Detection of autoantibodies to the diabetes-associated antigen IA-2 by a sensitive enzyme-linked immunosorbent assay

The tyrosine phosphatase like protein IA-2 is an important autoantigen in i nsulin-dependent diabetes mellitus (type 1 diabetes). Autoantibodies to IA- 2 (IA-ZA) are present in the serum of patients with type 1 diabetes even be fore the onset of the disease. Previously, we reported on a radioimmune ass ay to detect IA-ZA, using E. coil-derived I-125-labelled IA-2 as antigen. A lthough this assay could be shown to be equivalent to the common reference method for IA-ZA detection (radioligand assays using in vitro synthesised S -35-methionine labelled antigen), the disadvantages of both assays with res pect to synthesis and handling of the radioactive antigen limit their use i n routine labarotories. In this study, we have evaluated a non-radioactive enzyme-linked immunosorbent assay (ELISA) for the simple detection of IA-ZA . We report on an ELISA where the biotinylated intracytoplasmic part of IA- 2 (IA-2ic) is captured on streptavidin-coated plates. The sensitivity of th e ELISA was similar to the validated radioligand assay, as it detected 47 o f 69 (69%) patients with type 1 diabetes as compared to 46 of 68 (67%) with the reference method for IA-ZA detection (radioligand assays using in vitr o synthesised 35S-methionine labelled antigen). Only 2 of 50 (4 %) patients with autoimmune thyroid disease and 1 of 114 (1 %) healthy controls were d etected in the ELISA, confirming specificity. There was a significant corre lation between the ELISA and the radioligand assay (r = 0.64, p < 0.001). W e conclude that this ELISA is suitable to detect IA-ZA in the serum of pati ents with type 1 diabetes with a similar sensitivity and specificity to the radioligand assay. This ELISA will allow rapid and simple measurement of I A-ZA where the radioligand assay is inconvenient or not available.