Endometrial caspase 1 and interleukin-18 expression during the estrous cycle and peri-implantation period of porcine pregnancy and response to early exogenous estrogen administration

Maternal recognition of pregnancy in the pig: A servomechanism involving sex steroids, cytokines and prostaglandins

Maternal recognition of pregnancy (MRP) is a term utilized in mammals to describe pathways in which the conceptus alters the endometrial environment to prevent regression of corpora lutea to ensure continued production of progesterone (P4) required for establishment and maintenance of pregnancy. For nearly 40 years after publication of the endocrine/exocrine theory, conceptus estrogen (E2) was considered the primary maternal recognition signal in the pig. Conceptus production of prostaglandin E2 (PGE2) was also considered to be a major factor in preventing luteolysis. An addition to E2 and PGE2, pig conceptuses produce interleukin 1B2 (IL1B2) and interferons (IFN) delta (IFND) and gamma (IFNG). The present review provides brief history of the discovery of E2, PGs and IFNS which led to research investigating the role of these conceptus secreted factors in establishing and maintaining pregnancy in the pig. The recent utilization of gene editing technology allowed a more direct approach to investigate the in vivo roles of IL1B2, E2, PGE2, AND IFNG for establishment of pregnancy. These studies revealed unknown functions for IFNG and ILB2 in addition to PGE2 and E2. Thus, pregnancy recognition signal is via a servomechanism in requiring sequential effects of P4, E2, IL1B2, PGE2 and IFNG. Results indicate that the original established dogma for the role of conceptus E2 and PGs in MRP is a far too simplified model that involves the interplay of numerous mechanisms for inhibiting luteolysis, inducing critical elongation of the conceptuses and resolution of inflammation in pigs.

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

Mating modifies the expression of crucial oxidative-reductive transcripts in the pig oviductal sperm reservoir: is the female ensuring sperm survival?

Background

Mating induces large changes in the female genital tract, warranting female homeostasis and immune preparation for pregnancy, including the preservation of crucial oxidative status among its pathways. Being highly susceptible to oxidative stress, sperm survival and preserved function depend on the seminal plasma, a protection that is removed during sperm handling but also after mating when spermatozoa enter the oviduct. Therefore, it is pertinent to consider that the female sperm reservoir takes up this protection, providing a suitable environment for sperm viability. These aspects have not been explored despite the increasing strategies in modulating the female status through diet control and nutritional supplementation.

Aims

To test the hypothesis that mating modifies the expression of crucial oxidative-reductive transcripts across the entire pig female genital tract (cervix to infundibulum) and, particularly in the sperm reservoir at the utero-tubal junction, before ovulation, a period dominated by estrogen stimulation of ovarian as well as of seminal origin.

Methods

The differential expression of estrogen (ER) and progesterone (PR) receptors and of 59 oxidative-reductive transcripts were studied using a species-specific microarray platform, in specific segments of the peri-ovulatory sow reproductive tract in response to mating.

Results

Mating induced changes along the entire tract, with a conspicuous downregulation of both ER and PR and an upregulation of superoxide dismutase 1 (SOD1), glutaredoxin (GLRX3), and peroxiredoxin 1 and 3 (PRDX1, PRDX3), among other NADH Dehydrogenase Ubiquinone Flavoproteins, in the distal uterus segment. These changes perhaps helped prevent oxidative stress in the area adjacent to the sperm reservoir at the utero-tubal junction. Concomitantly, there were a downregulation of catalase (CAT) and NADH dehydrogenase (ubiquinone) oxidoreductases 1 beta subcomplex, subunit 1 (NDUFB1) in the utero-tubal junction alongside an overall downregulation of CAT, SOD1, and PRDX3 in the ampullar and infundibulum segments.

Conclusions

Natural mating is an inducer of changes in the expression of female genes commanding antioxidant enzymes relevant for sperm survival during sperm transport, under predominant estrogen influence through the bloodstream and semen. The findings could contribute to the design of new therapeutics for the female to improve oxidative-reductive balance.

