Uterine microbial disease affects half of all dairy cattle after parturition, causing infertility by disrupting uterine and ovarian function. Infection with Escherichia coli, Arcanobacterium pyogenes, and bovine herpesvirus 4 causes endometrial tissue damage. Toll-like receptors on endometrial cells detect pathogen-associated molecules such as bacterial DNA, lipids, and lipopolysaccharide (LPS), leading to secretion of cytokines, chemokines, and antimicrobial peptides. Chemokines attract neutrophils and macrophages to eliminate the bacteria, although persistence of neutrophils is associated with subclinical endometritis and infertility. Cows with uterine infections are less likely to ovulate because they have slower growth of the postpartum dominant follicle in the ovary, lower peripheral plasma estradiol concentrations, and perturbation of hypothalamic and pituitary function. The follicular fluid of animals with endometritis contains LPS, which is detected by the TLR4/CD14/LY96 (MD2) receptor complex on granulosa cells, leading to lower aromatase expression and reduced estradiol secretion. If cows with uterine disease ovulate, the peripheral plasma concentrations of progesterone are lower than those in normal animals. However, luteal phases are often extended in animals with uterine disease, probably because infection switches the endometrial epithelial secretion of prostaglandins from the F series to the E series by a phospholipase A2-mediated mechanism, which would disrupt luteolysis. The regulation of endometrial immunity depends on steroid hormones, somatotrophins, and local regulatory proteins. Advances in knowledge about infection and immunity in the female genital tract should be exploited to develop new therapeutics for uterine disease.

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Purulent disease of the uterus develops in 40% of dairy cows after parturition, when the epithelium of the endometrium is disrupted to expose the underlying stroma to bacteria. The severity of endometrial pathology is associated with isolation of Trueperella pyogenes. In the present study, T. pyogenes alone caused uterine disease when infused into the uterus of cattle where the endometrial epithelium was disrupted. The bacterium secretes a cholesterol-dependent cytolysin, pyolysin (PLO), and the plo gene was identical and the plo gene promoter was highly similar amongst 12 clinical isolates of T. pyogenes. Bacteria-free filtrates of the T. pyogenes cultures caused hemolysis and endometrial cytolysis, and PLO was the main cytolytic agent, because addition of anti-PLO antibody prevented cytolysis. Similarly, a plo-deletion T. pyogenes mutant did not cause hemolysis or endometrial cytolysis. Endometrial stromal cells were notably more sensitive to PLO-mediated cytolysis than epithelial or immune cells. Stromal cells also contained more cholesterol than epithelial cells, and reducing stromal cell cholesterol content using cyclodextrins protected against PLO. Although T. pyogenes or plo-deletion T. pyogenes stimulated accumulation of inflammatory mediators, such as IL-1beta, IL-6, and IL-8, from endometrium, PLO did not stimulate inflammatory responses by endometrial or hematopoietic cells, or in vitro organ cultures of endometrium. The marked sensitivity of stromal cells to PLO-mediated cytolysis provides an explanation for how T. pyogenes acts as an opportunistic pathogen to cause pathology of the endometrium once the protective epithelium is lost after parturition.

-The outcome of an udder infection is influenced by the pathogen species. We established a strictly defined infection model to better analyze the unknown molecular causes for these pathogen-specific effects, using Escherichia coli and Staphylococcus aureus strains previously asseverated from field cases of mastitis. Inoculation of quarters with 500 CFU of E. coli (n = 4) was performed 6 h, 12 h, and 24 h before culling. All animals showed signs of acute clinical mastitis 12 h after challenge: increased somatic cell count (SCC), decreased milk yield, leukopenia, fever, and udder swelling. Animals inoculated with 10 000 CFU of S. aureus for 24 h (n = 4) showed no or only modest clinical signs of mastitis. However, S. aureus caused clinical signs in animals, inoculated for 72 h-84 h. Real-time PCR proved that E. coli inoculation strongly and significantly upregulated the expression of β-defensins, TLR2 and TLR4 in the pathogen inoculated udder quarters as well as in mammary lymph nodes. TLR3 and TLR6 were not significantly regulated by the infections. Immuno-histochemistry identified mammary epithelial cells as sites for the upregulated TLR2 and β-defensin expression. S. aureus, in contrast, did not significantly regulate the expression of any of these genes during the first 24 h after pathogen inoculation. Only 84 h after inoculation, the expression of β-defensins, but not of TLRs was significantly (> 20 fold) upregulated in five out of six pathogen inoculated quarters. Using the established mastitis model, the data clearly demonstrate a pathogen-dependent difference in the time kinetics of induced pathogen receptors and defense molecules.toll-like receptor / mastitis / beta-defensin / mammary epithelial cell

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