Establishment of microbial infections in the re-productive tract can have negative consequences for reproductive function of the postpartum female (Kasi-manickam et al., 2004; Dobson et al., 2008; Gautam et al., 2009). In a large study involving 5719 postpartum
PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Maternal immunological adjustments to pregnancy and parturition
in ruminants and possible implications for postpartum uterine health: Is there a prepartum–postpartum nexus?1
P. J. Hansen*2
*Department of Animal Sciences, D. H. Barron Reproductive and Perinatal Biology Research Program, and Genetics Institute, University of Florida, Gainesville 32611-0910
ABSTRACT: Establishment of microbial infections in the reproductive tract can have negative consequences for reproductive function of the postpartum female. Most periparturient cows experience bacterial contami-nation of the uterus after parturition, but only a fraction of these develop subclinical or clinical disease. It is not well understood why one female resolves uterine infec-tions after parturition while another develops disease. Perhaps those that develop metritis or endometritis are exposed to a greater bacterial load at parturition than those that successfully restore the uterus to a healthy condition. A second possibility is that females that develop bacterial disease have compromised immune function, either systemically or in the reproductive tract and associated lymph nodes. Here, the possibil-ity is raised that maternal immunological adjustments to the presence of the allogeneic conceptus may predis-pose some females to metritis or endometritis. Several regulatory processes ensure that adaptive immune responses against paternal antigens on the conceptus are downregulated during pregnancy. Among these are immunosuppressive effects of progesterone, local accu-mulation of immune cells that can inhibit infl ammation
and T cell responses, including M2 macrophages and γδ T cells, and differentiation of regulatory T cells to inhibit alloreactive lymphocytes. Some immunologi-cal adjustments to the conceptus also make the uterus more susceptible to bacterial infection. For example, progesterone not only depresses skin graft rejection but also reduces uterine capacity to eliminate bacterial infections. Macrophages of M2 phenotype can inhibit infl ammation and facilitate persistence of some micro-bial infections. At parturition, immune defenses in the uterus may be further weakened by loss of the lumi-nal epithelium of the endometrium, which is part of the innate immune system, as well as by disappearance of intraepithelial γδ T cells that produce the antibacte-rial proteins granulysin and perforin. It is currently not known whether molecules and cells that inhibit immune responses during pregnancy persist after parturition but, if so, they could contribute to compromised immune function in the uterus. It is hypothesized that indi-vidual variation in immune adjustments to pregnancy and parturition and the reversal of these changes in the postpartum period are important determinants of sus-ceptibility of the uterus to infection.
1Based on a presentation at the Physiology and Endocrinology Symposium titled “Reproductive-Immune Interactions” during the Joint Annual Meeting, July 15–19, 2012, Phoenix, AZ, with publication sponsored by the American Society of Animal Science, Champaign, IL, and the Journal of Animal Science.
2Corresponding author: [email protected] .eduReceived October 3, 2012.Accepted December 17, 2012.
Published December 2, 2014
Hansen1640
dairy cows, fi rst service pregnancy rate was 39.4% for cows diagnosed with metritis in the fi rst 65 d postpartum, 38.7% for cows diagnosed with clinical endometritis and 51.4% for cows in which no disease was diagnosed dur-ing the fi rst 65 d postpartum (Santos et al., 2011).
As has been highlighted by Sheldon et al. (2009), virtually all cows experience bacterial contamination of the uterus after calving (Fig. 1), but only a fraction of these develop subclinical or clinical disease. In the re-mainder of cases, immune defenses in the uterus are ca-pable of eliminating the bacteria responsible for uterine infectious disease. In cattle, these most commonly are Escherichia coli and Trueperella (previously Arcano-bacterium) pyogenes and, less commonly, anaerobic bacteria such as Prevotella and Fusobacterium species (Sheldon et al., 2009).
It is important for developing approaches to reduce incidence of bacterial diseases of the uterus to under-stand what determines whether or not a postpartum fe-male successfully clears bacteria from the uterus after calving. One possibility is that females that develop metritis or endometritis are exposed to a greater bacte-rial load at parturition than those that successfully re-store the uterus to a healthy condition. Perhaps micro-bial contamination of the reproductive tract is at a scale that overwhelms uterine defense mechanisms. A second possibility is that females that develop bacterial disease
have compromised immune function, either systemically or in the reproductive tract and associated lymph nodes.
There is indeed evidence to implicate inadequate im-mune function as a cause of uterine disease. In one study, peripheral blood leukocytes of cows that developed en-dometritis were less capable of phagocytosis prepartum than those of cows that did not develop endometritis (Kim et al., 2005). Also, at calving, cows that subse-quently developed metritis had reduced glycogen con-tent in circulating neutrophils (Galvão et al., 2010a) and reduced expression of tumor necrosis factor α (TNFA) by E. coli-stimulated monocytes (Galvão et al., 2012). Moreover, the incidences of metritis and endometritis have sometimes been reduced by antioxidant treatments that improve neutrophil function (Hansen, 2012).
Initially, the postpartum female is poorly positioned to eliminate bacteria from the uterus. The loss of integrity of the epithelial lining of the endometrium during the ear-ly postpartum period (Moller, 1970) removes a physical barrier to bacterial attachment mediated by mucins (Da-vies et al., 2008) and allows ingress of bacteria into the endometrial stroma. Loss of the epithelium also removes an important source of antibacterial peptides (Davies et al., 2008) and proteins (Tekin and Hansen, 2003). The epithelium is also an important component of the innate immune system that expresses toll-like receptors (TLR) that trigger infl ammation (Davies et al., 2008) and which can participate in antigen presentation, at least in humans (Wallace et al., 2001). In addition, physical clearance by discharge of products of infl ammation through the cervix may be impeded by the position of the uterus in the body. In the mare, differences between females in ability for physical clearance are related to susceptibility to post-breeding endometritis (Troedsson and Liu, 1991).
The early postpartum female has also just completed a prolonged period when immune function in the uterus is suppressed because of the need to limit maternal im-mune responses against the allogeneic conceptus. Unless the sire and dam have identical major histocompatibility complex (MHC) genes, the conceptus is an allograft that can be recognized as foreign by the mother. Conceivably, an important determinant of whether a female develops metritis or endometritis after parturition is the degree of uterine immunosuppression before parturition and the rate at which immune function in the uterus is restored to a pregravid condition. The purpose of this review is to highlight the immunological adaptations of the female to the presence of the conceptus and to speculate how such adaptations could potentially compromise antimicrobial mechanisms in the reproductive tract after parturition. The focus is on ruminants, although concepts from other species will be introduced as appropriate.
Figure 1. Postpartum changes in the percentage of cows in which bac-teria can be isolated from the uterus (circles) and in the percentage diagnosed with metritis (red), clinical endometritis (orange), and subclinical metritis (white). Note that the authors defi ne metritis in the cow as the presence of an abnormally enlarged uterus and a purulent uterine discharge in the fi rst 21 d postpartum. Clinical endometritis is defi ned as the presence of a purulent uterine discharge detectable in the vagina 21 d or more postpartum or muco-purulent discharge detectable in the vagina after 26 d postpartum. Subclinical endometritis is infl ammation of the endometrium that results in a signifi cant reduction in reproductive performance in the absence of signs of clinical en-dometritis and with infl ammation, which is usually characterized by presence of >5.5 or 10% polymorphonuclear neutrophils in uterine lavage or cytobrush samples. Reproduced from Sheldon et al. (2009) with permission of Biology of Reproduction. See online version to view fi gure in color.
