title: 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.
abstract: 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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway. hbham@online.no
authors.forename: H B
authors.initials: HB
authors.lastname: Hammer
authors.forename: E A
authors.initials: EA
authors.lastname: Haavardsholm
authors.forename: T K
authors.initials: TK
authors.lastname: Kvien
mesh_terms: D001172:Arthritis, Rheumatoid / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood*; D039841:Leukocyte L1 Antigen Complex / Q000097:blood*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000097:blood; D012217:Rheumatoid Factor / Q000097:blood*
chemical_list: D015415:Biomarkers; D007070:Immunoglobulin A; D007075:Immunoglobulin M; D039841:Leukocyte L1 Antigen Complex; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012217:Rheumatoid Factor