Rheumatoid adherent synovial cells produce B cell differentiation factor activity neutralizable by antibody to B cell stimulatory factor-2/interleukin 6.

B cell differentiation factor (BCDF) activity assayed on SKW6-CL4 cells was found in adherent synovial cell (ASC) conditioned medium. ASC of patients with RA (n = 8) produced significantly larger amounts of BCDF than those of patients with osteoarthritis (n = 5) (219.0 +/- 212.1 vs 25.5 +/- 12.4 units/microgram.DNA, p less than 0.01). ASC clones, established by the limiting dilution technique, also produced this factor. Experiments with several neutralizing antibodies revealed that this BCDF is inhibited by anti-B cell stimulatory factor-2/interleukin 6 antibody (anti-BSF-2/IL-6 ab) up to 90%, but not by antiinterleukin 1, antiinterleukin 2 or antiinterferon-r antibodies. Our data suggest that ASC could participate in the B cell differentiation process in joint space by producing a molecule which has a similar active site to BSF-2/IL-6.