Prepartum determinants of postpartum uterine health 1641
Immunosuppressive Actions of Progesterone on the Uterus: Consequences for Survival of the Allogeneic Conceptus
Progesterone has been referred to as Nature’s Immu-nosuppressant (Siiteri et al., 1977). Such a designation is an exaggeration; direct effects of progesterone on lym-phocyte function require large, usually pharmacological doses, and may involve destabilization of the plasma membrane rather than signaling through a specifi c re-ceptor (Monterroso and Hansen, 1993). Nonetheless, progesterone does inhibit immune function in the uterus at physiologically-relevant concentrations. Most rel-evant for the success of pregnancy is the action of pro-gesterone to inhibit tissue graft responses. Progesterone can prevent or delay rejection of tissue allografts in the uterus of the rat (Watnick and Russo, 1968) and sheep (Reimers and Dziuk, 1974; Hansen et al., 1986; Padua et al., 2005) and prolong survival of xenografts in the sheep uterus (Majewski and Hansen, 2002). An example of allograft survival in the uterus of an ewe treated with progesterone is shown in Fig. 2.
Graft rejection responses involve central effector and regulatory actions of T lymphocytes (Valujskikh and Li, 2007) and, in some cases, natural killer (NK) cells (Kroemer et al., 2008) and B-cells (Everly and Terasaki, 2012). Progesterone treatment in ewes causes a decline in endometrial lymphocyte numbers (Gottshall and Han-sen, 1992). It has been proposed (Padua and Hansen, 2010) that the graft-promoting effect of progesterone in the sheep involves induction of an endometrial secre-tory product with immunoregulatory properties called
SERPINA14 (previously termed uterine milk protein or uterine serpin). The SERPINA14 gene exists in a subset of mammals including cetartiodactyls, horses, pigs, and some carnivores (Padua et al., 2010). In the sheep, con-centrations of SERPINA14 in uterine fl uid reach milli-gram per milliliter concentrations (Moffatt et al., 1987). At this concentration, SERPINA14 can block T cell pro-liferative responses (Segerson et al., 1984; Peltier et al., 1999; Tekin et al., 2006), NK-cell activity (Liu and Han-sen, 1993; Tekin and Hansen, 2002), and antibody pro-duction (Skopets et al., 1995). Coincidentally, prolonged exposure to progesterone (~30 d) is required both for its allograft-promoting actions (Reimers and Dziuk, 1974) and for the induction of large amounts of SERPINA14 (Leslie and Hansen, 1991).
The endometrium also produces SERPINA14 dur-ing pregnancy in the cow under the infl uence of proges-terone (Leslie et al., 1990; Leslie and Hansen, 1991) but it is not known whether it is immunoregulatory in the cow or other species. Moreover, estrogen can also ap-parently regulate SERPINA14 production in the cow be-cause amounts of SERPINA14 mRNA in endometrium are high at estrus (Ulbrich et al., 2009).
Immunosuppressive Actions of Progesterone on Uterine Antimicrobial Responses
In addition to affecting allograft survival, progester-one blunts antimicrobial responses in the uterus. Treat-ment of ovariectomized females with progesterone re-duced the clearance of experimentally-introduced bacte-
Figure 2. Two examples of immunosuppressive actions of progesterone on uterine immune function: prolongation of skin graft survival (left panel) and reduction in antibacterial defense (right panel). The left panel shows a uterus from an ovariectomized ewe treated with progesterone for 60 d in which a skin allograft and autograft were placed in a separate uterine horn after 30 d of treatment. Note that both grafts are presented after 30 d of grafting. When a similar experiment was performed with ovariectomized ewes treated with vehicle, the autograft survived but the allograft was resorbed by 30 d (Padua et al., 2005). The right panel shows the fraction of postpartum ewes in which uterine infections were established after intrauterine deposition of Trueperella pyogenes and Escherichia coli. Ovariectomy was performed on d 14 postpartum, hormonal treatments were administered from d 15 to 20, intrauterine inoculation was on d 20, and examination of uterine infections was on d 25. Whereas only 2 of 12 ewes treated with the sesame oil vehicle became infected, all 12 ewes treated with progesterone (P4) did so (P < 0.001). Results are from Lewis (2003). See online version to view fi gure in color.
Hansen1642
ria in the uterus of cattle (Rowson et al., 1953) and sheep (Lewis, 2003; see Fig. 2) as well as of mares (Ganjam et al., 1982; Evans et al., 1986), rats (Kaushic et al., 2000), and gilts (Wulster-Radcliffe et al., 2003). An indication of the importance of progesterone for regulating anti-bacterial responses in the uterus is the observation that delaying ovulation in postpartum dairy cows through administration of an implant containing the GnRH ago-nist Deslorelin improved uterine health (Silvestre et al., 2009). Interestingly, however, there is no evidence that cows that resume estrous cycles early after calving are more likely to develop uterine disease; the converse might be true (Galvão et al., 2010b).
Unlike for its graft-promoting effects, progesterone can compromise antibacterial responses after only a short exposure; for example, after 5 d in sheep (Lewis, 2003). Thus, there are differences in the mechanisms by which progesterone compromises allograft rejection versus those in which it reduces antimicrobial defenses. Some effects of progesterone may be mediated by in-hibition of PGF2α release from the uterus. Short-term treatment with progesterone reduces uterine secretion of PGF2α (Silvia et al., 1991; Lewis, 2003) and administra-tion of PGF2α reduced severity of bacterial infection in ovariectomized ewes treated with progesterone (Lewis and Wulster-Radcliffe, 2006).
The mechanisms by which progesterone reduce com-petence of the reproductive tract to clear microorganisms is incompletely understood. In the mare, physical removal of material from the uterus through the cervix is reduced by progesterone (Evans et al., 1986). In sheep, progester-one inhibited leucoytic infi ltration in response to bacterial inoculation (Brinsfi eld et al., 1964) but, in the cow, there was no effect of progesterone on the number of neutrophils recovered from the uterus of ovariectomized females after infusion of oyster glycogen or cell-free fi ltrate of a bacte-rial culture (Lander Chacin et al., 1990; Subandrio et al., 2000). In these same studies, progesterone did not affect functional capacity of uterine neutrophils, as determined in chemotaxis and phagocytosis assays.
There is also little indication that progesterone re-duces humoral immunity in the uterus. In ovariecto-mized cows, progesterone had no signifi cant effect on total IgG or IgA recovered from the uterus (Lander Cha-cin et al., 1990). Uterine content of IgG in the cow has been variously reported to be greater at estrus than dur-ing the luteal phase (Whitmore and Archbald, 1977) or vice versa (Brenner et al., 1995).
