IgM rheumatoid factor elaboration by blood, bone marrow, and synovial mononuclear cells in patients with rheumatoid arthritis.

IgM rheumatoid factor (RF) elaboration by rheumatoid arthritis (RA) synovial, bone marrow, and blood mononuclear cells (MNC) is reported. IgM RF was prepared from RF-positive sera by sequential euglobulin precipitation, Sephacryl S300 gel filtration, and IgG-Sepharose affinity chromatography. Purified material, which contained no detectable IgG or IgA, was used in an enzyme-linked immunosorbent assay (ELISA) to quantitate cellular elaboration of IgM RF. Excellent standard curves (r2 = 0.98) were obtained without nonspecific binding of samples or antisera to IgG-coated microtiter plates and without cross-reactivity of standards with antisera other than anti-IgM. We found RA blood MNC (11 patients) spontaneously averaged 15 ng/ml IgM RF (6% of total IgM produced), but elaborated 254 ng/ml IgM RF following pokeweed mitogen (PWM) stimulation (22 patients), exceeding that of 13 normal controls. Bone marrow MNC spontaneously (4 patients) produced 71 ng/ml IgM RF and secreted 78 ng/ml IgM RF with PWM stimulation (9 patients). In contrast synovial fluid MNC (5 patients) spontaneously elaborated 6652 ng/ml IgM RF, significantly (P less than 0.05) more than blood or bone marrow MNC; PWM-stimulated synovial fluid MNC (5 patients) produced 5472 ng/ml IgM RF. These observations confirm selective localization of activated, IgM RF-producing cells to the rheumatoid synovial space.