RESEARCH ARTICLE Crossreactive Autoantibodies Directed against Cutaneous and Joint Antigens Are Present in Psoriatic Arthritis

. These authors contributed equally to this work. Background: Psoriatic arthritis (PsA) is a chronic inflammatory disease of unknown origin, characterized by erosions and new bone formation. Diagnosis of PsA is mainly clinical and there are no biomarkers available. Moreover in PsA autoantibodies have not been described so far. Indeed an autoimmune origin has been suggested but never proven. Aim of the study was to investigate the possible presence of autoantibodies typically associated with PsA. Methods:We used pooled IgG immunoglobulins derived from 30 patients with PsA to screen a random peptide library in order to identify disease relevant autoantigen peptides. Results: Among the selected peptides, one was recognised by nearly all the patients ’ sera. The identified peptide (PsA peptide: TNRRGRGSPGAL) shows sequence similarities with skin autoantigens, such as fibrillin 3, a constituent of actin microfibrils, desmocollin 3, a constituent of the desmosomes and keratin 78,