Bovine neutrophils recruited by endotoxin to a teat cistern continuously produce oxygen radicals and show increased phagocytosis and extracellular chemiluminescence

In vitro effects of Escherichia coli lipopolysaccharide on the function and gene expression of neutrophils isolated from the blood of dairy cows

The objectives of this study were to investigate the effect of Escherichia coli lipopolysaccharide (LPS) on the function of bovine neutrophils (PMNL) collected from mid lactation cows and determine the differential effects of LPS on gene expression of PMNL purified from early and mid lactation cows. The PMNL from mid lactation cows (187±13 d postpartum) were incubated with 0, 1, 25, and 50 μg/mL of LPS for 120 min, and the generation of reactive oxygen species (ROS), PMNL extracellular traps (NET), chemotaxis, and killing of Staphylococcus aureus were determined. Incubation of PMNL with 25 μg/mL of LPS increased intracellular ROS by 79% in mitogen-stimulated PMNL. Addition of 50 μg/mL of LPS enhanced intracellular ROS by nonstimulated and stimulated PMNL by 184 and 154%, respectively. Nonstimulated PMNL incubated with 25 and 50 μg/mL of LPS had a 105% increase in NET. Addition of LPS had no effect on subsequent PMNL chemotaxis or killing of Staph. aureus. To examine the effect of LPS on the expression of genes involved in PMNL function and cytokine production, mRNA was purified from PMNL isolated from mid lactation (146±2 postpartum; n=10) and early lactation cows (7 d postpartum; n=10), after a 120-min incubation with 0 or 50 μg/mL of LPS. Amounts of interleukin-8 (IL-8), tumor necrosis factor (TNF), bactericidal/permeability-increasing protein (BPI), myeloperoxidase (MPO), superoxide dismutase 2 (SOD2), NADPH oxidase 4 (NOX4), Cytochrome b-245, α polypeptide (CYBA), histone H2A/1 (H2A/1), and histone H2B-like (H2B) mRNA were determined relative to that of β-actin by real-time quantitative PCR. Regardless of stage of lactation, PMNL incubated with 50 μg/mL of LPS had 537 and 45% higher mRNA contents of IL-8 and SOD2 compared with 0 μg/mL LPS, respectively. In addition, LPS augmented the expression of TNF, BPI, and CYBA (2,908, 59, and 158% compared with controls, respectively) only in PMNL from mid lactation cows. Addition of LPS did not affect mRNA levels of MPO, NOX4, H2A/1, or H2B. Independent of LPS treatment, PMNL from mid lactation cows had 99% higher mRNA contents of IL-8 compared with PMNL from early lactation cows. The PMNL from early lactation cows had a 634% increase in MPO mRNA expression relative to that from mid lactation cows. These results support that LPS directly stimulates PMNL to produce ROS and express NET. In addition, LPS enhances the generation of ROS by PMNL in response to other stimuli and increases the expression of genes encoding inflammatory mediators and enzymes involved in the production of ROS. Finally, reduced PMNL gene expression of IL-8 (regardless of LPS activation), TNF, CYBA, and BPI (upon stimulation with LPS) in early lactation may elucidate several mechanisms by which PMNL may become immune-incompetent during this period.

Neutrophil extracellular trap formation by bovine neutrophils is not inhibited by milk

Neutrophils are the first line of defense in a mammary gland infection. However, the process of neutrophil transmigration across a membrane and ingestion of fat and/or casein when incubated in milk have been shown to inhibit bacterial phagocytosis and oxidative burst functions. Recently, a killing mechanism has been described whereby stimulated neutrophils release nuclear and granule material in fibrous webs that physically trap and kill bacteria. We demonstrate that these neutrophil extracellular traps are also produced by bovine blood neutrophils stimulated with PMA/ionomycin. Importantly, neutrophil extracellular traps can be formed when neutrophils have been incubated for up to 6h in milk prior to stimulation. This contrasts milk's rapid inhibition of bacterial phagocytosis and oxidative burst functions in the neutrophil. Furthermore, stimulation of neutrophils with bacteria common to mammary gland infections leads to neutrophil extracellular traps being formed in milk. Some bacteria tested stimulated enhanced formation of neutrophil extracellular traps in milk compared to culture media. Therefore, being unaffected by incubation in milk may indicate an important role for neutrophil extracellular traps in defense against mastitis.

