Time-Course Analyses Addressing the Acquisition of DBA Lectin Reactivity in Mouse Lymphoid Organs and Uterus During the First Week of Pregnancy

Recognition factors of Dolichos biflorus agglutinin (DBA) and their accommodation sites

Dolichos biflorus agglutinin (DBA) is one of the well known plant lectins that are widely used in clinical serology to differentiate human blood group A1 and A2 erythrocytes and also applied to glycobiology. However, the knowledge of recognition factors of polyvalent (super) glycotopes in glycans and the roles of functional group and epimer in monosaccharide (sub-monosaccharide recognition factor) have not been well established. The size and shape of the recognition (combining) site of DBA has not been clearly defined. In this study, many importnat recognition factors of DBA-glycan binding were characterized by our established enzyme-linked lectinosorbent (ELLSA) and inhibition assays. The results of these assays showed that the intensity profile of the recognition factors for the major combining site of DBA was expressed by Mass relative potency (Mass R.P.) and shown by decreasing order of high density of polyvalent GalNAcα1 → (super glycotopes, 3.7 × 103) >> the corresponding β anomers >> monomeric GalNAcα1 → related glycotopes (GalNAc as 1.0) >> their GalNAc β-anomers >> Gal (absence of NHCH3CO at carbon-2 of GAlNAc) and GlcNAc (different epimer of Carbon-4 in GalNAc). From the all data available, it is proposed that the combining site of DBA should consist of a small cavity shape as major site and most complementary to monomeric GalNAcα → located at both terminal reducing end (Tn) and nonreducing end of glycan chains, and with a wide and broad area as subsite to accomodate from mono- to tetra-saccharides (GalNAcβ, Galβ1 → 3/4GlcNAc, lFuc1 → 2Galβ1 → 3/4GlcNAc, GalNAcβ1 → 3Galα1 → 4Galβ1 → 4Glc) at the nonreducing side. In this study, it has provided the most (comprehensive) recognition knowledge of DBA-glycan interactions at the factors of glycotope, super glycotope/sub-monosaccharide levels. Thus, it should expand and upgrade the conventional concept of the combining (recognition) site of DBA since 1980s.

Maternal hyperthyroidism alters the immunological mediators profile and population of natural killers cells in decidua of rats

Decidual immunological mediators modulate placental formation, decidualization and fetal development. However, the effect of maternal hyperthyroidism on decidual immunology needs further research. The aim of this study was to evaluate the population of uterine natural killer cells (uNKs) and the expression of immunological mediators in the decidua of female rats throughout pregnancy. Wistar rats were used and hyperthyroidism was induced by daily administration of L-thyroxine (T4) throughout pregnancy. The population of uNK cells in decidua was evaluated by immunostaining Lectin DBA, as well as the expression of interferon γ (INFγ), macrophage migration inhibitory factor (MIF), interleukin 15 (IL-15) and inducible nitric oxide synthase (iNOS) at 7, 10, 12, 14 and 19 days of gestation (DG). Maternal hyperthyroidism reduced the DBA+ uNK cell population in the decidua at 7 (P < 0.05) and 10 (P < 0.01) DGs compared to that in the control group, while it increased in the basal decidua (P < 0.05) and metrial gland (P < 0.0001) at the 12th DG. Hyperthyroidism also increased immunostaining of IL-15 (P < 0.0001), INFγ (P < 0.05), and MIF (P < 0.05) in the 7th DG, and increased immunostaining of IL-15 (P < 0.0001) and MIF (P < 0.01) in ^the 10th DG. However, excess thyroxine reduced IL-15 expression in the metrial gland and/or basal decidua in the 12th (P < 0.05), 14th (P < 0.01), and 19th (P < 0.001) DGs, as was also observed for INFγ in the basal decidua (P<0.001) and metrial gland (P < 0.0001) in the 12th DG. Regarding iNOS, an antiinflammatory cytokine, lower expression was observed in the basal decidua of hyperthyroid animals at 7 and 12 DGs (P < 0.05), whereas an increase occurred in the 10th DG (P < 0.05). These data demonstrate that maternal hyperthyroidism in female rats, particularly between 7 and 10 DGs, reduces the population of DBA+ uNKs in the decidua and increases the expression of inflammatory cytokines, suggesting a more proinflammatory environment in early pregnancy caused by this gestational disease.

Uterine natural killer cell biology and role in early pregnancy establishment and outcomes

Objective

While immune cells were originally thought to only play a role in maternal tolerance of the semiallogenic fetus, an active role in pregnancy establishment is becoming increasingly apparent. Uterine natural killer (uNK) cells are of specific interest because of their cyclic increase in number during the window of implantation. As a distinct entity from their peripheral blood counterparts, understanding the biology and function of uNK cells will provide the framework for understanding their role in early pregnancy establishment and adverse pregnancy outcomes.

Evidence Review

This review discusses unique uNK cell characteristics and presents clinical implications resulting from their dysfunction. We also systematically present existing knowledge about uNK cell function in three processes critical for successful human embryo implantation and placentation: stromal cell decidualization, spiral artery remodeling, and extravillous trophoblast invasion. Finally, we review the features of uNK cells that could help guide future investigations.

