Identification of Unique Antigenic Determinants in the Amino Terminus of IA-2 (ICA512) in Childhood and Adult Autoimmune Diabetes: New Biomarker Development

Abstract

OBJECTIVEThe characterization of diverse subtypes of diabetes is a dynamic field of clinical research and an active area of discussion. The objective of this study was to identify new antigenic determinants in the neuroendocrine autoantigen IA-2 (ICA512) and assess whether circulating autoantibodies directed to new IA-2 epitopes identify autoimmune diabetes in young and adult populations with diabetes.RESEARCH DESIGN AND METHODSClinically diagnosed patients with type 2 diabetes (n = 258; diabetes duration: 0.01–31 years) were evaluated using a new biomarker detecting autoantibodies directed to the extracellular domain of the neuroendocrine autoantigen IA-2 (IA-2ec). The proportion of IA-2ec autoantibodies was also evaluated in newly diagnosed patients with type 1 diabetes (n = 150; diabetes duration: 0.04–0.49 years). In addition, IA-2 (intracellular domain), GAD65, and zinc transporter 8 autoantibodies were assayed.RESULTSIA-2ec autoantibodies were detected in patients with type 1 diabetes and, surprisingly, in 5% of patients with type 2 diabetes without serologic responses to other IA-2 antigenic epitopes or other islet autoantigens. We also assessed the ability of IA-2ec–derived peptides to elicit CD4+ T-cell responses by stimulating peripheral blood mononuclear cells from patients with type 1 diabetes (n = 18) and HLA-matched healthy subjects (n = 13) with peptides and staining with the peptide/DQ8-specific tetramers, observing disease-associated responses to previously unreported epitopes within IA-2ec.CONCLUSIONSWe developed a new antibody biomarker identifying novel antigenic determinants within the N terminus of IA-2. IA-2ec autoantibodies can be detected in patients with type 1 diabetes and in a subgroup of adult autoimmune patients with type 2 diabetes phenotype negative for conventional islet autoantibody testing. These observations suggest that islet autoimmunity may be more common in clinically diagnosed type 2 diabetes than previously observed.

Increasing ICA512 autoantibody titers predict development of abnormal oral glucose tolerance tests

“…The use of IA-2 tetramers may also be useful to better understand how changes in T-cells responses over time correlate with autoantibody responses. 21 In conclusion, we demonstrate that autoantibody titers, particularly of ICA512, correlate with abnormal OGTT results in subjects at risk for disease. Future studies will investigate the utility of changes in autoantibody titers to predict outcomes in prevention studies of type 1 diabetes.…”

“…Finally, given our observations of increased rates of abnormal OGTTs with increased ICA512 titers, it may be useful to utilize ICA512 titers in a post‐hoc fashion to analyze outcomes in subjects from ongoing clinical trials that look to prevent development of dysglycemia or type 1 diabetes. The use of IA‐2 tetramers may also be useful to better understand how changes in T‐cells responses over time correlate with autoantibody responses …”

Autoantibodies Directed Toward a Novel IA-2 Variant Protein Enhance Prediction of Type 1 Diabetes

“…T1D-associated AAb to IA-2 are mainly directed against epitopes within the cytoplasmic domain (11). Recently, we described antibody responses to the extracellular domain of IA-2 in subjects with T1D (12).…”

Comment on Mulukutla et al. Autoantibodies to the IA-2 Extracellular Domain Refine the Definition of “A+” Subtypes of Ketosis-Prone Diabetes. Diabetes Care 2018;41:2637–2640

“…Even these illustrative figures show that the constructs used were cleaved as the sera reacted with both the full-length and cleaved products (although the existence of such products was not discussed). The recent article by Mulukutla et al (1) suffers from the same issues as it completely adopted the methodology that was used in the abovementioned studies (2,3).…”