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The aim of the current study was to investigate whether polymorphonuclear leukocyte (PMN) diapedesis and viability are influenced by steroid hormones. Using an in vitro model with different types of cell layers (bovine mammary epithelial cells and fibroblasts), we investigate whether steroid hormone treatments (17beta-estradiol, progesterone, and dexamethasone) have an influence on the diapedesis capacity and viability of PMN. In addition, we studied apoptosis of PMN in the in vitro model and evaluated the influence of different types of cell layers and steroid hormone treatments on this process. A significant decrease in the number of viable PMN in the lower compartment of the in vitro model (i.e., number of migrated PMN x viability after migration) was found after 17beta-estradiol treatment, whereas no influence was detected after progesterone or dexamethasone treatment. The effect of 17beta-estradiol was not due to a lower viability before migration as none of the treatments caused a significant effect on the viability before diapedesis. This treatment effect was not influenced by endogenous 17beta-estradiol or progesterone levels before isolation because there was no correlation between these plasma levels and PMN diapedesis capacity or viability. Furthermore, migration through epithelial cells caused a significant decrease in viability of PMN due to increased apoptosis but not necrosis.

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-In the period around parturition, cows experience an increased susceptibility for the development of Escherichia coli mastitis. This increased susceptibility has been correlated with a decreased functionality of neutrophils. In the current study, it is suggested that the decreased neutrophil functionality may be induced by the extensive alterations in sex steroid levels occurring around parturition. It was first hypothesized that 17β-estradiol and progesterone influence the viability, apoptosis and necrosis of blood neutrophils from cows in their last month of gestation. Subsequently, it was hypothesized that 17β-estradiol modulates the expression of CD11b, CD18 or CD47 thereby explaining its influence on the migration of bovine neutrophils. Neither 17β-estradiol nor progesterone significantly influenced viability, apoptosis or necrosis in spontaneous apoptosis conditions. However, when apoptosis was induced with TNF-α and gliotoxin, progesterone exerted a survival effect (P < 0.05). In addition, 17β-estradiol treatment of bovine blood neutrophils significantly decreased the expression of CD47 (P < 0.05) but not of CD11b or CD18. It can be concluded that 17β-estradiol and progesterone do not affect spontaneous apoptosis of bovine blood neutrophils while a survival effect was observed for progesterone on induced neutrophils apoptosis. Moreover, our results concerning the influence of 17β-estradiol on the CD11b, CD18 and CD47 expression extend previous demonstrations of the suppressive effect of 17β-estradiol on neutrophils migration and indicate that the altered expression of CD47 may contribute to this phenomenon. sex steroid / β 2 -integrin / CD47 / viability / polymorphonuclear neutrophil leukocyte