Effects of early pregnancy on uterine lymphocytes and endometrial expression of immune-regulatory molecules in dairy heifers.

Natural killer (NK) cells are essential for establishment of human and rodent pregnancies. The function of these and other cytotoxic T cells (CTL) is controlled by stimulatory and inhibitory signaling. A role for cytotoxic cells during early pregnancy in cattle has not been described, but regulation of their function at the fetal-maternal interface is thought to be critical for conceptus survival. The hypothesis that the relative abundance of CTL and expression of inhibitory signaling molecules is increased by the conceptus during early pregnancy was tested. The proportions of lymphoid lineage cells and expression of inhibitory signaling molecules in the endometrium during early pregnancy in dairy heifers were determined using flow cytometry, immunofluorescence, and real-time PCR on days 17 and 20 of pregnancy and day 17 of the estrous cycle. Results revealed an increased percentage of NKp46+ and CD8+ cells in the uterus of pregnant heifers. Furthermore, a large percentage of uterine immune cells coexpressed these proteins. Compared to cyclic heifers, CD45+ uterine cells from pregnant heifers exhibited greater degranulation. Endometrium from pregnant heifers had greater mRNA abundance for the inhibitory molecules, CD274 and lymphocyte activating gene 3 (LAG3), and greater cytotoxic T lymphocyte-associated protein 4 (CTLA4), molecules that can interact with receptors on antigen-presenting cells and induce lymphocyte tolerance. This study demonstrates a dynamic regulation of both cytotoxic immune cells and tolerogenic molecules during the peri-implantation period that may be required to support establishment of pregnancy and placentation.

Luteal cells from functional and regressing bovine corpora lutea differentially alter the function of gamma delta T cells.

The luteal microenvironment is thought to direct the function of resident immune cells to facilitate either luteal function or regression. To determine if luteal cells from functional (Days 10-12) and regressing (8 h after administration of prostaglandin F2alpha) corpora lutea (CL) induce different responses in γδ T cells, luteal cells were cocultured with autologous γδ T cells isolated from peripheral blood. Proliferation, functional phenotypes, and cytokine synthesis were analyzed by flow cytometry. To determine if the luteal cells from functional CL induce hyporesponsiveness in γδ T cells, γδ(+) cells were cocultured with midcycle luteal cells and further stimulated with concanavalin A. Coculture of γδ(+) cells with midcycle luteal cells did not inhibit concanavalin A-induced proliferation. In a proliferation assay, luteal cells from midcycle CL predominantly induced proliferation of γδ(+) WC1(-) cells (P < 0.05), while luteal cells from regressing CL predominantly induced proliferation of γδ(+)WC1(+) cells (P < 0.05). Analysis of intracellular cytokines indicated that midcycle luteal cells increased the proportion of γδ(+) cells containing interleukin 10 (P < 0.05), but reduced the proportion of γδ(+) cells containing interferon gamma (IFNG; P < 0.05). There were no changes in the proportions of γδ(+) cells synthesizing interleukin 4 or tumor necrosis factor. Unexpectedly, coculture of γδ(+) cells with luteal cells from regressing CL had no effect on any of the cytokines analyzed. These data support the hypothesis that the function of resident T cells is differentially modulated depending on the status of the CL.

Progesterone effects on lymphocytes may be mediated by membrane progesterone receptors.

Luteal cell-induced proliferation of T lymphocytes devoid of the nuclear progesterone receptor (PGR) is inhibited by progesterone. Functional effects of progesterone on bovine lymphocytes and the expression of membrane progesterone receptors (mPRs) alpha (PAQR7), beta (PAQR8), gamma (PAQR5), and progesterone receptor membrane component 1 (PGRMC1) mRNA were analyzed in corpus luteum (CL) and lymphocytes. Progesterone and a cell-impermeable progesterone conjugate caused a dose-dependent decrease in IL2 receptor α-subunit (IL2RA) mRNA and an increase in interleukin 2 (IL2) mRNA concentrations in cultured PBMCs. In luteal tissues, concentrations of PAQR7 and PAQR8 mRNA were lower in CL collected on day 11 compared with day 18, whereas PGRMC1 and PGR mRNA were greater on day 11 than on day 18. The mRNA of all three PAQRs and PGRMC1 were detected in bovine T lymphocytes, but not in B cells/monocytes. Progesterone increased intracellular Ca(++) and reduced the phosphorylation of zeta-chain-associated protein kinase 70 (Zap70). A specific, saturable, and single progesterone binding site with a steroid specificity characteristic of mPRs was demonstrated by saturation and competitive binding assays using T lymphocyte membranes, and PAQR7 receptors were localized on the plasma membranes by immunofluorescence. Thus, progesterone induces specific and rapid functional effects on T lymphocytes in the absence of PGR. The mPRs are potential intermediaries of the cell-surface actions of progesterone because they are expressed in lymphocytes, the actions of progesterone are mimicked by a cell-impermeable form of progesterone, and specific, saturable progesterone binding, which is characteristic of mPRs, is present on lymphocyte membranes.

The interface of the immune and reproductive systems in the ovary: lessons learned from the corpus luteum of domestic animal models.

The dynamic changes that characterize the female reproductive system are regulated by hormones. However, local cell-to-cell interactions may mediate responsiveness of tissues to hormonal signals. The corpus luteum (CL) is an excellent model for understanding how immune cells are recruited into tissues and the role played by those cells in regulating tissue homeostasis or demise. Leukocytes are recruited into the CL throughout its lifespan, and leukocyte-derived cytokines have been found in corpora lutea of all species examined. The proinflammatory cytokines inhibit gonadotropin-stimulated steroidogenesis, profoundly stimulate prostaglandin synthesis by luteal cells, and promote apoptosis. However, there is mounting evidence that leukocytes and luteal cells communicate in different ways to maintain homeostasis within the functional CL. Domestic animals have provided important information regarding the presence and role of immune cells in the CL.