Bensulide exposure causes cell division cycle arrest and apoptosis in porcine trophectoderm and uterine luminal epithelial cells

As the use of herbicides in agriculture has increased worldwide, the importance of identifying unexpected toxic effects on non-target organisms is emerging. Bensulide is used on various agricultural crops as an organophosphate herbicide; however, it can pose a high risk to non-target organisms because of its long half-life and accumulative potential. Despite its high risk, the hazardous effects of bensulide on implantation and mechanisms in cells have not been reported. Therefore, in this study, intracellular mechanisms and potential risk of implantation failure were identified in porcine trophectoderm (pTr) and uterine luminal epithelial (pLE) cells derived from pigs with human-like molecular mechanisms in implantation. The LC₅₀ values of bensulide were 5.21 mg/L in pTr cells and 6.49 mg/L in pLE cells. Both cell lines were exposed to bensulide at concentrations <5 mg/L in subsequent experiments. Treatment with 5 mg/L bensulide activated ERK1/2 and JNK. Disrupted mitochondrial membrane potentials of both cell types were identified. In addition, mitochondrial Ca²⁺ concentration increased to 261.24% and 228.04% in pTr and pLE cells, respectively, and cytoplasmic Ca²⁺ concentrations decreased by approximately 50% in both cell types. The abnormal regulation of various intracellular environments by bensulide causes cell division cycle arrest and apoptosis. Finally, 5 mg/L bensulide inhibited transcription of implantation-related genes. Collectively, our results suggest that bensulide may interrupt implantation during early pregnancy by disrupting maternal-fetal interaction.

Evaluation of the molecular response of corpora lutea to manganese-amino acid complex supplementation in gilts

Porcine pregnancy establishment and maintenance are dependent on the formation of functional corpora lutea (CL). Manganese (Mn) is critical for CL function as it is a cofactor for Mn superoxide dismutase and enzymes involved in cholesterol synthesis. Previously, we have shown that luteal Mn content increased and luteal progesterone (P₄) concentration decreased in the CL of gilts fed diets supplemented with an Mn–amino acid complex (Availa-Mn; Zinpro Corporation) compared with controls fed Mn sulfate. Importantly, serum P₄ increased from 0 (estrus onset) to 12 d post estrus (dpe), as expected, but P₄ abundance in circulation was not affected by dietary Mn source (P = 0.15). We hypothesized that a more bioavailable Mn source (which results in increased luteal Mn content) would alter the luteal proteome and abundance of mRNA associated with steroid biogenesis during the mid-luteal phase of the estrous cycle. Postpubertal gilts (n = 32) were assigned to one of the four gestation diets. The control diet (CON) contained 20 ppm of supplemental Mn in the form of Mn sulfate. Three additional diets included 20 (TRT1), 40 (TRT2), or 60 (TRT3) ppm of supplemental Mn in the form of a Mn–amino acid complex instead of Mn sulfate. Dietary treatment began at estrus synchronization (approximately 20 d before estrus) and continued through 12 dpe when gilts were euthanized and tissues were collected. Protein and total RNA extracts from the CL were used for proteomic analysis via label-free liquid chromatography with tandem mass spectrometry to assess global protein abundance and quantitative real-time polymerase chain reaction (qRT-PCR) to assess specific mRNA abundance, respectively. Compared with CON, 188, 382, and 401 proteins were differentially abundant (P < 0.10) in TRT1, TRT2, and TRT3, respectively. Gene Ontology enrichment software revealed that proteins involved in P₄ signaling and cholesterol synthesis were downregulated in CL of gilts fed Mn–amino acid complex compared with controls. Quantitative RT-PCR showed that relative transcript abundance of genes encoding steroidogenic enzymes (CYP11A1 and StAR) in CL tissue was decreased in gilts from TRT2 compared with CON (P = 0.02), but TRT1 and TRT3 were not affected (P ≥ 0.30). Collectively, these data support our hypothesis that a more bioavailable dietary Mn source may influence luteal function by altering the abundance of protein and mRNA involved in steroidogenesis.

