Relationship between IgG2b‐inducing activity in rheumatoid arthritis synovial fluid and other well‐known cytokines and inflammatory mediators

Abstract

In the present study, we sought to identify the T cell‐replacing factor which selectively induces IgG2b antibody formation in lipopolysaccharide‐activated mouse spleen cells in vitro and in vivo, and which is present in the synovial fluid (SF) of rheumatoid arthritis (RA) patients. The protein A plaque assay was used to measure IgM, IgG1, IgG2b, and IgG3 plaque‐forming cells. An enzyme‐linked immunosorbent assay was used to measure interleukin‐6 (IL‐6) levels in RA SF. We found that IgG2b induction by RA SF is not caused by IL‐6, IL‐1, or any other inflammatory cytokines or mediators, such as transforming growth factor β, platelet‐derived growth factor, nerve growth factor, fibroblast growth factor, epidermal growth factor, elastase, colla‐genase, and phospholipase A2. IgG2b‐inducing factor in RA SF has unique biological properties compared with those of the interleukins and inflammatory mediators known to be present in RA SF.