Anti-C1q antibodies as a marker for disease activity in systemic lupus erythematosus and lupus nephritis

Background Systemic lupus erythematosus (SLE) is a chronic multisystem inflammatory autoimmune disease that is characterized by a number of immunological abnormalities. Disease onset is triggered by illdefined environmental factors in genetically susceptible individuals. C1q plays a key role in apoptotic cell and immune complex removal, and hence it is a very important functional molecule in SLE pathogenesis. Investigation of the relationship between peripheral lymphocyte apoptosis and serum levels of anti C1q autoantibodies in SLE patients suggests that increased serum levels of antiC1q autoantibodies are responsible for apoptosis and may play a pathogenic role in SLE patients, especially in active disease. Objectives The aim of this study was to measure the serum level of anti C1q in SLE patients, and to evaluate the correlation between anti C1q and SLE disease activity, especially renal activity. Patients and methods Fifty SLE patients diagnosed according to the Systemic Lupus International Collaborating Clinics classification criteria 2012 and 33 healthy volunteers who were age and sex matched were included in the study. SLE activity was assessed using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), and renal activity was assessed using the renal SLEDAI. AntiC1q was estimated using enzymelinked immunosorbent assay kit. Results Serum antiC1q was significantly higher in SLE patients (64.86 ± 27.88 U/ml) compared with healthy controls (30.15 ± 13.93 U/ml) (P < 0.000). There was a significantly positive correlation between antiC1q and the SLEDAI (P = 0.035, r = 0.299) and the renal SLEDAI (P = 0.025, r = 0.316). AntiC1q has a sensitivity and specificity of 92.7 and 66.7%, respectively, a positive predictive value of 92.7%, negative predictive value of 66.7%, and 88.0% accuracy for detecting SLE disease activity, whereas for lupus nephritis diagnosis antiC1q has a sensitivity and specificity of 94.12 and 50.0%, respectively, a positive predictive value of 80.0%, negative predictive value of 80.0%, and 80.0% accuracy. Conclusion Our results support the finding that antiC1q level might be used as a marker for SLE activity and not lupus nephritis in adult SLE patients