Increased leukotriene B4 production, complement C3 conversion and acid hydrolase enzyme concentrations in different leucocyte sub-populations of dogs with atopic dermatitis

Various markers of the inflammatory response were measured in peripheral blood mononuclear cells (PBMCs) and polymorphonuclear neutrophils (PMNs) from 31 dogs with atopic dermatitis (AD). The variables assayed included chemiluminescence, acid hydrolase enzyme concentrations, leukotriene B(4) (LTB(4)) production and complement C3 conversion. The results were compared to those derived from a population of clinically healthy dogs. Dogs with AD exhibited a significant increase in median LTB(4) production in PMNs compared to controls (0.94 versus 0.00 ng/10(6) cells; P<0.01). Significant increases in the median concentrations of intracellular beta-galactosidase (PBMC fraction - 0.42 versus 0.25 mU/10(6) cells; P<0.05) (PMN fraction - 0.47 versus 0.12 mU/10(6) cells; P<0.01) and beta-glucuronidase (PBMC fraction - 0.52 versus 0.27 mU/10(6) cells; P<0.05) were also evident in the AD group. Although median maximum chemiluminescence values for both leucocyte sub-populations were higher in controls, the differences recorded were not significant (P>0.05). However, the median time taken to reach maximum chemiluminescence was significantly shorter in the PMN fraction of dogs with AD (7.00 versus 10.00 min; P<0.01). Atopic dogs had a significant increase in the median percentage conversion of complement C3 to C3b (66.0 versus 57.3%; P<0.01). The results of this study indicate a priming of the inflammatory response in dogs with AD. The role of LTB(4) in the pathogenesis of canine AD and the potential efficacy of leukotriene antagonists in the treatment of this disorder warrant further investigation.

Viability of Milk Neutrophils and Severity of Bovine Coliform Mastitis

To study the host-pathogen interactions during Escherichia coli mastitis, we first determined whether E. coli infection would change blood and milk polymorphonuclear neutrophil (PMN) chemiluminescence (CL) and viability. We then hypothesized that when E. coli invade the mammary gland, the viable PMN in milk would efficiently phagocytose and destroy E. coli before establishment of infection. We observed that the phagocytosis-dependent and independent CL were closely linked to PMN viability and were crucial to the outcome of mastitis. Maximal PMN influx and colony-forming units in infected quarters appeared at postinfection hours (PIH) 6 to 24. This further boosted PMN recruitment through bone marrow-blood barrier as well as blood-milk barrier. The survival of recruited PMN in the E. coli-infected quarters was much higher than that of noninfected quarters. Chemiluminescence activity of PMN from the infected quarters significantly increased following E. coli infection, even exceeding that of blood at PIH 6, 12, and 18 to 24; no such increase was observed in noninfected quarters, suggesting that the various responses of milk PMN to stimuli resulted largely from PMN viability. The highest CL intensity and durability was observed in milk PMN from infected quarters at PIH 12. Whereas an increased viability of PMN in the noninfected quarters was only significant at PIH 6, the viability of PMN in infected quarters was long lasting and significantly higher at PIH 6 to 72. Importantly, higher preinfection milk PMN viability correlated with bacterial clearance, which was accompanied by faster recovery. Our study strongly supports the hypothesis that boosting milk PMN viability could be a strategy with which to prevent or reduce the severity of coliform mastitis in dairy cows. This strategy might be achieved through strengthening bone marrow functionality.