Mature high-affinity immune responses to (pro)insulin anticipate the autoimmune cascade that leads to type 1 diabetes.

Children at risk for type 1 diabetes can develop early insulin autoantibodies (IAAs). Many, but not all, of these children subsequently develop multiple islet autoantibodies and diabetes. To determine whether disease progression is reflected by autoantibody maturity, IAA affinity was measured by competitive radiobinding assay in first and subsequent IAA-positive samples from children followed from birth in the BABYDIAB cohort. IAA affinity in first positive samples ranged from less than 10(6) l/mol to more than 10(11) l/mol. High affinity was associated with HLA DRB1*04, young age of IAA appearance, and subsequent progression to multiple islet autoantibodies or type 1 diabetes. IAA affinity in multiple antibody-positive children was on average 100-fold higher than in children who remained single IAA positive or became autoantibody negative. All high-affinity IAAs required conservation of human insulin A chain residues 8-13 and were reactive with proinsulin. In contrast, most lower-affinity IAAs were dependent on COOH-terminal B chain residues and did not bind proinsulin. These data are consistent with the concept that type 1 diabetes is associated with sustained early exposure to (pro)insulin in the context of HLA DR4 and show that high-affinity proinsulin-reactive IAAs identify children with the highest diabetes risk.

Stratification of type 1 diabetes risk on the basis of islet autoantibody characteristics.

Family history of type 1 diabetes and autoantibodies to the islet antigens insulin (IAA), glutamate decarboxylase (GADA), and the protein tyrosine phosphatase-like protein IA-2 (IA-2A) are strong predictors of type 1 diabetes, but the rate of progression to diabetes in multiple islet autoantibody-positive relatives varies widely. We asked whether detailed characterization of islet autoantibodies that included determination of titer, epitope specificity, and IgG subclass would improve diabetes prediction in a large cohort of autoantibody-positive relatives. The study shows a strong association between risk and high titer, broad antibody responses to IA-2 and insulin. The highest risks were associated with high-titer IA-2A and IAA, IgG2, IgG3, and/or IgG4 subclass of IA-2A and IAA, and antibodies to the IA-2-related molecule IA-2beta. Using models based on these antibody characteristics, autoantibody-positive relatives can be classified into groups with risks of diabetes ranging from 7 to 89% within 5 years.

Elimination of dietary gluten does not reduce titers of type 1 diabetes-associated autoantibodies in high-risk subjects.

OBJECTIVE: Removal of the dietary wheat protein gluten protects against autoimmune diabetes in animal models. Furthermore, elimination of dietary gluten reduces the frequency of type 1 diabetes in patients with celiac disease. Herein we test the hypothesis that gluten is the driving antigen for type 1 diabetes-associated islet autoimmunity. RESEARCH DESIGN AND METHODS: Seven autoantibody-positive, first-degree relatives of patients with type 1 diabetes were placed on a gluten-free diet for 12 months followed by gluten reexposure for 12 months. Gliadin antibodies as well as the diabetes-related antibodies insulin autoantibody (IAA), GAD antibody (GADA), and tyrosin phosphatase IA2 antibody (IA-2A) were measured every 3 months; oral glucose tolerance tests were performed every 6 months. Changes in autoantibody titers were compared with those observed in a matched historical cohort. RESULTS: A reduction in IgG gliadin antibody titers was observed during the gluten-free period, but titers of diabetes-associated autoantibodies changed independently of gluten exposure. Type 1 diabetes-associated islet autoantibody levels at the end of the gluten-free diet period were not significantly different from those before commencement of the diet (P = 0.2) or at the end of the gluten reexposure period (P = 0.4). Changes in individual subjects were identified, but no differences were noted between the gluten-free and the gluten re-exposure periods, and the changes were similar to those observed in the historical control cohort (P = 1.0). Major titer reductions (>50%) in the gluten-free period were observed in only one subject for all antibodies. Type 1 diabetes developed in this subject and in a second subject during the gluten reexposure period. CONCLUSIONS: The findings do not support the hypothesis that gluten is a driving antigen in type 1 diabetes.

Two distinctly HLA-associated contiguous linear epitopes uniquely expressed within the islet antigen 2 molecule are major autoantibody epitopes of the diabetes-specific tyrosine phosphatase-like protein autoantigens.

The related tyrosine phosphatase-like proteins islet Ag (IA)-2 and IA-2beta are autoantigens of type 1 diabetes in humans. Autoantibodies are predominantly against IA-2, and IA-2-specific epitopes are major autoantibody targets. We used the close homology of IA-2 and IA-2beta to design chimeras and mutants to identify humoral IA-2-specific epitopes. Two major IA-2 epitopes that are absent from the related autoantigens IA-2beta and IA-2Delta 13 splice variant ICA512.bdc were found contiguous to each other within IA-2 juxtamembrane amino acids 611-620 (epitope JM1) and 621-630 (epitope JM2). JM1 and JM2 are recognized by sera from 67% of patients with IA-2 Abs, and relatives of patients with type 1 diabetes having Abs to either JM epitope had a >50% risk for developing type 1 diabetes within 6 years, even in the absence of diabetes-associated HLA genotypes. Remarkably, the presence of Abs to one of these two epitopes was mutually exclusive of the other; JM2 Abs and not JM1 Abs were found in relatives with HLA DR3/4, DR4/13, or DR1/4 genotypes; and the binding of autoantibodies to the JM2 epitope, but not the JM1 epitope, markedly affected proteolysis of IA-2. This is a unique demonstration of HLA-associated B cell responses to epitopes within a single autoantigen in humans and is consistent with modification of Ag processing by specific Ab-influencing peptide presentation by HLA molecules.