title: The association of immunoglobulin A, immunoglobulin G and anti-cyclic citrullinated peptide antibodies with disease activity in seronegative rheumatoid arthritis patients.
abstract: BACKGROUND
  Rheumatoid arthritis (RA) is a common autoimmune disease that is associated with progressive disability, systemic complications, and early death. The present study was aimed to investigate the level of immunoglobulin G (IgG) and IgA isotypes and anti-cyclic citrullinated peptide (CCP) antibody and to assess their association with disease severity based on disease activity score (DAS-28) in patients with IgM rheumatoid factor (IgM-RF) negative RA.
  
  
  METHODS
  In this cross-sectional study, 62 RA patients with IgM-RF negative were assessed. Radiographs were obtained for all RA patients. The RF (IgG, and IgA) and anti-CCP were measured by using the enzyme-linked immunosorbent assay. Values of cut-off points over 15 UI/mL for IgA IgA-RF, 20 UI/mL for IgG-RF and over 20 units for anti-CCP were considered positive. DAS-28 score was compared in regard to the IgA-RF and IgG-RF and anti-CCP positivity using Mann-Whitney test.
  
  
  RESULTS
  DAS-28 score in IgA-RF positive was significantly higher than IgA-RF negative (mean score, 6.03 ± 0.33 vs. 5.44 ± 0.76 respectively, P = 0.035). In IgG-RF positive patients, DAS-28 score was similar to patients with IgG-RF negative (5.64 ± 0.59 vs. 5.46 ± 0.78 respectively, P = 0.396). Furthermore, in patients with anti-CCP positive DAS-28 score was significantly higher than patients with anti-CCP negative (5.72 ± 0.61 vs. 5.38 ± 0.79 respectively, P = 0.049).
  
  
  CONCLUSIONS
  Findings indicated that there was a significant association between the amounts of IgA and anti-CCP with severity of disease in RF negative RA patients while there was no significant association between the amounts of IgG and severity of RA disease.
authors.affiliation: Department of Rheumatology, Alzahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mansoor
authors.initials: M
authors.lastname: Karimifar
authors.affiliation: Department of Rheumatology, Noor and Aliasghar Hospital, Isfahan, Iran.
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Moussavi
authors.affiliation: Department of Internal Medicine, Alzahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mehran
authors.initials: M
authors.lastname: Babaei
authors.affiliation: Department of Epidemiology, School of Health and Nutrition, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Akbari
keywords: Disease activity score-28; immunoglobulin A; immunoglobulin G; rheumatoid factor; seronegative rheumatoid arthritis