Skip to main content
ARS Home » Research » Publications at this Location » Publication #145206
Title: THE BOVINE NEUTROPHIL: STRUCTURE AND FUNCTION IN BLOOD AND MILK

Author
item Paape, Max
item Bannerman, Douglas
item ZHAO, XIN - MCGILL UNIV, CANADA
item LEE, JAI-WEI - MCGILL UNIV, CANADA

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2003
Publication Date: 9/1/2003
Citation: Paape, M.J., Bannerman, D.D., Zhao, X., Lee, J. 2003. The bovine neutrophil; structure and function in blood and milk. Veterinary Research. Vol. 34, pp. 597-627.

Interpretive Summary: When bacteria invade the mammary gland they release potent toxins that act as signals for recruitment of neutrophils, a type of white blood cell that ingest and destroy bacteria. Scientists at the USDA-ARS in Beltsville discovered that in the neutrophils eagerness to seek and destroy the invading bacteria, they mistakenly consume enormous numbers of fat globules that are floating along with bacteria in the milk. Soon, the neutrophils become completely rounded because as they ingest the fat they also consume their own cell membrane and loose the tentacles that normally protrude from the cell surface that are used to trap and eat bacteria. Once they become round neutrophils loose their ability to ingest bacteria. The bacteria quickly take advantage of the situation, go on the offense and rapidly multiply within the confines of the gland. Soon, a massive infection develops and millions of neutrophils migrate from blood into milk and into the bacterial hoard. In their haste to kill the bacteria, the neutrophils release potent chemicals that destroy not only some of the bacteria but also some of the epithelial cells lining the ducts and alveoli within the udder. Enormous numbers of delicate milk producing mammary cells are destroyed, resulting in permanent scarring of the gland and lost milk production. Scientists are now trying to determine what makes fat globules so appealing to neutrophils. Once this is known, strategies can be developed that will steer neutrophils away from fat globules and towards bacteria.

Technical Abstract: Polymorphonuclear neutrophil leukocytes (PMN) form the first line of cellular defense against invading pathogens. The PMN is characterized by a polymorphic segmented nucleus, numerous cytoplasmic granules that provide constituents for killing bacteria, large stores of glycogen for energy and a highly convoluted surface that is used for phagocytosis of bacteria and formation of intracellular phagocytic vacuoles. Numerous receptors are present on the PMN surface. Some receptors are used to detect chemoattractants that allow PMN to migrate towards areas of inflammation. Other receptors bind immunoglobulins and compliment components that allow PMN to initiate phagocytic and bactericidal functions. Scientists at the USDA, Beltsville, observed a change in morphology in PMN when they leave blood and enter milk. In milk, PMN ingest milk fat globules and casein that result in large intracellular membrane bound vacuoles. Internalization of the cell membrane leads to a loss of pseudopodia and cell rounding. Cytoplasmic granules migrate and fuse to vacuoles forming phagolysosomes. This loss of membrane and cytoplasmic granules result in diminishment of PMN phagocytic and bactericidal activities and compromise intramammary defense.