The bovine neutrophil: Structure and function in blood and milk

Abstract

-Migration of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland provide the first line of defense against invading mastitis pathogens. Bacteria release potent toxins that activate white blood cells and epithelial cells in the mammary gland to secrete cytokines that recruit PMN that function as phagocytes at the site of infection. While freshly migrated PMN are active phagocytes, continued exposure of PMN to inhibitory factors in milk such as fat globules and casein, leads to altered PMN morphology and reduced phagocytosis. In the course of phagocytosing and destroying invading pathogens, PMN release chemicals that not only kill the pathogens but that also cause injury to the delicate lining of the mammary gland. This will result in permanent scarring and reduced numbers of milk secretory cells. The life span of PMN is limited by the onset of apoptosis. To minimize damage to mammary tissue, PMN undergo a specialized process of programmed cell death known as apoptosis. Macrophages quickly engulf and phagocytose apoptotic PMN, thereby minimizing the release of PMN granular contents that are damaging to tissue. The PMN possess an array of cell surface receptors that allow them to adhere and migrate through endothelium and to recognize and phagocytose bacteria. One receptor found on phagocytes that is receiving considerable attention in the control of infections by Gram-negative bacteria is CD14. Binding of lipopolysaccharide (LPS) to membrane bound CD14 causes release of tumor necrosis factor-a and sepsis. Binding of LPS to soluble CD14 shed from CD14-bearing cells results in neutralization of LPS and rapid recruitment of PMN to the site of infection. Recent advances in the fields of genomics and proteomics should greatly enhance our understanding of the PMN role in controlling intramammary infections in ruminants. Further, manipulation of PMN, through either recombinant proteins such as soluble CD14 that enhance PMN response or agents that mediate PMN apoptosis, may serve as novel therapeutics for the treatment of mastitis.

Possible role of interferon tau on the bovine corpus luteum and neutrophils during the early pregnancy

“…PMNs are the most important immune cells as the first line of cellular defence against acute inflammatory reaction (Paape et al 2003). PMNs have been detected in the CL in cows, humans and rats during the oestrous (menstrual in humans) cycle and early pregnancy (Brannstrom et al 1994, Best et al 1996, Brannstrom & Friden 1997, Jiemtaweeboon et al 2011.…”

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

“…neutrophils) is originated from the blood through the chemotaxis and diapedesis in response to a local aggression (Paape et al 2003). With this in mind, it is well known that the percentage of neutrophils markedly increased during IMIs (Pyörälä 2003, Mira et al 2013, as demonstrated here by the positive correlation between the milk SCC and the percentage of milk PMNs.…”

“…With this in mind, variations among cows in neutrophil activity might explain differences in susceptibility of the mammary gland to infection (Paape et al 2003). Regarding our results, it is possible to measure the presence of the PMNs targeting the immune function, which could help in the development of a new method to select cow with a better immune response, although more studies are necessary.…”

“…The PMN is a highly active cell so shortly after the migration of PMN to mammary gland, if it continually stays in the milk this phagocyte starts to change morphology and decrease its function as it englobes fat globules and casein. Thus, the prolonged exposure to milk compounds reduces the PMN capacity to produce reactive oxygen species (ROS) and phagocytosed pathogens, what means that milk PMN are less responsive to pathogens since they have already been activated by the milk compounds (Paape et al 2003). In face of, as milk neutrophils are largely recruited during infection, we speculated that the neutrophil functions can be used to diagnose mastitis.…”

The role of oxidative stress and inflammatory response in the pathogenesis of mastitis in dairy cows

“…Inflammatory response during mastitis is marked by the increased blood flow in infected tissue, increased vascular permeability, leukocyte migration from blood vessels into interstitial space and accumulation of leukocytes at the site of trauma (Tkalčević and Hrvačić, 2011). Bacteria release toxins which activate leukocytes and epithelial cells in the mammary gland to release cytokines which attract numerous polymorphonuclear leukocytes (PMN) functioning as phagocytic cells at the site of infection (Paape et al, 2003). PMN such as neutrophils and macrophages are the first cells infiltrating the site of trauma (Wellnitz et al, 2012).…”