Islet Autoantibody Analysis: Radioimmunoassays.

Type 1 diabetes (T1D) is a chronic inflammatory disease, caused by the immune mediated destruction of insulin-producing β-cells in the islets of the pancreas (Ziegler and Nepom, Immunity 32(4):468-478, 2010). Semiquantitative assays with high specificity and sensitivity for T1D are now available to detect antibodies to the four major islet autoantigens: glutamate decarboxylase (GADA) (Baekkeskov et al., Nature 347(6289):151-156, 1990), the protein tyrosine phosphatase-like proteins IA-2 (IA-2A) and IA-2β (Notkins et al., Diabetes Metab Rev 14(1):85-93, 1998), zinc transporter 8 (ZnT8A) (Wenzlau et al., Proc Natl Acad Sci U S A 104(43):17040-17045, 2007), and insulin (IAA) (Palmer, Diabetes Metab Rev 3(4):1005-1015, 1987). More than 85 % of cases of newly diagnosed or future T1D can be identified by testing for antibodies to GADA and/or IA-2A/IAA, with 98 % specificity (Bingley et al., Diabet Care 24(2):398, 2001). Overall, radioimmunoassay (RIA) is considered the de facto gold standard format for the measurement of T1D autoantibodies (Bottazzo et al., Lancet 2(7892):1279-1283, 1974; Schlosser et al., Diabetologia 53(12):2611-2620, 2010). Here we describe current methods for autoantibody measurement using RIA. These fluid phase assays use radiolabeled ligands and immunoprecipitation to quantify autoantibodies to GAD, IA-2, ZnT8, and insulin (Bonifacio et al., J Clin Endocrinol Metab 95(7):3360-3367, 2010; Long et al., Clin Endocrinol Metab 97(2):632-637, 2012; Williams et al., J Autoimmun 10(5):473-478, 1997).