Partial Biochemical Characterization and Purification of IgG2b Inducing Factor as a New Cytokine from Synovial Fluid of Patients with Rheumatoid Arthritis

Abstract

Rheumatoid arthritis synovial fluid (RA-SF) contains a novel biological activity, which selectively induces IgG2b antibody production in lipopolysaccharide (LPS)-activated mouse spleen cells in vitro and in vivo. Our previous studies have shown that this activity is not functionally identical to other well-known cytokines and interleukins. In this study we demonstrate the partial purification and biochemical characterization of the IgG2b inducing activity in RA-SF. Biochemical characterization revealed that the IgG2b inducing activity in RA-SF has the following properties: it is a protein, sensitive to pH > 11 and < 4, which is precipitated by 50% of saturated ammonium sulphate and has a molecular weight of 50-70 kDa; it binds to Cibacron-blue and heparin and its activity is not mediated by immunoglobulins or immune complexes, which are present in RA-SF. Biochemical characteristics of the IgG2b inducing activity also differ from other cytokines and interleukins. The term IgG2b inducing factor is proposed for this novel activity.