Anti-C1q Antibodies In Systemic Lupus Erythematosus-relationship With Disease Activity And Renal Involvement

BACKGROUND: In recent years, anti-C1q antibodies with potential pathogenic and diagnostic relevance have recognized in SLE. Their presence is strongly correlated with lupus nephritis. The increase in anti-C1q antibodies were suitable for differentiating between active and inactive patients and for correlating positively with systemic lupus erythematosus (SLE) nephritis and for identifying those with active nephritis.OBJECTIVE: To investigate the relation between the presence and concentration of anti-C1q Ab and disease activity and renal involvement in patients with systemic lupus erythematosus (SLE) compared to other connective tissue diseases.METHODS Anti-c1q Ab were measured by enzyme-linked immunosorbant assay (ELISA) in 93 patients with SLE: 33 patients had active disease with lupus nephritis, 12 Active disease without nephritis, 9 inactive disease with nephritis and 39 inactive disease without nephritis. As control groups we included 31 healthy blood donors and 69 diseased controls (rheumatoid arthritis (n=12), ankylosing Spondylitis (n=2), Wegener granulomatosis (n=3), Behcet disease (n=8), systemic sclerosis (n=5 ), matomyositis/polymyositis (n=8), primary Sj(o|¨)gren syndrome (n=18), undifferentiated connective tissue disease (n=6), autoimmune hepatopathies (n=7)) and 31 normal controls . Complement levels (C3, C4), hemoglobin, blood cell count, ESR, ALB, anti-nucleosome antibodies (AnuA), anti-dsDNA antibodies, anti-Smith antibodies (anti-Sm), anti-nuclear antibodies (ANA), antineutrophil cytoplasmic autoantibodies (ANCA) were determined in parallel. Disease activity was assessed using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI).RESULT Anti-C1q Ab were positive in 40.9%, anti-dsDNA Ab in 40.9% and AnuA in 62.8% of patients with SLE, respectively. AnuA were more sensitive and specific than anti-C1q Ab in distinguishing SLE patients. (AnuA: sensitivity62.4%, specificity 99%; anti-C1q:sensitivity 40.9%,specificity 96%). Significantly higher levels of anti-C1q Ab were found in patients with active disease compared with those with inactive SLE. Serum level of anti-C1q Ab showed a strongly positive correlation with SLEDAI score, proteinuria, WBC and AnuA and a negative correlation with disease duration, C3, C4, and ALB. Serum level of anti-C1q Ab were not related to the degree of serum creatinine or BUN. The incidence of renal involvement in patients with positive anti-C1q Ab was higher than that in anti-C1q Ab negative group. The presence of anti-C1q Ab was significantly higher in active patients in active patients compared with inactive patients. Frequency of anti-C1q Ab, AnuA, anti-dsDNA Ab and anti-Sm were significantly higher between patients with and without nephritis.Frequency of anti-C1q Ab, AnuA and anti-dsDNA Ab were significantly higher between patients with and without disease active. Frequency of anti-C1q Ab were significantly higher between patients active nephritis and inactive nephritis, and active disease and inactive disease without nephritis. But both AnuA and anti-dsDNA Ab were only significantly higher between patients active nephritis and inactive nephritis. Furthermore, in patients with active nephritis both anti-C1q Ab and AnuA were detectable in 63.6% and none were negative for both antibodies. In contrast, in 60 patients without active nephritis neither anti-C1q Ab nor AnuA were detectable.CONCLUSION Anti-C1q antibodies are closely related to the pathogenesis of SLE and LN. It had potential utility as a diagnostic tool and disease activity marker..The presence of anti-C1q antibodies,anti-nucleosome antibodies,anti-dsDNA antibodies in SLE are related to disease activity and lupus nephritis. Combination of those antibodies can strongly promote the diagnosis of active lupus nephritis.