Bone marrow origin of decidual cell precursors in the pseudopregnant mouse uterus

Stromal cells of the endometrium and decidua: in search of a name and an identity

Human endometrial and decidual stromal cells are the same cells in different environments (non-pregnancy and pregnancy, respectively). Although some authors consider decidual stromal cells to arise solely from the differentiation of endometrial stromal cells, this is a debatable issue given that decidualization processes do not end with the formation of the decidua, as shown by the presence of stromal cells from both the endometrium and decidua in both undifferentiated (non-decidualized) and decidualized states. Furthermore, recent functional and transcriptomic results have shown that there are differences in the decidualization process of endometrial and decidual stromal cells, with the latter having a greater decidualization capacity than the former. These differences suggest that in the terminology and study of their characteristics, endometrial and decidual stromal cells should be clearly distinguished, as should their undifferentiated or decidualized status. There is, however, considerable confusion in the designation and identification of uterine stromal cells. This confusion may impede a judicious understanding of the functional processes in normal and pathological situations. In the present article we analyse the different terms used in the literature for different types of uterine stromal cells, and propose that a combination of differentiation status (undifferentiated, decidualized) and localization (endometrium, decidua) criteria should be used to arrive at a set of accurate, unambiguous terms. The cell identity of uterine stromal cells is also a debatable issue: phenotypic, functional and transcriptomic studies in recent decades have related these cells to different established cells. We discuss the relevance of these associations in normal and pathological situations.

Dmp1Cre-directed knockdown of parathyroid hormone-related protein (PTHrP) in murine decidua is associated with a life-long increase in bone mass, width, and strength in male progeny

Parathyroid hormone-related protein (PTHrP, gene name Pthlh) is a pleiotropic regulator of tissue homeostasis. In bone, Dmp1Cre-targeted PTHrP deletion in osteocytes causes osteopenia and impaired cortical strength. We report here that this outcome depends on parental genotype. In contrast to our previous report using mice bred from heterozygous (flox/wild type) Dmp1Cre.Pthlh^f/w parents, adult (16-week-old and 26-week-old) flox/flox (f/f) Dmp1Cre.Pthlh^f/f mice from homozygous parents (Dmp1Cre.Pthlh^f/f(hom) ) have stronger bones, with 40% more trabecular bone mass and 30% greater femoral width than controls. This greater bone size was observed in Dmp1Cre.Pthlh^f/f(hom) mice as early as 12 days of age, when greater bone width was also found in male and female Dmp1Cre.Pthlh^f/f(hom) mice compared to controls, but not in gene-matched mice from heterozygous parents. This suggested a maternal influence on skeletal size prior to weaning. Although Dmp1Cre has previously been reported to cause gene recombination in mammary gland, milk PTHrP protein levels were normal. The wide-bone phenotype was also noted in utero: Dmp1Cre.Pthlh^f/f(hom) embryonic femurs were more mineralized and wider than controls. Closer examination revealed that Dmp1Cre caused PTHrP recombination in placenta, and in the maternal-derived decidual layer that resides between the placenta and the uterus. Decidua from mothers of Dmp1Cre.Pthlh^f/f(hom) mice also exhibited lower PTHrP levels by immunohistochemistry and were smaller than controls. We conclude that Dmp1Cre leads to gene recombination in decidua, and that decidual PTHrP might, through an influence on decidual cells, limit embryonic bone radial growth. This suggests a maternal-derived developmental origin of adult bone strength. © 2021 American Society for Bone and Mineral Research (ASBMR).

Endometrial stem cells: origin, biological function, and therapeutic applications for reproductive disorders

PURPOSE OF REVIEW

Endometrial stem cells (ESCs) are multipotent cells that are thought to originate locally in the endometrium as well as in the bone marrow (BM). They have remarkable plasticity and hold promise as an autologous source for regenerative medicine. This review focuses on recent studies that have advanced our understanding of the biology and function of ESCs and BM-derived stem cells (BMDSCs) as related to physiological reproductive processes and pathologies. Moreover, it reviews recent data on potential therapeutic applications of stem cells to endometrial disorders that lead to reproductive failure.

RECENT FINDINGS

Growing evidence from basic and preclinical studies suggests that ESCs participate in endometrial tissue regeneration and repair. Recent evidence also suggests that ESCs and BMDSCs play important roles in physiological reproductive functions including decidualization, implantation, pregnancy maintenance, and postpartum uterine remodeling. Initial preclinical and clinical studies with ESCs and BMDSCs suggest they have the potential to provide new therapies for various endometrial disorders associated with reproductive failure.

SUMMARY

Uterine ESCs and BMDSCs appear to play an important biological role in reproductive success and failure, and have the potential to become treatment targets for reproductive diseases including recurrent implantation failure, thin endometrium, Asherman, and recurrent pregnancy loss.

Characterization of highly proliferative decidual precursor cells during the window of implantation in human endometrium

Pregnancy depends on the wholesale transformation of the endometrium, a process driven by differentiation of endometrial stromal cells (EnSC) into specialist decidual cells. Upon embryo implantation, decidual cells impart the tissue plasticity needed to accommodate a rapidly growing conceptus and invading placenta, although the underlying mechanisms are unclear. Here we characterize a discrete population of highly proliferative mesenchymal cells (hPMC) in midluteal human endometrium, coinciding with the window of embryo implantation. Single-cell transcriptomics demonstrated that hPMC express genes involved in chemotaxis and vascular transmigration. Although distinct from resident EnSC, hPMC also express genes encoding pivotal decidual transcription factors and markers, most prominently prolactin. We further show that hPMC are enriched around spiral arterioles, scattered throughout the stroma, and occasionally present in glandular and luminal epithelium. The abundance of hPMC correlated with the in vitro colony-forming unit activity of midluteal endometrium and, conversely, clonogenic cells in culture express a gene signature partially conserved in hPMC. Cross-referencing of single-cell RNA-sequencing data sets indicated that hPMC differentiate into a recently discovered decidual subpopulation in early pregnancy. Finally, we demonstrate that recurrent pregnancy loss is associated with hPMC depletion. Collectively, our findings characterize midluteal hPMC as novel decidual precursors that are likely derived from circulating bone marrow-derived mesenchymal stem/stromal cells and integral to decidual plasticity in pregnancy.

