The relationship between autoantibody and complement levels in the sera of patients with systemic lupus erythematosus.

The goal of these studies was to elucidate the relationship between levels of autoantibodies and complement (C3/C4) in the sera of patients with systemic lupus erythematosus (SLE) and thereby provide a framework for interpreting serological biomarkers in the context of current therapy. Anti-RNA-binding proteins (RBPs) were measured by enzyme-linked immunofluorescence assay (ELFA); ANA and autoantibodies to C1q and dsDNA were measured by ELISA; and levels of C3 and C4 were measured by immunoturbidimetry. In univariate analyses, anti-dsDNA, anti-C1q, anti-Sm, anti-U1RNP, and anti-RNP-70 were associated with low C3 and low C4 levels. In Lasso logistic regression and decision tree analysis, however, only anti-dsDNA and anti-C1q showed a relationship with complement in contrast to the other antinuclear antibodies. These studies support the important relationship between levels of anti-dsDNA and complement and further suggest that anti-C1q antibodies may also lead to complement activation, alone or in concert with other autoantibodies.