Decreased production of suppressive-B-cell factor by synovial membrane B-lymphocytes in rheumatoid arthritis

Suppressive-B-cell factor (SBF) is an autoregulatory B-cell lymphokine produced by heat-aggregated-IgG stimulated B-lymphocytes which suppresses polyclonal immunoglobulin production. SBF production by rheumatoid arthritis (RA) patients' peripheral blood B-lymphocytes inversely correlates with disease activity and in vitro rheumatoid factor production. To further define the role of SBF in the pathogenesis of RA, the present study measured SBF production by surgically-obtained synovial membrane mononuclear leukocytes. SBF production by RA synovial leukocytes was similar to the levels previously described for RA peripheral blood leukocytes. Both RA and osteoarthritis (OA) synovial leukocytes produced significantly less SBF than leukocytes obtained from otherwise healthy patients with plica. OA patients produced less SBF than RA patients, but the difference was not statistically significant. SBF values for combined RA patients and controls with OA or plica correlated with the degree of histological plasma cell infiltration providing further evidence for SBF production by cells of the B-lymphocyte lineage. Depletion studies also demonstrated that synovial SBF was produced by B-lymphocytes. The molecular weight (34,000) of synovial SBF was similar to the molecular weight of peripheral blood SBF. Decreased SBF production by RA synovial B-lymphocytes is a functional abnormality in RA which may contribute to the perpetuation of synovial rheumatoid factor production and chronic synovial inflammation.