Adult bone marrow progenitors become decidual cells and contribute to embryo implantation and pregnancy

Decidua is a transient uterine tissue shared by mammals with hemochorial placenta and is essential for pregnancy. The decidua is infiltrated by many immune cells promoting pregnancy. Adult bone marrow (BM)-derived cells (BMDCs) differentiate into rare populations of nonhematopoietic endometrial cells in the uterus. However, whether adult BMDCs become nonhematopoietic decidual cells and contribute functionally to pregnancy is unknown. Here, we show that pregnancy mobilizes mesenchymal stem cells (MSCs) to the circulation and that pregnancy induces considerable adult BMDCs recruitment to decidua, where some differentiate into nonhematopoietic prolactin-expressing decidual cells. To explore the functional importance of nonhematopoietic BMDCs to pregnancy, we used Homeobox a11 (Hoxa11)-deficient mice, having endometrial stromal-specific defects precluding decidualization and successful pregnancy. Hoxa11 expression in BM is restricted to nonhematopoietic cells. BM transplant (BMT) from wild-type (WT) to Hoxa11-/- mice results in stromal expansion, gland formation, and marked decidualization otherwise absent in Hoxa11-/- mice. Moreover, in Hoxa11+/- mice, which have increased pregnancy losses, BMT from WT donors leads to normalized uterine expression of numerous decidualization-related genes and rescue of pregnancy loss. Collectively, these findings reveal that adult BMDCs have a previously unrecognized nonhematopoietic physiologic contribution to decidual stroma, thereby playing important roles in decidualization and pregnancy.

Transcriptional Factor PU.1 Regulates Decidual C1q Expression in Early Pregnancy in Human

C1q is the first recognition subcomponent of the complement classical pathway, which in addition to being synthesized in the liver, is also expressed by macrophages and dendritic cells (DCs). Trophoblast invasion during early placentation results in accumulation of debris that triggers the complement system. Hence, both early and late components of the classical pathway are widely distributed in the placenta and decidua. In addition, C1q has recently been shown to significantly contribute to feto-maternal tolerance, trophoblast migration, and spiral artery remodeling, although the exact mechanism remains unknown. Pregnancy in mice, genetically deficient in C1q, mirrors symptoms similar to that of human preeclampsia. Thus, regulated complement activation has been proposed as an essential requirement for normal successful pregnancy. Little is known about the molecular pathways that regulate C1q expression in pregnancy. PU.1, an Ets-family transcription factor, is required for the development of hematopoietic myeloid lineage immune cells, and its expression is tissue-specific. Recently, PU.1 has been shown to regulate C1q gene expression in DCs and macrophages. Here, we have examined if PU.1 transcription factor regulates decidual C1q expression. We used immune-histochemical analysis, PCR, and immunostaining to localize and study the gene expression of PU.1 transcription factor in early human decidua. PU.1 was highly expressed at gene and protein level in early human decidual cells including trophoblast and stromal cells. Surprisingly, nuclear as well as cytoplasmic PU.1 expression was observed. Decidual cells with predominantly nuclear PU.1 expression had higher C1q expression. It is likely that nuclear and cytoplasmic PU.1 localization has a role to play in early pregnancy via regulating C1q expression in the decidua during implantation.

Endometrial regenerative cells for treatment of heart failure: a new stem cell enters the clinic

Heart failure is one of the key causes of morbidity and mortality world-wide. The recent findings that regeneration is possible in the heart have made stem cell therapeutics the Holy Grail of modern cardiovascular medicine. The success of cardiac regenerative therapies hinges on the combination of an effective allogeneic “off the shelf” cell product with a practical delivery system. In 2007 Medistem discovered the Endometrial Regenerative Cell (ERC), a new mesenchymal-like stem cell. Medistem and subsequently independent groups have demonstrated that ERC are superior to bone marrow mesenchymal stem cells (MSC), the most widely used stem cell source in development. ERC possess robust expansion capability (one donor can generate 20,000 patients doses), key growth factor production and high levels of angiogenic activity. ERC have been published in the peer reviewed literature to be significantly more effect at treating animal models of heart failure (Hida et al. Stem Cells 2008).

Current methods of delivering stem cells into the heart suffer several limitations in addition to poor delivery efficiency. Surgical methods are highly invasive, and the classical catheter based techniques are limited by need for sophisticated cardiac mapping systems and risk of myocardial perforation. Medistem together with Dr. Amit Patel Director of Clinical Regenerative Medicine at University of Utah have developed a novel minimally invasive delivery method that has been demonstrated safe and effective for delivery of stem cells (Tuma et al. J Transl Med 2012). Medistem is evaluating the combination of ERC, together with our retrograde delivery procedure in a 60 heart failure patient, double blind, placebo controlled phase II trial. To date 17 patients have been dosed and preliminary analysis by the Data Safety Monitoring Board has allowed for trial continuation.

The combined use of a novel “off the shelf” cell together with a minimally invasive 30 minute delivery method provides a potentially paradigm-shifting approach to cardiac regenerative therapy.

An adult uterine hemangioblast: evidence for extramedullary self-renewal and clonal bilineage potential

Stem cells exhibit long-term self-renewal by asymmetric division and multipotent differentiation. During embryonic development, cell fate is determined with predictable orientation, differentiation, and partitioning to form the organism. This includes the formation of a hemangioblast from which 2 derivative cell clusters commit to either a hematopoietic or an endothelial lineage. Frequently, it is not clear whether tissue resident stem cells in the adult originate from the bone marrow. Here, we show that blast colony-forming cells exhibiting bilineage (hematopoietic and vascular) potential and long-term self-renewal originate from the uterus in the mouse. This is the first in vitro and in vivo evidence of an adult hemangioblast retained from development in the uterus. Our findings offer new understanding of uterine cell renewal and turnover and may provide insights and opportunities for the study of stem cell maintenance.

