Quantitative detection of class-specific rheumatoid factors using mouse monoclonal antibodies and the biotin/streptavidin enhancement system

An enzyme-linked immunosorbent assay (ELISA) for the quantitative detection of rheumatoid factors (RF) was developed using mouse monoclonal antibodies against human IgG, IgA and IgM together with the biotin/streptavidin enhancement system. One hundred and eight patients with rheumatoid arthritis (RA) of whom 47 had a positive serum latex agglutination assay, 100 healthy controls and 95 diseased controls (25 systemic lupus erythematosus (SLE), 25 ankylosing spondylitis, 20 osteoarthritis and 25 bronchial asthma) were evaluated for the presence of IgG-, IgA- and IgM-RF by ELISA. Elevated levels of IgG-, IgA-, and IgM-RF could be demonstrated in respectively 94%, 91% and 98% of serum samples from RA patients with a positive latex test and in 72%, 69% and 8% of serum samples from RA patients with a negative latex test. In the latter patient group, increased levels of one or more RF isotypes could be detected m 82% of the patients. Except for the presence of IgG-RF in serum of 20% of the SLE patients, increased levels of RF isotypes were present in less than 5% of the diseased controls. Highly significant correlations were found between serum IgM-RF levels as detected by ELISA and those of the latex and the Rose-Waaler agglutination assays. Positive correlations were also found between the serum levels of the three RF isotypes investigated and between the levels of RF isotypes as measured in serum and synovial fluid of the same patient. Compared to agglutination assays, the ELISA for the quantitative detection of RF isotypes is a more reproducible and sensitive test which avoids some of the problems encountered in earlier ELISA methods.