Subclasses of human IgG anti-Fab antibodies: parameters for optimum detection.

In this study we have defined the parameters needed for the optimum detection of anti-Fab antibodies in the serum of patients with rheumatoid arthritis. We have found that the majority of the anti-Fab antibodies are of the IgG3 and IgG4 subclasses which were not optimally detected using polyclonal heterologous anti-human IgG antisera; subclass-specific antibodies instead were needed. Additionally we determined that dissociation of circulating immune complexes by dialysis against urea for 3-7 days was also needed for the detection of these antibodies. Lastly we have shown that the dissociated complexes can recombine with their target Fab molecules, and therefore separation of the anti-Fab antibodies from the other immunoglobulins by chromatofocusing may enhance the detection of these antibodies. When the above conditions were fulfilled it was determined that IgG anti-Fab antibodies could be detected in rheumatoid arthritis and normal sera and that acidic IgG3 and IgG4 subclasses predominated. However, IgG3 levels were 10.5-fold higher in rheumatoid arthritis sera (p less than 0.05) and IgG4 levels 5-fold higher (p less than 0.01) than in normal sera.