Rheumatoid factor associated with a secretory component in rheumatoid arthritis

The authors' objective was to study the serum secretory immunoglobulin A (S-IgA) concentration and the presence of rheumatoid factor (RF) complexed with a secretory component (SC) in rheumatoid arthritis (RA). Sixty-three RA patients were studied. There were 49 healthy subjects in the control group. The S-IgA concentration and the presence of IgA isotype RF were determined by ELISA in the serum. The presence of SC complexed to RF (SC-RF) was studied by a sandwich-type enzyme-linked immunosorbent assay with an antibody against the SC used to capture S-immunoglobulin, and associated anti-globulin activity was revealed with a peroxidase-conjugated human IgG Fc fragment. We observed a significant increase in S-IgA in RA (mean 76.8 micrograms/ml +/- 152.9 S.D.), as compared to controls (mean 13.6 micrograms/ml +/- 11.9 S.D.) (P < 0.01). Forty-one per cent of RA patients presented a S-IgA concentration above the upper threshold, but we did not observe any association with disease activity. S-IgA concentration was correlated with the presence of IgA-RF. Twenty-seven RA patients had a positive SC-RF versus one in the control group (P < 0.01). The presence of SC-RF was associated with an increased S-IgA concentration (P < 0.0001), and the presence of RF-IgA (P < 0.002). However, no association with disease activity was noted. Our study showed that serum S-IgA was increased in RA, and that part of the RF were complexed with SC. These results suggest contribution of mucosal lymphocytes in the pathogenesis of RA.