A key event in the activation of host defenses against microorganisms is recognition of the presence of the or-ganisms by TLR and other pattern recognition receptors that bind to specifi c bacterial nucleic acids, lipids, and li-popolysaccharides (LPS) and activate local synthesis of antibacterial peptides and infl ammatory chemokines and
cytokines (Sheldon et al., 2009). The bovine endome-trium expresses TLR on epithelial and stromal cells and produces an array of antibacterial peptides (Davies et al., 1008; Sheldon et al., 2009). This bacterial recognition system may be downregulated to some extent by proges-terone. In vitro, treatment of epithelial or stromal cells isolated from bovine endometrium with progesterone re-duced induction of secretion of PG caused by exposure to LPS (Herath et al., 2006). Also, analysis of bovine abattoir-derived material indicated that expression in the endometrial luminal epithelium of three genes involved in infl ammation (CXCL5, IL1B, and IL8) is reduced dur-ing the luteal phase as compared with the periovulatory period (Fischer et al., 2010).
Role of Regulatory Immune Cells in Control of Uterine Immune Function during Pregnancy
Regulatory T Cells. Regulatory T cells (Treg) are a class of CD4+ T lymphocyte involved in suppression of autoimmune responses and infl ammation caused by infection and tissue injury, metabolic disturbances, and other causes (Gobert and Lafaille, 2012). Differentia-tion is under control of the forkhead box P3 (FOXP3) transcription factor and takes place in 2 anatomical sites. One class of Treg cells is derived in the thymus (natural or tTreg cells) whereas another class, called pTreg, is de-rived by differentiation of peripheral CD4+ T cells (Litt-man and Rudensky, 2010).
The pTreg cells are particularly important for lim-iting infl ammation at mucosal surfaces (Josefowicz et al., 2012). These cells are also critical to the survival of the allogeneic conceptus. Indeed, a major enhancer for FOXP3 necessary for differentiation of pTreg cells but not tTreg cells called conserved noncoding sequence 1 (CNS1) arose during evolution in placental mammals (Samstein et al., 2012). The relative number of Treg cells in blood, spleen, and lymph nodes increase during pregnancy in mice (Aluvihare et al., 2004) and in blood of humans (Somerset et al., 2004). At least a portion of the pTreg cells that differentiate during pregnancy are specifi c for paternal alloantigen (Samstein et al., 2012). In mice, antibody-mediated depletion of Treg cells de-creased litter size in allogeneic pregnancies but not in syngeneic pregnancies (Aluvihare et al., 2004; Shima et al., 2010). Similarly, female mice defi cient for CNS1 had reduced litter sizes in allogeneic pregnancies but not syngeneic pregnancies (Samstein et al., 2012).
Circulating Treg cells have been identifi ed in the cow (Gerner et al., 2010) and sheep (Rocchi et al., 2011), but it is not known whether or not numbers change during pregnancy. One characteristic of circulating Treg cells is high expression of another marker, CD25. The propor-tion of circulating CD4+ T lymphocytes that were also
Prepartum determinants of postpartum uterine health 1643
positive for CD25 was greater for pregnant cows at d 33 to 34 of gestation and in the periparturient period than for nonpregnant cows (Fig. 3; Oliveira and Hansen, 2008).
Macrophages. Macrophages function not only in phagocytosis and antigen presentation, but also exert im-munoregulatory roles. Differentiation of macrophages is dependent on the cytokine milieu. In the presence of infl ammatory cytokines such as interferon-γ (IFNG) and TNFA or bacterial lipopolysaccharide, macrophages dif-ferentiate along the M1 activation pathway to promote infl ammation. In contrast, differentiation in the presence of Th2 cytokines IL-4 and IL-13, leads to M2 activation to produce a macrophage that causes immunosuppres-sion (Varin and Gordon, 2009). In the human, decidual macrophages exhibit an M2 phenotype (Gustafsson et al., 2008) and potentially limit immune responses directed against the conceptus.
Based on expression of the markers CD68 and CD14, cells characteristic of macrophages are very abundant in
the stromal compartment of the endometrium of pregnant cows (Oliveira and Hansen, 2008; Oliveira and Hansen, 2009) and sheep (Tekin and Hansen, 2004). Moreover, endometrial CD14+ cells in the cow express a variety of genes characteristically expressed by macrophages (Oliveira et al., 2010). At least a fraction of endometrial macrophages have differentiated along the M2 pathway. Twelve genes characteristic of M2-activated macrophages (SLCO2B1, GATM, MRC1, ALDH1A1, PTGS1, RNASE6, CLEC7A, DPEP2, CD163, CCL22, CCL24, and CDH1) were upregulated in CD14+ cells isolated from the endo-metrium of pregnant cows as compared with CD14+ cells from peripheral blood (Oliveira et al., 2010).
In unilaterally-pregnant ewes, in which pregnancy was confi ned surgically to 1 uterine horn, CD68+ cells accumulated in endometrium of both horns, although to a greater degree in the horn containing the conceptus (Tekin and Hansen, 2004). Thus, regulation of macro-phage accumulation involves both systemic and local factors. Progesterone is not the systemic signal because treatment of ovariectomized ewes with progesterone did not result in an increase in numbers of CD68+ cells in the endometrium (Tekin and Hansen, 2004).
γδ T cells. The most abundant lymphocyte popula-tion in the endometrium of sheep during all but early pregnancy is the γδ T cell (Fig. 4); as much as 13% of the cells in the luminal epithelium during pregnancy are γδ T cells (Lee et al., 1992; Nasar et al., 2002). Accumu-lation of γδ T cells in the endometrium is apparently due to a systemic signal because it occurs in both pregnant and nonpregnant uterine horns of unilaterally-pregnant ewes (Majewski et al., 2001). Presence of γδ T cells in the endometrium of pregnant females is not a unique characteristic of sheep because a similar phenomenon has been reported in mice (Suzuki et al., 1995; Arck et al., 1999) and humans (Fan et al., 2011). To date, the presence of γδ T cells in the endometrium of pregnant cows has not been reported.
The γδ T cell is defi ned by the presence of a T cell re-ceptor (TCR) formed by γ and δ subunits instead of the α and β subunits that characterize the more well-studied αβ T cell. The γδ T cells have some features of the in-nate immune system and others of the adaptive immune system. The antigenic repertoire of the TCR is more limited than for αβ T cells and γδ T cells do not require antigen presentation to recognize some antigens, partic-ularly bacterial lipids and stress-induced proteins related to major histocompatibility Class I antigens (Wesch et al., 2011). The γδ T cells can be cytotoxic to bacteria (Dieli et al., 2001), protozoa (Farouk et al., 2004), and tumor cells (Li et al., 2012). In addition, γδ T cells can be involved in cellular regulation. Decidual γδ T cells in mice have been reported to inhibit lymphocyte func-tion through secretion of transforming growth factor-β
Figure 3. Differences in lymphocyte populations in peripheral blood between nonpregnant (NP) and periparturient (P) cows. Panel A shows the percentage of cells in the lymphocyte gate that were positive for cluster of differentiation molecule (CD)4, CD8, and CD25, while panel B shows the percentage of cells in the lymphocyte gate that are positive for both CD4 and CD25. Panel C shows the percentage of CD4+ cells that are also CD25+. Reproduced from Oliveira and Hansen (2008) with permission of the Society for Reproduction and Fertility.
