Complement-fixing activity of rheumatoid synovial fluid.

Haemolytic complement activity has been shown to be reduced in synovial fluid of patients with rheumatoid arthritis as compared with patients with inflammatory effusions of similar protein content due to other causes (Hedberg, 1963; Pekin and Zvaifler, 1964; Fostiropoulous, Austen, and Bloch, 1965; Peltier, Coste, and Delbarre, 1966; Townes and Sowa, 1970). Anticomplementary activity was not observed, however, except as subsequently reported by Hedberg (1967). Using unheated synovial fluid and a period of incubation with a complement source, we have demonstrated anticomplementary or complementfixing activity in a significant number of rheumatoid synovial effusions. This activity demonstrates a pattern of complement-component fixation identical to that of antigen-antibody complexes or gamma globulin aggregates. In order clearly to differentiate this activity from poorly defined anticomplementary activities associated with contaminated, aged, or extensively manipulated biological fluids, we refer to this activity as complement-fixing. The frequency, specificity, and stability characteristics of this complement-fixing activity, are presented below with preliminary observations on its clinical correlates.