Reactive oxygen and nitrogen species regulate porcine embryo development during pre-implantation period: A mini-review

Significant porcine embryonic loss occurs during conceptus morphological elongation and attachment from d 10 to 20 of pregnancy, which directly decreases the reproductive efficiency of sows. A successful establishment of pregnancy mainly depends on the endometrium receptivity, embryo quality, and utero-placental microenvironment, which requires complex cross-talk between the conceptus and uterus. The understanding of the molecular mechanism regulating the uterine-conceptus communication during porcine conceptus elongation and attachment has developed in the past decades. Reactive oxygen and nitrogen species, which are intracellular reactive metabolites that regulate cell fate decisions and alter their biological functions, have recently reportedly been involved in porcine conceptus elongation and attachment. This mini-review will mainly focus on the recent researches about the role of reactive oxygen and nitrogen species in regulating porcine embryo development during the pre-implantation period.

Evidence of haptoglobin in the porcine female genital tract during oestrous cycle and its effect on in vitro embryo production

Recent evidence supports involvement of the acute phase protein haptoglobin in numerous events during mammalian reproduction. The present study represents an in-depth investigation of haptoglobin expression and secretion in the porcine oviduct and uterus, and assesses its effect on porcine in vitro embryo production. A systematic study was made of sows in different oestrous stages: late follicular, early luteal and late luteal stages. Relative haptoglobin mRNA abundance was quantified by RT-qPCR. In addition, expression of the protein was analysed by immunohistochemistry and the results were complemented by Western-blot and proteomic analyses of the oviductal and uterine fluids. In vitro porcine fertilization and embryo culture were carried out in the presence of haptoglobin. The results indicate that haptoglobin mRNA expression in the porcine oviduct and uterus is most abundant during the late luteal stage of the oestrous cycle. By means of Western blot and proteomic analyses haptoglobin presence was demonstrated in the oviduct epithelium and in the oviductal and uterine fluids in different stages of the oestrous cycle. The addition of haptoglobin during gamete co-incubation had no effect on sperm penetration, monospermy or efficiency rates; however, compared with the control group, blastocyst development was significantly improved when haptoglobin was present (haptoglobin: 64.50% vs. control: 37.83%; p < 0.05). In conclusion, the presence of haptoglobin in the oviduct and uterus of sows at different stages of the oestrous cycle suggests that it plays an important role in the reproduction process. The addition of haptoglobin during in vitro embryo production improved the blastocyst rates.

Effects of n-acetyl-cysteine supplementation in late gestational diet on maternal-placental redox status, placental NLRP3 inflammasome, and fecal microbiota in sows1

Although n-acetyl-cysteine (NAC) has been shown to efficiently alleviate oxidative stress, inflammatory response, and alter gut microbiota, little attention has been focused on their interactions with placental metabolic status of sows. The effects of NAC on the placental redox status, function, inflammasome, and fecal microbiota in sows were explored to clarify the correlation between the fecal microbiota and placenta. Sows were divided into either the control group or the NAC group which received dietary 0.5% NAC supplementation from day 85 of gestation to delivery. Plasma redox status, placental growth factors, nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome, fecal microbial metabolites, and communities were evaluated. Compared with the control group, although NAC did not ameliorate reproductive performance of sows (P > 0.05), it significantly improved maternal-placental health, which was accompanied by increased activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), decreased level of malondialdehyde (MDA), and lowered expression of interleukin (IL)-1β and IL-18 through inhibiting NLRP3 inflammasome (P < 0.05). Additionally, NAC significantly increased placental insulin-like growth factors (IGFs) and E-cadherin contents (P < 0.05), elevated the expression of genes involved in angiogenesis and amino acids transporters (P < 0.05), and decreased the microtubule-associated protein light chain 3B (LC3B) and Beclin-1 protein expression (P < 0.05). Furthermore, NAC increased the relative abundances of fecal Prevotella, Clostridium cluster XIVa, and Roseburial/Eubacterium rectale (P < 0.05), which were negatively correlated with placental NLRP3 and positively with solute carrier family 7, member 8 (Slc7a8; P < 0.05). In conclusion, NAC supplementation during late gestation alleviated maternal-placental oxidative stress and inflammatory response, improved placental function, and altered fecal microbial communities.