Hansen1644
(Suzuki et al., 1995). Decidual γδ T cells in humans can support trophoblast growth in vitro via proliferative and antiapoptotic actions caused by secretion of IL-10 (Fan et al., 2011). Experiments in the mouse using antibodies that deplete specifi c subtypes of γδ T cells indicate that there are separate abortogenic and fetoprotective sub-populations of γδ T cells, with the latter arising later in pregnancy than the former (Arck et al., 1999).
The main roles of endometrial γδ T cells in the sheep appear to be antibacterial and immunoregulatory. Intraep-ithelial γδ T cells in the luminal epithelium are highly granulated (Lee et al., 1992; Meeusen et al., 1993. The granules contain the antibacterial protein granulysin (Fox et al., 2010). In addition, mRNA for profi lin, which is in-volved in destruction of intracellular pathogens (Stenger, 2001) can be identifi ed (Fox and Meeusen, 1999). The capacity for immunoregulation is indicated by expression of IFNG, TNFA, TGFB, and IL10 from γδ T cells isolated from endometrial epithelium of pregnant ewes (Fox et al., 1998).
Natural Killer Cells. Accumulation of NK cells in the uterine endometrium is one of the notable cellular changes in the uterus during pregnancy in a variety of species, including humans and rodents (Manaster and Mandelboim, 2010; Soares et al., 2012), pigs (Tayade et al., 2007), and horses (Noronha et al., 2012). Their function has been studied best in the mouse and human. In the former species, NK cells have been implicated in playing a role in vascular remodeling through secretion of IFNG (Zhang et al., 2011). In the human, uterine NK cells have been associated with a variety of pregnancy disorders including preeclampsia and recurrent pregnan-cy failure (Lash and Bulmer, 2011) with at least some of
the problem being associated with aberrant recognition of trophoblast MHC antigens by killer inhibitory recep-tors on NK cells (Chazara et al., 2011).
Until recently, antibodies that reliably recognized NK cells have not been available for ruminants. Thus, little is known about the presence, regulation, or func-tion of endometrial NK cells in the cow or sheep. Cells with functional properties characteristic of NK cells have been demonstrated in the endometrium of pregnant ewes (Segerson and Beetham, 2000; Tekin and Hansen, 2003). Recently, cells reactive to an antibody recogniz-ing the NK-cell receptor, NKp46, were detected in low abundance in endometrium of nonpregnant ewes (Con-nelley et al., 2011). Whether NK cells increase in num-ber in the endometrium during pregnancy is not known. In the sheep, there was no difference in cytotoxic activ-ity toward an NK-cell target cell between nonpregnant and pregnant ewes (Tekin and Hansen, 2003).
Changes in Systemic Immune Function during the Periparturient Period
Parturition is accompanied by coordinated changes in metabolism and function of the mammary gland, di-gestive tract, uterus, and cervix that is driven by changes in circulating hormones such as progesterone, estrogen, cortisol, and PG (Wood, 1999). Given the interaction be-tween the immune system with the endocrine and meta-bolic systems (Stofkova, 2009; Pittman, 2011), changes in immune function in the periparturient period are to be expected. Indeed, there are extensive data that such changes occur in a way that could compromise compe-tence of the female to clear microorganisms from the
Figure 4. Intraepithelial γδ T cells in the luminal epithelium of the endometrium of the pregnant sheep. The left panel is an example of localization of γδ T cells in the luminal epithelium from the pregnant uterine horn of a unilaterally pregnant ewe at 140 d of gestation. The image is reproduced from Majewski et al. (2001) with permission of Immunology. The right panel shows changes in the percentage of luminal epithelial cells that are positive for the γδ T cell receptor during late gestation, at parturition and in the fi rst 3 d postpartum. Data are redrawn from Nasar et al. (2002). See online version to view fi gure in color.
Prepartum determinants of postpartum uterine health 1645
reproductive tract. Alterations in the endocrine control of parturition could contribute to female susceptibility to uterine infection; circulating estradiol concentrations at calving were greater in cows that developed metritis than cows that did not (Galvão et al., 2010a). Among the changes reported in immune function in late gestation or the periparturient period in the systemic vasculature are a reduction in circulating IgG and IgM concentrations (Herr et al., 2011), reduced neutrophil function (Kehrli et al., 1989; Hoeben et al., 2000; Rinaldi et al., 2008), an increase in neutrophil numbers (Meglia et al., 2005) and γδ T cells (Oliveira and Hansen, 2008), no change in number of CD8+ T cells (Ohtsuka et al., 2006; Oliveira and Hansen, 2008), a decrease in the number of CD68+ cells (Oliveira and Hansen, 2008) and eosinophils (Meglia et al., 2005), and either a decrease (Ohtsuka et al., 2006) or no change (Oliveira and Hansen, 2008) in the number of CD4+ T cells.
Antibacterial Defenses in the Postpartum Uterus: Speculations About a Prepartum–Postpartum Nexus
As shown in Fig. 5, adaptive immune responses against paternal antigens on the conceptus are down-regulated during pregnancy. Among the regulatory pro-cesses responsible for inhibition is an immunosuppres-sive role for progesterone (Reimers and Dziuk, 1974; Hansen et al., 1986; Majewski and Hansen, 2002; Padua et al., 2005), as well as differentiation of regulatory im-mune cells that can inhibit infl ammation and T cell re-sponses. These cells include the M2 macrophage (Gus-tafsson et al., 2008; Oliveira et al., 2010), γδ T cell (Lee et al., 1992; Suzuki et al., 1995), and Treg cell (Aluvihare et al., 2004; Shima et al., 2010; Samstein et al., 2012). Some of the immunological adjustments to the presence of the conceptus also make the uterus more susceptible to bacterial infection. Thus, for example, progesterone not only depresses skin graft rejection, but also reduces uterine capacity to eliminate bacterial infections (Row-son et al., 1953; Lewis, 2003). The M2 macrophages can inhibit infl ammation and facilitate persistence of some microbial infections (Varin and Gordon, 2009).
Figure 5. Cross-talk between the regulatory systems controlling mater-nal immune responses against the conceptus and microorganisms during ges-tation. Adaptive immune responses against paternal antigens on the conceptus are downregulated during pregnancy. For example, cytotoxic T cells are in-hibited by regulatory T cells (1), derived from peripheral precursors, proges-terone-induced endometrial proteins such as the uterine serpin, SERPINA14 (2), γδ T cells, through secretion of transforming growth factor-β (TGFB; 3), and M2 macrophages (4). Some of these immunological adjustments to the presence of the conceptus also make the uterus more susceptible to bacterial infection. Progesterone not only alters allograft rejection responses, but also acts through some largely unknown mechanism independent of SERPIN14 to inhibit antimicrobial responses in the uterus (5). The M2 macrophages also inhibit infl ammation (6), and SERPINA14 can inhibit B cell function (7). One cellular change associated with pregnancy, accumulation of γδ T cells in the luminal epithelium, may facilitate removal of bacteria through synthesis of proteins like granulysin and perforin (8). Note that the drawings for this fi gure and Fig. 6 are speculative: they combine concepts derived from sheep, cattle, and other species and not all of the pathways shown have been established in any one species. See online version to view fi gure in color.
