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B A Croy

Publications and source records attributed to B A Croy.

At least 109 records · Page 6Linked to original sources
PubMed1987

Mouse embryonic cells become susceptible to CTL lysis after midgestation.

The susceptibility of murine embryonic cells to CTL lysis has been assessed. Zona-free blastocysts were not lysed during 6 hr incubation with CTL sensitized against the embryonic genotype and remained capable of implantation and normal development in vivo as well as outgrowth in vitro. Freshly dissociated cells from postimplantation embryos before the 13th day of gestation were not lysed in a 51Cr-release assay, but cells from 13- to 16-day embryos were susceptible to lysis. Cells from Day 12 embryos cultured for 40 hr in the presence or absence of interferon became susceptible to CTL lysis. Cultured cells from Day 10 embryos were only lysed following culture in medium containing interferon. Cell populations lysed in the CTL assay remained resistant to lysis by NK effector cells. These experiments indicate that the murine fetus is protected from the maternal immune system at least during the first half of pregnancy by an intrinsic ability of early embryonic cells to resist cell mediated lysis. Suppression of maternal CTL responses may not be essential for fetal survival until later stages of gestation.

Animals↗
PubMed1987

Influence of the swine major histocompatibility complex on reproductive traits in miniature swine.

Three swine leukocyte antigen (SLA)-defined strains of miniature swine and one recombinant strain were examined to evaluate the influence of the SLA Complex on litter size and piglet survivability. To separate the effects of sire and dam SLA haplotype from other sire and dam effects, a general linear model was employed to analyse data from 58 litters. Analysis of variance showed that sire and dam haplotype each contributed significantly to the variability observed in litter size among the sire and dam SLA combinations examined (P less than 0.0001, P less than 0.05, respectively). Sow SLA-haplotype as well as sire and dam effects other than those related to haplotype were significant factors contributing to survival until weaning (8 weeks) (P less than 0.10, P less than 0.07, P less than 0.001, respectively), but sire SLA-haplotype did not contribute significantly to this trait. Expected and observed haplotype frequencies of offspring in each litter were compared using chi-square analysis. A discrepancy was observed only in offspring from SLAa/d by SLAa/d matings, for which significantly fewer SLAa/a piglets were weaned than expected (P less than 0.06). Laparotomy during day 35-50 of pregnancy suggested that litter size was not an accurate estimate of ovulation rate and that ovulation rate was similar for dams of ad, ac and dd haplotypes.

Animals↗
PubMed1987

Immunological and para-immunological mechanisms in spontaneous abortion: recent insights and future directions.

Unexplained spontaneous abortion in humans is currently thought to be related to genetic or immunologic factors. Animal models of spontaneous abortion have been used to try to gain some insight into the problems in humans. From studies of animal models there is increasing evidence that a variety of mechanisms may initiate pregnancy failure and participation of immunologic effectors may be a secondary event. Recent studies indicate that murine abortion that occurs spontaneously (without deliberate immunization by the investigator) may be initiated by para-immunologic host effector cells such as NK cells, macrophages and their toxins that possess selective toxicity which is not antigen-specific. The potential importance of local non-specific suppressive mechanisms in the uterus is also highlighted by their ability to block non-specific para-immune effector cell activation, and by their potential relationship to growth factors in decidual supernatants that promote placental cell growth in vitro. Levels of non-specific suppression do not appear low when fetal death can be attributed to a genetic mutation. The concept that different tissue components of the feto-placental unit serve as targets of different immunologic and para-immunologic effectors is defined. The new insights into the pathophysiology of murine abortion and its correction can provide a useful framework for further analysis of the role of para-immunologic effector mechanisms in unexplained abortion in humans and in non-murine veterinary conditions.

Abortion, Spontaneous↗
PubMed1986

Immune presensitization and local intrauterine defences as determinants of success or failure of murine interspecies pregnancies.

