A monoclonal antibody based enzyme-linked immunosorbent assay for the determination of GAD65, the smaller isoform of glutamic acid decarboxylase.

An enzyme-linked immunosorbent assay for GAD65, the smaller form of glutamic acid decarboxylase and an important autoantigen related to Type 1 diabetes, is described. The competitive binding assay is based on a monoclonal antibody specifically reactive with GAD65. The assay is suitable for quantification of this enzyme between 40 and 300 pg/microliter. The intraassay coefficients of variation (cv) are between 5.6% and 8.9% and the interassay cvs lie between 9.4% and 17.3%. The covalent binding of the antigen to magnetic beads as the solid phase makes the assay also applicable for quantification of GAD65 in tissue homogenates with a high concentration of detergent. The GAD65 content of islets isolated from newborn Lewis rat was detected to be 310 pg/islet. However, GAD65 was not detectable in mouse islets.