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Title: VARIATION AMONG GOATS IN THE ABILITY OF THEIR POLYMORPHONUCLEAR NEUTROPHIL LEUKOCYTES AND MAMMARY SECRETIONS TO SUPPORT PHAGOCYTOSIS: INHIBITORY EFFECTS OF MILK FAT GLOBULES

Author
item Paape, Max
item CONTRERAS, A - MURCIA, SPAIN
item Ledbetter, Tonya

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2003
Publication Date: 7/1/2004
Citation: Paape, M.J., Contreras, A., Ledbetter, T.K. 2004. Variation among goats in the ability of their polymorphonuclear neutrophil leukocytes and mammary secretions to support phagocytosis: inhibitory effects of milk fat globules. Small Ruminant Research. 54:183-189.

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 that is used to form the stomach inside the cell that contain the fat globules. Once they are round they become totally defenseless and the invading bacteria simply bounce off and away from these engorged cells. 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 that quickly turns clinical. 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 toward bacteria.

Technical Abstract: The objectives of this study were to determine if fat globules and casein in goat milk were inhibitory to phagocytosis by polymorphonuclear neutrophils (PMN) isolated from blood, and to determine if variation existed among goats in the ability of PMN to phagocytose and in the ability of milk whey to support phagocytosis. In the presence of either serum, whole milk, skimmed milk or milk whey, PMN were incubated with Staphylococcus aureus. Both pooled serum and pooled whey had a concentration-dependent effect on PMN phagocytosis (P < 0.01). In the presence of pooled serum, whole milk but not skimmed milk reduced (P < 0.01) phagocytosis when compared to serum and whey. Differences existed (P < 0.01) among goats in the ability of PMN to phagocytose and in the ability of milk whey to support phagocytosis. The inhibition of PMN phagocytosis by fat globules could contribute to susceptibility to intramammary infection by mastitis pathogens. Variation among goats in PMN phagocytose and in mammary secretions to support phagocytosis may contribute to differences among goats in resistance to mastitis.