Prokaryotic Expression of Bioactive Zinc Transporter 8 Antigens and Detection of Diabetes Specific Autoantibodies in a Single Dot Immunogold Filtration Assay.

Abstract

Type 1 diabetes mellitus is an autoimmune disease, and islet autoantibodies secreted by auto-reactive plasma cells are diagnostic indicators of the immune processes. Autoantibodies to zinc transporter 8 (ZnT8) have been identified as a novel reliable biomarker for the prediction, diagnosis, monitoring, and prognosis of autoimmune diabetes, complementing the panel of existing diagnostic autoantibodies. Although the enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay are the most frequently used testing methods, they do not allow simultaneous detection of multiple autoantibodies. Another obstacle is the cost of ZnT8 production for antibody assays. This study aimed to develop a cost-effective expression system for the production of two ZnT8 C-terminal fragments containing main ZnT8 antigen epitopes and establish an improved reliable and rapid assay for the detection of anti-ZnT8 antibodies with a potential to simultaneously measure multiple autoantibodies. The coding codons of the human ZnT8 were optimized for prokaryotic expression and the mutation was achieved using site-directed mutagenesis. A total of 42 newly diagnosed type 1 diabetes patients (16 males and 26 females) and 100 healthy controls (57 males and 43 females) were enrolled for sera. The dot immunogold filtration assay (DIGFA) was evaluated by comparing with ELISA as the "gold standard". Two ZnT8 antigens (arginine and tryptophan ZnT8 at position 325) were successfully produced. We established a rapid DIGFA method for the simultaneous detection of anti-ZnT8 antibodies, with the sensitivity, specificity, accuracy, Youden index, and positive and negative likelihood ratio being 64.3%, 96.4%, 85.7%, 0.607, 18.0, and 0.370, respectively, and the results did not significantly differ from those for ELISA (p = 0.22). These results demonstrate that the pColdII expression system is suitable for the production of bioactive ZnT8 antigens and that DIGFA can be a rapid, reliable, and highly specific method for the detection of ZnT8 antibodies, which can be potentially applied to identify a panel of diabetes-specific autoantibodies simultaneously.