Results

It is clear the uNK cells are intimately involved in multiple facets of early pregnancy. This is accomplished directly, through the secretion of factors that regulate stromal cells and trophoblast function; and indirectly, via interaction with other maternal cell types present at the maternal-fetal interface. Current work also suggests that uNK cells are a heterogenous population, with subsets that potentially accomplish different functions.

Conclusion

Establishment of pregnancy through successful embryo implantation and placentation requires crosstalk between multiple maternal cell types and invading fetal trophoblast cells. Defects in this process have been associated with multiple adverse perinatal outcomes including hypertensive disorders of pregnancy, placenta accreta, and recurrent miscarriage though the mechanism underlying development of these defects remain unclear. Abnormalities in NK cell number and function which would disrupt physiological maternal-fetal crosstalk, could play a critical role in abnormal implantation and placentation. It is therefore imperative to dissect the unique physiological role of uNK cells in pregnancy and use this knowledge to inform clinical practice by determining how uNK cell dysfunction could lead to reproductive failure.

Distinctive phenotypes and functions of innate lymphoid cells in human decidua during early pregnancy

During early pregnancy, decidual innate lymphoid cells (dILCs) interact with surrounding maternal cells and invading fetal extravillous trophoblasts (EVT). Here, using mass cytometry, we characterise five main dILC subsets: decidual NK cells (dNK)1–3, ILC3s and proliferating NK cells. Following stimulation, dNK2 and dNK3 produce more chemokines than dNK1 including XCL1 which can act on both maternal dendritic cells and fetal EVT. In contrast, dNK1 express receptors including Killer-cell Immunoglobulin-like Receptors (KIR), indicating they respond to HLA class I ligands on EVT. Decidual NK have distinctive organisation and content of granules compared with peripheral blood NK cells. Acquisition of KIR correlates with higher granzyme B levels and increased chemokine production in response to KIR activation, suggesting a link between increased granule content and dNK1 responsiveness. Our analysis shows that dILCs are unique and provide specialised functions dedicated to achieving placental development and successful reproduction.

As an interface between maternal and fetal tissues, decidua hosts immune cells specialized in fostering a successful pregnancy. Here the authors carry out high-dimensional characterization of function, morphology and surface markers of human decidual innate lymphoid cells (ILCs), identifying subsets with features distinct from blood ILC.

Uterine natural killer cell partnerships in early mouse decidua basalis

The decidua basalis of developing mouse implantation sites is highly enriched in CD45⁺ leukocytes. In intact, syngeneically mated C57BL/6 decidua basalis examined at gestation day 8.5 by whole-mount in situ immunohistochemistry, leukocyte, but not trophoblast, conjugations were reported. Nothing is known regarding time course, frequency, composition, or importance of physiologic decidual CD45⁺ cell pairing. In this study, we confirmed the presence of anti-CD54⁺/anti-CD11a⁺ immune synapses in CD45⁺ decidual cell conjugates and characterized their cellular heterogeneity. Conjugated cell pairs were virtually absent before implantation (virgin and gestation days 3.5 and 4.5), were infrequent at gestation day 5.5, but involved 19% of all CD45⁺ cells by gestation day 8.5, then declined. By gestation day 8.5, almost all CD45⁺ cells coexpressed CD31, and 2 CD45⁺CD31⁺ cells composed most conjugates. Conjugation partners were defined for 2 nonoverlapping uterine natural killer cell subsets (Ly49C/I ⁺/Dolichos biflorus agglutinin lectin^- and Ly49C/I^-/Dolichos biflorus agglutinin lectin⁺). Ly49C/I⁺ uterine natural killer cells were the major subset from before mating up to gestation day 6.5. At gestation day 5.5/6.5, uterine natural killer cell conjugates involving Ly49C/I ⁺ cells were more abundant. By gestation day 8.5/9.5, Dolichos biflorus agglutinin lectin⁺ uterine natural killer cells were the dominant subset with Dolichos biflorus agglutinin lectin⁺/Dolichos biflorus agglutinin lectin⁺ homologous conjugates and Dolichos biflorus agglutinin lectin⁺/Dolichos biflorus agglutinin lectin^- heterologous conjugates dominating uterine natural killer cell pairings. At gestation day 6.5, both Ly49C/I⁺/CD45⁺ and Dolichos biflorus agglutinin lectin⁺/CD45⁺ heterologous conjugate pairs strongly engaged antigen-presenting cells (CD11c⁺, CD68⁺, or major histocompatibility complex class II⁺). By gestation day 8.5, dominant partners of Ly49C/I⁺/CD45⁺ and Dolichos biflorus agglutinin lectin⁺/CD45⁺ heterologous conjugates are T cells (CD8⁺ >CD4⁺). Heterologous conjugates that did not involve uterine natural killer cells occurred but did not suggest antigen presentation to T cells. These data identify gestation day 6.5-8.5 in the pregnant mouse as a critical window for leukocyte interactions that may establish immune regulation within implantation sites.