Multipotent Menstrual Blood Stromal Stem Cells: Isolation, Characterization, and Differentiation

The stromal stem cell fraction of many tissues and organs has demonstrated to exhibit stem cell properties such as the capability of self-renewal and multipotency, allowing for multilineage differentiation. In this study, we characterize a population of stromal stem cells derived from menstrual blood (MenSCs). We demonstrate that MenSCs are easily expandable to clinical relevance and express multipotent markers such as Oct-4, SSEA-4, and c-kit at the molecular and cellular level. Moreover, we demonstrate the multipotency of MenSCs by directionally differentiating MenSCs into chondrogenic, adipogenic, osteogenic, neurogenic, and cardiogenic cell lineages. These studies demonstrate the plasticity of MenSCs for potential research in regenerative medicine.

Decidualization of the human endometrial stromal cell: an enigmatic transformation

Changes in human endometrium are essential to allow the establishment of pregnancy. These changes are induced in vivo by progesterone, and include appearance within the tissue of a specific uterine natural killer cell, characterized by an abundant expression of CD56. Changes also occur in the stromal cells, which undergo a characteristic decidualization reaction. Decidualized stromal cells are derived from the fibroblast-like cells within the endometrium, which maintain their progesterone receptors in the presence of progesterone. Prolonged exposure to progesterone induces a rounded cell characterized by release of prolactin and insulin-like growth factor binding protein-1 (IGFBP-1), and expression of tissue factor. Additional changes include the secretion of interleukin (IL)-15, vascular endothelial growth factor, and surface expression of zinc dependent metalloproteinases such as CD10 and CD13. In vitro, elevated intracellular cAMP as well as progesterone is necessary for decidualization. In vivo, these conditions may be provided by progesterone from the corpus luteum, by prostaglandin E, a stimulator of adenyl cyclase, and relaxin, which has recently been shown to be a phosphodiesterase inhibitor. Given the co-distribution of uterine natural killer cells and decidualized stromal cells, a mutual interaction might provide the correct regulatory environment for successful implantation, and penetration of the maternal blood vessels by trophoblastic cells.

Life Cycle of Decidual Cells

The decisive events in the development of decidual cells (DC) are presented through examples of human and rodent decidua. Human decidua is formed by large decidual cells (LDC), endometrial granulated cells (eGC), and small decidual cells. The LDC form the main type of decidual membranes, which determine the morphological characteristics of the decidua as a tissue. Immediate precursor cells of LDC are located below the basement membrane of the uterine epithelium before and during implantation. At the next stage of differentiation, LDC acquire a spindle-like shape. Rodent LDC form an epithelium-like structure with gland properties at the terminal stage of differentiation. The single-cell structure of human decidua is a derivative of the epithelial organization of rodent decidua. Spindle-like rat LDC are characterized by a high level of protein, RNA, and DNA synthesis and by intensive proliferation. At the beginning of pregnancy, a cell proliferation predominates over cell loss. By Days 12-13 of rat pregnancy LDC loss reaches 80% per day. Terminally differentiated LDC (tLDC) disappear from decidua due to apoptosis. Apoptosis of tLDC and the exhaustion of their precursors account for the disappearance of LDC in the middle of rat pregnancy. Human term decidua is composed of living cells. Human LDC (hLDC) comprise the largest part of human decidual cells (hLDC). hLDC account for 60-90% of hDC but their relative amount can decrease to 35% in the case of significant cell loss under unfavorable conditions. A decrease of LDC is not accompanied by DC proliferation. The lack of ability of decidua to compensate for DC loss suggests DC is a growing type of cell population without cambial cells. LDC function largely by blebbing and budding. Human and rat endometrial granulated cells (eGC) are characterized by a low level of natural killer (NK) activity and a high level of natural suppressor (NS) activity. The combination of NK and NS properties is characteristic of the eGC immunoregulatory function. Other functions of decidua include control of inflammation and trophoblast growth and expansion in the uterus. The life span of decidual cells is limited by pregnancy.

Antigen phenotype of cultured decidual stromal cells of human term decidua

We previously reported that decidual stromal cells (DSC) from early human decidua express antigens associated with hematopoietic cells and develop different immune functions. Here we study the antigenic phenotype of DSC from term decidua and compare it with the phenotype reported for DSC from early decidua. Decidual stromal cells were isolated from human term deciduas and maintained in culture until highly purified DSC cultures were obtained. Most term DSC, like most early DSC, expressed CD10. Term DSC expressed antigens specific for follicular dendritic cells (FDC), such as DRC-1 (CD21L) and HJ2, together with CD21, CD23 and CD80, which are detected on FDC as well. Also like early DSC, term DSC were negative for CD3, CD14, CD15 and CD45. Although early DSC were reported to be HLA-DR-positive and CD86-positive, these antigens were not expressed by term DSC. These discrepant results suggest that two types of cells, or cells at different stages of differentiation (decidualization) were selected during culture of decidual cells from different periods of gestation. This possibility was further supported by the finding that term DSC expressed desmin and prolactin, two markers of decidualization, whereas these molecules have not previously been detected in early DSC.

Isolation and identification of apoptosis inducing nucleosides from CD57(+)HLA-DRbright natural suppressor cell line

The CD57(+)HLA-DRbright natural suppressor (57.DR-NS) cell line derived from human decidual tissue generated the apoptosis in K562/Molt4 target cells mediated by soluble factors released into the culture supernatant. The factors in the culture fluid of the 57. DR-NS cell line were isolated by the physicochemical procedures as follows, first by a preparative octadecyl sorbent column, further by thin-layer-chromatography (TLC), finally by reverse-phase high-performance liquid chromatography (HPLC). The six major components (P1-P6) obtained by HPLC demonstrated the generation of apoptotic cell death of target cells. The physicochemical characters of six active components were strongly suggested to be nucleosides and their modified forms in nature. Then, the physicochemical structures of the six active components were finally determined by fast atom bombardment-mass spectrometry (FAB-MS) and nuclear magnetic resonance (1H NMR) spectrometry as follows: P1, 2'-deoxyuridine; P2, ribothymidine; P3, 2'-O-methyluridine; P4, thymidine; P5, 2'-O-methylinosine; P6, 2'-O-methylguanosine. Thus, we collectively named them "apoptosis inducing nucleosides (AINs)." Then, we demonstrated that the induction of apoptosis in target cells by the 57.DR-NS cell line was mediated by a series of AINs.

