title: A comparison between IgG- and IgA-class antibodies to cyclic citrullinated peptides and to modified citrullinated vimentin in early rheumatoid arthritis and very early arthritis.
abstract: OBJECTIVE
  Because of their slightly higher sensitivity, it has been argued that antibodies to modified citrullinated vimentin (anti-MCV) are superior to antibodies to cyclic citrullinated peptides (anti-CCP), while others claim that anti-CCP is preferable because of higher diagnostic specificity for rheumatoid arthritis (RA). We evaluated IgG- and IgA-class anti-MCV and anti-CCP as diagnostic and prognostic markers in early arthritis.
  
  
  METHODS
  Two Swedish arthritis populations were examined: 215 patients with early RA (≤ 12 months' duration) from the Swedish TIRA-1 cohort, and 69 patients with very early arthritis (≤ 3 months' duration) from the Kronoberg Arthritis Incidence cohort, in which 22% were diagnosed with RA. IgG anti-CCP and anti-MCV antibodies were analyzed with commercial kits. These tests were modified for IgA-class antibody detection. Results were related to disease course, smoking habits, and shared epitope status.
  
  
  RESULTS
  In the TIRA-1 cohort, occurrence of IgG anti-MCV and IgG anti-CCP showed a 93% overlap, although IgG anti-MCV had higher diagnostic sensitivity. Twenty-four percent tested positive for IgA anti-MCV compared to 29% for IgA anti-CCP. In the Kronoberg Arthritis Incidence cohort, 15% tested positive for IgG anti-MCV and 6% for IgA anti-MCV, compared to 10% positive for IgG anti-CCP and 3% positive for IgA anti-CCP, revealing that anti-CCP had higher diagnostic specificity for RA. As previously reported for IgA anti-CCP, IgA anti-MCV antibodies occurred in a small proportion of high-level IgG antibody-positive sera and were associated with a more aggressive disease course. Smokers were more often positive for antibodies to citrullinated proteins, most strikingly among the patients who were IgA anti-MCV-positive.
  
  
  CONCLUSIONS
  The occurrences of IgG-class anti-MCV and anti-CCP in early RA largely overlap. The sensitivity of anti-MCV is slightly higher, while the diagnostic specificity is higher for anti-CCP. In both instances a positive test predicts an unfavorable disease course, possibly slightly more so for anti-MCV. Although associated with a more active disease over time, IgA-class anti-CCP or anti-MCV do not add any diagnostic advantage.
authors: Rheumatology Clinic, Falun Hospital, Falun, Sweden. anna.svard@ltdalarna.se
authors: Anna
authors: A
authors: Svärd
authors: Alf
authors: A
authors: Kastbom
authors: Maria K
authors: MK
authors: Söderlin
authors: Åsa
authors: Å
authors: Reckner-Olsson
authors: Thomas
authors: T
authors: Skogh
mesh_terms: D001168:Arthritis / Q000175:diagnosis / Q000453:epidemiology / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000453:epidemiology / Q000276:immunology*; D015331:Cohort Studies; D003937:Diagnosis, Differential; D018450:Disease Progression; D000939:Epitopes; D005500:Follow-Up Studies; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007074:Immunoglobulin G / Q000097:blood*; D015994:Incidence; D010456:Peptides, Cyclic / Q000276:immunology*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D012907:Smoking / Q000009:adverse effects; D013548:Sweden / Q000453:epidemiology; D014746:Vimentin / Q000276:immunology*
chemical_list: D000939:Epitopes; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D010456:Peptides, Cyclic; D014746:Vimentin; C487763:cyclic citrullinated peptide