INVOLVEMENT OF NEUTROPHIL HYDROLYTIC ENZYMES IN THE MODIFICATION OF CIRCULATING IMMUNE COMPLEXES UNDER THE CIRCUMSTANCES OF EXPERIMENTAL SEPSIS

Abstract

Introduction. Neutrophils play an important role in the innate immune response. While patrolling the body, they find pathogens and destroy them by means of phagocytosis, degranulation, or formation of neutrophil extracellular traps (NETs). The latter process is accompanied by the release of chromatin along with granular enzymes, such as neutrophil elastase. Neutrophil-released enzymes are capable of breaking not only pathogens but also components of the host organism. Objectives. In the current work, we investigated the NETs effect on the composition of circulating IgG-IgM immune complexes at different stages of experimental sepsis-induced in laboratory mice. Research methods. In our study, we used an animal model of induced sepsis. The levels of circulating IgG and IgM, as well as IgG-IgM-containing immune complexes in sera were evaluated by using an enzyme-linked immunosorbent assay. Sera collected before induction of sepsis served as a negative control. Neutrophil elastase activity in serum samples was measured after adding fluorogenic neutrophil elastase substrate. NET formation was studied by staining with propidium iodide and was detected using a fluorescence microscope. Results. It was demonstrated that under septic conditions, the level of circulating IgG does not change significantly. The content of total IgM increased rapidly immediately after sepsis induction and reached its maximum 7 days later, remaining at high levels till the end of the experiment (16 days). Unlike total IgG and IgM, IgG-IgM-containing immune complexes were formed 3 days after sepsis induction, their maximum was observed on 7-9th day and then dropped. The decrease in the amount of circulating IgG-IgM-containing immune complexes was accompanied by the enhanced level of neutrophil elastase activity (a marker of NETs formation). Conclusions. Thus, the appearance of modified immunoglobulin complexes that are non-specific for the healthy organism in the process of acute inflammation can be initiated by NETs and released hydrolytic enzymes of neutrophil granules. Disclosures. The authors declare no conflict of interests. Author contribution. RB designed the study; RB, TD, SP: performed the experiments; RB, TD, SP: wrote the manuscript.

Keywords

• neutrophil extracellular traps; acute inflammation; igg-igm-containing immune complex; neutrophil elastase