Endometrial leukocytes are altered numerically and functionally in women with implantation defects

PROBLEM

A significant cohort of women with autoimmune thyroid disease (ATD) also suffer from reduced fertility. The finding that neither exogenous hormones nor donor eggs correct the infertility suggests that the problem involves an inherent endometrial defect.

METHOD OF STUDY

Endometrial leukocyte populations in women with ATD were quantitated by immunohistochemistry. A semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique was used to examine the expression of transforming growth factor (TGF)-beta 1, interleukin (IL)-4, IL-10, and interferon (IFN)-gamma in the endometrial samples.

RESULTS

A significant increase in the endometrial T-cell population was observed in women with ATD compared to controls. The relative abundance of IL-4 and IL-10 was decreased in women with ATD compared to controls, whereas IFN-gamma was increased. No difference was noted in the abundance of TGF-beta 1. The source of cytokine production for IL-4, IL-10, and IFN-gamma was the endometrial leukocytes.

CONCLUSIONS

Both the leukocyte numbers and cytokine expression profile were altered significantly in a well-defined group of women with implantation defects.

Cultured human decidual stromal cells express antigens associated with hematopoietic cells

Although decidual stromal cells (DSC) have classically been considered to play a nutritional role during pregnancy, several reports have demonstrated that they can also exert different immune activities. Furthermore, some authors have occasionally found antigens on DSC normally expressed by immune cells. In this study, we isolated and cultured 12 human DSC lines and studied them with immunocytochemistry and flow cytometry using monoclonal antibodies against antigens associated with hematopoietic cells. Decidual stromal cells exhibited a constant phenotype: they were CALLA (CD10)-positive and DR-positive, although the expression of CD45, the leukocyte common antigen, was found to be very weak or negative. We also detected myelomonocytic antigens CD11b (CR3), CD13, CD16 (Fc gamma RIII) and CD36, although DSC lacked CD14, CD15 and CD33. B cell antigens CD20, CD21 (CR3), CD23 (Fc epsilon RII) and CD24 were expressed. DRC-1, an antigen detected on follicular dendritic cells (FDC), was also observed on DSC. When these cells were cultured in the presence of progesterone, they expressed desmin and prolactin (PRL), findings that confirmed their identity as DSC. The phenotype described, together with the immune activities reportedly carried out by DSC, suggest that DSC may play a role in the maternal-fetal immune relationship.

Constitutive secretion of interleukin-6 by human decidual stromal cells in culture. Regulatory effect of progesterone

PROBLEM

Although several studies have demonstrated that decidual stromal cells (DSC) can secrete cytokines in culture, none of these studies documented the purity of the cultures. Since other cells of the decidua, such as macrophages and epithelial cells, also produce cytokines, it is important to ensure purity of the culture so that cytokine production can be ascribed with confidence to DSC.

METHOD

DSC from early human pregnancies were highly purified and maintained in culture. Basal secretion by these cells of IL-6, together with other cytokines considered critical for pregnancy (IL-1 beta, TNF alpha and IFN gamma), was measured with immunological techniques.

RESULTS

We found that DSC in culture produce insignificant quantities of IL-1 beta, TNF alpha and IFN gamma, but appreciable amounts of IL-6. The production of this later cytokine was, however, inhibited by the effect of progesterone.

CONCLUSIONS

Basal production of IL-6 by DSC may be involved in physiological functions at the maternal-fetal interface. Nevertheless, the secretion of this cytokine is regulated by progesterone, probably to prevent excessive production of this cytokine from triggering an inflammatory response that might compromise pregnancy.

The maternal leucocyte response to the endometrial cups in horses is correlated with the developmental stages of the invasive trophoblast cells

Invading trophoblasts form endometrial cups in the endometrium of the pregnant mare. In the present study we characterized the maternal leucocyte response to endometrial cups from their formation to their regression. The maternal leucocyte response was correlated with the stages of trophoblast development. (1) Aggregates of CD4+ and CD8+ cells were present between the migrating and differentiating endometrial cup trophoblasts and surrounding the forming endometrial cups. (2) Numbers of CD4+ cells within the mature endometrial cups were much reduced. At the periphery of the endometrial cups CD4+ and CD8+ cells were found in patchy accumulations around endometrial glands; small clusters of CD79+ B lymphocytes were present as well. (3) Scattered CD4+ and CD8+ cells were found within dying endometrial cups; areas of cell death were infiltrated with neutrophils. Large aggregates of CD4+ cells and CD8+ cells, and small but numerous clusters of CD79+ cells and eosinophils, were found outside of the dying endometrial cups. The CD4+ or CD8+ cells were mostly CD3+ T cells; some were probably macrophages which can express both of these markers in horses. The correlation between the developmental stages of the endometrial cup trophoblast and the maternal leucocyte response suggests a complicated cytokine-mediated regulatory network.

Implantation and decidualization in rodents

This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.

Cytokines and growth factors in implantation

A variety of cell types at the blastocyst implantation site produce cytokines and growth factors that could play an important role in the implantation process. Furthermore, receptors for cytokines and growth factors have been detected on embryonic and trophoblastic cells. The purpose of the article is to review the published literature on the effect of cytokines and growth factors on implantation events, and to present recent data from our laboratory on effects of growth factors and cytokines on mouse blastocyst implantation events in vitro.

Distribution of hyaluronan in the mouse endometrium during the periimplantation period of pregnancy

The tissue distribution of stromal hyaluronan (HA) in the periimplantation mouse uterus was studied histochemically using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is present around proliferating stromal cells in both the pregnant and pseudopregnant mouse uterus prior to their differentiation into the decidualized phenotype. Decidualization is accompanied by clearance of HA from the extracellular matrix (ECM). This clearing is part of an intrinsic developmental program of the differentiating deciduum. A specific embryonic signal from the implanting conceptus is not required for this phenomenon to occur, since a similar response could be induced in deciduoma produced by artificial stimulation of a receptive uterus. Clearing of HA from the antimesometrial stroma is consistent with the hypothesis that the HA-negative decidual cell may be involved in restricting the invasion of trophoblast cells during embryo implantation. Retention of HA within angiogenic regions of the decidua basalis implies a functional role for this molecule in placental vascularization.

