Distribution of activated B lymphocytes in the circulation and synovial fluid in rheumatoid arthritis

The circulating peripheral blood of 13/28 patients with definite or classical rheumatoid arthritis (RA) had increased numbers of spontaneous in vivo active immunoglobulin-producing B lymphocytes detected by a reverse hemolytic PFC assay (mean = 3000 (1310-7920) Ig PFC/10(6) B cells) compared to an age/sex-matched control population (mean = 550 (300-900) Ig PFC/10(6) B cells). Among the remaining 16 RA patients who had normal numbers (less than 900 Ig PFC/10(6)) of such circulating B cells, 5 patients had increased numbers of activated B cells in the synovial fluid and 6 patients had no increase. Extraarticular features (nodules and vasculitis) in 11/13 patients and advanced but relatively inactive synovitis characterized those RA patients with increased numbers of active circulating B cells. In contrast, extraarticular features were seldom observed (1/16) among the remaining patients with normal numbers of active circulating B cells. Among these patients, more active generalized synovitis characterized those patients with increased numbers of active synovial fluid B cells compared to those patients with normal numbers. These studies imply that in RA patients, whose disease is primarily articular, active Ig synthesis is limited to the synovial compartment, while in those with extraarticular features active Ig-producing B cells also appear in the circulation.