Circulating Level of Neutrophil Extracellular Traps Is Not a Useful Biomarker for Assessing Disease Activity in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of life-threatening disorders, and frequently affects the kidneys. This study investigated whether the circulating neutrophil extracellular traps (NETs) levels were associated with disease activity of AAV. We collected serum samples from 34 patients with AAV in active stage and 62 patients with AAV in remission. Cell free DNA in serum was quantified using the Quant-iT PicoGreen assay. NETs associated MPO-DNA complexes, citrullinated-histone H3-DNA (cit-H3-DNA) complexes and the concentration of deoxyribonuclease I (DNase I) were quantified using ELISA. The activity of DNase I was quantified using radial enzyme-diffusion method. Associations between circulating levels of NETs with clinico-pathological parameters were analyzed. Serum levels of NETs in active AAV patients were significantly higher than those in healthy controls, and the level of cell free DNA correlated with C-reactive protein (CRP). However, no correlation was found between MPO-DNA complexes or cit-H3DNA complexes level and CRP. Also there was no significant correlation between NETs level and initial serum creatinine, estimated glomerular filtration rate (eGFR), crescents formation or Birmingham Vasculitis Activity Score (BVAS). Furthermore, there was no significant difference of serum levels of cell free DNA or MPO-DNA complexes between active stage and remission of AAV. In conclusion, circulating levels of NETs cannot be used as a biomarker to assess disease activity in AAV patients.