APOPTOSIS OF BOVINE NEUTROPHILS DURING MASTITIS EXPERIMENTALLY INDUCED WITH ESCHERICHIA COLI OR ENDOTOXIN

Authors: VAN OOSTVELDT, KAAT - BELGIUM; Tomita, Grant; Paape, Max; CAPUCO, ANTHONY - USDA ARS BELTSVILLE MD; BURVENICH, CHRISTIAN - GENT, BELGIUM

Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2001
Publication Date: 3/1/2002
Citation: Van Oostveldt, K., Tomita, G., Paape, M.J., Capuco, A.V., Burvenich, C. 2002. Apoptosis of Bovine Neutrophils During Mastitis Experimentally Induced with Escherichia Coli or Endotoxin. American Journal of Veterinary Research. 63(3): 448-453.

Interpretive Summary: Invasion of udder tissue by mastitis causing bacteria causes a rapid migration of neutrophils into the invading bacteria. The neutrophils release potent oxidants that destroy not only some of the bacteria but also some of the secretory epithelial cells within the udder. Because the life span of neutrophils in tissue is very brief, their death within a few hours safter leaving the blood circulatory system will lead to the release of their chemical arsenal causing further damage to the epithelium. Scientists at the USDA working with scientists at the University of Ghent, Belgium, discovered that neutrophils from cows undergo programmed cell death. Programmed cell death, or apoptosis, is a critical event in the pathology of disease. As neutrophils undergo programmed death, blebbing and contortion of the membrane surrounding the neutrophil occurs. This is followed by a rapid shrinkage of the cell. These dying cells are swiftly eaten by professional scavengers called macrophages which digest not only the cell but also all of the toxic chemicals. Thus, the macrophages prevent further damage to the milk secretory cells of the udder. Without programmed cell death, the neutrophils would swell and burst, dumping all of their toxic chemicals into the udder tissue causing extensive damage and permanent scarring of the mammary gland. Without this programmed cell death, the cow would never be able to produce the amount of milk it was genetically designed to produce.

Technical Abstract: Apoptosis regulates the clearance of neutrophils from the inflammatory site without inducing additional inflammatory reactions. In the current study, the percentage of apoptotic neutrophils was determined in blood samples taken from cows with E. coli mastitis or endotoxin induced mastitis following an in vitro incubation period of 3 h. A flow cytometric technique was used to detect apoptosis and necrosis of bovine neutrophils using fluorescein isothiocyanate labeled annexin-V in combination with propidium iodide. On average, no significant changes were detected during endotoxin challenge. However, E. coli challenge increased the level of apoptotic neutrophils in blood and a peak was observed 18 h after challenge (P<0.01). At this time, 20% of the neutrophils were apoptotic compared to control levels (5%). During E. coli and endotoxin challenge, studies have shown that spontaneous respiratory burst activity was increased. Because no accelerated apoptosis was detected during endotoxin mastitis, we sugges that acceleration of neutrophil apoptosis during mastitis caused by increased respiratory burst is minimal. Other studies have shown that the cytokine tumor necrosis factor-alpha (TNFa), which is absorbed in the plasma during an inflammatory reaction, is less absorbed during endotoxin induced mastitis compared to E. coli induced mastitis. It is also known that TNFa induces apoptosis in neutrophils. Therefore, it is thought that the absorption of TNFa in plasma might be responsible for the accelerated apoptosis during E. coli mastitis whereas during endotoxin mastitis the concentration of TNFa in plasma might not be high enough to induce accelerated apoptosis of neutrophils.