Assessment of Paratuberculosis Vaccination Effect on In Vitro Formation of Neutrophil Extracellular Traps in a Sheep Model

Vaccination of domestic ruminants against paratuberculosis has been related to homologous and heterologous protective effects that have been attributed to the establishment of a trained immune response. Recent evidence suggests that neutrophils could play a role in its development. Therefore, we propose an in vitro model for the study of the effect of paratuberculosis vaccination on the release of neutrophil extracellular traps (NETs) in sheep. Ovine neutrophils were obtained from non-vaccinated (n = 5) and vaccinated sheep (n = 5) at different times post-vaccination and infected in vitro with Mycobacterium avium subsp. paratuberculosis (Map), Staphylococcus aureus (SA), and Escherichia coli (EC). NETs release was quantified by fluorimetry and visualized by immunofluorescence microscopy. Typical NETs components (DNA, neutrophil elastase, and myeloperoxidase) were visualized extracellularly in all infected neutrophils; however, no significant percentage of extracellular DNA was detected in Map-infected neutrophils compared with SA- and EC-infected. In addition, no significant effect was detected in relation to paratuberculosis vaccination. Further assays to study NETs release in ovine neutrophils are needed. Preliminary results suggest no implication of NETs formation in the early immune response after vaccination, although other neutrophil functions should be evaluated.