Sex steroid hormones do not influence the oxidative burst activity of polymorphonuclear leukocytes from ovariectomized cows in vitro

During the periparturient period, dairy cows are subjected to physiological changes that may induce immunosuppression and an increased susceptibility of the animal to bacterial infections such as mastitis. The incidence of clinical environmental mastitis is high during the last period of gestation, at parturition and during the first month of lactation, suggesting a potential influence of sex steroid hormones. Efficient functioning of polymorphonuclear leukocytes (PMN) is necessary during the early phase of infection to clear the mammary gland from invading pathogens. The purpose of this study was to investigate the effect of sex steroid hormones on the oxidative burst activity of isolated PMN from ovariectomized cows. Ovariectomy was performed to minimize the interference of endogenous estrogen and progesterone levels, which are known to vary extensively during the estrus cycle. Isolated PMN were incubated with different concentrations of 17beta-estradiol, estrone or progesterone. A flow cytometric technique was used to quantify the oxidation of intracellular 2',7'-dichlorofluorescin by the oxidative burst system of PMN following stimulation with phorbol myristate acetate. Staurosporine was used as a positive control for our in vitro model. No statistically significant changes in PMN oxidative burst activity were observed at physiological or pharmacological levels of the three sex steroid hormones. A large variation existed in the oxidative burst activity among cows. In an additional experiment, the expression of estrogen receptor alpha and of progesterone receptor in PMN was evaluated immunohistochemically. No specific staining was detected for both receptors in isolated PMN following incubation with different concentrations of sex steroid hormones.