Abstract
BackgroundLupus 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.MethodsSera 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.ResultsThe 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).ConclusionAnti-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.
Highlights
Lupus nephritis is considered to be a principal cause of morbidity and mortality in Systemic lupus erythematosus (SLE)
We detected the serum levels of C1q, presence of anti-C1q antibodies in the circulation, and renal C1q deposition, and further analyzed their associations with clinical and pathological activity in a large cohort of Chinese patients with lupus nephritis
The primary end-point was defined as death, and secondary end points were defined as end-stage renal disease (ESRD) or doubling of serum creatinine levels
Summary
Patients Sera and renal biopsies from 218 consecutive patients with renal biopsy-proven lupus nephritis, diagnosed from 2000 to 2008 at Peking University First Hospital were collected on the day of renal biopsy. Direct immunofluorescence examination Fresh frozen renal specimens were stained immediately after the renal biopsy with fluoresceinisothiocyanatelabelled rabbit anti-human immunoglobulin G (IgG), immunoglobulin A (IgA), immunoglobulin M (IgM), C3c, C1q and fibrin antibodies (DAKO A/S, Copenhagen, Denmark). FITC-labeled goat anti-rabbit IgG (Zhongshan Golden Bridge Biotechnology, Beijing, China; diluted 1:60) was used as a secondary antibody at 37°C for 30 min. After three washes with phosphate buffered saline (PBS), sections were incubated in 3% BSA for 30 min at room temperature. After washing with PBS 3 times for 3 min, mouse anti-human C1q (diluted 1:400; Abcam, Cambridge, UK) was added as primary antibody for 30 min at 37°C. Serum samples Sera from patients with lupus nephritis were obtained from peripheral blood at the time of renal biopsy.
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