title: High prevalence of anti-C1q antibodies in biopsy-proven active lupus nephritis.
abstract: BACKGROUND
  Anti-C1q antibodies (anti-C1q) have been shown to correlate positively with systemic lupus erythematosus (SLE) nephritis. Several clinical studies indicated a high negative predictive value, suggesting that active lupus nephritis is rarely seen in patients with no anti-C1q. However, the true prevalence of anti-C1q at the time of active lupus nephritis has not been well established. The aim of this study was to determine prospectively the prevalence of anti-C1q in proven active lupus nephritis at the time of the renal biopsy.
  
  
  METHODS
  In this prospective multi-centre study, we investigated adult SLE patients undergoing renal biopsy for suspected active lupus nephritis. Serum samples were taken at the time of the biopsy and analysed for the presence of anti-C1q in a standardized way. The activity of lupus nephritis was classified according to the renal histology. Biopsies were also analysed for the presence of glomerular IgG, C1q and C3 deposition.
  
  
  RESULTS
  A total of 38 patients fulfilling at least 4/11 American College of Rheumatology (ACR) criteria for the diagnosis of SLE were included. Out of this, 36 patients had proliferative (class II, III or IV) and two had class V lupus nephritis. All but one patient with proliferative lupus nephritis were positive for anti-C1q (97.2%) compared with the 35% of control SLE patients with inactive lupus nephritis and 25% of SLE patients without lupus nephritis ever. All patients were positive for glomerular C1q (36/36) and 37/38 patients had glomerular IgG deposits. Anti-C1q strongly decreased during successful treatment.
  
  
  CONCLUSIONS
  Anti-C1q have a very high prevalence in biopsy-proven active lupus nephritis, thus a negative test result almost excludes active nephritis. The data support the hypothesis of a pathogenic role of anti-C1q in lupus nephritis.
authors.affiliation: Internal Medicine B and Clinical Immunology lab, University Hospital Basel, Hebelstr. 20, CH-4031 Basel, Switzerland. marten.trendelenburg@unibas.ch
authors.forename: Marten
authors.initials: M
authors.lastname: Trendelenburg
authors.forename: Margarita
authors.initials: M
authors.lastname: Lopez-Trascasa
authors.forename: Eliska
authors.initials: E
authors.lastname: Potlukova
authors.forename: Solange
authors.initials: S
authors.lastname: Moll
authors.forename: Stephan
authors.initials: S
authors.lastname: Regenass
authors.forename: Véronique
authors.initials: V
authors.lastname: Frémeaux-Bacchi
authors.forename: Jorge
authors.initials: J
authors.lastname: Martinez-Ara
authors.forename: Eva
authors.initials: E
authors.lastname: Jancova
authors.forename: Mari Luz
authors.initials: ML
authors.lastname: Picazo
authors.forename: Eva
authors.initials: E
authors.lastname: Honsova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tesar
authors.forename: Salima
authors.initials: S
authors.lastname: Sadallah
authors.forename: Jürg
authors.initials: J
authors.lastname: Schifferli
mesh_terms: D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood*; D015922:Complement C1q / Q000276:immunology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007668:Kidney / Q000473:pathology*; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis / Q000276:immunology / Q000473:pathology; D008181:Lupus Nephritis / Q000175:diagnosis / Q000276:immunology* / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies
chemical_list: D001323:Autoantibodies; D015922:Complement C1q