Bovine neutrophils form extracellular traps in response to the gastrointestinal parasite Ostertagia ostertagi

Authors: MENDEZ, JONATHAN - University Of Maryland; SUN, DONGLEI - University Of Maryland; Tuo, Wenbin; ZHENGGUO, XIAO - University Of Maryland

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2018
Publication Date: 12/4/2018
Citation: Mendez, J., Sun, D., Tuo, W., Zhengguo, X. 2018. Bovine neutrophils form extracellular traps in response to the gastrointestinal parasite Ostertagia ostertagi. Scientific Reports. 8:17598. https://doi.org/10.1038/s41598-018-36070-3
DOI: https://doi.org/10.1038/s41598-018-36070-3

Interpretive Summary: A wide-spread parasite, Ostertagia ostertagi (OO) leads to billions of dollars of cattle production losses annually. Scientists are unclear why cattle immune systems can't resist the disease. Neutrophils, the immune system's white blood cell first responders, release neutrophil extracellular traps (NETs) to contain many pathogens. In this project, we studied how OO regulates the formation of NETs in cattle. Our study validated that OO extract (ostertagi larval soluble extract) caused NET production. Consistent with existing literature, we demonstrated that induced NETs were dependent on two enzymes - NADPH oxidase and myeloperoxidase. Like OO extract, Live OO stage 4 larvae and a free-living soil nematode, Caenorhabditis elegans, also caused neutrophils to form NETs. This suggests that bovine NET production is a mechanism against a broad range of pathogens. This is the first report demonstrating OO-induced NET formation by cattle neutrophils and is a potential mechanism against infection by the immune system of cattle. The information provides researchers with a better understanding of cattle immunity to the parasite and will benefit vaccine development.

Technical Abstract: Ostertagia ostertagi (OO) is a widespread parasite that causes chronic infection in cattle and leads to annual losses of billions of dollars in the cattle industry. It remains unclear why cattle are unable to mount an effective immune response despite a large influx of immune cells to the infected abomasal mucosa and draining lymph nodes. Neutrophils, the immune system's first responders, have the capacity to release neutrophil extracellular traps (NETs) to contain various pathogens, including some parasites. In the present study, the mechanisms by which O. ostertagi influence bovine NET formation were investigated. O. ostertagi larval soluble extract (OO extract) was able to induce typical NETs by purified neutrophils in vitro, confirmed by co-localization of extracellular DNA with typical NET-associated proteins histone and neutrophil elastase (NE). Consistent with existing literature, inhibition assays demonstrated that these OO extract-induced NETs were dependent upon the enzymes NADPH oxidase and myeloperoxidase (MPO). Live OO stage 4 larvae (L4) stimulated neutrophils to form NETs similar to those induced by OO extract. Unexpectedly, bovine neutrophils also released NETs in response to Caenorhabditis elegans, a free-living soil nematode, suggesting that bovine NET production may be a conserved mechanism against a broad range of nematodes. This is the first report demonstrating O. ostertagi-induced NET formation by bovine neutrophils, a potentially underappreciated mechanism in the early immune response against nematode infections.