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 was established for anti-C1q and anti nucleosome 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 anti nucleosome 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.