Effect of cortisol on the bactericidal function of the bovine milk neutrophil in vitro

Milk neutrophils and Staphylococcus aureus were incubated for 2 hours at a 1:1 ratio in sterile common milk media with various cortisol concentrations. Milk neutrophils were harvested twice at a weekly interval from 6 cows. Mean percentage of phagocytosis (+/- SD) was 20.2 +/- 10.1, 34.6 +/- 21.0, 27.2 +/- 17.8, 30.3 +/- 21.4, and 23.9 +/- 16.7 for treatments with 0, 20, 40, 60, and 10,000 ng/ml. Mean percentage of kill was 12.7 +/- 12.4, 14.9 +/- 11.2, 11.2 +/- 10.9, 12.1 +/- 12.3, and 6.6 +/- 10.3, for 0, 20, 40, 60, and 10,000 ng/ml treatments. Mean percentage of efficiency of kill, a measure of the ability of neutrophil to kill phagocytized bacteria, was 49.5 +/- 40.0, 53.5 +/- 38.8, 46.9 +/- 38.0, 34.9 +/- 35.2, and 27.3 +/- 32.8, respectively. The pharmacologic concentration (10,000 ng/ml) of cortisol depressed kill, whereas physiologic concentrations (20, 40, and 60 ng/ml) of cortisol increased phagocytosis, but did not affect kill.