Concentration of interleukin-1 beta in serum and synovial fluid in patients with rheumatoid arthritis and those with osteoarthritis.

The concentration of interleukin-1 beta (IL-1 beta) in serum and synovial fluid of the knee of patients with rheumatoid arthritis (RA) and those with osteoarthritis (OA) was examined using a recently developed radioimmunoassay method. The serum concentration of IL-1 beta was below the detection limit of 0.25 ng/ml in all RA and OA patients. The IL-1 beta concentration in the synovial fluid was higher in RA patients than in OA patients. In RA patients, a significant correlation was demonstrated between the synovial fluid IL-1 beta concentration and the erythrocyte sedimentation rate, C-reactive protein level, synovial fluid white blood cell count and Lansbury index. The synovial fluid IL-1 beta concentration decreased with the reduction of the rheumatoid activity by the medication, but tended to increase or remain high when inflammatory activity of RA could not be adequately controlled. The IL-1 beta concentration, easily determined, shows promise as a new quantitative indicator of rheumatoid activity.