The association of immunoglobulin A, immunoglobulin G and anti‑cyclic citrullinated peptide antibodies with disease activity in seronegative rheumatoid arthritis patients

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. Materials and 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). Conclusion: 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.