Macrophage colony stimulating factor controls macrophage recruitment to the cycling mouse uterus

Progesterone and estrogen induce uterine epithelial cells to produce macrophage colony stimulating factor (CSF-1), and mouse uterine epithelial cells produce large amounts of CSF-1 during embryo development. The present study demonstrated that estrogen and progesterone each induce uterine CSF-1 gene transcription and translation detectable by Northern blotting and bioassay. Intrauterine CSF-1 production was greater in the presence of both estrogen and progesterone than following exposure to either hormone alone. CSF-1 mRNA was detectable in the uterus throughout the estrous cycle while CSF-1 bioactivity was detected only during proestrus. CSF-1 production was directly related to the presence of macrophages in the uterus. Ovariectomy, which was rapidly followed by a loss of uterine CSF-1 gene transcription, also was followed by a dramatic decrease in the number of uterine macrophages. Both uterine CSF-1 and uterine macrophages were reconstituted in a dose-dependent manner by systemic administration of estrogen or progesterone. High concentrations of circulating estrogen and progesterone increased the number of macrophages in the uterus and increased their accumulation near epithelial surfaces. Similar relationships were observed in the uterus of cycling mice. Macrophages accumulated in the uterus following intraluminal injection of recombinant human CSF-1 to ovariectomized mice, directly demonstrating the ability of CSF-1 to recruit macrophages from peripheral blood into the uterus. These studies demonstrated that estrogen and progesterone stimulation of CSF-1 production by mouse uterine epithelial cells controls recruitment and distribution of macrophages in the uterus during the estrous cycle.

Leukocyte distribution in the pseudopregnant mouse uterus

Pseudopregnancy, induced by mating females with vasectomized males, is a frequently used model for studying pregnancy-like uterine changes in the absence of an embryo. Leukocytes make a significant contribution to uterine cellularity during pregnancy. The present study was designed to determine whether changes in numbers and distribution of leukocytes in the uterus during pseudopregnancy and following intraluminal injection of a deciduogenic stimulus parallel changes observed during the first eight days of pregnancy. Common leukocyte antigen positive (CLA+) cells, macrophages (F4/80+ cells), and granulocytes were assessed between days 1 and 8 of pseudopregnancy using qualitative and quantitative immunohistochemistry. High numbers of CLA+ leukocytes were present on days 1 and 2. Those were comprised primarily by macrophages, polymorphonuclear leukocytes, and eosinophils. High concentrations of leukocytes were detected in the endometrium, and some granulocytes were observed migrating through the luminal epithelium. Leukocytes, principally macrophages, were reduced in number and were distributed throughout the endometrium on days 3 and 4. Introduction of oil to the uterine lumen on day 4 stimulated primary decidualization. Decidual cells were CLA- and F4/80-, and, as decidualization proceeded, CLA+ and F4/80+ cells decreased in number in the anti-mesometrial uterus and were detected primarily in the deep endometrium. Later, a secondary decidualization zone developed in the mesometrial aspect of the uterus. Unlike the initial decidual reaction, which was relatively free of leukocytes, the secondary decidual zone contained very high numbers of CLA+ and F4/80+ cells. The uninjected uterine horn remained relatively unchanged from days 3 through 8.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemopoietic origin of certain decidual cell precursors in murine pregnancy

The possible hemopoietic origin of certain precursors of uterine decidual cells appearing during normal murine pregnancy was investigated in semiallogeneic hemopoietic chimeras with retained or regained fertility. Chimeras were produced by three different methods in two donor-host combinations: F1 [BALB/c female x C3H/HeJ male] cells introduced into the parental strain BALB/c female hosts or F1 [CBA/J female x C57BL/6 male] cells introduced into CBA/J female hosts. Prenatal chimeras (PN) were made by reconstituting mouse fetuses (day 13-17) with 10(6)-10(7) adult bone marrow or fetal liver cells through the yolk sac and they were allowed to be delivered naturally. Neonatal chimeras (NN) were made by injecting 1-2 x 10(7) adult bone marrow cells into the anterior facial vein of neonatal mice (less than 24 hr old). In both cases, experimental animals were raised to maturity. Ovary-transplanted chimeras (OT) were made by injecting 10(7) bone marrow cells into lethally irradiated (9.5 Gy) young adult female mice, followed 6 weeks later with bilateral orthotopic transplants of syngeneic ovary grafts to restore fertility. All female chimeras produced by the three different methods were mated with syngeneic male partners to produce normal pregnancy. The extent of chimerism at the cellular level was determined in all cases by a radioautographic identification of the H-2 phenotype of splenic lymphocytes and decidual cells and macrophages in the collagenase-dispersed decidua at day 11-16 of normal pregnancy, following a sandwich labelling with monospecific anti-H-2 antibodies and 125I-protein A. Morphological discrimination of typical decidual cells from macrophages in the collagenase-dispersed decidua was carried out on the basis of several distinctive markers: presence of surface Dec-1 and Thy-1 and absence of surface F4/80 or latex phagocytosis for decidual cells, in contrast to macrophages which were phagocytic and expressed F4/80 but not Dec-1 or Thy-1. While the degree of hemopoietic chimerism (judged by the incidence of donor-derived lymphocytes in the spleen) varied from animal to animal, in all three groups (PN, NN, and OT) comprising a total of 26 chimeras, the percentage of typical decidual cells expressing donor H-2 phenotype showed an excellent correlation with that for small lymphocytes in the spleen. These results reveal that at least a subpopulation of typical decidual cells of the pregnant uterus has a hemopoietic genealogy. A possible familial relationship of these cells to granulated metrial gland cells remains unclear.

