Ovarian steroids do not affect bovine endometrial cytokine or chemokine responses to Escherichia coli or LPS in vitro

The risk of bacterial infection of the endometrium causing uterine disease in cattle is increased in the progesterone-dominated luteal phase of the ovarian cycle, while oestrogens or oestrus are therapeutic or protective against disease. The first line of defence against bacteria, such as Escherichia coli that cause inflammation of the endometrium, is the innate immune system, which recognises bacterial lipopolysaccharide (LPS). This study tested the hypothesis that cyclic variation in ovarian hormone concentrations alters innate immune responses within the bovine endometrium. Ex vivo organ cultures of endometrium, and in vitro cultures of endometrial epithelial and stromal cells, and peripheral blood mononuclear cells (PBMCs), all mounted inflammatory responses to E. coli or LPS, with secretion of inflammatory mediators interleukin 1b (IL1b), IL6 and IL8, and increased expression of mRNA encoding IL1B, IL6, CXCL8 (IL8) and CCL5. However, these inflammatory responses, typical of innate immunity, were not affected by the stage of ovarian cycle in which the endometrium was collected for organ culture, or by exogenous oestradiol or progesterone. Although a dexamethasone-positive control reduced inflammation stimulated by E. coli or LPS, treatment with oestradiol or progesterone, or inhibitors of oestradiol or progesterone nuclear receptors, did not affect endometrial cell or PBMC secretion of IL1b, IL6 or IL8, or IL1B, IL6, CXCL8 and CCL5 gene expression. In conclusion, the stage of the oestrus cycle or ovarian steroids did not modulate the innate immune response in the bovine endometrium in vitro.