IgA isotype rheumatoid factor in rheumatoid arthritis: clinical implications

To study the clinical, biological and radiological characteristics of RA with a predominant increase of IgA isotype rheumatoid factor (IgA-RF) over IgM-RF.

The presence of IgA-RF was determined by a sandwich-type ELISA with an antibody against the human IgA used to capture the immunoglobulin. Associated RF activity was revealed with a peroxidase-conjugated human IgG Fc fragment. Forty-nine RA patients were studied, of whom 19 had an increase in IgA-RF (38%). The control group comprised 30 RA patients without IgA-RF.

None of the patients had isolated IgA-RF. In the selected 19 RA patients, the OD of IgA-RF (0.971 +/- 0.62 U) was higher than the IgM-RF (mean OD: 0.675 +/- 0.522 U). A statistically significant correlation was found between IgA-RF and IgM-RF (r = 0.64, p < 0.0001). No correlation was noted between the IgA concentration and the IgA-RF titer. The two groups were comparable for age, disease duration, sex ratio and previous DMARD use. We observed that patients with RA associated with increased IgA-RF more often had the sicca syndrome, but no other extra-articular features. RA patients with IgA RF also had more erosive disease: the mean Larsen score at the hand and wrist was 76 (SD = 68) versus 54 (SD = 60) in the controls, p < 0.02. Replacement surgery for the hip or knee was necessary in 47% of the RA patients with IgA-RF, versus 13% in the controls, p < 0.01. No association of IgA-RF with disease activity was noted.

Our study showed that RA patients with a predominant increase of IgA-RF had a more erosive disease and a high frequency of associated sicca syndrome.