Intracellular reactive oxygen species production and phagocytosis of Staphylococcus aureus by milk neutrophils as tool to diagnose mastitis and identify susceptible dairy cows

Abstract

The immune response capacity of the mammary gland plays a major role to determine if mastitis will or not be established. Thus, we hypothesize that a better understanding of polymorphonuclear neutrophil leukocyte (PMN) function will elucidate mechanisms that will improve our knowledge of how we could avoid an inflammatory process by increasing the immune capacity of the cow, and even further, to search for a tool to diagnose mastitis or a possible way to select and identify non-susceptible animals. The present study utilized 112 quarters from 28 Holstein dairy cows that were divided into quarters milk samples with somatic cell count (SCC) <2×105 cells mL-1 (n=72) and SCC >2×105 cells mL-1 (n=40). The percentages of milk PMNs and the levels of intracellular reactive oxygen species (ROS) and the phagocytosis of Staphylococcus aureus by milk neutrophils were evaluated by flow cytometry. Our results showed a higher percentage of neutrophils in quarter milk samples with high SCC (P=0.0003), and this group also had a significantly higher percentage of neutrophils that produced ROS (P=0.008). On the other hand, the phagocytosis intensity of S. aureus by milk neutrophils was higher in quarters with low SCC (P=0.003), suggesting a better mammary gland immunity against invading pathogens. Analyzing the results of the predictive values of the measured PMN functions, they cannot be used isolated as a good diagnosis test since none of them had a satisfactory sensitivity and specificity values, which was also confirmed by the Youden index values being far from one. In conclusion, the assessment of milk bovine neutrophil functions could improve our understanding of the cellular basis of mastitis. Although, the intracellular ROS production and S. aureus phagocytosis by milk neutrophil did not have high predictive values to detect intramammary infections, our results strengthen the idea that that poor bovine mammary gland neutrophil phagocytic ability may be associated with high SCC, and might be considered to identify susceptible dairy cows to mastitis.

Natural Agents against Bovine Mastitis Pathogens

“…They have also found their place as natural preservatives in the pharmaceutical, food, and cosmetic industry [ 43 ]. ROS production is linked with the inflammatory process and is provided by netrophils in milk [ 46 ].…”

Systemic inflammatory biomarkers and somatic cell count in dairy cows with subclinical mastitis

“…It has been show that even under healthy conditions of daily handling or milking, leukocytes are present in the mammary gland ( Sordillo, 2018 ). Increased SCC and influx of PMN are seen in cows with subclinical mastitis ( Alhussien et al., 2016 ; Molinari, Blagitz, Della Libera, Batista & Souza, 2018 ).…”

Evaluation of Recombinant Bovine Interleukin-8 (rbIL-8) as a Treatment for Chronic Intramammary Infection in Dairy Cows

“…In addition, the infused groups presented greater mean fluorescence for both dyes ( Figure 6 ) and more high-fluorescence neutrophils in the milk compared with the control groups ( Figure 5 A), which could be partially attributed to the fact that the control group had fewer neutrophils isolated than the chronic groups (3.36 ± 0.18 vs. 3.87 ± 0.09, respectively). Another study reported that cows with mastitis have a greater number of neutrophils positive for ROS compared to non-mastitis cows after being challenged with Staphylococcus aureus [ 21 ]. Perhaps, neutrophils from chronic mastitis cows are in an active state and are capable of eliciting phagocytosis but do not resolve the infection.…”