Background/Purpose:  Juvenile dermatomyositis (JDM), a systemic autoimmune vasculopathy, and juvenile idiopathic arthritis (JIA) are representative rheumatic diseases in children. However the pathogenesis of these diseases are still poorly defined. More research in this area is required on identification of disease-specific biomarkers for clinical assessment. Anti-endothelial cell antibodies (AECA) have been detected in rheumatic diseases such as vasculitis. We aimed to detect target antigens for AECA in patients with pediatric rheumatic diseases comprehensively by proteomics and to investigate their clinical significance.

Methods:  To comprehensively detect target antigens for AECA, we separated proteins extracted from human aortic endothelial cells by two-dimensional electrophoresis and then transferred them onto membranes. Autoantigens that were positive only in pediatric rheumatic disease sera from three patients with JDM and two patients with JIA but not in healthy children sera were detected by western blotting. The detected proteins were identified by peptide mass finger-printing. Bound IgG antibodies to antigens were detected using standard methods.

Results: We successfully identified 738 proteins out of eighteen protein spots that were candidate targets of AECA in pediatric rheumatic diseases. Antibodies appeared to target proteins with specific functions, e.g., ATP-related proteins (37%), muscle-related proteins (19%), calcium regulated protein and/or calcium binding proteins (13%) and redox related proteins (10%). Among the 140 muscle-related proteins were myosin light polypeptide 6 (MYL6) and myosin-9 (MYH9). IgG autoantibodies to MYL6 were detected in 20% of the patients with JDM (n=61) using ELISA assays. However, 50% of the untreated JDM patients with active disease (n=10) had anti-MYL6 antibodies, in contrast to 12% (p<0.05) of the patients with JIA (n=17) and in 16% (p=0.05) of control children (n=25). IgG autoantibodies to MYH9 were detected in 31% of the active patients with JDM (n=35), (50% of the untreated JDM patients with active disease), in comparison to 27% of the patients with JIA (n=15) and 12% (p<0.05) of control children. Among the 74 redox related proteins were peroxiredoxins (Prxs). IgG autoantibodies to Prx2 were detected in 24% of the active patients with JDM (n=25), (30% of the untreated JDM patients with active disease) and in 20% of the active patients with JIA (n=10), (40% of the untreated JIA patients with active disease) in contrast to 0% (p<0.05) of control children (n=20). Furthermore one of the identified 738 proteins was Von Willebrand Factor (vWF). IgG autoantibodies to vWF were detected in 20% of the active patients with JIA (40% of the untreated JIA patients with active disease), in comparison to 4% of the active patients with JDM and 0% of control children.

Conclusion:  IgG antibodies to MYL6, MYH9, Prx2 and vWF were detected in the sera from patients with pediatric rheumatic diseases, respectively. These antibodies were directed against autoantigens correlated with skeletal muscle function, redox functions and the coagulation/fibrinolytic systems and may be useful markers for pediatric rheumatic diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/novel-autoantigens-for-anti-endothelial-cell-antibodies-in-pediatric-rheumatic-diseases-identified-by-proteomics/