Anti-IFI16 antibodies and their relation to disease characteristics in systemic lupus erythematosus

Objective: Several studies have shown the presence of anti-IFI16 antibodies in systemic lupus erythematosus (SLE), Sjogren Syndrome (SjS), systemic sclerosis (SSc) and other autoimmune diseases. However, the significance of anti-IFI16 antibodies in SLE has not been fully characterized. The aim of this study was to investigate associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE. Methods: An enzyme-linked immunosorbent assay (ELISA) kit was used to measure anti-IFI16 antibodies in the sera of 168 SLE patients, 46 patients with any type of primary glomerulonephritis (GN) and 182 healthy controls (HCs). Associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE were statistically evaluated using both univariate and multivariate analysis. Results: Significantly higher anti-IFI16 titres were observed in SLE patients compared to both non-SLE GN and HCs (median levels: 270.1 U/ml vs 132.1 U/ml, p = 0.001, and 52.9 U/ml, p < 0.0001, respectively). With cut-off levels corresponding to the 95th percentile of the control population (113 U/ml), 63% of the SLE patients tested positive for anti-IFI16 autoantibodies, compared to just 24% of patients with primary non-SLE GN and 5% of HCs. The presence of anti-IFI16 antibodies inversely correlated with proteinuria (univariate analysis) and C3 hypocomplementaemia (univariate and multivariate analyses). Conclusions: The inverse correlations observed between anti-IFI16 positivity, proteinuria and C3 hypocomplementaemia suggest that anti-IFI16 antibodies do not contribute to renal inflammation in SLE; indeed they may even prevent complement consumption. Anti-IFI16 antibodies hold the potential to serve as a new biomarker of disease activity in SLE.