Calprotectin (a major leucocyte protein) is associated with the levels of anti-CCP and rheumatoid factor in a longitudinal study of patients with very early rheumatoid arthritis.

BACKGROUND: Calprotectin is a major granulocyte and monocyte protein, and plasma levels of calprotectin are strongly associated with inflammation in patients with rheumatoid arthritis (RA). OBJECTIVE: To explore the associations between calprotectin and serological, inflammatory, and clinical assessments in a longitudinal study of patients with very early RA. PATIENTS AND METHODS: In 61 RA patients (77% females, mean age 57.9 years, disease duration 132 days), laboratory and clinical assessments were performed at baseline and after 3, 6, and 12 months. RESULTS: Calprotectin levels were higher in patients positive vs. negative for anti-cyclic citrullinated peptide (anti-CCP), immunoglobulin M rheumatoid factor (IgM-RF), and IgA-RF (p<0.001-0.05). The 1-year averaged level of calprotectin correlated significantly with the mean levels of these three serological markers (p<0.05). In multiple regression analyses, adjusting for age, sex, and disease duration, calprotectin was associated with anti-CCP (p = 0.045), and both calprotectin and erythrocyte sedimentation rate (ESR) were associated with IgM-RF (p = 0.003 and 0.03, respectively). Calprotectin correlated significantly with the inflammatory markers at all examinations [C-reactive protein (CRP); r = 0.60-0.70, p<0.001, ESR; r = 0.55-0.57, p<0.001] as well as with the 28-joint disease activity score (DAS28; r = 0.28-0.33, p<0.05). CONCLUSION: This is the first study that shows significant associations between the levels of calprotectin and anti-CCP, IgA-RF, and IgM-RF in very early RA. In addition, significant correlations were found between calprotectin and markers of disease activity.