IDDM) in the BB Wistar rat, and this effect is likely due to immunosuppression by dCF. In the present study, we examined the effect of altering the dose and scheduling of dCF on prevention of IDDM in the BB rat. When rats were treated from day 25 of age with 2.5, 4, or 10 mg of dCF/kg/week, the percentage of diabetes-free animals at 120 days of age was 40, 60, and 80% respectively, compared with 10% for control animals, demonstrating increased protection against IDDM with increased dCF dose. Histological assessment of the pancreata from animals that became diabetic revealed a marked mononuclear infiltrate and a loss of positive staining for beta cell granules. In contrast, pancreata from animals that remained diabetes-free appeared normal. Protection against IDDM by dCF was time dependent and only occurred if treatments were initiated by day 30 of age. In addition, the protective effect persisted after drug withdrawal. Further studies are required to determine the optimum duration of therapy with dCF to prevent IDDM and to examine the immunological mechanism responsible for this effect.

Increased prevalence of diabetes-related autoantibodies in celiac disease

Forty-four nondiabetic patients with celiac disease (CD) were examined for the presence of insulin-dependent diabetes mellitus (IDDM)-related autoantibodies. Islet cell antibodies (ICA) were detected in 2 of 44 (4.5%). None of the 200 age- and sex-matched healthy controls was ICA positive (p < 0.05). Competitive anti-insulin antibodies (CIAA) were detected in 1 of 44 (2.5%) patients. First-phase insulin reserve (FPIR), stimulated insulin reserve (SIR), and glycosylated hemoglobin (GHB) levels were normal in the autoantibody-positive patients. Our data suggest that, like first-degree relatives of IDDM patients, CD patients are characterized by an increased prevalence of diabetes-related autoantibodies. Further follow-up is needed to determine whether the presence of these autoantibodies in nondiabetic CD patients predicts future IDDM.

Insulin secretion by pancreas of athymic mice injected with peripheral mononuclear cells from insulin-dependent diabetic patients

We studied the effect of peripheral blood mononuclear cells (PBMNC) from insulin-dependent diabetic (IDDM) children on the insulin secretion pattern of the pancreas from recipient athymic mice. PBMNC from healthy controls or IDDM patients in different stages of disease were injected into athymic mice. PBMNC from newly diagnosed IDDM children elicited basal nonfasting hyperglycemia and in vitro inhibition of the first and second phases of glucose-stimulated insulin secretion in recipient mice. Animals injected with cells from chronically IDDM children showed normoglycemia, abnormal tolerance to glucose, and inhibition of first-phase insulin secretion. Mitomycin C treatment of MNC from IDDM patients abolished insulin secretion inhibition in recipient mice. PBMNC from newly diagnosed and chronically IDDM patients showed positive anti-beta-cell cellular immune aggression. Mice injected with cells from patients during the remission period showed normoglycemia and no alteration of insulin secretion patterns. When relapsed to their former clinical stage, injection of the cells significantly inhibited first-phase glucose-induced insulin secretion in recipients. PBMNC from newly diagnosed IDDM patients were found to migrate to the pancreas of recipient mice preferably as compared with cells from controls. Cells from chronically IDDM patients cultured with concanavalin A (Con A) increased insulin secretion inhibition; despite this, cells from children during the remission period cultured with Con A failed to modify insulin secretion in recipients. These results show that injection of PBMNC from diabetic patients leads to insulin secretion impairment in recipient mice pancreas, and provide a basis for the study of mechanisms involved in the onset and modulation of anti-beta-cell cellular immune aggression induced by human PBMNC.

Baclofen, a gamma-aminobutyric acid-b receptor agonist, delays diabetes onset in the non-obese diabetic mouse

Glutamic acid decarboxylase (GAD) is the enzyme responsible for the synthesis of gamma-aminobutyric acid (GABA). GAD has been identified as a 64-kDa antigen expressed in pancreatic beta-cells, to which autoantibodies are generated prior to the onset of type 1 (insulin-dependent) diabetes mellitus. GAD may therefore be an initiating factor in beta-cell destruction. We administered baclofen, a GABA-B receptor agonist, to non-obese diabetic (NOD) mice in an attempt to down-regulate GAD expression and thereby reduce the incidence of diabetes. Twenty-four female NOD mice were given baclofen in their drinking water at a final dose of 50 mg/kg body weight daily from weaning to 30 weeks of age. Twenty-four sex- and litter-matched mice were used as controls. At 30 weeks there was no difference in the incidence of diabetes in the treated group compared with the controls. However, there was a significant delay in the onset of diabetes in the treated group (P < 0.001, parallelism test). The degree of insulitis and the GAD activity in the pancreas per mg of protein were unchanged by baclofen treatment with respect to controls. These results suggest that baclofen may be effective in delaying diabetes onset in NOD mice by stimulating GABA activity, as this neurotransmitter, localised in the islets, may modulate insulin secretion and the antigen expression associated with it.