Selective presence of IgG2b inducing factor in synovial fluid of patients with rheumatoid arthritis

The factor, that we have defined and called IgG2b inducing factor, in synovial fluid of rheumatoid arthritis patients (RA-SF) has previously been well characterized both in vitro and in vivo revealing that RA-SF induces a significantly higher IgG2b antibody production in LPS activated murine spleen cells. This activity was separated from the hitherto identified cytokines or factors in RA-SF. In this study we have compared the IgG2b inducing activity in RA-SF with synovial fluid from patients with non-RA arthritides. Here we show that the IgG2b inducing activity is significantly enriched in patients with RA compared to patients with non-RA arthritides and it is not found in healthy, post-traumatic, control groups. We do not yet know the implications of this finding for the disease progress of rheumatoid arthritis, but we believe that the identification of this B cell differentiation factor might elucidate the mechanism leading to hyperactivation of B cells in rheumatoid arthritis.