Complement metabolism in the seronegative arthritides.

The complement system, through the action of its nine components and various cleavage products, plays a major role in the inflammatory response. In rheumatoid arthritis a depression of total haemolytic complement (Hedberg, 1963, 1964, 1967; Pekin and Zvaifler, 1964; Fostiropoulos, Austen, and Bloch, 1965; Barnett, Bienenstock, and Bloch, 1966; Peltier, Coste, and Delbarre, 1966; Vaughan, Barnett, Sobel, and Jacox, 1968; Ruddy and Austen, 1970; Gligore, Bolosiu, Dutu, and Podut, 1971) and the concentrations of individual components (Fostiropoulos and others, 1965; Ruddy and Austen, 1970; Ruddy, Everson, Schur, and Austen, 1971; Britton and Schur, 1971) in synovial fluid compared with serum has been accepted as evidence ofintra-articular complement activation, and has been confirmed by the finding of conversion products of C3 (Zvaifler, 1969; Hedberg, Lundh, and Laurell, 1970), cleavage products of C5, and the trimolecular chemotactic factor C567 (Ward and Zvaifler, 1971). Increased catabolic rates for C3 have also beenfound in synovial fluid (Ruddy, Muller-Eberhard, and Austen, 1971). In most of the above-mentioned studies, the serum complement system appeared to be normal. Activation of the complement system in the joint cavity is thought to be due to fixation by immune complexes consisting of IgG and rheumatoid factor. Although the presence of IgG antiglobulin factors in various seronegative arthritides has been documented (Torrigiani and Roitt, 1967; Torrigiani, Ansell, Chown, and Roitt, 1969; Torrigiani, Roitt, Lloyd, and Corbett, 1970; Panush, Bianco, and Schur, 1971), the status of the complement system in these diseases has not been described. In this paper we report the results ofmeasurements of the Clq, C3, and C7 components of complement, glycine-rich-fl-glycoprotein (GBG or C3 proactivator) concentrations in the plasma of patients with seronegative forms of arthritis. In addition, we have used crossed antibody electrophoresis for measuring C3 conversion and immunoelectrophoresis for GBG conversion, an important index of alternate pathway activation (Gotze and Muller-Eberhard, 1971).