Characterization of the Th Profile of the Bovine Endometrium during the Oestrous Cycle and Early Pregnancy

Abstract

Despite extensive research in the area of cow fertility, the extent to which the maternal immune system is modulated during pregnancy in cattle remains unclear. Therefore, the objective of the current study was to characterize the presence and response profile of B, T-helper (LTh), T- cytotoxic (LTc), gamma delta-T (γδT) and natural killer (NK) lymphocytes in terms of cell number, distribution and cytokine expression in bovine endometrial tissue to pregnancy. Endometrial tissue samples were collected from beef heifers on Days 5, 7, 13 and 16 of the estrous cycle or pregnancy. Samples were analysed by immunofluorescence to identify the presence and abundance of B-B7 (B-cells), CD4 (LTh), CD8 (LTc), γδT cell receptor (TCR) and CD335/NKp46 (NK cells) -positive immune cells. Quantitative real time PCR (QPCR) was carried out to analyse mRNA relative abundance of FOXP3 (a marker of regulatory T (Treg) cells) and a panel of immune factors, including MHC-I, LIF, Interleukins 1, 2, 6, 8, 10, 11,12A, IFNa and IFNG. Results indicate that B-B7+ cells are quite populous in bovine endometrial tissue, CD4+ and CD8+ -cells are present in moderate numbers and γδTCR+ and CD335+ cells are present in low numbers. Pregnancy affected the total number and distribution pattern of the NK cell population, with the most significant variation observed on Day 16 of pregnancy. Neither B lymphocytes nor T lymphocyte subsets were regulated temporally during the oestrous cycle or by pregnancy prior to implantation. mRNA transcript abundance of the immune factors LIF, IL1b, IL8 and IL12A, IFNa and IFNG, expression was regulated temporally during the estrous cycle and LIF, IL1b, IL-10, IL11, IL12A were also temporally regulated during pregnancy. In conclusion, the endometrial immune profile of the oestrous cycle favours a Th2 environment in anticipation of pregnancy and the presence of an embryo acts to fine tune this environment.

Embryo maternal immune interactions in cattle

“…Using fluorescent labeling of lymphocyte subset markers on endometrial sections, we identified CD4+, CD8+, gamma delta T and FoxP3+ lymphocyte populations in both pregnant and cyclic cattle from day 5 to 16 of pregnancy/oestrous cycle. The population sizes did not appear to be temporally regulated during the oestrous cycle, or by the presence of an embryo (Oliveira et al, 2013). Although the population size did not alter, the gene expression profile of these cells was temporally modified; inflammatory/Th1 immune factors IFNA, LIF, IL1B, IL8, and IL12A were down regulated during the luteal phase of the oestrus cycle, while Th2 factors LIF and IL10 were upregulated.…”

“…Using immunofluorsecent labeling of CD335+ cells, we found these cells to be surprisingly elusive in bovine endometrial tissue, in cyclic animals and particularly during the early stages of pregnancy (Oliveira et al, 2013). There is evidence from an vitro study suggesting that uterine NK cell expansion could be restricted by IFNT (Skopets et al, 1992).…”

The role of placental MHC class I expression in immune-assisted separation of the fetal membranes in cattle

“…Findings regarding maternal MHC class I expression in the placentomes area conflicting, with studies reporting no expression , downregulation (Low et al, 1990) and normal expression (Lynge et al, 2014). Although numbers were low, NK cells have been detected in the endometrium of pregnant cattle (Oliveira et al, 2013). Based on the analogy between bovine and human NC-MHC class I, expression of NC-MHC class I on bovine trophoblasts may inhibit NK cells and contribute to the induction of regulatory T cells.…”

“…In humans reduced levels of regulatory T cells in the placenta and peripheral blood are associated with pre-eclampsia and preterm labor (Quinn and Parast, 2013) and depletion of regulatory T cells in allogeneic pregnancies in mice leads to failure of gestation (Aluvihare et al, 2004), showing the importance of regulatory T cells for successful pregnancy other species. Foxp3+ has been detected in the bovine placenta (Oliveira et al, 2013) and levels of CD4 CD25 T cells rise in peripheral blood of pregnant cows (Oliveira and Hansen, 2008).…”

“…Instead, γδ T cells were shown to act as regulatory cells (Hoek et al, 2009), of which low numbers have been detected in the endo-and myometrium of pregnant cattle (Oliveira et al, 2013).…”