Three methods for producing fertile hemopoietic chimeras in mice

Three methods for producing semiallogeneic (F1----parental) hemopoietic chimeras with retained or regained fertility are detailed here. Prenatal (PN) chimeras were produced by injecting F1 ([BALB/c female x C3H/HeJ male] or [CBA/J female x C57BL/6 male]) fetal liver (days 13-18) or adult bone marrow cells (10(6)-10(7) cells/20 microliters/embryo) into the yolk-sac cavities of days 13-17 gestation BALB/c or CBA/J embryos, respectively, and allowing them to be born naturally. Neonatal (NN) chimeras were made by introducing F1 bone marrow cells (1-2 x 10(7) cells/0.25 ml) into newborn (less than 24 hr old) female mice through the anterior facial vein. Female mice were raised to maturity in both cases. Ovary-transplanted (OT) chimeras were made by first irradiating (9.5 Gy) and repopulating young female adult mice with 10(7) F1 bone marrow cells, followed by bilateral orthotopic transplantation of syngeneic ovarian tissue six weeks later. Females reconstituted with the above three methods were mated with normal syngeneic males and sacrificed at 11-16 days of pregnancy to evaluate hemopoietic chimerism. This was determined in all cases by a radioautographic evaluation of the extent of donor H-2 phenotype marker expression on splenic small lymphocytes, after an indirect labelling of single-cell suspensions with monospecific antibody and [125I]protein-A. Results indicate that hemopoietic chimerism was best in the PN group (0.3-78.1%, mean = 27.1); intermediate in the OT group (5.8-38.2%, mean = 18.1); and low in the NN group (0-14%, with one exception, which was 83.6%). Observed fertility was best for BALB/c host PN chimeras.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric analysis of the histology of spontaneous fetal resorption in a murine pregnancy

Immunopathology of the spontaneous resorption phenomenon in the CBA x DBA/J murine model was explored using morphometric analysis. Accompanying the previously reported presence of natural killer (NK) cells in resorptive feto-placental units we find major changes in tissue morphology indicating that early infiltration of the feto-placental unit by maternal leukocytes plays a direct role with NK cells in fetal demise. Total number of cell nuclei per field and total nuclear area per field were significantly elevated in feto-placental units containing abnormally increased NK cell presence before detectable resorption as early as day 7 of gestation. This difference persisted throughout all stages of early gestation up to and including the final resorption event at day 10 to 12. Increases in cell density were also detected in areas of the embryonic unit not associated with NK infiltration. These results demonstrate that the spontaneous resorption phenomenon in this model involves: (i) Early (day 7-8) cellular infiltration of the decidual-ectoplacental cone junction associated with the presence in this area of NK cells. (ii) Late (day 8-9) cellular infiltration of the ectoplacental cone.

Suppression of lymphocyte alloreactivity by early gestational human decidua. I. Characterization of suppressor cells and suppressor molecules

We examined the immunosuppressor role of the first trimester human decidua on lymphocyte alloreactivity in vitro in order to identify (1) the major cell classes in the decidua mediating the suppressor effect; (2) the stages in the lymphocyte alloreactive responses susceptible to the suppressor effects of the decidua; and (3) the precise nature of the suppressor molecules. Irradiated (2800 R), Ficoll-Paque-separated nucleated cells of the collagenase-dispersed early gestational (6.5-9.5 weeks menstrual age) decidua containing 70-94% typical decidual cells (identified on the basis of distinctive morphology and numerous cytoplasmic or surface markers) or their plastic-nonadherent fractions further enriched for decidual cells (approximately 96% pure) caused a strong dose-dependent suppression of the one way mixed lymphocyte reaction (MLR, i.e., proliferative response measured on Days 3, 4, or 5), when added at the onset of the mixed lymphocyte cultures (MLC). As few as 10(3) decidual cells caused a detectable inhibition of the MLR exhibited by 10(5)-1.5 X 10(5) responder lymphocytes. A smaller degree of suppression was noted with the plastic-adherent fractions of the early decidua (which retained all macrophages and granulocytes, but still included many decidual cells) or unfractionated cells of later gestational (10-13 weeks) decidua containing a higher incidence of leukocytes, granulocytes, and macrophages in particular, or the plastic-adherent fraction thereof, enriched for macrophages. Thus, decidual cells seem to represent an important suppressor cell class in the early gestational human decidua; however, suppression by decidual leukocytes, macrophages in particular, was also evident. The suppressor effect was unrelated to the major histocompatibility phenotype of the responder or the stimulator cells. It was not caused by cell crowding, since an equivalent number of irradiated K562 erythroleukemia cells had little effect on the MLR. The effect was exerted during both the initiation and the progression of the MLR. A delay in the addition of regulator cells progressively minimized the effect on the Day 4 MLR, but did not abolish it completely even when added as late as on Day 3. The major class of mediator molecules was identified as prostaglandins, primarily PGE2, on the basis of the following results: (1) the presence of indomethacin (10(-5) M) or varying dilutions of an anti-PGE2 antibody abrogated this suppression substantially or completely. (2) Addition of pure PGE2 (3 X 10(-7) to 1.1 X 10(-5) M), but not PGF2 alpha, reproduced a dose-dependent suppressor effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Vitamin D metabolism in pregnant and pseudopregnant rats: identification of 25-hydroxycholecalciferol-1-hydroxylase in decidual tissue

Elevated levels of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are found in late pregnancy but the factors responsible for this are not known. To determine if the maternal-fetal calcium flux or the presence of a previously described extrarenal 25-hydroxycholecalciferol-1-hydroxylase (25(OH)-D3-1-hydroxylase) play a role, serum calcium and 1,25(OH)2D3 were measured in pregnant, nonpregnant, and decidua-bearing pseudopregnant rats. Serum calcium was 8.74 +/- 0.26 mg/dl (mean +/- SEM) in nonpregnant rats. In pregnant rats, serum calcium was not significantly different from nonpregnant controls on day 12 and only slightly higher on day 15. Pseudopregnant rats were significantly hypercalcemic on days 12 (11.93 +/- 0.19 mg/dl) and 15 (11.45 +/- 0.23 mg/dl) compared with nonpregnant rats (P less than 0.001). In nonpregnant controls the serum level of 1,25(OH)2D3 was 44.6 +/- 6.3 pg/ml. Levels in pregnant rats were not significantly different on days 12 or 15 but tended to be higher by day 15 (75.2 +/- 19.7 pg/ml). Pseudopregnant rats had levels of 72.6 +/- 13.5 pg/ml on day 12 and 102.8 +/- 10.9 pg/ml on day 15, the latter of which was significantly higher than nonpregnant values (P less than 0.05). 25(OH)D3-1-hydroxylase activity was determined in whole tissue homogenates of placenta and decidua. Placenta from pregnant rats and decidua from pregnant and pseudopregnant rats both formed putative 1,25(OH)2D3 in short-term incubation with 25(OH)D3 as identified by comigration with authentic 1,25(OH)2D3 on high pressure liquid chromatography (HPLC).(ABSTRACT TRUNCATED AT 250 WORDS)

