Diagnostic and prognostic significance of anti-C1q antibodies in systemic lupus erythematosus

Purpose of review The presence of a wide variety of autoantibodies is a characteristic finding in systemic lupus erythematosus. Autoantibodies against nuclear proteins, such as anti-nuclear and anti-double-stranded DNA antibodies, are used as diagnostic markers in systemic lupus erythematosus. Renal involvement is frequently found in systemic lupus erythematosus and is an important risk factor for death. Therefore, markers for the diagnosis and follow-up of nephritis are very important. Anti-C1q autoantibodies are strongly associated with renal involvement in systemic lupus erythematosus. This study will review recent findings on the pathogenic role and clinical importance of anti-C1q antibodies in lupus nephritis. Recent findings Recent clinical studies have clearly emphasized the diagnostic relevance of anti-C1q autoantibody levels in patients with lupus nephritis. With a possible negative predictive value of 100%, anti-C1q autoantibodies are the only exclusive antibodies associated with the involvement of a single organ in systemic lupus erythematosus. Next to the clinical findings, the pathogenic significance of anti-C1q antibodies has been shown in an animal model. The deposition of autologous C1q in healthy glomeruli of mice after the infusion of anti-C1q antibodies induces moderate tissue damage. Summary The latest insight into the pathogenesis of anti-C1q autoantibodies in the development of lupus nephritis and the recently demonstrated clinical importance of anti-C1q autoantibodies for the diagnosis of lupus nephritis support the value of further investigations. New diagnostic methods for the detection of anti-C1q and an accurate follow-up of antibody levels might be of use in clinical practice.