The effects of in vitro exposure to progesterone and estradiol-17β on the activity of canine neutrophils.

To date, only limited information about the influence of ovarian hormones on canine immune system cells has been available. The study investigated the in vitro influence of progesterone and estradiol-17β on the activity of canine neutrophils. Treatment of cells by both hormones led to a significant decrease in phagocytosis- induced oxidative burst as detected using luminometry after stimulation with opsonised zymosan. The increase in oxidative burst, not connected with phagocytosis, was recorded after stimulation with a soluble stimulator. Using flow cytometry, the tendency of both hormones to decrease the production of reactive oxygen species associated with phagocytosis of Escherichia coli was also evident, although not significant. Suppression of canine neutrophil activity is not connected with pathogen recognition capabilities, since the expression of Toll-like receptor 4 was unaffected. This study reveals that both hormones have a suppressive effect on the activity of canine neutrophils and thus might contribute to the aetiology of pyometra.