Detection of macrophages and the characterization of Fc receptor-bearing cells in the mouse decidua, placenta and yolk sac using the macrophage-specific monoclonal antibody F4/80

Detection of Math6-Expressing Cell Types in Murine Placenta

The transcription factor Math6, mouse atonal homolog 6, belongs to the family of highly conserved basic helix-loop-helix transcription factors. It plays an important role in embryonic development and shows a wide expression pattern in murine tissues. The placenta, as a life-sustaining transient organ for the fetus, also depends on the expression of Math6. The adverse effects of deleting Math6 in mice, leading to deficient placental development and pregnancy loss, have already been demonstrated by us. Until now, detailed investigations regarding the specific mechanisms underlying the improper placental development in these murine mutants have failed, as the Math6 expression could not be confined to a specific cell type due to the lack of a highly specific Math6 antibody. To circumvent this problem, we used transgenic mice, where Math6 is marked with a Flag sequence that functions as a specific epitope. Tissues from these transgenic mice were used to establish immunohistochemical staining and fluorescence-activated cell sorting (FACS). The establishment of these methods yielded initial findings pertaining to the identification of Math6-expressing cell types and their localization. Our results reveal that Math6 shows a wide expression pattern in both maternal and fetal components of the murine placenta. It shows expression in various cell types, but predominantly in trophoblast giant cells, endothelial cells and macrophages. The largest subpopulation that we detected in the group of Math6-positive cells were identified as DBA+ uterine natural killer cells. These findings reveal information and a chance for further investigation on the involvement of Math6 in placental development and the molecular pathomechanisms of spontaneous abortion.

CLEC4F is an inducible C-type lectin in F4/80-positive cells and is involved in alpha-galactosylceramide presentation in liver

CLEC4F, a member of C-type lectin, was first purified from rat liver extract with high binding affinity to fucose, galactose (Gal), N-acetylgalactosamine (GalNAc), and un-sialylated glucosphingolipids with GalNAc or Gal terminus. However, the biological functions of CLEC4F have not been elucidated. To address this question, we examined the expression and distribution of murine CLEC4F, determined its binding specificity by glycan array, and investigated its function using CLEC4F knockout (Clec4f-/-) mice. We found that CLEC4F is a heavily glycosylated membrane protein co-expressed with F4/80 on Kupffer cells. In contrast to F4/80, CLEC4F is detectable in fetal livers at embryonic day 11.5 (E11.5) but not in yolk sac, suggesting the expression of CLEC4F is induced as cells migrate from yolk cells to the liver. Even though CLEC4F is not detectable in tissues outside liver, both residential Kupffer cells and infiltrating mononuclear cells surrounding liver abscesses are CLEC4F-positive upon Listeria monocytogenes (L. monocytogenes) infection. While CLEC4F has strong binding to Gal and GalNAc, terminal fucosylation inhibits CLEC4F recognition to several glycans such as Fucosyl GM1, Globo H, Bb3∼4 and other fucosyl-glycans. Moreover, CLEC4F interacts with alpha-galactosylceramide (α-GalCer) in a calcium-dependent manner and participates in the presentation of α-GalCer to natural killer T (NKT) cells. This suggests that CLEC4F is a C-type lectin with diverse binding specificity expressed on residential Kupffer cells and infiltrating monocytes in the liver, and may play an important role to modulate glycolipids presentation on Kupffer cells.

Identification of mature plasma cells in early rat yolk sac. A possible origin from the endodermal cell layer: immunohistochemistry and immunoelectron microscopic study

Plasma cells play a pivotal role in the immune system and are responsible for the synthesis and release of immunoglobulins. Numerous in vitro culture experiments on the yolk sac demonstrated the generation of mature cells of the myeloid and lymphoid lineages under appropriate culture conditions. However, there are no reports describing the development of mature lymphoid cells in the yolk sac so far. For this reason, we undertook this study to investigate the development of antibody-containing plasma cells during early yolk sac haematopoiesis. Immunohistochemistry and immunoelectron microscopy were employed in the study. Results of this work demonstrated very weak immune staining for the intracytoplasmic IgA, IgG, and IgM at days 10 and 11 of embryonic life, while dark staining was obtained at 12 days. Positive staining was localized to the endodermal cell layer. Electron microscopic examinations revealed the existence of cells with the typical characteristics of plasma cells inside the endodermal cell layer, which may suggest their endodermal origin. To further verify the nature of these cells, intracytoplasmic immunoglobulins were demonstrated by immunoelectron microscopy. The present study demonstrated emergence of mature functioning plasma cells in early rat yolk sac. In a previous work we hypothesized the possibility of endodermal origin of yolk sac macrophages. This study adds additional evidence to support that hypothesis. The possible role of plasma cells in the yolk sac is discussed.

