IgG 1 subclass specificity for IgG rheumatoid factors in patients with rheumatoid arthritis

Objective. To investigate the significance of IgG rheumatoid factors (IgG R F) in the pathogenesis of rheumatoid arthritis IRA), and to determine the s pecificity of IgG subclasses binding with IgG RF in RA (RA IgG RF) compared to IgG RF in normal subjects (NS IgG RF). Methods. The reactivities of RA IgG RF and NS IgG RF for various IgG subcla sses were studied by ELISA and inhibition assay, using purified IgG heavy c hains of different Ige subclasses. Results. In ELISA, the optical density (OD) value of the reaction of RA IgG RF with IgG I was significantly higher than with IgG 2, 3, or 3 (p < 0.01) . Similarly, the OD value of the reaction of NS IgG RF with IgG 1 was signi ficantly higher than with IgG 3, 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)1 but not by IgG 4. The extent of inhibition by IgG 1 was signifi cantly greater than that by IgG 2, 3, ol 4 (p < 0.05). In contrast, the OD value of the reaction of NS IgG RF was not significantly inhibited by any o f the IgG subclasses. Conclusion. 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 inhi bition assay, it can be inferred that RA Ige RF exhibits higher affinity fo r IgG than NS IgG RF.