Utility of anti-C1q and anti-nucleosome antibodies in systemic lupus erythematosus and lupus nephritis in southwestern Colombia

Abstract

IntroductionLupus nephritis (LN) is one of the most prevalent and severe complications of systemic lupus erythematosus (SLE), requiring reliable urine and serum biomarkers to evaluate it. Anti-nucleosome and anti-C1q antibodies are associated with LN in several geographic regions. Also, southwest Colombia has a heterogeneous ethnicity, which motivated the evaluation of the frequency and relationship of such markers with LN in this region. MethodsA cross-sectional study was conducted in a health centre in south-west Colombia in 84 patients diagnosed with SLE (57 without LN; 27 with LN) between 2016 and 2018. Demographic and clinical and laboratory features, including anti-dsDNA, complement, and anti-C1q and anti-nucleosome antibodies were compared in these patients. ELISA immunoassays were performed to measure the antibodies of interest in blood samples. Statistical analysis was carried out using STATA14 software (StataCorp, College Station, Texas, USA). Quantitative variables were summarised as means or medians and compared with Mann–Whitney or Two-sample t test. Categorical variables were shown as proportions, and compared with Chi-squared or Fisher's exact test. Correlation analysis between quantitative variables was calculated using Spearman's correlation. ResultsOf all 84 patients, 27 patients had LN, of which 16 (59.2%) had a positive test for anti-nucleosome antibodies and 10 (37%) for anti-C1q antibodies. An association was found between anti-C1q and proliferative forms of LN and newly diagnosed LN. A correlation was found between anti-nucleosome and anti-C1q antibodies, and anti-dsDNA and low serum complement concentrations. ConclusionAlthough both markers were found in variable percentages in SLE patients and seem not to be specific markers of LN in our population, anti-C1q was associated with proliferative forms of LN and de novo LN.