Prevalence and Clinical Associations of Anti-C1q Antibodies in Paediatric Systemic Lupus Erythematosus in Indian Children

Abstract

Paediatric systemic lupus erythematosus (pSLE) is a heterogeneous, chronic autoimmune disease characterised by multi-system inflammation and the production of antibodies-directed self-antigens. Anti-C1q has been associated with SLE as well as other connective tissue diseases. They have been considered as a marker for disease activity and the presence of nephritis. To determine the prevalence of anti-C1q antibodies in the paediatric SLE and to determine clinical associations of elevated anti-C1q antibody levels, especially with lupus nephritis. All consecutive children with SLE on treatment with immunosuppressive drugs attending our clinic were recruited. After obtaining informed consent, blood samples were tested for anti-C1q antibodies by a commercially available ELISA kit. The prevalence of anti-C1q and its association with lupus nephritis were determined. Out of a total 150 children with SLE, anti-C1q positivity was present in 95 children (64%), at a cut-off value of 20 U/mL. Children with proteinuria, low C3, low C4 and anti-dsDNA positivity had significantly more anti-C1q antibody positivity. Children with lupus nephritis were significantly more likely to have anti-C1q antibody positivity than children without renal involvement (74% vs. 51%, p = .02). Among the children with lupus nephritis, children with active renal disease were more likely to have anti-C1q positivity than in children with quiescent disease (88% vs. 53%, p = .002). Anti-C1q antibodies had a sensitivity of 74% and specificity of 54% at a cut-off value of 22 U/L for renal disease in pSLE. In our study, children with lupus nephritis were significantly associated with elevated anti-C1q antibodies, and children with active renal disease had higher anti-C1q positivity than those with quiescent disease. Anti-C1q levels showed significant associations with low C3, low C4 and anti-dsDNA positivity. Anti-C1q levels did not show significant associations with clinical features of SLE like malar rash, arthritis and CNS involvement. Anti-C1q antibody titres were found to have a positive correlation with renal disease and hence could be used as an adjunctive biomarker in monitoring the disease activity in children with lupus nephritis.