Sequential studies of complement activation in systemic lupus erythematosus.
C1 and C3 activation, measured as C1r-C1s-C1 inactivator C1s-C1r-C1IA complexes in serum and circulating C3d were studied in serial samples from 33 patients with SLE. All patients demonstrated exacerbations during observation periods of 10-30 months and were divided into groups according to principal clincal features (mild SLE, severe extra-renal SLE, and lupus glomerulonephritis). Increased C1 activation was consistently found during exacerbation. C3d in plasma was a feature associated with severe disease flares. Activation of C1, but not of C3, was documented before flare-ups of disease activity, but such predictive information was mostly restricted to patients with extra-renal disease. C2 cleavage in plasma, studied serially in a few patients, appeared to be closely associated with C1 activation. Circulating immune complexes, measured with solid-phase C1q assay, did not always increase before development of clinical manifestations. Remission of symptoms was paralleled by decreasing concentrations of C1r-C1s-C1IA and of, when present, C3d. Similar findings were made for immune complexes but only in severe disease. Persisting C3d was observed in 3 patients, who subsequently developed renal failure. C1q levels were transiently low during flare-ups of lupus glomerulonephritis, but otherwise the concentrations of C1q, C4 and C3 did not show consistent patterns of variation in relation to disease activity.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000936:Antigen-Antibody Complex / Q000378:metabolism; D003167:Complement Activation; D003172:Complement C1 / Q000378:metabolism; D003175:Complement C2 / Q000378:metabolism; D003176:Complement C3 / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D013997:Time Factors
D000936:Antigen-Antibody Complex; D003172:Complement C1; D003175:Complement C2; D003176:Complement C3; D003181:Complement C4