To explore the relationship between serum immunoglobulin (Ig) levels and the positivity rate for auto- antibodies in patients with rheumatoid arthritis (RA).
The levels of immunoglobulins (IgG, IgM, IgA) and rheumatoid factor (RF) were measured using Olympus AU600 system, and indirect immunofluorescence and immunoblotting methods were employed respectively for detecting the autoantibodies in the serum from 40 RA patients and 30 normal adults. Statistical analysis of the relation between the Ig levels and autoantibodies was performed.
Compared with normal control group, significantly higher serum IgA, IgG and IgM levels were detected in RA patients (P < 0.01), and at least one autoantibody was present in the serum sample from 26 out of the 40 RA patients, who had the highest RF positivity rate of 20% (8 cases). The serum IgA level in autoantibody-positive patients was significantly higher than that in autoantibody-negative ones (P < 0.01), and in the 18 patients with serum IgA level beyond the normal range, 15 (83.3%) were positive for autoantibody, while in the 22 patients with normal serum IgA level, the autoantibody positivity rate was only 50% (11/22), showing significant difference (P < 0.05).
Serum immunoglobulins A (IgA) level is closely associated with the positivity rate for autoantibodies in RA patients, and RA patients with serum IgA level beyond the normal range was more likely to be positive for the autoantibodies.