Putatively immuno-incompetent Mus musculus females exhibited failure to support pregnancy of Mus caroli embryos. These results for M. musculus females (i.e. treated by cyclosporine A, of the nu/nu genotype, and as an interspecies chimaera) can be explained in immunological terms. Mus musculus females possessed pre-sensitized cytotoxic T cells against Mus caroli antigen. Nu/nu mice possessed activated NK cells and macrophages, and selectively discriminated against Mus caroli embryos early in pregnancy unlike normal +/+ females; the requirement for T cells to activate non-specific cytotoxic effector mechanisms was bypassed in nu/nu mice. Mus caroli are not inbred, and interspecies chimaeras which are tolerant of the antigens on the Mus musculus donor strain were not tolerant of cells from unrelated Mus caroli. Interspecies chimaeras also behaved as if they were pre-sensitized to Mus caroli. Our results show that Mus caroli embryos recruit fewer active suppressor cells even when gestating in Mus caroli decidua as compared to Mus musculus embryos in Mus musculus decidua and that the ability of Mus caroli placental cells to directly inhibit cytotoxic effector cell killing was inherently less than the inhibitory activity of placental cells from Mus musculus. Mus caroli embryos therefore appear to be less well defended against maternal immune attack even when gestating in a uterus possessing compatible Mus caroli decidual tissue.

Animals↗
PubMed1985

Characterization of immune effector cells present in early murine decidua.

It has been suggested that murine decidual cells act as an important immunoregulatory population localized to the pregnant uterus. We have examined early murine decidua to determine if immune effector cells occur in the decidual environment in proximity to the conceptus. High levels of natural killer (NK) cell activity were found consistently in decidual cell suspensions with peak activity occurring on Day 6.5 of gestation. NK activity declined as pregnancy proceeded and was not significant by Day 12.5 of gestation. Decidual cell suspensions did not appear to contain significant numbers of functional B or T effector cells. No antipaternal T-cell response could be demonstrated even in the decidua of immune mice. Lack of T-cell responses was attributed to the absence of T cells from decidua rather than to their inactivation because precursors of cytotoxic T lymphocytes (pCTL) could not be detected in decidual cell suspensions. Furthermore, the levels of pCTL detectable in spleen cell suspensions could not be reduced by mixing spleen cells with 7.5-day decidual cells. These results suggest that B cells and T cells may not occur in early decidua while NK cells are present and regulated independently.

Animals↗
PubMed1985

Characterization of murine decidual natural killer (NK) cells and their relevance to the success of pregnancy.

The identification of lytic cells in 6.5-day to 9.5-day murine decidua as NK cells has been extended. The cells with natural killer (NK) activity in early decidua were nonphagocytic and heterogeneous in size as assessed by velocity sedimentation at unit gravity. The numbers of lytic cells were reduced by treatment with anti-asialo GM1 in vivo and they were absent from the decidua of bg/bg mice. Thus, decidual NK cells were not distinct from NK cells in other tissues. The decline in the levels of decidual NK activity as pregnancy progressed was attributed to their regulation by other cells present in decidua by midgestation. The development of NK activity in decidua was dependent upon the presence of an embryo, however, decidual NK cells were not essential for successful pregnancy because viable offspring were obtained from mice lacking decidual NK activity. It was shown that NK cells from either spleen or decidua were unlikely to cause damage to embryos during the first half of pregnancy as freshly dissociated 9.5- and 11.5-day embryonic cells resisted NK lysis. Furthermore, blastocysts were not damaged by coincubation with splenic or decidual NK cells and were viable upon subsequent embryo transfer. These studies indicate that decidual NK cells are not essential for successful pregnancy and are not necessarily detrimental to early embryos. It is suggested that decidual NK cells may play other nonimmunological roles during embryonic development.

Animals↗
PubMed1985

Effects of alterations in the immunocompetent status of Mus musculus females on the survival of transferred Mus caroli embryos.

The role of the immune system in promoting the midterm death of Mus caroli embryos transferred to the Mus musculus uterus was studied in vivo by transferring M. caroli blastocysts to recipients with altered immune status. Transfers of embryos to chimaeric mothers (Mus musculus in equilibrium Mus caroli), which were expected to be tolerant of species antigens, resulted in survival of M. musculus embryos but death of M. caroli embryos. The preferential survival of M. musculus embryos was explained by showing that M. musculus embryos can survive in the M. caroli uterus. Transfers to T cell-deficient mice of genotype nu/nu and to NK cell-deficient mice of genotype bg/bg as well as treatment of normal transfer recipients with Cyclosporin A or anti-Ia antiserum failed to prolong survival. However, immunization of recipients with M. caroli lymphocytes promoted more rapid and uniform failure of the interspecies pregnancy. Cytotoxic cells were detected in the resorbing embryos on Day 10.5 in immune pregnancies and on Day 12.5 in non-immune pregnancies and these cells were promiscuous in their pattern of lysis, showing equal reactivity against M. caroli, transfer recipient and 3rd party target cells. These experiments show that failure of M. caroli embryos in the M. musculus uterus is complex, but probably does not involve responses by classical cytotoxic T lymphocyte or natural killer cell pathways. Participation of the immune system in the resorption process, however, is confirmed and is associated with generation of promiscuous cytolytic cells.

