Auto-reactions, autoimmunity and psoriatic arthritis.

Evidence from the literature suggests that autoimmune processes may drive features of psoriatic arthritis (PsA). Such hypothesis is supported by the evidence that class I major histocompatibility complex (MHC) genes are associated with susceptibility to develop PsA and auto-reactive cells, such as CD8 T cells, T helper (h) 17 and plasma cells, have been demonstrated in PsA. However, no autoantigens have ever been demonstrated in PsA. The presence of a new autoantibody system, anti-carbamylated protein (anti-CarP) antibodies, has been identified in rheumatoid arthritis (RA) patients. These autoantibodies have been associated with a worse disease progression independent of anti-citrulline antibodies (ACPA). In PsA, anti-CarP antibodies have not been evaluated yet. We aimed at analyzing, for the first time, the anti-CarP antibodies in sera of patients with active PsA who were negative for ACPA in order to explore both their presence and their relationship with disease activity. A total of 70 individuals, 30 patients with diagnosis of PsA (according to CASPAR criteria) and 40 healthy controls (HC) were enrolled. We found significantly increased levels of anti-CarP antibodies in PsA patients compared with HC (P<0.0001). Our findings indicate that anti-CarP antibodies are detectable with high specificity and sensibility in PsA patients suggesting an autoimmune background of PsA. Anti-CarP antibodies can be useful in improving the diagnosis of PsA and are correlated with disease activity.