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

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Background: 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. Objectives: 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. Methods: 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. Results: 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. Conclusion: 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.