Animals↗
PubMed1985

Genetic identification of tissue of origin of cellular populations within the mouse placenta.

The mouse haemochorial placenta is a complex mixture of maternal cells and foetal trophectoderm and inner cell mass (ICM)-derived cells. The majority of the placental tissue is assumed to be trophoblast in origin but the exact extent and localization of the ICM and maternal contribution has not previously been determined. Using embryo transfer and reconstituted blastocyst techniques, combined with isozymal and in situ genetic markers, we have established that about 70% of the 13 to 15-day placenta is trophectoderm-derived, 30% is maternal in origin, and 4% develops from the ICM. Nearly all of the maternal contribution was confined to the spongiotrophoblast region and all of the ICM contribution was confined to the labyrinthine trophoblast region, where it formed the foetal blood capillaries and the endodermal sinuses. Using the same genetic markers, we showed that cell suspension techniques commonly used to produce 'trophoblast' cell preparations from placenta do not enrich for trophoblast, and, indeed, that collagenase, the preferred dissociation technique for cell viability, produced cell suspensions in which ICM and maternal cells were preferentially dissociated. No method for producing pure trophoblast populations has yet been found. Some unusually high ICM contributions to the placenta were found in reconstituted blastocyst experiments using ICMs isolated from early 3.5-day blastocysts, suggesting that these ICMs may have contributed to the trophectoderm layer of the blastocyst. These and other experiments suggest that the inner cell mass lineage may not be closed until some time after formation of the blastocyst.

Animals↗
PubMed1984

Recruitment of cytotoxic cells by ectopic grafts of xenogeneic, but not allogeneic, trophoblast.

In previous studies we showed that survival of Mus caroli embryos in the Mus musculus uterus was dependent on trophoblast genotype; M musculus trophoblast was protective while M caroli trophoblast was not. In this report we compare the immune response of M musculus to ectopic grafts of pure trophoblast of M caroli and M musculus genotypes to elucidate further differences between the properties of trophoblast from the two species that might account for the failure of M caroli trophoblast to protect the fetus. Grafts of M caroli or DBA/2J ectoplacental cone (EPC) or embryonic tissue (E) were placed beneath the renal capsule of Ha(ICR) mice that were untreated or had been immunized with M caroli lymphocytes or with P815 mastocytoma cells. No consistent morphological difference could be demonstrated between the xenografts and allografts by gross or histological examination. Cellular infiltration of allogeneic and xenogeneic EPC graft sites occurred in immunized mice within 5 days of grafting. Cells specifically cytotoxic to M caroli lymphoblasts were isolated from the xenogeneic graft sites, but no allogeneically sensitized cytotoxic cells could be demonstrated. These results show that xenoantigens expressed on trophoblast induce a cytotoxic immune response more readily than alloantigens.

Animals↗
PubMed1984

Local active suppression by suppressor cells in the decidua: a review.

The immunological survival of the antigen-bearing mammalian feto-placental unit is determined by the functional properties of the tissues at the feto-maternal interface. Antigen-specific systemic suppressor mechanisms such as suppressor T cells and nonantigen-specific suppressive serum factors appear not to play a major role in protection of the fetus. A novel type of non-MHC specific suppressor cell accumulates locally in the decidua of successfully allopregnant mice. This decidua-associated suppressor is a small lymphocytic cell possessing cytoplasmic granules, lacks T cell markers, and is deficient in number and activity at the implantation sites of viable xenogeneic Mus caroli embryos gestating in the uterus of Mus musculus animals at the time that maternal lymphoid cells begin to infiltrate the xenoembryos. These Mus caroli embryos subsequently resorb. Further experimental studies suggest that the trophoblast cells associated with successful pregnancy recruit bone-marrow derived maternal non-T suppressor cells to the decidua and thus, by an indirect mechanism, may act to protect the fetus from effector cells of the mother's immune system.

Animals↗
PubMed1983

Interspecific hybrids and chimeras in mice.

