title: Serum levels and renal deposition of C1q complement component and its antibodies reflect disease activity of lupus nephritis.
abstract: BACKGROUND
  Lupus nephritis is considered to be a principal cause of morbidity and mortality in SLE. Few studies focus on the association between anti-C1q antibodies in circulation and renal C1q deposition in human lupus nephritis. In this study, we detected the serum levels of C1q, presence of anti-C1q antibodies in circulation, renal C1q deposition and further analyzed their associations with clinical and pathological activity in a large cohort of Chinese lupus nephritis patients.
  
  
  METHODS
  Sera and renal biopsies from 218 consecutive patients with lupus nephritis with long-term follow up data were studied. Sera were tested for levels of C1q and anti-C1q autoantibodies. Associations of levels of C1q, anti-C1q autoantibodies with renal deposition of C1q, clinical and histopathological data and renal outcome were further investigated.
  
  
  RESULTS
  The levels of serum C1q were significantly lower in lupus nephritis than that in normal controls [33.81 ± 20.36 v.s. 61.97 ± 10.50 μg/ml (P < 0.001)]. The prevalence of anti-C1q antibodies, ratios of glomerular and vascular deposition of C1q in patients with lupus nephritis were 42.7% (93/218), 71.6% (156/218) and 86.2% (188/218), respectively. The serum C1q levels and anti-C1q antibodies were associated with SLEDAI scores (P < 0.001, P = 0.012, respectively), renal total activity indices scores (P < 0.001, P < 0.001, respectively). Granular positive staining of C1q and IgG by immunofluorescence was co-localized almost completely along the glomerular capillary wall and mesangial areas. Patients with anti-C1q antibodies presented with significantly lower serum C1q levels than those without it (23.82 [0.60, 69.62] μg/ml v.s. 37.36 [0.64, 82.83] μg/ml, P < 0.001). The presence of anti-C1q antibodies was associated with the presence of glomerular C1q deposition (P < 0.001), but not with the presence of renal vascular C1q deposition (P = 0.203).
  
  
  CONCLUSIONS
  Anti-C1q autoantibodies were closely associated with serum levels of C1q and glomerular deposition of C1q. Kidney is at least one of the target organs of anti-C1q autoantibodies.
authors.affiliation: Renal Division, Department of Medicine, Peking University First Hospital; Institute of Nephrology, Peking University; Key laboratory of Renal Disease, Ministry of Health of China; Key Laboratory of Chronic Kidney Disease Prevention and Treatment, Ministry of Education of China, Beijing 100034, Peoples' Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Tan
authors.forename: Di
authors.initials: D
authors.lastname: Song
authors.forename: Li-hua
authors.initials: LH
authors.lastname: Wu
authors.forename: Feng
authors.initials: F
authors.lastname: Yu
authors.forename: Ming-hui
authors.initials: MH
authors.lastname: Zhao
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood*; D015922:Complement C1q / Q000378:metabolism*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007678:Kidney Glomerulus / Q000378:metabolism*; D008181:Lupus Nephritis / Q000097:blood* / Q000175:diagnosis; D008297:Male; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D015922:Complement C1q