title: Prospective analysis of C1 dissociation and complement activation in patients with systemic lupus erythematosus.
abstract: OBJECTIVE
  To evaluate the results of complement analysis for assessment of disease activity and severity, and prediction of flares in systemic lupus erythematosus (SLE).
  
  
  METHODS
  Patients with mild extra-renal flares, severe extra-renal flares or flares of lupus glomerulonephritis were followed for eight months, with investigations being performed every second month. Findings in initial samples four months before the flares were compared with findings in a control group with stable disease. C-reactive protein, and circulating C1q, C4 and C3 were determined together with two types of complexes containing C1 inhibitor (C1 INH), C1 INH-C1r-C1s and C1 INH-C1r-C1s-C1 INH, and the C3 breakdown product C3d.
  
  
  RESULTS
  Enhanced formation of C1 INH-C1r-C1s appeared to be a marker of low specificity and was mainly seen in patients with extra-renal disease. Concentrations of C1 INH-C1r-C1s-C1 INH, C3d, C1q and C3 clearly varied according to disease activity in patients with severe disease. Interestingly, high C1 INH-C1r-C1s-C1 INH values were found four months before the flares in all but one patient with lupus glomerulonephritis. Assessment of the relative predictivity for a subsequent flare indicated low C1q to be the most reliable marker, the predictivity of the complexes being: low C1q > high C1 INH-C1r-C1s-C1 INH > low C3 > high C3d > low C4.
  
  
  CONCLUSIONS
  The importance of C1q and C1-related events in SLE may be underestimated. In addition, our results demonstrate the relevance of serial complement analysis for the assessment of disease activity and severity.
authors.affiliation: Department of Rheumatology, Lund University Hospital, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Jonsson
authors.forename: G
authors.initials: G
authors.lastname: Sturfelt
authors.forename: U
authors.initials: U
authors.lastname: Mårtensson
authors.forename: L
authors.initials: L
authors.lastname: Truedsson
authors.forename: A G
authors.initials: AG
authors.lastname: Sjöholm
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000378:metabolism*; D016022:Case-Control Studies; D003167:Complement Activation / Q000502:physiology*; D015922:Complement C1q / Q000378:metabolism*; D003176:Complement C3 / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
chemical_list: D003176:Complement C3; D003181:Complement C4; D015922:Complement C1q; D002097:C-Reactive Protein