Complement Breakdown Products in Plasma from Patients with Systemic Lupus Erythematosus and Patients with

ment of the complement system in various diseases was obtained by the direct quantitation of breakdown prod-ucts of C3 and of properdin factor B. The methods used were based, first, on the separation of native and frag-mented molecules according to their molecular size through a precipitation with polyethylene glycol and, secondly, on an immunochemical quantitation, using specific antisera for the major antigens of C3 and fac-tor B. The sensitivity and the specificity of these meth-ods were demonstrated by activation of complement in vitro with generation of C3 and factor B fragments. A clinical investigation was carried out in 41 patients with systemic lupus erythematosus (SLE), 31 with membranoproliferative glomerulonephritis (MPGN), 26 with other types of glomerulonephritis, and 6 with se-vere alcoholic cirrhosis of the liver. The following ob-servations were made: (a) an elevated plasma level of C3d fragment of C3 was found in 68 % of SLE pa-tients, in 87 % of MPGN patients, in 62 % of patients with other hypocomplementemic nephritis, and in 15% of those with normocomplementemic nephritis, but in only 33 % of patients with liver cirrhosis and very low levels of C3; (b) a significant difference was ob-served between the levels of C3 obtained with either anti-"native " C3 or anti-C3c sera for immunochemical quantitation, in patients with SLE or MPGN, indicating the presence of "altered " or fragmented C3 in plasma; (c) an elevated plasma level of Ba fragment of pro-perdin factor B was found in 46 % of SLE patients, in 67 % of MPGN patients, in 50 % of patients with othe