Figure 6. Reduction in antimicrobial defense mechanisms in the endo-metrium during the periparturient period. The loss of the luminal epithelium in the early postpartum period (1) removes an important physical barrier to bacteria (mediated in part by mucins such as MUC1), a source of antimi-crobial peptides (AMP), and through synthesis of Toll-like receptors (TLR) and other pattern recognition receptors, a surveillance system to trigger in-fl ammation in response to microbial infection. In addition, functional activity of circulating neutrophils is reduced around parturition so that cells migrat-ing into the uterus in response to infl ammation have suboptimal capacity to phagocytose microbes (2). The γδ T cells, which are probably antimicrobial, are rapidly eliminated from the endometrium coincident with parturition (3). It is not yet clear whether cells and molecules that cause immunosuppression during pregnancy participate in immune regulation after parturition. Proges-terone concentrations decline precipitously with parturition so the immuno-suppressive actions of this hormone dissipate in the postpartum period (4). However, some of the products of progesterone action, such as the uterine serpin, SERPINA14, could conceivably persist in the uterus for some time af-ter parturition (5). It is possible, too, that antiinfl ammatory M2 macrophages remain in the endometrium during the postpartum period (6). See online ver-sion to view fi gure in color.
Hansen1646
Nonetheless, many host defense mechanisms re-main intact in the reproductive tract of the pregnant fe-male, including an endometrial epithelium that produces perforin (Tekin and Hansen, 2003) and possibly other antimicrobial products. The endometrial epithelium pre-sumably acts as a physical barrier to bacterial ingress even though luminal epithelium forms a syncytium with invading trophoblast (Wooding, 1992). Moreover, there is good reason to believe that intraepithelial δγ T cells in the uterine endometrium exert an antibacterial function (Fox and Meeusen, 1999; Fox et al., 2010).
As illustrated in Fig. 6, uterine susceptibility to bac-terial infection increases in the immediate postpartum period. The loss of the luminal epithelium in the early postpartum period (Moller, 1970) removes an important physical barrier to bacteria, a source of antimicrobial molecules and, through synthesis of TLR and other pat-tern recognition receptors, a surveillance system to trig-ger infl ammation in response to microbial infection. Fur-thermore, reduced functional activity of circulating neu-trophils (Kehrli et al., 1989; Hoeben et al., 2000; Rinaldi et al., 2008) means that cells migrating into the uterus in response to infl ammation have suboptimal capac-ity to phagocytose microbes. Finally, γδ T cells, which are probably antimicrobial during pregnancy (Fox and Meeusen, 1999; Fox et al., 2010), are rapidly eliminated from the ovine endometrium coincident with parturition (Lee et al., 1992; Nasar et al., 2002). The number of γδ T cells then begins to increase by d 3 postpartum (Nasar et al., 2002), but it is not known whether these new cells are differentiated toward an antimicrobial phenotype.
SUMMARY AND CONCLUSIONS
What is not known is the extent to which molecules and cells that inhibit immune responses during preg-nancy persist after parturition. Progesterone concentra-tions decline precipitously with parturition so the immu-nosuppressive actions of this hormone dissipate in the postpartum period. However, some of the products of progesterone action, such as SERPINA14, could con-ceivably persist in the uterus for some time after par-turition. Similarly, kinetics of removal of endometrial M2 macrophages during the postpartum period is not known. Perhaps individual variation in immune adjust-ments to pregnancy and parturition and the reversal of these changes in the postpartum period are important determinants of susceptibility of the uterus to infection. The question is worthy of more investigation. A better understanding of the immunological adjustments in the reproductive tract to pregnancy and parturition could lead to strategies for reducing uterine infections in the postpartum period.
LITERATURE CITEDAluvihare, V. R., M. Kallikourdis, and A. G. Betz. 2004. Regulatory
T cells mediate maternal tolerance to the fetus. Nat. Immunol. 5:266–271.
Arck, P. C., D. A. Ferrick, D. Steele-Norwood, P. J. Egan, K. Croitoru, S. R. Carding, J. Dietl, and D. A. Clark. 1999. Murine T cell de-termination of pregnancy outcome. Cell. Immunol. 196:71–79.
Brenner, J., M. Shemesh, L. S. Shore, S. Friedman, Z. Bider, U. Moalem, and Z. Trainin. 1995. A possible linkage between go-nadal hormones, serum and uterine levels of IgG of dairy cows. Vet. Immunol. Immunopathol. 47:179–184.
Brinsfi eld, T. H., H. W. Hawk, and H. F. Righter. 1964. Interaction of progesterone and oestradiol on induced leucocytic emigration in the sheep uterus. J. Reprod. Fertil. 8:293–296.
Chazara, O., S. Xiong, and A. Moffett. 2011. Maternal KIR and fetal HLA-C: A fi ne balance. J. Leukoc. Biol. 90:703–716.
Connelley, T., A. K. Storset, A. Pemberton, N. MacHugh, J. Brown, H. Lund, and I. W. Morrison. 2011. NKp46 defi nes ovine cells that have characteristics corresponding to NK cells. Vet. Res. 42:37.
Davies, D., K. G. Meade, S. Herath, P. D. Eckersall, D. Gonzalez, J. O. White, R. S. Conlan, C. O’Farrelly, and I. M. Sheldon. 2008. Toll-like receptor and antimicrobial peptide expression in the bovine endometrium. Reprod. Biol. Endocrinol. 6:53.
Dieli, F., M. Troye-Blomberg, J. Ivanyi, J. J. Fournié, A. M. Kren-sky, M. Bonneville, M. A. Peyrat, N. Caccamo, G. Sireci, and A. Salerno. 2001. Granulysin-dependent killing of intracellular and extracellular Mycobacterium tuberculosis by Vγ9/Vδa2 T lymphocytes. J. Infect. Dis. 184:1082–1085.
Dobson, H., S. L. Walker, M. J. Morris, J. E. Routly, and R. F. Smith. 2008. Why is it getting more diffi cult to successfully artifi cially inseminate cows? Animal 2:1104–1111.
Evans, M. J., J. M. Hamer, L. M. Gason, G. S. Graham, A. C. Asbury, and C. H. Irvine. 1986. Clearance of bacteria and non-antigenic markers following intra-uterine inoculation into maiden mares: Effect of steroid hormone environment. Theriogenology 26:37–50.
Everly, M. J., and P. I. Terasaki. 2012. The state of therapy for re-moval of alloantibody producing plasma cells in transplantation. Semin. Immunol. 24:143–147.
Fan, D. X., J. Duan, M. Q. Li, B. Xu, D. J. Li, and L. P. Jin. 2011. The decidual gamma-delta T cells up-regulate the biological func-tions of trophoblasts via IL-10 secretion in early human preg-nancy. Clin. Immunol. 141:284–292.
Farouk, S. E., L. Mincheva-Nilsson, A. M. Krensky, F. Dieli, and M. Troye-Blomberg. 2004. γδ T cells inhibit in vitro growth of the asexual blood stages of Plasmodium falciparum by a granule exocytosis-dependent cytotoxic pathway that requires granuly-sin. Eur. J. Immunol. 34:2248–2256.
Fischer, C., M. Drillich, S. Odau, W. Heuwieser, R. Einspanier, and C. Gabler. 2010. Selected pro-infl ammatory factor transcripts in bovine endometrial epithelial cells are regulated during the oestrous cycle and elevated in case of subclinical or clinical en-dometritis. Reprod. Fertil. Dev. 22:818–829.
