Evaluation of the Performance of an Indirect Immunofluorescence Assay for the Detection of Anti-MDA5 Antibodies.

Anti-melanoma differentiation-associated protein 5 (MDA5) antibody (Ab) positive dermatomyositis (anti-MDA5 DM) is a rare systemic autoimmune disease; further, its prognosis can be rapidly fatal due to pulmonary involvement. The identification and quantification of anti-MDA5 Abs, which serve as a highly specific biomarker of the disease, is a critical step for the establishing of both the diagnosis and monitoring of the disease's activity. The development of a simple, fast, low-cost, and specific detection system of anti-MDA5 Ab is therefore highly desirable for the purposes of routine laboratory diagnosis. Here, we developed a human cell line that stably expresses MDA5 and evaluated its analytical performance in order to detect anti-MDA5 Abs by the utilization of indirect immunofluorescence (IIF). Serum samples from 23 anti-MDA5 DM patients and 22 anti-MDA5 Abs negative myositis readings, which were obtained at time of diagnosis, were analyzed by IIF on MDA5-transfected cells. The results were compared with those obtained with specific semi-quantitative (immunodot) and quantitative (ELISA) assays. A specific cytoplasmic pattern was found solely with the sera of anti-MDA5 DM patients. The sensitivity and specificity of IIF on MDA5-transfected cells were 96% and 100%, respectively, compared with ELISA. The anti-MDA5 Abs titers that were determined by this approach were consistent with the quantitative results obtained by ELISA. Baseline concentrations of anti-MDA5 Abs, either by ELISA or IIF, were not significantly different between surviving and deceased patients; further, they did not differ significantly according to clinical phenotypes. Overall, an IIF cell-based assay constitutes a simple, fast, and low-cost approach to identify and quantify anti-MDA5 Abs; moreover, it is as efficient as ELISA.