Anti‐C1q antibodies: association with nephritis and disease activity in systemic lupus erythematosus

Abstract

Background: Anti‐C1q antibodies have been described in systemic lupus erythematosus (SLE) as well as in other connective tissue diseases. They have been considered as a marker for disease activity and presence of nephritis.Objective: The aim of this study was to determine the prevalence of anti‐C1q antibodies in Brazilian lupus patients as well as analyze their association with different clinical and serologic parameters.Methods: Sera from 81 SLE patients, based on the American College of Rheumatology (ACR) criteria, were collected from a lupus referral outpatient clinic in Salvador, Brazil. Antibodies to C1q were detected by an enzyme‐linked immunoassay (ELISA) kit and antibodies to other cellular antigens identified by indirect immunofluorescence on HEp‐2 cell substrate (ANA), or Crithidia luciliae (dsDNA), and to nucleosome by ELISA. A cutoff of 20 U wasestablished for anti‐C1q and antinucleosome assays.Results: Anti‐C1q antibodies were detected in 39.5% (32/81) of SLE sera. The presence of anti‐C1q antibodies was associated with proteinuria (P=0.028) but not with other laboratory or clinical features, such as antinucleosome or anti‐dsDNA antibodies, hematuria, urinary casts or renal failure, leukopenia, pericarditis, pleuritis, malar rash, seizures, and psychosis. There was a positive correlation between the titers of anti‐C1q antibodies and the systemic lupuis erythematosus disease activity index (SLEDAI) score (r=0.370; P=0.001).Conclusion: This study in Brazilian SLE patients confirms previous findings of the association of anti‐C1q antibodies with nephritis and disease activity. J. Clin. Lab. Anal. 23:19–23, 2009. © 2009 Wiley‐Liss, Inc.

Fc RIIA Genotypes and Its Association with Anti-C1q Autoantibodies in Lupus Nephritis (LN) Patients from Western India

“…It was reported that IgG2 subclass of anti-C1q antibodies might be pathogenic and IgG3 subclass of anti-C1q might be more specific bio-marker for monitoring disease activity [21]. Maura et al had reported a positive correlation between high titres of anti-C1q antibodies, and SLEDAI scores in Brazilian SLE patients and had shown an association of anti-C1q antibodies with LN [22]. Our study also supported this finding.…”

The non-classical functions of the classical complement pathway recognition subcomponent C1q

“…Rosen and co-workers suggested that a considerable number of lupus autoantigens were clustered within apoptotic blebs [49,50]. This condition is further compounded by the presence of anti-C1q autoantibodies detected in the sera of a number of patients suffering from SLE [51][52][53][54][55]. The CRT binds to the CD91 and C1q, which is known to bind to the CRT through its collagenous "tail", forms a complex with CRT/CD91.…”

Anti-C1q autoantibodies from systemic lupus erythematosus patients activate the complement system via both the classical and lectin pathways

“…Our study primarily focused on the analysis of autoantibodies against intact C1q since these autoantibodies have been best described to correlate with SLE disease activity [34,35]. In addition, using intact C1q maybe best reflects the situation occurring in vivo, allowed the analysis of high-affinity antibodies, and avoided manipulations of the molecule as well as the presence of non-physiological components such as peptide 2J [29] and neutravidine [36].…”