Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/1999
Publication Date: N/A
Interpretive Summary: Bacterial infection of the bovine udder costs US dairymen $2 billion annually. Antibiotics are the major means of prophylaxis and therapy. This has resulted in development of increasingly resistant strains of bacteria and in antibiotic contamination of market milk. Researchers have sought means of enhancing the cow's natural defense against infection of the mammary gland. Because white blood cells (PMN) ar the major natural defense against infection of the udder they have received the lion's share of research on natural defense mechanisms. After PMN migrate from blood to milk they are less bactericidal. This has been attributed primarily to the engulfing of milk fat, which inhibits the ingestion of bacteria. Complexity of the udder prevents determination of the direct effect of PMN migration. The current study determined ability of PMN to engulf and destroy bacteria before and after migration across culured monolayers of udder cells. After migration PMN were less bactericidal, which showed that migration from blood to milk alone caused a decrease in the bactericidal ability of PMN. This procedure will also be used to study methods to enhance PMN migration from blood to milk while maintaining their bactericidal ability.
Technical Abstract: The effect of diapedesis on the phagocytic and oxidative burst activity of polymorphonuclear neutrophil (PMN) was examined using an in vitro cell culture system consisting of a monolayer of primary mammary epithelial cells. Isolated blood PMN from 10 cows were added to the basal side of the epithelial cell monolayer. Diapedesis was induced by the addition of complement factor C5a to the apical side of the monolayer. PMN phagoctosi of Staphylococcus aureus and oxidative burst were measured before diapedesis on PMN that were non-activated and activated by incubation with C5 and on PMN after diapedesis, using flow cytometry. Percentage PMN fluorescing due to phagocytosis of S. aureus and oxidative burst were reduced 21.2% and 14.4% after diapedesis. Preincubation in the presence of C5a had no effect on percentage PMN fluorescing due to phagocytosis or oxidative burst. The capacity for individual migrated PMN neutrophils to phagocytose S. aureus and to produce oxidative burst, as measured by the intensity due to oxidative burst, had no effect on intensity due to phagocytosis. These data show that PMN diapedesis across mammary epithelium results in decreased phagocytosis and oxidative burst of the PPN.