A quantitative ELISA for measurement of rheumatoid factor associated cross-reactive idiotypes in serum from patients with rheumatic diseases.

A sensitive ELISA for the quantitation of RF associated cross-reactive idiotypes (CRI) has been developed. CRI bearing IgM was captured by immobilized F(ab')2 fragments of monoclonal anti-CRI antibodies and revealed with isotype specific conjugates. Factors affecting sensitivity, specificity and reproducibility of the assay were assessed. The sensitivity limit was less than 10 ng/ml and the linear assay range for the CRI standard curve was from 80 to 500 ng/ml. Using this ELISA system we have quantitated serum levels of the CRI in different groups of patients with RA, early synovitis and normal individuals. Our results indicate a significant increase in the levels of the CRI in the patient groups compared to the normal subjects tested, and suggest involvement of a diverse repertoire of Ig variable region germline genes and/or somatic mutation in production of polyclonal RF in RA.