IL-1β, IL-2 and IL-4 concentration during porcine gestation

In pigs, given the type of epitheliochorial and non-invasive placenta, the trophoblast is in intimate contact with maternal tissues. The dialogue established between the conceptus and the endometrium involves, among others, the immune system, which minimizes the chances of rejection of the embryo and promotes the establishment of pregnancy. The aim of this work was to determine the concentration of IL-1β, IL-2 and IL-4 in sera and in extracts of maternal and fetal placenta from sows of different gestational periods. Reproductive tracts from 23 crossbreed sows, between 30 and 114 days of gestation (dg), and from 8 non-pregnant sows were used. The concentration of the cytokines was determined by ELISA. IL-1β, IL-2 and IL-4 demonstrated a similar pattern of concentration at the placental interface and serum; they were found elevated in tissues at 30 and 60-70 dg, and significantly decreased at term, period in which the cytokines were significantly increased in serum. These results show that IL-1β, IL-2, and IL-4 are differentially modulated during pregnancy and at term, and suggest an important role of these cytokines in defining the proinflammatory stage of these periods.

Genomic Analysis To Identify Signatures of Artificial Selection and Loci Associated with Important Economic Traits in Duroc Pigs

Identifying genetic basis of domestication and improvement in livestock contributes to our understanding of the role of artificial selection in shaping the genome. Here we used whole-genome sequencing and the genotyping by sequencing approach to detect artificial selection signatures and identify the associated SNPs of two economic traits in Duroc pigs. A total of 38 candidate selection regions were detected by combining the fixation index and the Composite Likelihood Ratio methods. Further genome-wide association study revealed seven associated SNPs that were related with intramuscular fat content and feed conversion ratio traits, respectively. Enrichment analysis suggested that the artificial selection regions harbored genes, such as MSTN, SOD2, MC5R and CD83, which are responsible for economic traits including lean muscle mass, fertility and immunization. Overall, this study found a series of candidate genes putatively associated with the breeding improvement of Duroc pigs and the polygenic basis of adaptive evolution, which can provide important references and fundamental information for future breeding programs.

Effects of human chorionic gonadotropin, estradiol, and progesterone on interleukin-18 expression in human decidual tissues

Interleukin (IL)-18 is a proinflammatory cytokine which mediates a myriad of inflammatory responses during pregnancy. Changes in IL-18 levels have been linked to complications during pregnancy. This study was designed to assess the effects of estradiol, human chorionic gonadotropin (hCG), and progesterone on IL-18 expression in human decidual tissues. Uterine deciduas from women with normal pregnancy, spontaneous abortion, and progesterone treated spontaneous abortion were collected, and the effects of hormones on the viability of decidual cells and IL-18 secretion were detected by MTT and ELISA assays. We found that Estradiol, hCG, and progesterone inhibited decidual cell growth independent of dosage and time.IL-18 secretion in the spontaneous abortion group was increased in the decidual cells over time, but all hormones significantly reduced its secretion (p < 0.05). Our results indicate that estradiol, hCG, and progesterone can reduce IL-18 secretion in the cultured endometrial stromal cells from patients who experienced spontaneous abortion to the levels observed following normal pregnancy. Progesterone can significantly reduce IL-18 expression and increase growth of CD56+ CD16- uNK cells, suggesting that these activities may underlie the mechanism by which progesterone improves pregnancy outcomes.

Interleukins, interferons, and establishment of pregnancy in pigs

Early pregnancy in mammals requires complex and highly orchestrated cellular and molecular interactions between specialized cells within the endometrium and the conceptus. Proinflammatory cytokines are small signaling proteins released by leukocytes that augment innate and adaptive immune responses. They are also released by the mammalian trophectoderm as the conceptus apposes the uterine surface for implantation. On approximately day 12 of development in pigs, the conceptus undergoes a rapid morphological transformation referred to as elongation while simultaneously releasing estrogens and a novel conceptus form of interleukin-1 beta (IL1β). Following elongation, pig conceptuses express interferon gamma (IFNγ) and, in lesser amounts, interferon delta (IFNδ). Significant IFN signaling takes place within the endometrium between day 14 and 18 of pregnancy as the conceptus intimately associates with the uterine epithelium. Based on studies carried out in pigs and other mammals, the combined spacio-temporal activities of conceptus estrogens, IL1β, and IFN set in motion a series of coordinated events that promote establishment of pregnancy. This is achieved through enhancement of conceptus development, uterine receptivity, maternal-fetal hemotropic exchange, and endometrial leukocyte function. These events require activation of specific signaling pathways within the uterine luminal epithelium, glandular epithelium, and stroma. Here, we review proinflammatory cytokine expression by pig conceptuses and the hypothesized actions of these molecules during establishment of pregnancy.

