Staphylococcus aureus is a frequent cause of mastitis in dairy cows. However, pathogenesis of the infection has not been completely defined. We report the invasion of two strains of S. aureus into a bovine mammary epithelial cell line and a bovine mammary epithelial cell primary culture. Invasion of S. aureus into bovine mammary cells was time-dependent. Transmission electron microscopy of bovine mammary cells invaded by S. aureus showed intracellular replication of the bacterium within membrane-bound vacuoles. Invasion was reduced significantly when bovine mammary epithelial cells were treated with inhibitors of F-actin microfilament polymerization but not when these cells were treated with inhibitors of microtubule formation. Results indicated that S. aureus is capable of invading and replicating inside bovine mammary epithelial cells. Data also suggested that S. aureus invasion of bovine mammary epithelial cells requires active participation of specific components of the cytoskeleton of the epithelial cell.

No abstract

In mammals, neutrophile polymorphonuclear leukocytes constitute one of the essential body defenses against disease. In a large mammal, such as the dairy cow, billions of neutrophils are mobilized to fight infection. For example, over 50 million neutrophils per milliliter milk are commonly in a mammary quarter inflicted with clinical mastitis. However, in spite of these numerous leukocytes, pathogenic organisms remain viable. Recent evidence indicates that bacteria are not eliminated from a diseased quarter because the phagocytic capacity of the neutrophils is reduced in the mammary gland. The morphology and physiology of the leukocyte is examined in this review in an attempt to explain why the phagocytic capacity of the neutrophil is reduced in the mammary gland of the bovine.

No abstract

No abstract

Neutrophils are the major defense against bacterial infection in the bovine mammary gland. Neutrophils migrate from blood into the lumen of the gland in response to inflammatory stimuli. This study describes the development of a system of cell culture that can be used to study neutrophil diapedesis through secretory and ductal mammary epithelial barriers. The culture system consists of successive layers of collagen, fibroblasts, collagen, and a confluent monolayer of secretory or ductal epithelial cells layered on a porous membrane. Confluence was determined by electrical resistance and trypan blue diffusion. Neutrophil diapedesis occurred from the basal to the apical surface of the monolayers. Purified complement C5a, fetal bovine serum that had been activated by zymosan, and fetal bovine serum that had been activated by Escherichia coli induced neutrophil diapedesis. Neutrophil diapedesis was greater across ductal cell monolayers. Blood neutrophils from five cows differed in their ability to migrate through the multilayered culture system in response to C5a. Monoclonal antibodies to C5a blocked diapedesis induced by purified C5a but had no effect on diapedesis induced by fetal bovine serum that had been activated by zymosan or by fetal bovine serum that had been activated by E. coli endotoxin, indicating that factors other than C5a were chemotactic for neutrophils. Monomeric IgG2, immune complexes, and E. coli endotoxin did not induce neutrophil diapedesis.

No abstract

No abstract