A new, label-free, bioimpedance assay designed to measure serum neutrophil extracellular trap (NET)-inducing activity may be used to evaluate patients with antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV), monitor treatment effectiveness, and test new therapies, according to a new study published in Kidney International.

The researchers recruited 62 patients presenting with active AAV with major organ involvement who participated in the prospective Maastricht vasculitis study between April 2019 and June 2021.

There were 35 patients with newly diagnosed AAV and 27 patients with relapsing disease. Of all participants, 38 had kidney involvement and 31 had lung complications.

The study authors isolated neutrophils, stimulated or inhibited the cells depending on the procedure, and performed NET visualization experiments. Using the novel technique, they analyzed the NET-inducing activity of serum at active disease, during the first 6 weeks of treatment, and after 6 months of treatment.

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According to the results, NET-inducing serum activity was detected in 47 patients with active AAV at study onset. After 6 weeks of treatment with immunosuppressive agents, NET-inducing activity was significantly reduced. A later increase at 6 months could possibly identify patients with AAV relapse.

Moreover, NET-inducing activity at the time of diagnosis appeared to be linked with kidney involvement and proteinuria. The researchers found NETs and typical ANCA-associated glomerulonephritis lesions in kidney tissue, which correlated with systemic serum NET-inducing activity

“The bio-impedance analysis has several advantages over other widely-used techniques to detect NETs such as Transmission Electron Microscopy, ELISAs, and immunofluorescence. The bio-impedance method is label-free, quantitative, informative about kinetics, and less time-consuming,” Aendekerk and colleagues wrote.

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“Furthermore, it does not require washing steps, which can affect the outcome by impairing essential adherence steps of neutrophils, inducing activation of neutrophils and/or removing extremely fragile NETs.”

The formation of NETs is one of the main events in the pathogenesis of AAV and glomerulonephritis. NETs are formed in the serum by the extrusion of neutrophil chromatin fibers laced with histones and enzymes, during the active stage of AAV. The more NETs are formed in serum, the more NETs can be found in the kidneys as well.


Aendekerk JP, Ysermans R, Busch MH, et al. Assessment of longitudinal serum neutrophil extracellular trap-inducing activity in anti-neutrophil cytoplasmic antibody-associated vasculitis and glomerulonephritis in a prospective cohort using a novel bio-impedance technique. Kidney Int. Published online April 21, 2023. doi:10.1016/j.kint.2023.03.029