Extracellular Trap Formation by Donkey Polymorphonuclear Neutrophils Against Toxoplasma gondii

Toxoplasma (T.) gondii is an obligatory intracellular apicomplexan parasite. The donkey is one of the intermediate hosts of T. gondii. There are almost no data about T. gondii infection in donkeys, apart from a few seroprevalence reports. The aim of the study was to detect the formation of extracellular traps by donkey polymorphonuclear neutrophils (PMNs) when exposed to T. gondii tachyzoites in vitro. Tachyzoites were observed to be entrapped within extracellular traps (NET) structures. Myeloperoxidase, neutrophil elastase (NE), and histone (H3) were observed in NET structures. NE and reactive oxygen species activity increased with time and was higher in the PMN-tachyzoite cocultures. Some tachyzoites were seen close localization to the nucleus of neutrophils. Degranulation and extracellular traps were observed simultaneously in some donkey neutrophils after incubation for 1 hour. The tachyzoite invasion rate decreased in PMN-tachyzoite cocultures in comparison to the controls. NETs can negatively affect the viability of entrapped tachyzoites in addition to their action of physical entrapment. NE may play a key role in the viability of T. gondii in donkeys. The amount of extracellular DNA increased with incubation time in the PMN-tachyzoite cocultures (P < .001). This is a first report regarding the formation of donkeys NETs after exposure to T. gondii tachyzoites in vitro. Unlike sheep and cattle PMN, degranulation and extracellular traps developed in the same neutrophil. Further studies focusing on signaling pathways may shed light on what determines the behavior of donkey neutrophils after exposure to T. gondii. (C) 2018 Elsevier Inc. All rights reserved.