Embryonic macrophages of early rat yolk sac: Immunohistochemistry and ultrastructure with reference to endodermal cell layer

Macrophages are multifunctional cells that participate in numerous biological processes; they actively phagocytose foreign particles and cell debris. Embryonic tissue macrophages are present at early stages of mammalian development; their ontogeny and function is still under investigation. Our study used immunohistochemistry and electron microscopy to investigate early rat yolk sac macrophages using mouse antirat macrophage monoclonal antibodies (mAb) Mar 1 and Mar 3 produced by our laboratory. Mar 3 mAb revealed the first emergence of immature macrophages in the rat yolk sac at fetal day nine coinciding with the beginning of yolk sac haemopoiesis that consisted mainly of erythropoiesis, while Mar 1 mAb detected specifically rat yolk sac macrophages at about the 13th to 14th day of gestation. Immunoreactivity against Mar mAbs was mainly located in the yolk sac endodermal cell layer, which may signify endodermal origin of the yolk sac macrophages. Ultrastructurally mature yolk sac macrophages contained numerous endocytic vesicles or vacuoles, well-developed Golgi saccules and many electron dense granules in their cytoplasm and a number of microvillous projections from the cell surface. After establishment of the circulation between yolk sac and embryo, Mar 3 positive cells were also demonstrated inside fetal undifferentiated mesenchymal tissue at fetal day 12. The study demonstrated the first emergence of immature yolk sac macrophages being among the earliest haemopoietic cells formed in mammalian development. Thus, Mar mAbs managed to detect macrophage differentiation antigens through their development early in the rat yolk sac.

The effect of restricted nutrition on uterine macrophage populations in mice

The abundant macrophage populations present in the endometrium are implicated in the tissue remodelling events and immunological changes necessary for pregnancy. Using two regimens of restricted nutrition (95 and 88% of ad libitum intake for 19 days), we have shown that moderately reduced food consumption can dramatically alter the number of endometrial macrophages and their immunoaccessory function in mice. Restricted nutrition also interfered with the estrous cycle, but the effects on endometrial macrophages were more extensive and qualitatively different than could be explained by diminished ovarian steroid hormone activity. Significantly less F4/80+ and Ia+ cells were found in the endometrium of food restricted mice than in ad libitum mice at the same estrous cycle stage. In the more severely restricted mice the losses were even greater than those seen after ovariectomy. In ad libitum fed animals, uterine but not peritoneal macrophages showed an ovarian hormone-dependent inhibitory phenotype in a splenocyte mitogenesis assay. Macrophages derived from both locations exhibited greater immunostimulatory activity following restricted nutrition. We conclude that endometrial macrophage populations are influenced by nutritional status and this may be mediated through both steroid hormone-dependent and -independent mechanisms. Nutritionally induced aberrations in the number or behaviour of endometrial macrophages during the estrous cycle or in early pregnancy could have important implications for the quality of the pre- and peri-implantation environment and the maternal immune response to pregnancy.

Presence of activated macrophages in a murine model of early embryo loss

PROBLEM

Even though our knowledge of the phenomenon at play at the fetoplacental interface has greatly advanced during the past years, a complete understanding of the reasons why the developing embryo is not rejected by maternal immune effector cells remains largely unknown.

METHODS

We have used immunohistochemistry with the macrophage-specific markers F4/80 and MHC II to study the relationship between decidual infiltration and resorption in murine models of embryo loss between days 6 and 10 of gestation.

RESULTS

Analysis of day 8 CBA/J x DBA/2 pregnancies has revealed 2 distinct populations of embryos. The majority (69.4%) expressed low levels of F4/80+ cells, but a minority (30.6%) expressed much higher level of the macrophage marker. In FBA/J x BALB/c, most embryos (91.7%) expressed low numbers of F4/80+ cells. As earlier experiments established that products of activated macrophages (TNF-alpha and nitric oxide) were implicated in embryo loss in this model, the activation status of the F4/80+ macrophages was assessed through the cell surface expression of MHC II. Again, a similar association was established: 30.6% of the CBA/J x DBA/2 embryos were infiltrated by significantly more MHC II+ cells than the control CBA/J x BALB/c mating. Finally, when coordinate expression of F4/80, MHC II and CD11b was assessed, it was found that an embryo significantly infiltrated by cells bearing one of the 3 markers was also heavily infiltrated by cells bearing the 2 other markers.

CONCLUSIONS

This study has shown that the augmented infiltration of the deciduum with maternal macrophages is an early event which precedes spontaneous abortion of the early embryo.

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.

