Neutrophil-Extracellular Traps, Cell-Free DNA, and Immunothrombosis in Companion Animals: A Review

Abstract

Immunothrombosis is a potentially beneficial physiological process that aids innate immunity and host defense against pathogen invasion. However, this process can also be damaging when it occurs to excess or in critical blood vessels. Formation of extracellular traps by leukocytes, particularly neutrophils, is central to our understanding of immunothrombosis. In addition to degranulation and phagocytosis, extracellular traps are the third mechanism by which neutrophils combat potential pathogens. These traps consist of extracellular DNA decorated with bactericidal cellular proteins, including elastase, myeloperoxidase, and cathepsins. Neutrophils can release these structures as part of a controlled cell-death process or via a process termed vital NETosis that enables the cells to extrude DNA but remain viable. There is accumulating evidence that NETosis occurs in companion animals, including dogs, horses, and cats, and that it actively contributes to pathogenesis. Numerous studies have been published detailing various methods for identification and quantification of extracellular trap formation, including cell-free DNA, measurements of histones and proteins such as high-mobility group box–1, and techniques involving microscopy and flow cytometry. Here, we outline the present understanding of these phenomena and the mechanisms of extracellular trap formation. We critically review the data regarding measurement of NETosis in companion animals, summarize the existing literature on NETosis in veterinary species, and speculate on what therapeutic options these insights might present to clinicians in the future.

NETs analysed by novel calprotectin‐based assays in blood donors and patients with multiple myeloma or rheumatoid arthritis: A pilot study

“…Calprotectin contributes to the antimicrobial activity of NETs by binding of zinc and manganese, but that property can also be responsible for cell and tissue damage . Methods for NET assays in body fluids have included quantitation of cell‐free DNA and neutrophil elastase, and there are ELISA methods for quantification of MPO‐DNA complexes, so‐called NET remnants . However, detection of calprotectin in complexes with a major DNA component by an immunoassay would give improved specificity and also allow rapid testing of large number of samples.…”

“…NETs contribute to the production of autoantibodies against citrullinated proteins in RA . NET release from neutrophils is emerging as an important factor in thrombogenesis, so‐called immunothrombosis, which takes place in sepsis (ie disseminated intravascular coagulation) and malignancy . Multiple myeloma is a typical example of a serious disease with immune imbalance and increased levels of proinflammatory cytokines such as IL‐6 and IL‐1 .…”

Elephant Genomes Elucidate Disease Defenses and Other Traits

“…Uncontrolled activation of these factors leads to immune induced disease pathogenesis through excessive inflammation. In humans and other mammals, neutrophil activation directly contributes to tissue damage through the release of neutrophil extracellular traps (NETs) 38,39 . Functional studies to compare cytokine secretion and NET release in response to infectious agents could confirm that genetic differences in innate immunity contribute to differences in disease susceptibility and outcomes between Asian and African elephants.…”

Utility of cell-free DNA concentrations and illness severity scores to predict survival in critically ill neonatal foals

“…Though there exists a lack of consensus on the origins of circulating cell-free DNA, it is believed that circulating levels are related cellular breakdown and active DNA-release mechanisms in host cells [31]. The concept of neutrophil extracellular traps, or NETs, involves the release of web-like scaffolds of cell-free DNA composed of extracellular chromatin which can enhance antimicrobial activity in the face of an infectious stimulus [32]. A model utilizing canine neutrophils has revealed that high-dose lipopolysaccharide stimulates the cells to undergo the production of NETs in vitro [33].…”