Toxoplasma gondii Triggers Neutrophil Extracellular Traps Release in Dogs

Abstract

Toxoplasma gondii (T. gondii) can cause zoonotic toxoplasmosis worldwide. Neutrophil extracellular traps (NETs) have been known as a novel effector mechanism against T. gondii infection in the innate system of humans, cats, and sheep. Dogs are the intermediate host of T. gondii, in which the use of NETs against T. gondii infection remains unclear. Thus, this study aims to examine the effects of T. gondii on NETs release in dogs, and to further investigate the mechanism involved in the process. T. gondii-triggered NETs were analyzed by scanning electron microscopy (SEM) and fluorescence confocal microscopy, and the mechanism of T. gondii-triggered NETs release was determined by using inhibitors and a fluorometric reader. The results showed that T. gondii tachyzoites significantly triggered NETs-like structures, which consisted of DNA decorated with neutrophil elastase (NE) and myeloperoxidase (MPO). Further investigations revealed that reactive oxygen species (ROS)-, NADPH oxidase-, Rac 1or p38 mitogen-activated protein kinase (MAPK)-signaling pathways were relevant to T. gondii tachyzoites-triggered NETs release. Moreover, zymosan-triggered NETs release was strikingly degraded by T. gondii tachyzoites treatment, indicating that T. gondii may escape from the NETs-based capture strategy. Taken together, promoting NETs release is suggested to limit motility and evade infection of T. gondii in dogs.

Extracellular Traps Released by Neutrophils from Cats are Detrimental to Toxoplasma gondii Infectivity

“…In a recent report, Wei and colleagues showed that treatment of dog neutrophils with the NADPH oxidase inhibitor diphenylene iodonium (DPI) prevented DNA release in response to T. gondii [35]. Similar results were obtained with donkey neutrophils [34].…”

“…Furthermore, we show that the cystogenic strain ME49 also induces NET release, and that production of NET by cat neutrophils in response to both virulent or cystogenic strains occurs either in a classical way, after a few hours, or in a rapid way, within the first 15 min of interaction with parasites. Early NET release has been previously shown for neutrophils from intermediate hosts in response to RH strain [30,31,34,35] and from bovine neutrophils stimulated with a related apicomplexan parasite, Besnoitia besnoiti [49]. Zhou and colleagues present evidence that bovine neutrophils produce NET within ≈30 min of interaction with B. besnoiti bradyzoites, and that the overall phenotype and crawling activities of neutrophils seem not to be affected by this event, suggesting that the rapid NET release is vital [49].…”

“…Therefore, it is tempting to speculate that the virulent RH tachyzoites we used in our assays are producing nucleases or other factors which could degrade NET and enable the survival and/or escape of at least part of the parasite population. Corroborating this hypothesis, Wei and colleagues recently showed that T. gondii tachyzoites from the same strain can degrade NET induced by zimosan [35]. Additional investigations are needed to elucidate the molecular factors involved there.…”

“…A few years later, production of NET in response to T. gondii infection was shown for other intermediate hosts. Neutrophils from dog [35], sheep and cattle [31], donkey [34], harbour seal [30], and dolphin [33] all release NET induced by this parasite. Moreover, Lacerda and colleagues recently showed that neutrophils from cats also produce NET in response to T. gondii [36], although without exploring its mechanism or NET toxicity to the parasite.…”

“…Release of NET can be triggered by an uncountable number of biological stimuli, including bacteria, fungus, viruses, helminths, and protozoans such as the pathogenic parasite T. gondii [24][25][26][27][28]. Neutrophils from different organisms release NET upon interaction with T. gondii, including those of mice, humans, dogs, cattle, sheep, donkey, harbor seals, and dolphins [29][30][31][32][33][34][35], all of which are intermediate hosts for the parasite. Recently, extracellular traps were also shown to be produced by cat neutrophils [36].…”