Neutrophil extracellular traps in the anti-infectious defense of human organism

Abstract

Background. Neutrophil extracellular traps (NETs) are net-like structures that have been investigated in inflammatory diseases. However, the presence of NETs in infected persons without clinical symptoms has not been yet studied.Aim. To reveal NETs in healthy persons during and after the H1N1 influenza pandemic as well as to study the functional activity of NETs.Materials and methods. The study included two groups of volunteers (n = 10 in each group) aged 20–25 years. The first group of volunteers was examined in the absence of acute diseases during one month before the study and in the absence of chronic diseases in the medical history. Volunteers of the second group were in contact with patients with influenza, but did not get sick. The comparative study also included patients with acute inflammation in the abdominal cavity (appendicitis, cholecystitis, abscess; 12 patients) and 9 patients with non-specific ulcerative colitis. Neutrophils were isolated from the blood by the traditional method of Ficoll density centrifugation. The number, morphology, and functional activity of NETs were determined (by capture of Klebsiella pneumoniae). SYBR Green I-based fluorescence microscopy was used to visualize and quantify NETs.Results. In healthy volunteers who were not in contact with infected patients, spontaneous NETs formation did not occur. Neutrophils of persons who were in contact with infected patients spontaneously formed NETs. In this case the number of NETs reached 8.58 ± 0.51%, and the size of NETs amounted to 39.68 ± 3.52 µm. NETs effectively captured cells of the tested microorganism, which was accompanied by retraction of network fibers and transformation of the network structure into a cloud-like one, which retained 89.38 ± 5.86 microbial cells. For comparison, the NETs in patients with acute inflammation in the abdominal cavity captured and bound 20.2 ± 1 .67 microbial cells and with non-specific ulcerative colitis – 5.53 ± 0.34 cells.Conclusion. High binding capacity of NETs is a factor contributing to effective defense of the body against the development of an infectious disease with manifested clinical symptoms.