To investigate the significance of IgG rheumatoid factors (IgG RF) in the pathogenesis of rheumatoid arthritis (RA), and to determine the specificity of IgG subclasses binding with IgG RF in RA (RA IgG RF) compared to IgG RF in normal subjects (NS IgG RF).
The reactivities of RA IgG RF and NS IgG RF for various IgG subclasses were studied by ELISA and inhibition assay, using purified IgG heavy chains of different IgG subclasses.
In ELISA, the optical density (OD) value of the reaction of RA IgG RF with IgG 1 was significantly higher than with IgG 2, 3, or 4 (p < 0.01). Similarly, the OD value of the reaction of NS IgG RF with IgG 1 was significantly higher than with IgG 2 or 4 (p < 0.05). In the inhibition assay, the OD value of the reaction of RA IgG RF was decreased by IgG 1, 2, and 3 (p < 0.01), but not by IgG 4. The extent of inhibition by IgG 1 was significantly greater than that by IgG 2, 3, or 4 (p < 0.05). In contrast, the OD value of the reaction of NS IgG RF was not significantly inhibited by any of the IgG subclasses.
RA IgG RF and NS IgG RF reacted most strongly with IgG 1. From the differences in reactivities between RA IgG RF and NS IgG RF in the inhibition assay, it can be inferred that RA IgG RF exhibits higher affinity for IgG than NS IgG RF.