[Comparative studies in patients with seropositive and seronegative chronic polyarthritis using the solid-phase ELISA...

Sera from patients with definite or classic rheumatoid arthritis (RA) were tested for their reactivity to the Fc fragment of human IgG using a solid phase Elisa with specificity for rheumatoid factors (RF) of classes IgM, IgG and IgA. For all RF classes tested the Elisa was reproducible both within and between different assays. IgM-RF-serum concentrations correlated well to the Waaler Rose titers (r = 0.88, p less than 0.001). No difference in RF-serum concentrations of any Ig class could be detected between patients with seronegative erosive RA and controls. In the sera of seropositive RA patients, however, significantly higher concentrations of all RF-classes were observed (IgM RF: seropos. x- = 454 +/- 805 IU/ml, seroneg. x- = 1.3 +/- 0.6 IU/ml, p less than 0.0005; IgG RF: seropos. x- = 17 +/- 28 U/ml, seroneg. x- = 2 +/- 1.8 U/ml, p less than 0.005; IgA RF: seropos. x- = 300 +/- 577 U/ml, seroneg. x- = 4 +/- 3.6 U/ml, p less than 0.005). In our seronegative RA patients at least one antigen of the HLA-B5 CREG could be observed. Together with the well documented frequency of HLA-DR4 in patients with seropositive RA, this finding points to possible, genetically determined regulative mechanisms, which control the presence of autoantibodies within rheumatoid arthritis.