1993 Volume 16 Issue 2 Pages 109-117
In radioimmunoassay or enzyme-linked immunosorbent assay (ELISA) for IgG rheumatoid factor (RF), IgM RF may interfere the results by binding of non-RF IgG. In order to destroy the IgM RF activity, dithiothreitol (DTT), a reducing agent, was used for testing IgG RF by means of IgG RF kit ED 001 (Eizai). In DTT-untreated and treated sera from 18 patients with RA, titers of IgG RFs were compared with the disease activity of rheumatoid arthritis (RA) assessed with Lansbury's activity index (AI). With DTT treatment of sera from 18 RA patients, IgM RF activity was completely abolished but the mean IgG RF activity was modestly decreased by 32.3%. The change in titers of DTT-untreated IgG RFs correlated significantly with the change in AI (68.6%, p<0.05%) and the change in titers of DTT-treated IgG RFs correlated also significantly with the change in AI (73.5%, p<0.01). In gel filtration analysis of IgG RF positive sera treated and untreated with DTT, from representative seropositive RA, IgG RFs were suggested to be present in serum as monomer, dimer, trimer or tetramer in forming self-association and some of IgG RFs bound to IgM RF in forming large complexes. From these data, it was suggested that DTT treatment was effective to assess the false positive serum for IgG RF. However, DTT treatment did not seem to be necessary to evaluate the relationship between IgG RF and AI.
