Calprotectin (a major S100 leucocyte protein) predicts 10-year radiographic progression in patients with rheumatoid arthritis

Background: Plasma levels of calprotectin, a major S100 leucocyte protein, are cross-sectionally associated with clinical and laboratory markers of inflammation and with radiographic damage in rheumatoid arthritis (RA). High amounts of calprotectin are found in synovial fluid from patients with RA. Objective: To examine whether calprotectin might be an independent predictor of joint destruction over time. Methods: 124 patients with RA were assessed at baseline and after 10 years with inflammatory markers (calprotectin, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR)), serological variables (antibodies to cyclic citrullinated peptide (anti-CCP), IgA rheumatoid factor (RF) and IgM RF) and radiographic and clinical assessments of joint damage (hand radiographs and Rheumatoid Arthritis Articular Damage (RAAD) score). Progression of radiographic damage was assessed according to the van der Heijde modified Sharp score. Results: At both examinations the highest calprotectin levels were found in patients positive for anti-CCP, IgA and IgM RF. Calprotectin had moderate to good correlations with inflammatory and serological markers (r=0.41-0.67). Patients with normal baseline calprotectin levels had a lower degree of joint damage. High univariate associations were found between baseline calprotectin levels and progression in the Sharp score as well as the RAAD score. Baseline calprotectin was independently associated with progression in the Sharp score and with the RAAD score in multiple linear regression analyses, including baseline levels of CRP, ESR, anti-CCP in addition to demographic variables. Conclusion: Calprotectin was an independent predictor of clinical and radiographic joint damage after 10 years. These findings support the proposal that calprotectin may be a prognostic biomarker for erosive disease in patients with RA