Fox, A., C. S. Lee, M. R. Brandon, and E. N. Meeusen. 1998. Effects of pregnancy on lymphocytes within sheep uterine interplacen-tomal epithelium. Am. J. Reprod. Immunol. 40:295–302.
Fox, A., J. F. Maddox, M. J. de Veer, and E. N. Meeusen. 2010. γδ TCR+ cells of the pregnant ovine uterus express variable T cell receptors and contain granulysin. J. Reprod. Immunol. 84:52–56.
Fox, A., and E. Meeusen. 1999. Sheep perforin: Identifi cation and expression by δγ T cells from pregnant sheep uterine epithelium. Vet. Immunol. Immunopathol. 68:293–296.
Prepartum determinants of postpartum uterine health 1647
Galvão, K. N., M. J. Felippe, S. B. Brittin, R. Sper, M. Fraga, J. S. Galvão, L. Caixeta, C. L. Guard, A. Ricci, and R. O. Gilbert. 2012. Evaluation of cytokine expression by blood monocytes of lactating Holstein cows with or without postpartum uterine disease. Theriogenology 77:356–372.
Galvão, K. N., M. J. Flaminio, S. B. Brittin, R. Sper, M. Fraga, L. Caixeta, A. Ricci, C. L. Guard, W. R. Butler, and R. O. Gil-bert. 2010a. Association between uterine disease and indicators of neutrophil and systemic energy status in lactating Holstein cows. J. Dairy Sci. 93:2926–2937.
Galvão, K. N., M. Frajblat, W. R. Butler, S. B. Brittin, C. L. Guard, and R. O. Gilbert. 2010b. Effect of early postpartum ovulation on fertility in dairy cows. Reprod. Domest. Anim. 45:e207–e211.
Ganjam, V. K., C. McLeod, P. H. Klesius, S. M. Washburn, R. Kwapien, B. Brown, and M. H. Fazeli. 1982. Effect of ovarian hormones on the phagocytic response of ovariectomized mares. J. Reprod. Fertil. Suppl. 32:169–174.
Gautam, G., T. Nakao, M. Yusuf, and K. Koike. 2009. Prevalence of endometritis during the postpartum period and its impact on subsequent reproductive performance in two Japanese dairy herds. Anim. Reprod. Sci. 116:175–187.
Gerner, W., M. Stadler, S. E. Hammer, D. Klein, and A. Saalmül-ler. 2010. Sensitive detection of Foxp3 expression in bovine lymphocytes by fl ow cytometry. Vet. Immunol. Immunopathol. 138:154–158.
Gobert, M., and J. J. Lafaille. 2012. Maternal-fetal immune tolerance, block by block. Cell 150:7–9.
Gottshall, S. L., and P. J. Hansen. 1992. Regulation of leucocyte sub-populations in the sheependometrium by progesterone. Immu-nology 76:636–641.
Gustafsson, C., J. Mjösberg, A. Matussek, R. Geffers, L. Matthiesen, G. Berg, S. Sharma, J. Buer, and J. Ernerudh. 2008. Gene ex-pression profi ling of human decidual macrophages: Evidence for immunosuppressive phenotype. PLoS One 3:e2078.
Hansen, P.J. 2012. Supplemental antioxidants to improve reproduc-tion in dairy cattle – why, when and how effective are they? In: P.C. Garnsworthy and J. Wiseman, editors. Recent advances in animal nutrition 2012, Nottingham University Press, Notting-ham, p. 37–52.
Hansen, P. J., F. W. Bazer, and E. C. Segerson. 1986. Skin graft sur-vival in the uterine lumen of ewes treated with progesterone. Am. J. Reprod. Immunol. Microbiol. 12:48–54.
Herath, S., D. P. Fischer, D. Werling, E. J. Williams, S. T. Lilly, H. Dobson, C. E. Bryant, and I. M. Sheldon. 2006. Expression and function of Toll-like receptor 4 in the endometrial cells of the uterus. Endocrinology 147:562–570.
Herr, M., H. Bostedt, and K. Failing. 2011. IgG and IgM levels in dairy cows during the periparturient period. Theriogenology 75:377–385.
Hoeben, D., E. Monfardini, G. Opsomer, C. Burvenich, H. Dosogne, A. de Kruif, and J. F. Beckers. 2000. Chemiluminescence of bovine polymorphonuclear leucocytes during the periparturient period and relation with metabolic markers and bovine preg-nancy-associated glycoprotein. J. Dairy Res. 67:249–259.
Josefowicz, S. Z., R. E. Niec, H. Y. Kim, P. Treuting, T. Chinen, Y. Zheng, D. T. Umetsu, and A. Y. Rudensky. 2012. Extrathymi-cally generated regulatory T cells control mucosal TH2 infl am-mation. Nature 482:395–399.
Kasimanickam, R., T. F. Duffi eld, R. A. Foster, C. J. Gartley, K. E. Leslie, J. S. Walton, and W. H. Johnson. 2004. Endometrial cy-tology and ultrasonography for the detection of subclinical en-dometritis in postpartum dairy cows. Theriogenology 62:9–23.
Kaushic, C., F. Zhou, A. D. Murdin, and C. R. Wira. 2000. Effects of estradiol and progesterone on susceptibility and early immune responses to Chlamydia trachomatis infection in the female re-productive tract. Infect. Immun. 68:4207–4216.
Kehrli, M. E. Jr., B. J. Nonnecke, and J. A. Roth. 1989. Alterations in bovine neutrophil function during the periparturient period. Am. J. Vet. Res. 50:207–214.
Kim, I. H., K. J. Na, and M. P. Yang. 2005. Immune responses during the peripartum period in dairy cows with postpartum endome-tritis. J. Reprod. Dev. 51:757–764.
Kroemer, A., X. Xiao, N. Degauque, K. Edtinger, H. Wei, G. Demir-ci, and X.C. Li. 2008. The innate NK cells, allograft rejection, and a key role for IL-15. J. Immunol. 180:7818–7826.
Lander Chacin, M. F., P. J. Hansen, and M. Drost. 1990. Effects of stage of the estrous cycle and steroid treatment on uterine im-munoglobulin content and polymorphonuclear leukocytes in cattle. Theriogenology 34:1169–1184.
Lash, G. E., and J. N. Bulmer. 2011. Do uterine natural killer (uNK) cells contribute to female reproductive disorders? J. Reprod. Immunol. 88:156–164.
Lee, C. S., E. Meeusen, K. Gogolin-Ewens, and M. R. Brandon. 1992. Quantitative and qualitative changes in the intraepithelial lymphocyte population in the uterus of nonpregnant and preg-nant sheep. Am. J. Reprod. Immunol. 28:90–96.
Leslie, M. V., and P. J. Hansen. 1991. Progesterone-regulated secre-tion of the serpin-like proteins of the ovine and bovine uterus. Steroids 56:589–597.
Leslie, M. V., P. J. Hansen, and G. R. Newton. 1990. Uterine secre-tions of the cow contain proteins that are immunochemically related to the major progesterone-induced proteins of the sheep uterus. Domest. Anim. Endocrinol. 7:517–526.