Genetic variant in interleukin-18 is associated with idiopathic recurrent miscarriage in Chinese Han population

Levels of IL-18 were significantly lower in women with recurrent miscarriage (RM) than those without idiopathic RM. IL-18 promoter single nucleotide polymorphisms were previously identified to have an impact on IL18 gene transcription activity and influence the level of IL-18 protein production. The aim of this study was to evaluate whether IL-18 gene polymorphisms are risk factors for idiopathic RM in Chinese Han population. Study subjects comprised of 484 idiopathic RM patients and 468 controls. Three polymorphisms (rs360717, rs187238, rs1946518) in IL-18 gene and serum IL-18 concentrations were assessed. rs187238 variant exhibits significant association with RM in additive and recessive genetic model (additive model p = 1.05 × 10⁻⁴, dominant model p = 0.025, recessive model p = 2.43 × 10⁻⁵). In contrast, rs360717 and rs1946518 are not significantly associated with RM. Serum IL-18 levels are significantly lower in RM cases than in control (111.98 ± 93.13 versus 148.74 ± 130.51 pg/mL, p = 7.42 × 10⁻⁷). There are lower levels of serum IL-18 in rs187238 homozygous mutant (CC) than homozygous wild-type (GG) in this study population, including cases and control groups (98.31 ± 86.46 versus 131.87 ± 115.02 pg/mL, p = 0.015). These results suggest that reduced IL-18 levels and rs187238 variant may contribute to pathogenesis of idiopathic RM in Chinese Han population.

Fn14 receptor appears as a modulator of ovarian steroid-related regulation of goat endometrial epithelial cell IL-18 expression

PROBLEM

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible 14 (Fn14) interactions affect the regulation of cytotoxic/immunotrophic pathways that are themselves under control of IL-18. The effect of Fn14 on regulation of endometrium IL-18 expression, however, remains unclear.

METHOD AND STUDY

The aim was to determine the mode of ovarian steroid action in regulating Fn14 expression by goat endometrial epithelial cells (EECs) in the presence and absence of endometrial stromal cells (ESCs). The possible role of Fn14 on the expression of IL-18 by EECs was also evaluated.

RESULTS

Opposite effects of E2 and/or P4 on the regulation of both Fn14 mRNA and protein expression by EECs were observed in the presence and absence of ESCs. Fn14 knockdown by blocking antibody or siRNA resulted in a decrease of IL-18 mRNA and protein levels in EECs cocultured with ESCs, and no significant difference of the IL-18 mRNA and protein levels in the EECs was observed between steroid treatment group and control group.

CONCLUSION

These findings confirm the importance of steroids in controlling Fn14 expression in goat EECs. Furthermore, Fn14 appears as a novel modulator of the steroid-related IL-18 expression in EECs in the presence of ESCs.

Cytokines from the pig conceptus: roles in conceptus development in pigs

Establishment of pregnancy in pigs involves maintaining progesterone secretion from the corpora lutea in addition to regulating a sensitive interplay between the maternal immune system and attachment of the rapidly expanding trophoblast for nutrient absorption. The peri-implantation period of rapid trophoblastic elongation followed by attachment to the maternal uterine endometrium is critical for establishing a sufficient placental-uterine interface for subsequent nutrient transport for fetal survival to term, but is also marked by the required conceptus release of factors involved with stimulating uterine secretion of histotroph and modulation of the maternal immune system. Many endometrial genes activated by the conceptus secretory factors stimulate a tightly controlled proinflammatory response within the uterus. A number of the cytokines released by the elongating conceptuses stimulate inducible transcription factors such as nuclear factor kappa B (NFKB) potentially regulating the maternal uterine proinflammatory and immune response. This review will establish the current knowledge for the role of conceptus cytokine production and release in early development and establishment of pregnancy in the pig.