Infiltrating decidual natural killer cells are associated with spontaneous abortion in mice

Immunohistochemistry was used to study a murine model which spontaneously aborts at a frequency of 25 to 30%. Our results show that natural killer (NK) cells are not only the predominant infiltrating cells in aborting feto-placental units, but that they also appear in a similar proportion of feto-placental units before abortion is detectable. The frequency of feto-placental units with significantly elevated NK infiltrates corresponds to the subsequent abortion frequency, indicating a causal relationship. Immunization of the mother with BALB/C splenocytes prevents these NK infiltrates and decreases the abortion frequency to normal levels. These results suggest for the first time that maternal NK cells may have an instrumental role in the etiology of spontaneous abortion.

Differential expression of class II major histocompatibility complex and Thy 1.2 antigens on mouse decidua

A differential expression of class II major histocompatibility complex (MHC) and Thy 1.2 antigens was detected on two morphologically distinct cell populations in short-term cultures of murine decidual tissue. Stromal type decidual cells expressed Thy 1.2, albeit transiently, and consistently lacked class II antigens. By contrast decidual macrophages expressed class II antigens and lacked Thy 1.2 antigens. Stromal type decidual cells, after culture in the presence of indomethacin, displayed no evidence of prostaglandin-mediated modulation of class II expression. These findings suggest that class II positive decidual macrophages are responsible for the antigen-presenting capacity of decidua.

The role of prostaglandins in the immunosuppressive effects of supernatants from adherent cells of murine decidual tissue

Supernatants from short-term cultures of murine decidual tissue (DS) were assessed for their regulatory effects on T cell lymphoproliferation and cytotoxic T lymphocyte (CTL) activity. DS non-specifically suppressed antigen- and mitogen-induced lymphoproliferation, spontaneous thymocyte proliferation, the mixed lymphocyte reaction (MLR) and CTL generation, but had no effect on CTL lytic activity. The immunosuppressive activity was lost after dialysis (14 kDa cut off). Supernatants from indomethacin-treated decidual tissue cultures (indomethacin-DS) lacked suppressive activity in the MLR, mitogen and thymocyte proliferation assays. Indomethacin-DS also showed markedly reduced or no suppressive effects on CTL generation. These findings suggest that prostaglandin production by the decidual component of the placenta could play a role in materno-fetal cellular interactions by regulating T cell lymphoproliferative responses and CTL generation.

Expression of rat transforming growth factor alpha mRNA during development occurs predominantly in the maternal decidua

Previous studies have shown that transforming growth factor alpha is expressed during rodent development. To establish the site(s) of transforming growth factor alpha mRNA expression during rat embryogensis, we performed in situ hybridization and Northern blot analyses on samples of embryonic and maternal tissues at various gestational ages. Our results indicate that the high levels of transforming growth factor alpha mRNA that are observed during early development are the result of expression in the maternal decidua and not in the embryo. Decidual expression appears to be induced after implantation, peaks at day 8, and then slowly declines through day 15 at which time the decidua is being resorbed. Expression of transforming growth factor alpha mRNA is highest in that region of the decidua adjacent to the embryo and is low or nondetectable in the uterus, placenta, and other maternal tissues. The developmentally regulated expression of transforming growth factor alpha mRNA in the decidua, together with the presence of epidermal growth factor receptors in this tissue, suggests that transforming growth factor alpha stimulates proliferation locally through an autocrine mechanism. Since epidermal growth factor receptors are present in the embryo and placenta, transforming growth factor alpha produced in the decidua may also act on these tissues through paracrine or endocrine mechanisms.

Immunolocalization of extracellular matrix proteins and collagen synthesis in first-trimester human decidua

The extracellular matrix (ECM) of first-trimester human decidua was examined with indirect immunofluorescence using affinity-purified antibodies to human collagen types I, III, IV, V, laminin, and fibronectin. In addition, the validity of the classification "mesenchymal-epithelioid" for differentiated decidual cells was addressed using antibodies to the intermediate filament proteins, vimentin, a mesenchymal marker, and keratin, an epithelial marker. Biosynthesis of extracellular matrix components was examined by radiolabeling of decidual explants in culture with 3H-proline, followed by immunoprecipitations of synthesized proteins with collagen type-specific antibodies. Immunofluorescence showed decidual cells are embedded in an extensive network of collagen types I and III, and intracytoplasmic staining suggested synthesis of these collagens by the decidual cells. Collagen type IV and laminin localized in the external lamina which surrounds the differentiated decidual cell, and some fluorescence was evident in the peripheral cytoplasm. Immunoreactive collagen type V was observed in close association with the external lamina and in the peridecidual matrix. Fibronectin localized throughout the decidual ECM and in fibrillar and punctuate patterns in the decidual cell cytoplasm. Differentiated decidual cells retained a "mesenchymal" intermediate filament cytoskeleton containing an abundance of vimentin filaments, but very few, if any, keratin filaments. Collagen types I, III, V, and to a lesser extent, IV, were immunoprecipitated from the medium of decidual explants after 24 hours of culture, demonstrating in vitro synthesis and secretion of these collagens by first trimester human decidua.

Expression of rat transforming growth factor alpha mRNA during development occurs predominantly in the maternal decidua

Previous studies have shown that transforming growth factor alpha is expressed during rodent development. To establish the site(s) of transforming growth factor alpha mRNA expression during rat embryogensis, we performed in situ hybridization and Northern blot analyses on samples of embryonic and maternal tissues at various gestational ages. Our results indicate that the high levels of transforming growth factor alpha mRNA that are observed during early development are the result of expression in the maternal decidua and not in the embryo. Decidual expression appears to be induced after implantation, peaks at day 8, and then slowly declines through day 15 at which time the decidua is being resorbed. Expression of transforming growth factor alpha mRNA is highest in that region of the decidua adjacent to the embryo and is low or nondetectable in the uterus, placenta, and other maternal tissues. The developmentally regulated expression of transforming growth factor alpha mRNA in the decidua, together with the presence of epidermal growth factor receptors in this tissue, suggests that transforming growth factor alpha stimulates proliferation locally through an autocrine mechanism. Since epidermal growth factor receptors are present in the embryo and placenta, transforming growth factor alpha produced in the decidua may also act on these tissues through paracrine or endocrine mechanisms.