Lewis, G. S. 2003. Role of ovarian progesterone and potential role of prostaglandin F2α and prostaglandin E2 in modulating the uterine response to infectious bacteria in postpartum ewes. J. Anim. Sci. 81:285–293.
Lewis, G. S., and M. C. Wulster-Radcliffe. 2006. Prostaglandin F2α upregulates uterine immune defenses in the presence of the immunosuppressive steroid progesterone. Am. J. Reprod. Immunol. 56:102–111.
Li, Z., H. Peng, Q. Xu, and Z. Ye. 2012. Sensitization of human os-teosarcoma cells to Vγ9Vδ2 T-cell-mediated cytotoxicity by zoledronate. J. Orthop. Res. 30:824–830.
Littman, D. R., and A. Y. Rudensky. 2010. Th17 and regulatory T cells in mediating and restraining infl ammation. Cell 140:845–858.
Liu, W.-J., and P. J. Hansen. 1993. Effect of the progesterone-induced serpin-like proteins of the sheep endometrium on natural-killer cell activity in sheep and mice. Biol. Reprod. 49:1008–1014.
Majewski, A. C., and P. J. Hansen. 2002. Progesterone promotes sur-vival of xenogeneic transplants in the sheep uterus. Hormone Res. 58:128–135.
Majewski, A. C., Ş Tekin, and P. J. Hansen. 2001. Local versus sys-temic control of numbers of endometrial T cells during preg-nancy in sheep. Immunology 102:317–322.
Manaster, I., and O. Mandelboim. 2010. The unique properties of uterine NK cells. Am. J. Reprod. Immunol. 63:434–444.
Meglia, G. E., A. Johannisson, S. Agenäs, K. Holtenius, and K. P. Waller. 2005. Effects of feeding intensity during the dry period on leukocyte and lymphocyte sub-populations, neutrophil func-tion and health in periparturient dairy cows. Vet. J. 169:376–384.
Meeusen, E., A. Fox, M. Brandon, and C. S. Lee. 1993. Activation of uterine intraepithelial γδ T-cell receptor-positive lymphocytes during pregnancy. Eur. J. Immunol. 23:1112–1117.
Hansen1648
Moffatt, J., F. W. Bazer, P. J. Hansen, P. W. Chun, and R. M. Rob-erts. 1987. Purifi cation, secretion and immunocytochemical localization of the uterine milk proteins, major progesterone-induced proteins in uterine secretions of the sheep. Biol. Re-prod. 36:419–430.
Moller, K. 1970. A review of uterine involution and ovarian activ-ity during the postparturient period in the cow. N. Z. Vet. J. 18:83–90.
Monterroso, V. H., and P. J. Hansen. 1993. Regulation of bovine and ovine lymphocyte proliferation by progesterone: Modulation by steroid receptor antagonists and physiological status. Acta En-docrinol. 129:532–535.
Nasar, A., A. Rahman, E. N. Meeusen, and C. S. Lee. 2002. Peri-partum changes in the intraepithelial lymphocyte population of sheep interplacentomal endometrium. Am. J. Reprod. Immunol. 47:132–141.
Noronha, L. E., K. E. Huggler, A. M. de Mestre, D. C. Miller, and D. F. Antczak. 2012. Molecular evidence for natural killer-like cells in equine endometrial cups. Placenta 33:379–386.
Ohtsuka, H., C. Watanabe, M. Kohiruimaki, T. Ando, D. Wata-nabe, M. Masui, T. Hayashi, R. Abe, M. Koiwa, S. Sato, and S. Kawamura. 2006. Comparison of two different nutritive condi-tions against the changes in peripheral blood mononuclear cells of periparturient dairy cows. J. Vet. Med. Sci. 68:1161–1166.
Oliveira, L. J., and P. J. Hansen. 2008. Deviations in populations of peripheral blood mononuclear cells and endometrial macro-phages in the cow during pregnancy. Reproduction 136:481–490.
Oliveira, L. J., and P. J. Hansen. 2009. Phenotypic characterization of macrophages in the endometrium of the pregnant cow. Am. J. Reprod. Immunol. 62:418–426.
Oliveira, L. J., S. McClellan, and P. J. Hansen. 2010. Differentiation of the endometrial macrophage during pregnancy in the cow. Plos One 5:e13213.
Padua, M. B., and P. J. Hansen. 2010. Evolution and function of the uterine serpins (SERPINA14). Am. J. Reprod. Immunol. 64:265–274.
Padua, M. B., A. A. Kowalski, M. Y. Cañas, and P. J. Hansen. 2010. The molecular phylogeny of uterine serpins and its relationship to evolution of placentation. FASEB J. 24:526–537.
Padua, M. B., Ş. Tekin, T. E. Spencer, and P. J. Hansen. 2005. Actions of progesterone on uterine immunosuppression and endometrial gland development in the uterine gland knockout (UGKO) ewe. Mol. Reprod. Dev. 71:347–357.
Peltier, M. R., W.-J. Liu, and P. J. Hansen. 1999. Regulation of lym-phocyte proliferation by uterine serpin: Interleukin-2 mRNA production, CD25 expression and responsiveness to interleu-kin-2. Exp. Biol. Med. 223:75–81.
Pittman, Q. J. 2011. A neuro-endocrine-immune symphony. J. Neu-roendocrinol. 23:1296–1297.
Reimers, T. J., and P. J. Dziuk. 1974. The survival of intrauterine skin autografts and allografts in sheep. J. Reprod. Fertil. 38:465–467.
Rinaldi, M., P. Moroni, M. J. Paape, and D. D. Bannerman. 2008. Differential alterations in the ability of bovine neutrophils to generate extracellular and intracellular reactive oxygen species during the periparturient period. Vet. J. 178:208–213.
Rocchi, M. S., S. R. Wattegedera, D. Frew, G. Entrican, J. F. Hunt-ley, and T. N. McNeilly. 2011. Identifi cation of CD4+CD25high Foxp3+ T cells in ovine peripheral blood. Vet. Immunol. Immu-nopathol. 144:172–177.
Rowson, L. E. A., G. A. Lamming, and R. M. Fry. 1953. The relation-ship between ovarian hormones and uterine infection. Vet. Rec. 65:335–340.
Samstein, R. M., S. Z. Josefowicz, A. Arvey, P. M. Treuting, and A. Y. Rudensky. 2012. Extrathymic generation of regulatory T cells in placental mammals mitigates maternal-fetal confl ict. Cell 150:29–38.
Santos, J. E. P., R. S. Bisinotto, E. S. Ribeiro, F. S. Lima, L. F. Greco, C. R. Staples, and W. W. Thatcher. 2011. Applying nutrition and physiology to improve reproduction in dairy cattle. In: M. F. Smith, M. C. Lucy, J. L. Pate, and T. E. Spencer, editors, Repro-duction in Domestic Ruminants VII. Nottingham Univ. Press, Nottingham, UK. p. 387–403.
Segerson, E. C., and P. K. Beetham. 2000. High-density ovine en-dometrial cells exhibit natural killer activity during early preg-nancy. Theriogenology 54:1207–1214.
