To compare the histological characteristics of the synovium between seropositive and seronegative rheumatoid arthritis (RA), synovial tissue was obtained from 19 patients with rheumatoid factor-positive (RF+) RA, 11 with rheumatoid factor-negative (RF-)RA and 11 non-RA controls.
There were no differences in the frequency of each histological feature or histological scores between RF+ and RF-RA. However, significant differences in the frequency of histological findings such as lining cell proliferation and inflammatory cell infiltration were found both between RF+ RA and non-RA controls, and between RF-RA and non-RA controls. Analysis of clinical parameters and histology in all RA patients revealed that the level of serum C-reactive protein and the erythrocyte sedimentation rate were directly correlated with the inflammatory cellular infiltration score. Immunohistological staining using a monoclonal antibody against IgM rheumatoid factor (RF) was positive in some plasma cells in the synovium of both RF+ and RF-RA patients, while no IgM-RF-positive cells were observed in the synovium of non-RA controls.
RF serostatus does not necessarily reflect the histology of synovial inflammation.