Caprine endometrial stromal cells modulate the effects of steroid hormones on cytokine secretion by endometrial epithelial cells in vitro

The main purpose of this study was to examine the effects of 17β-estradiol (E(2)) and progesterone (P(4)) on cytokine secretion by caprine endometrial epithelial cells (EEC) in vitro. Epithelial cells grown alone or in co-culture with stromal cells (ESC) were treated with E(2) or P(4), or both. Homogeneity of the endometrial cell populations was ascertained immunocytochemically. The quantities of cytokines secreted in this system were assessed by ELISA and their protein expression by Western blot. The exposure of EEC to P(4) alone or in combination with E(2) significantly increased the amount of TGF-β1, TNF-α and IL-18 secretion, whereas E(2) had no effect on the synthesis of these cytokines. When epithelial cells were co-cultured with ESC, the secretion of TGF-β1, TNF-α and IL-18 by EEC significantly increased compared to that by EEC alone. However, the treatment with both steroids decreased the secretion of TNF-α, IL-18 and TGF-β1 by EEC in the presence of ESC. In contrast to TGF-β1, TNF-α and IL-18, the secretion of leukemia inhibitory factor (LIF) by EEC was not affected by E(2) and/or P(4) either directly or indirectly. The present results indicate that the interactions between caprine endometrial stromal and epithelial cells can modulate the secretion of TGF-β1, TNF-α and IL-18 by EEC exposed to E(2) and/or P(4)in vitro.

Stromal-epithelial interactions modulate the effect of ovarian steroids on goat uterine epithelial cell interleukin-18 release

A primary role of epithelial-stromal interactions in mediating steroid hormone action in the uterus has been established. The present study was undertaken to determine the mode of ovarian steroid action in regulating IL-18 release by goat endometrial epithelial cells (EECs) in the presence and absence of endometrial stromal cells (ESCs). Primary and telomerase-immortalized goat EECs grown alone or cocultured with ESCs were treated with two ovarian steroids, 17β-estradiol (E(2)) and progesterone (P(4)). The IL-18 mRNA and protein expression in EECs were studied by reverse transcript (RT) PCR, ELISA, and Western blot assay. The E(2) and/or P(4) treatment of EECs led to a significant increase in both IL-18 mRNA and protein expression either in the primary or in the immortalized EECs compared with that in EECs without the steroid treatment. However, in the presence of ESCs, IL-18 expression by EECs treated with steroids was significantly decreased compared with cells untreated with E(2) and/or P(4). In addition, significantly high abundance of IL-18 mRNA and protein expression by primary and telomerase-immortalized goat EECs was observed in the presence of ESCs compared with those cells without ESCs. These findings suggest that steroids are important for the control of IL-18 expression in goat EECs. Underlying ESCs are needed to mediate the inhibitory effects of steroids on the IL-18 secretory activity of goat EECs in vitro. The IL-18 abundance expressed by goat EECs in vitro are enhanced by underlying ESCs without the treatment of E(2) and/or P(4).

Interaction of the conceptus and endometrium to establish pregnancy in mammals: role of interleukin 1β

Implantation and the establishment of pregnancy in mammals involves an intricate interplay of hormones, cytokines, growth factors, proteins, lipids, ions and the extracellular matrix between the uterine epithelium, stroma, immune cells and the conceptus trophectoderm. The divergent nature of implantation in the mouse, human and pig provides not only an interesting contrast in the establishment of pregnancy and early embryonic development but also intriguing similarities with regard to early endometrial-conceptus signaling. An interesting pro-inflammatory cytokine expressed in a number of mammalian species during the period of implantation is interleukin-1β (IL1B). The presence of IL1B might be involved with immunotolerance at the maternal-placental interface and has been proposed as one of the mediators in placental viviparity. The production of IL1B and other proinflammatory cytokines might play a role in establishing pregnancy through modulation of the nuclear factor kappa-B (NFKB) system in a number of species. A model for the regulation of cellular progesterone receptor expression and NFKB activation for endometrial receptivity and conceptus attachment is continuing to evolve and is discussed in the present review.