Interspecific hybrids and chimeras in mammals provide unique tools for investigating problems in genetics and embryology, because of the degree of disparity between the two component genotypes. We have attempted to produce hybrids and chimeras between Mus musculus, the laboratory mouse, and Mus caroli, a wild species of mouse from Southeast Asia. M. musculus and M. caroli do not normally interbreed, although sterile hybrids can be produced at a low rate by artificial insemination. Extrinsic problems of genotypic incompatibility between the fetus and the maternal environment seem to be involved in poor hybrid survival, since M. caroli blastocysts also die when transferred to the M. musculus uterus. Death is associated with the generation of maternal T-cells which are cytotoxic to M. caroli target cells in vitro. It is not yet clear whether this immune response is the primary cause of death or is secondary to breakdown of some other components of the fetal-maternal interaction. It is clear, however, that it is the trophoblast layer that mediates survival or death of the foreign embryonic cells in the M. musculus juterus, since M. caroli inner cell mass cells can survive to term after injection into M. musculus blastocysts: Viable interspecific chimeras result. Even more convincing evidence is provided by the production of viable M. caroli offspring by trophoblast vesicle reconstitution using trophoblast of M. musculus genotype and inner-cell mass of M. caroli type. Studies of properties of isolated trophoblast tissues have indicated that M. caroli trophoblast may differ from M. musculus in both its antigenic and immunosuppressive properties. Elucidation of trophoblast-uterine interactions in these various interspecific pregnancies is being aided by the development of an in situ marker system, which can distinguish cells of the two species in sectioned material by in situ hybridization with a M. musculus satellite DNA probe. This same marker is also proving a very powerful tool for analyzing cell lineage development in chimeras.

Animals↗
PubMed1982

Histological and immunological studies of post implantation death of Mus caroli embryos in the Mus musculus uterus.

Mus caroli blastocysts surgically transferred to the Mus musculus uterus implant and develop successfully during the first 9.5 days of gestation. At this time, the trophoblast giant cell area becomes infiltrated with lymphocytes and, subsequently, massive hemorrhage occurs, associated with embryo death. This process is specific for the xenogeneic embryos and does not affect adjacent allogeneic embryos present in the same uterus. Cells taken from the resorbing tissues contain a population of large Thy 1+, Lyt 1+, Lyt 2+ cytotoxic cells capable of lysing Mus caroli concanavalin A blasts in vitro. It is suggested that failure of the Mus caroli embryos in the Mus musculus uterus is mediated by the maternal immune system and that the xenogeneic blastocyst transfer system provides a suitable animal model system for studies of mechanisms that prevent rejection of the fetal allograft.

Animals↗
PubMed1982

Interspecific chimeras in mammals: a new experimental system.

The first viable interspecific chimeras in mammals have been made by mixing embryonic cells from two species of mouse, Mus musculus and Mus caroli. These chimeras resemble intraspecific chimeras in M. musculus in their patterns of mosaicism. They provide an interesting experimental system for studying interactions between cells of the two species. Three separate but related areas of investigation utilizing these chimeras are described. 1) In situ DNA-DNA hybridization using a cloned repetitive DNa sequence from M. musculus has enabled M. caroli and M. musculus cells to be distinguished in bone marrow spreads from chimeras. Further refinement of this technique should allow use of this in situ marker system for detailed analysis of cell distribution in chimeras. Such a ubiquitous marker system is not yet available in M. musculus. 2) Breeding interspecific chimeras has increased production of interspecific hybrids, which are very useful for studies of genetic interactions between the two species. 3) Mus caroli embryonic cells can survive in the M. musculus uterus in a chimera, although M. caroli embryos alone die around d 11 to 16 of pregnancy in M. musculus. Investigation of this phenomenon has implicated immune effector mechanisms in death of M. caroli embryos and has revealed the importance of trophoblast genotype for survival of foreign cells in the uterine environment.

Animals↗
PubMed1982

Importance of trophoblast genotype for survival of interspecific murine chimaeras.

Interspecific chimaeras between Mus musculus and Mus caroli were made by injection of M. musculus inner cell masses (ICMs) into M. caroli blastocysts, and by aggregation of 8-cell embryos. Both types of chimaera were transferred to M. musculus recipients: the former did not survive to term, but viable chimaeras were produced following embryo aggregation. Previous experiments have shown that chimaeras produced by injection of M. caroli ICMs into M. musculus blastocysts are viable, whereas M. caroli blastocysts cannot survive in the M. musculus uterus. There results indicate that the presence of trophoblast cells of maternal uterine genotype allows M. caroli in equilibrium M. musculus chimaeras to survive in the M. musculus uterus. It is suggested that M. musculus trophoblast components may protect the M. caroli embryonic cells from maternal immune rejection.

Animals↗