Neutrophil function in vitro: diapedesis and phagocytosis.

The function of neutrophils within the mammary gland was modeled in vitro to include diapedesis and phagocytosis. The bovine mammary cell line, MAC-T3, provided a mammary epithelial monolayer for use as a biologically meaningful barrier to neutrophil diapedesis. Features included characteristic transepithelial resistance, tight junctional complexes, and polarity. Continuous readings of transepithelial resistance indicated a stable resistance over several hours. Staphylococcus aureus, at concentrations of 1 x 10(7) and 2 x 10(9) cfu/ml, did not appear to have any deleterious effects on monolayer integrity over short-term (1 to 2 h) exposure. Neither resting nor challenged neutrophils caused short-term damage to the monolayer. Transepithelial resistance of the monolayers remained unchanged even as neutrophils were actively migrating through the monolayer. Further work using the MAC-T3 cell line and electrical resistance to assess cell monolayer integrity could provide much insight into the mechanisms underlying degeneration of mammary epithelial cells. The ability of neutrophils to phagocytose foreign particles is important for protection of the mammary gland. Neutrophils from proven bulls varied in their rate and capacity of phagocytosis. Correlations between neutrophil function and production traits were negative and small. In vitro analysis of neutrophil function provides another tool for the study of natural mastitis resistance.