Segerson, E. C., R. J. Moffatt, F. W. Bazer, and R. M. Roberts. 1984. Suppression of phytohemagglutinin-stimulated lympho-cyte blastogenesis by ovine uterine milk protein. Biol. Reprod. 30:1175–1186.
Sheldon, I. M., J. Cronin, L. Goetze, G. Donofrio, and H. J. Schuberth. 2009. Defi ning postpartum uterine disease and the mechanisms of infection and immunity in the female reproductive tract in cattle. Biol. Reprod. 81:1025–1032.
Shima, T., Y. Sasaki, M. Itoh, A. Nakashima, N. Ishii, K. Sugamura, and S. Saito. 2010. Regulatory T cells are necessary for implan-tation and maintenance of early pregnancy but not late preg-nancy in allogeneic mice. J. Reprod. Immunol. 85:121–129.
Siiteri, P. K., F. Febres, L. E. Clemens, R. J. Chang, B. Gondos, and D. Stites. 1977. Progesterone and maintenance of pregnancy: Is progesterone Nature’s immunosuppressant? Ann. N. Y. Acad. Sci. 286:384–397.
Silvestre, F. T., J. A. Bartolome, S. Kamimura, A. C. Arteche, S. M. Pancarci, T. Trigg, and W. W. Thatcher. 2009. Postpartum sup-pression of ovarian activity with a Deslorelin implant enhanced uterine involution in lactating dairy cows. Anim. Reprod. Sci. 110:79–95.
Silvia, W. J., G. S. Lewis, J. A. McCracken, W. W. Thatcher, and L. Wilson, Jr. 1991. Hormonal regulation of uterine secretion of prostaglandin F2α during luteolysis in ruminants. Biol. Reprod. 45:655–663.
Skopets, B., Liu, W.-J., and P. J. Hansen. 1995. Effects of endome-trial serpin-like proteins on immune responses in sheep. Am. J. Reprod. Immunol. 33:86–93.
Soares, M. J., D. Chakraborty, M. A. Karim Rumi, T. Konno, and S. J. Renaud. 2012. Rat placentation: An experimental model for investigating the hemochorial maternal-fetal interface. Placenta 33:233–243.
Somerset, D. A., Y. Zheng, M. D. Kilby, D. M. Sansom, and M. T. Drayson. 2004. Normal human pregnancy is associated with an elevation in the immune suppressive CD25+ CD4+ regulatory T-cell subset. Immunology 112:38–43.
Stenger, S. 2001. Cytolytic T cells in the immune response to myco-bacterium tuberculosis. Scand. J. Infect. Dis. 33:483–487.
Stofkova, A. 2009. Leptin and adiponectin: From energy and meta-bolic dysbalance to infl ammation and autoimmunity. Endocr. Regl. 43:157–168.
Subandrio, A. L., I. M. Sheldon, and D. E. Noakes. 2000. Peripheral and intrauterine neutrophil function in the cow: The infl uence of endogenous and exogenous sex steroid hormones. Theriogenol-ogy 53:1591–1608.
Suzuki, T., K. Hiromatsu, Y. Ando, T. Okamoto, Y. Tomoda, and Y. Yoshikai. 1995. Regulatory role of γδ T cells in uterine intraepi-thelial lymphocytes in maternal antifetal immune response. J. Immunol. 154:4476–4484.
Prepartum determinants of postpartum uterine health 1649
Tayade, C., Y. Fang, and B. A. Croy. 2007. A review of gene expres-sion in porcine endometrial lymphocytes, endothelium and tro-phoblast during pregnancy success and failure. J. Reprod. Dev. 53:455–463.
Tekin, Ş., and P. J. Hansen. 2002. Natural-killer like cells in the sheep: Functional characterization and regulation by pregnan-cy-associated proteins. Exp. Biol. Med. 227:803–811.
Tekin, Ş., and P. J. Hansen. 2003. Lymphocyte-mediated lysis of sheep chorion: Susceptibility of chorionic cells to third-party and maternal cytotoxic lymphocytes and presence of cells in the endometrium exhibiting cytotoxicity toward natural-killer cell targets. Theriogenology 59:787–800.
Tekin, Ş., and P. J. Hansen. 2004. Regulation of numbers of macro-phages in the endometrium of the sheep by systemic effects of pregnancy, local presence of the conceptus, and progesterone. Am. J. Reprod. Immunol. 51:56–62.
Tekin, Ş., M. B. Padua, A. M. Brad, M. L. Rhodes, and P. J. Hansen. 2006. Expression and properties of recombinant ovine uterine serpin. Exp. Biol. Med. 231:1313–1322.
Troedsson, M. H., and I. K. Liu. 1991. Uterine clearance of non-antigenic markers (51Cr) in response to a bacterial challenge in mares potentially susceptible and resistant to chronic uterine infections. J. Reprod. Fertil. Suppl. 44:283–288.
Ulbrich, S. E., T. Frohlich, K. Schulke, E. Englberger, N. Wald-schmitt, G. J. Arnold, H. D. Reichenbach, M. Reichenbach, E. Wolf, H. H. D. Meyer, and S. Bauersachs. 2009. Evidence for estrogen-dependent uterine serpin (SERPINA14) expression during estrus in the bovine endometrial glandular epithelium and lumen. Biol. Reprod. 81:795–805.
Valujskikh, A., and X. C. Li. 2007. Frontiers in nephrology: T cell memory as a barrier to transplant tolerance. J. Am. Soc. Nephrol. 18:2252–2261.
Varin, A., and S. Gordon. 2009. Alternative activation of macro-phages: Immune function and cellular biology. Immunobiology 214:630–641.
Wallace, P. K., G. R. Yeaman, K. Johnson, J. E. Collins, P. M. Guyre, and C. R. Wira. 2001. MHC Class II expression and antigen presentation by human endometrial cells. J. Steroid Biochem. Mol. Biol. 76:203–211.
Watnick, A. S., and R. A. Russo. 1968. Survival of skin homografts in uteri of pregnant and progesterone-estrogen treated rats. Proc. Soc. Exp. Med. 128:1–4.
Wesch, D., C. Peters, H. H. Oberg, K. Pietschmann, and D. Kabelitz. 2011. Modulation of γδ T cell responses by TLR ligands. Cell. Mol. Life Sci. 68:2357–2370.
Whitmore, H. L., and L. F. Archbald. 1977. Demonstration and quan-titation of immunoglobulins in bovine serum, follicular fl uid, and uterine and vaginal secretions with reference to bovine viral diarrhea. Am. J. Vet. Res. 38:455–457.
Wood, C. E. 1999. Control of parturition in ruminants. J. Reprod. Fertil. Suppl. 54:115–126.
Wooding, F. B. P. 1992. Current topic: The synepitheliochorial pla-centa of ruminants: Binucleate cell fusions and hormone pro-duction. Placenta 13:101–113.
Wulster-Radcliffe, M. C., R. C. Seals, and G. S. Lewis. 2003. Pro-gesterone increases susceptibility of gilts to uterine infections after intrauterine inoculation with infectious bacteria. J. Anim. Sci. 81:1242–1252.
Zhang, J., Z. Chen, G. N. Smith, and B. A. Croy. 2011. Natural killer cell-triggered vascular transformation: Maternal care before birth? Cell. Mol. Immunol. 8:1–11.