Kinetics and regulation of 25-hydroxycholecalciferol 1 alpha-hydroxylase from cells isolated from human term decidua

Kinetics and regulation of 25-hydroxycholecalciferol 1 alpha-hydroxylase from cells isolated from term human decidua were studied. The production of 1 alpha,25-dihydroxycholecalciferol (calcitriol) was linear with time for up to 6 h and was directly proportional to the number of cells up to 20 X 10(6)/dish at a substrate concentration of 100 nM. Under these conditions the apparent Km was 88 nM and the Vmax 3.0 pmol/10(6) cells. The production of [3H]calcitriol was inhibited by 0.1 nM (P less than 0.01) and 1 nM (P less than 0.005) unlabeled calcitriol. Unlike the kidney enzyme and for reasons that remain unclear, neither inorganic phosphate salts nor parathyroid hormone had any acute effect on the calcitriol production. Further studies are required to delineate the regulatory mechanism of this enzyme.

The metrial gland

The information available about the metrial gland of the pregnant rodent uterus with its content of granulated metrial gland (GMG) cells is reviewed. Recent research shows that GMG cells differentiate from bone marrow cells and supports the suggestion that GMG cells are involved in the immunological relationship between mother and foetus. There is probably a complex association between GMG cells and stromal cells of the metrial gland, and it is suggested that the association between GMG cells and the placental labyrinthine cells represents a functional interaction.

Studies on endometrial cells in human pregnancy by monoclonal antibodies

By immunizing mice with endometrial cells from pregnant women, we obtained two hybridoma clones, 9D3 (IgG1) and 9E3 (IgG3), secreting monoclonal antibodies (MoAbs) that selectively stained endometrial stromal cells having prolactin in their cytoplasm, but did not stain glandular epithelium nor small lymphoid cells. From examination of tissues, cells and cell lines, it was found that 9E3 antigen was broadly distributed among various mesenchymal cells, while 9D3 antigen was distributed on a more restricted spectrum of mesenchymal cells, skin basal cells and a promonocytic cell line (U937). Neither of these antibodies stained peripheral blood cells, bone marrow cells or endometrium of the proliferating phase. Furthermore, 9D3 MoAb reacted with all melanoma cell lines and squamous cell lines examined. The antigenic molecule that was recognized by 9D3 MoAb had a molecular weight of 94,000.

Characterization of hematogenous cellular constituents of the murine decidua: a surface marker study

Decidual tissue, which includes typical (stromal type) decidual cells as well as infiltrating leukocytes, appears to play a local immunoregulatory role in the maintenance of pregnancy in nature. The present study evaluated the contribution of numerous leukocyte subsets characterized on the basis of morphology combined with cell surface markers to the development of murine decidua during syngeneic (CBA female X CBA male) and allogeneic (CBA female X C57BL/6 male) pregnancy. Collagenase dispersed decidua were subjected to total and differential counts and cell surface labeling for a radioautographic identification of various markers: S-IgM on B cells, Thy-1 on T cells, neither marker on null lymphocytes, Lyt- (1 or 2 or 1,2) antigens on T cell subsets, Mac-1 and I-A on macrophages, using 125I-labeled monoclonal antibodies or a sandwich labeling with 125I-protein A. The total cellularity of decidua basalis showed a biphasic rise in both pregnancies, with peaks on day 11 and days 15 and 16, but the allopregnant decidua showed a higher accumulation of all cell types indicating that an allogeneic conceptus causes an augmented deciduogenesis. The number of decidual cells, the most frequent cell class, rose to a peak on day 11 followed by a decline possibly due to cell death. The number of lymphocytes, the next frequent cell class, showed a parallel pattern initially, followed by a sharp secondary rise on day 16. This rise may be due to a withdrawal of progesterone, an antiinflammatory hormone. Null cells predominated amongst decidual lymphocytes (45-80%), as well as in the progestational endometrium (53%), indicating a hormonal control of their accumulation. The frequency of B cells was low (10-13%) and T cells (25-45%) comparable to that in the blood, with Lyt-1 only class being the most common T cell subset. Allopregnant decidua also showed a late rise in the total number of Lyt-2 only cells which may have a suppressor function. Macrophages, the next common leukocyte class, all expressed Mac-1. Their number rose to a plateau by day 12, but at a higher level in allopregnancy. I-A (needed for antigen presentation) was expressed by an increasing proportion (5-60%) of macrophages with advancing gestation. These findings provide a basis for further functional studies.

Radioautographic analysis of surface markers on decidual cells shared by cells of the lymphomyeloid tissues

Stromal type decidual cells recovered from the murine decidua by a mild collagenase dispersion procedure contain immunoregulatory cells whose ultimate precursors may originate from the bone marrow. To explore the familial relationship of these cells with other cells of the immune system, a battery of cell surface markers recognized on lymphomyeloid cells were examined and quantitated at the morphological level on typical stromal type decidual cells of the dispersed CBA mouse decidua at 8-14 days of syngeneic pregnancy, using a sensitive radioautographic technique. Cells were either labeled directly by exposure to 125I-labeled monoclonal antibodies against Thy-1, Mac-1, or Lyt antigens or indirectly by a sequential exposure to monoclonal anti-I-Ak (Ia.17) or monospecific anti-I-JK antibodies and 125I-labeled Protein A. Decidual cells were found to be Thy-1+/- (13-73% positive, the incidence rising with advancing gestation in the decidua basalis), Mac-1+/- (present of 6-11% on day 8 and 17-32% on day 12), I-A-, 1-J-, and Lyt-. Macrophages within the decidua were Thy-1-, Lyt-, Mac-1+, and I-A+/- (present on 5-61% of cells, the incidence rising with advancing gestation).(ABSTRACT TRUNCATED AT 250 WORDS)