Background Systemic sclerosis (SSc) is a systemic autoimmune disease that clinically manifests as progressive fibrosis of the skin and internal organs. Antinuclear autoantibodies can be detected in over 90% of patients. The three most frequent SSc-specific autoantibodies, anti-centromere antibodies (ACAs), anti-topoisomerase antibodies (ATAs), and anti-RNA polymerase III antibodies (ARAs) are found in over 50% of SSc patients. However, in many patients specificities of autoantibodies are not known. We have recently conducted high-content autoantibody profiling studies of SSc, systemic autoimmune diseases (AID), and healthy controls and found in addition to diagnostic autoantibodies novel SSc-associated autoantibodies.
Objectives In this study, novel SSc-associated autoantibody marker candidates were re-evaluated using complementary autoantibody measurement platforms and assay formats. Autoantibody specificities were analyzed for their association with clinical subsets in independent samples.
Methods An undirected autoantibody screening approach against 6,912 recombinant human proteins.was undertaken in serum samples of 100 SSc patients and related overlap syndromes. Thirty % of SSc patients were previously tested negative for ACA and ATA. The control groups comprised 794 AID patients (systemic lupus erythematosus, rheumatoid arthritis/RA, early RA, ankylosing spondylitis) and 343 healthy controls. Seven antigens were selected based on univariate statistics, frequency and high reactivity in SSc for which panel tests were developed. The specificity and sensitivity of these candidate antigens was analyzed in additional SSc and AID samples.
Results In the test cohort, 40% of SSc patients were anti-CENPB and 40% were anti-topoI positive. The frequency of seven candidate SSc-autoantigens ranged from 32.2% to 11% in the SSc cohort, of which KDM6B and BICD2 showed the highest frequency in SSc (32.2% and 31.1%, respectively). Five autoantibody targets CENPB, KDM6B, BICD2 and two additional antigens (antigen IDs PASSC3, PASSC4) were positively associated with limited SSc, while anti-topoI and three autoantibodies (IDs PASSC5, PASSC6, and PASSC7) were more abundant in diffuse SSc. Fifty percent of ACA and ATA-negative SSc patients had autoantibodies against the seven novel autoantigen candidates. The genes encoding for these proteins were found being enriched in pathways of histone modifications and chromatin remodeling suggesting their involvement in epigenetic processes.
Conclusions Using a combination of Luminex bead-arrays for high-throughput autoantibody profiling and complementary Assay development provides an attractive route to discover and verify novel SSc-associated autoantibodies. By measuring 7 antigens the number of autoantibody positive SSc patients increased from 68% to 84%. Interestingly, genes encoding these novel autoantigens have been implicated in epigenetic processes.
Disclosure of Interest P. Budde Employee of: Protagen AG, H.-D. Zucht Employee of: Protagen AG, J. Schulte-Pelkum Employee of: Protagen AG, D. Wirtz Employee of: Protagen AG, P. Schulz-Knappe Employee of: Protagen AG, K. Conrad: None declared, N. Hunzelmann: None declared, M. Schneider: None declared