The uterine lumen of the pregnant guinea-pig contains a large macrophage population

Cellular constituents of the uterine lumen were investigated. Fourteen pregnant sows of 40 + days' gestation were anaesthetized and naturally occurring peritoneal fluid was collected. A uterine horn was delivered and 0.25 ml Gey's solution injected into the uterine lumen to collect free cells. The fluid was aspirated into a syringe and the cells extracted, counted and prepared for phagocytosis experiments and microscopy. The cells were stained with alpha-naphthyl-acetate-esterase (ANAE) to determine the fraction that was non-specific esterase-positive, a feature of mononuclear phagocytes. Differential cells counts were also made. Both uterine and peritoneal compartments yielded large numbers of cells (greater than 10(6)/ml). Peritoneal fluid cells were 47 +/- 6 per cent (SD) macrophages and 49 +/- 6 per cent eosinophils (the remainder being 'other' cells); 47 +/- 6 per cent also stained positively for ANAE. Uterine cells were 78 +/- 12 per cent macrophages, the remainder being mostly lymphocytes (18 +/- 11 per cent); 85 +/- 13 per cent stained positively with ANAE. Electron microscopy of the uterine cells confirmed that most had morphology consistent with being mononuclear phagocytes. Uterine and peritoneal cells phagocytized carbon particles and yeast cells when incubated at 37 degrees C. The origin and role of this macrophage population is unknown but uterine lumenal macrophages may be present to remove antigen-antibody complexes thus facilitating uptake of maternally derived IgG by the fetal yolk sac.

Immunoregulation and prostaglandin production by mechanically-derived and enzyme-derived murine decidual cells

Uterine cells from pregnant mice release soluble mediators which suppress in vitro immune responses non-specifically. Two methodologic approaches have been employed to obtain regulatory cells, and, although all cell populations derived by both methods were immunosuppressive, different factors and possibly different mechanisms of suppression appear to have been involved. The current study was designed to determine how suppression by mechanically and enzymatically derived cells might differ. Both enzymatically and mechanically derived cell populations suppressed mixed lymphocyte reactions non-specifically, mediated their effects through release of soluble factors, were immunosuppressive whether added at initiation or near the end of culture, suppressed generation of both IL-1 and IL-2, and suppression was not reversible with IL-1, IL-2, gamma interferon or combinations of the above. Immunosuppression by enzymatically derived, but not mechanically derived cells, was reversible with indomethacin. Enzymatically derived cells, but not mechanically derived cells, produced considerable amounts of PGE2. Morphological and immunohistochemical analysis revealed significant numbers of macrophages in both populations. Enzymatic treatment of mechanically derived cells did not increase the output of PGE2 when cells were cultured in vitro. The results suggest that, despite several similarities, enzymatically and mechanically derived cell populations are distinct and produce a distinct profile of soluble suppressive molecules.

The killing of mouse trophoblast cells by granulated metrial gland cells in vitro

Mouse placental cell preparations have been maintained in culture, and the types of cell that attached to the culture dish were classified according to morphological criteria. However, these morphological criteria were insufficient to determine from which trophoblast layer in the placenta all of the types of cell found in the cultures originated. Some placental cell preparations were co-cultured with granulated metrial gland (GMG) cells and these cultures were studied using time-lapse video. Various responses to contacts between GMG cells and trophoblast cells were observed. These responses included the killing of trophoblast cells by GMG cells.

Antigen presenting capacity of murine decidual tissue in vivo

Antigen presenting cells (APC) within murine decidual tissue in vivo have been shown to process the soluble antigen ovalbumin after intravenous administration and to present it in a form recognizable by immune T lymphocytes. In vivo antigen pulsed decidual APC stimulated T cell proliferation as efficiently as splenic APC and in an MHC restricted manner. In addition, anti-class II antibody plus complement treatment significantly reduced decidual antigen presenting capacity in vitro. These findings show that class II positive cells within the decidua can present antigen effectively in vivo and may therefore serve as APC for the presentation of fetal antigens to the maternal immune system during pregnancy.

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.

Antigen presenting cells in human decidual tissue. II: Accessory cells for the development of anti-trinitrophenyl cytotoxic T lymphocytes

Antigen presenting cells were isolated from early human decidua or peripheral blood by elution with EDTA of cells that after Ficoll-Paque separation bear receptors for, and have bound to, fibronectin. Decidual antigen presenting cells (DAPCs) co-cultured with TNP-modified autologous T cells induced the development of cytotoxic anti-TNP T lymphocytes with an efficiency comparable to that of peripheral blood antigen presenting cells (PAPCs). Treatment with anti HLA-class II antibody plus complement and UV radiation resulted in substantial inhibition of the accessory cell function. The T cell mediated lysis of TNP-modified targets is restricted by the major histocompatibility complex. Our results show that HLA-class I molecules are the most prominent restriction elements. The relevance of these data to the immunological mechanisms operating at the feto-maternal interface is discussed.