Blood polymorphonuclear leukocyte responses against Staphylococcus aureus in primiparous and pluriparous Lacaune and Santa Inês ewes

Abstract In this study, we evaluated the viability, intracellular production of reactive oxygen species (ROS) and phagocytosis of Staphylococcus aureus by blood polymorphonuclear leukocytes (PMNLs) in primiparous and pluriparous Santa Ines and Lacaune ewes. Blood was collected from 14 Santa Ines ewes (seven primiparous and seven pluriparous) and 14 Lacaune ewes (seven primiparous and seven pluriparous). The viability of PMNLs, intracellular ROS production, and S. aureus phagocytosis were evaluated using flow cytometry. No parity effect on blood’s PMNLs functionality was found. However, comparing primiparous and pluriparous ewes, we noticed a difference in the opsonized phagocytic response to S. aureus, suggesting that pluriparous ewes could be better protected against S. aureus, although further field studies are needed. Antibody-mediated opsonization of S. aureus was associated with a lower intensity of S. aureus phagocytosis in both primiparous and pluriparous ewes, while it had no effect on the percentage of S. aureus phagocytosis. The percentage and geometric mean fluorescence intensity (GMFI) of S. aureus phagocytosis behaved differently in Lacaune and Santa Ines ewes, which could be explained by breed and farm effects. The intensity of intracellular ROS production by PMNLs when stimulated with S. aureus was higher than that of unstimulated basal PMNLs in both primiparous and pluriparous ewes, while no effect on the percentage of PMNLs that produced ROS was observed. Thus, our study provides novel insights into PMNLs’ functionality in primiparous and pluriparous ewes, which could impact their health, although further research is needed to extrapolate conclusions to the field.