Anti-C1Q Antibody as A Marker In Systemic Lupus Erythematosus

Objective: To study the correlation of anti C1q antibodies with disease activity in patients with systemic lupus erythematosus (SLE). Study Design: Cross sectional, observational study. Place and Duration of study: The Department of Immunology, Armed Forces Institute of Pathology, Rawalpindi in collaboration with Military Hospital, Rawalpindi, Pakistan Institute of Medical Sciences, Islamabad and Benazir Bhutto Hospital, Rawalpindi, from Jan 2012 to Dec 2013. Material and Methods: Patients with a clinical diagnosis of SLE were included in the study on fulfilling revised American College of Rheumatology (ACR) criteria (1997). Main outcome measures were SLE disease activity index (SLEDAI) score and anti C1q antibody levels in serum. SLEDAI scores were calculated for each patient on the basis of physical examination, patient interviews and previous clinical records. Anti C1q antibody levels in the serum were determined by enzyme-linked immunosorbent assay (ELISA) and correlated with the SLEDAI scores by calculating Pearson’s correlation coefficient ‘r’. The cutoff value for anti C1q antibody positivity in the serum was determined by evaluating the serum levels of anti C1q antibodies in 25 healthy subjects and was 12 U/ml. Results: Six male and forty nine female SLE patients with an age range of 16-47 years (mean 34.5 years) and 8-70 years (mean 31.7 years) respectively were studied. The correlation between anti C1q levels and SLEDAI scores in all patients was demonstrated by calculating the correlation coefficient and was not significant (r=0.19, p=0.14). However, there was an inverse correlation between anti C1q levels and SLEDAI scores in patients with severe disease and this was statistically significant (r=–0.448, p=0.037). The difference in anti C1q antibody positivity between patients with and without nephritis was not significant. The anti C1q antibody levels correlated poorly with anti double stranded deoxyribonucleic acid (dsDNA) antibody positivity. A significantly higher percentage of patients with evidence of complement consumption was found to be positive for anti C1q antibodies (p=0.01). This significance was only seen in patients with reduced C3 levels (p=0.04) and not reduced C4 levels (p=0.23) or both (p=0.23). Anti C1q antibody levels had significant inverse correlation with serum C3 levels. (p=0.007). Conclusion: A significant inverse correlation was found between SLEDAI scores and serum anti C1q antibody levels in patients with severe SLE. The anti C1q antibody positivity is significantly higher in patients with reduced C3 levels.