In vivo generation of decidual natural killer cells from resident hematopoietic progenitors

Decidual natural killer cells accumulate at the fetal-maternal interface and play a key role in a successful pregnancy. However, their origin is still unknown. Do they derive from peripheral natural killer cells recruited in decidua or do they represent a distinct population that originates in situ? Here, we identified natural killer precursors in decidua and uterus of pregnant mice. These precursors underwent rapid in situ differentiation and large proportions of proliferating immature natural killer cells were present in decidua and uterus as early as gestation day 4.5. Here, we investigated the origin of decidua- and uterus-natural killer cells by performing transfer experiments of peripheral mature natural killer cells or precursors from EGFP(+) mice. Results showed that mature natural killer cells did not migrate into decidua and uterus, while precursors were recruited in these organs and differentiated towards natural killer cells. Moreover, decidua- and uterus-natural killer cells displayed unique phenotypic and functional features. They expressed high levels of the activating Ly49D receptor in spite of their immature phenotype. In addition, decidua- and uterus-natural killer cells were poorly cytolytic and produced low amounts of IFN-γ, while they released factors (GM-CSF, VEGF, IP-10) involved in neo-angiogenesis and tissue remodeling. Our data reveal in situ generation of decidual natural killer cells and provide an important correlation between mouse and human decidual natural killer cells, allowing further studies to be carried out on their role in pregnancy-related diseases.

Uterine natural killer cells severely decrease in number at gestation day 6 in mice

Uterine natural killer (uNK) cells remarkably increase in number after implantation. NK cells or their precursors migrate from the blood stream and contribute to the increase. However, the contribution of uNK cells present in the virgin uterus has been unclear. To elucidate this issue, we examined uterine leukocyte subsets during pregnancy in BALB/c mice. The most dramatic change was the massive decrease in CD11b⁻ or Gr-1⁻ cells at gestation day (gd) 6. Uterine NK cells at gd 0 were CD11b⁻, and severely decreased at gd 6. The decrease was selective, and the proportion of other cells examined did not decrease. Uterine NK cells almost recovered at gd 12. These cells at gd 12 were more mature and/or activated in terms of expression of CD11b, CD27, CD127, or B220 than at gd 0. CXCL12 expression was observed on uterine cells at gd 0 or 6, but not at gd 12, whereas CXCR4 was detected on uNK cells at gds 0 and 12. A much higher expression of IL-15 in uterine cells or interferon-gamma expression in uNK cells was observed at gd 12 than at gd 0. IL-15 receptor alpha chain was detected on uNK cells at gd 12, but not at gd 0. Taken together, these findings were consistent with our interpretation that uNK cells present at gd 0 do not contribute to the increase of uNK cell number after implantation, and NK cells or their precursors migrate into the uterus, mature, and produce interferon-gamma to support pregnancy.

Natural killer cell-triggered vascular transformation: maternal care before birth?

Natural killer (NK) cells are found in lymphoid and non-lymphoid organs. In addition to important roles in immune surveillance, some NK cells contribute to angiogenesis and circulatory regulation. The uterus of early pregnancy is a non-lymphoid organ enriched in NK cells that are specifically recruited to placental attachment sites. In species with invasive hemochorial placentation, these uterine natural killer (uNK) cells, via secretion of cytokines, chemokines, mucins, enzymes and angiogenic growth factors, contribute to the physiological change of mesometrial endometrium into the unique stromal environment called decidua basalis. In humans, uNK cells have the phenotype CD56(bright)CD16(dim) and they appear in great abundance in the late secretory phase of the menstrual cycle and early pregnancy. Gene expression studies indicate that CD56(bright)CD16(dim) uterine and circulating cells are functionally distinct. In humans but not mice or other species with post-implantation decidualization, uNK cells may contribute to blastocyst implantation and are of interest as therapeutic targets in female infertility. Histological and genetic studies in mice first identified triggering of the process of gestation spiral arterial modification as a major uNK cell function, achieved via interferon (IFN)-γ secretion. During spiral arterial modification, branches from the uterine artery that traverse the endometrium/decidua transiently lose their muscular coat and ability to vasoconstrict. The expression of vascular markers changes from arterial to venous as these vessels dilate and become low-resistance, high-volume channels. Full understanding of the vascular interactions of human uNK cells is difficult to obtain because endometrial time-course studies are not possible in pregnant women. Here we briefly review key information concerning uNK cell functions from studies in rodents, summarize highlights concerning human uNK cells and describe our preliminary studies on development of a humanized, pregnant mouse model for in vivo investigations of human uNK cell functions.

Expression of the vasoactive proteins AT1, AT2, and ANP by pregnancy-induced mouse uterine natural killer cells

Angiotensin II receptor type 1 (AT1) activation leads to vasoconstriction and type 2 receptor (AT2) leads to vasodilation. Atrial natriuretic peptide (ANP) antagonizes the effects of AT1. In human and murine pregnancies, uterine natural killer (uNK) cells closely associate with decidual blood vessels. Protein localization of AT1, AT2, and ANP to mouse uNK cells was examined between gestation days (gds) 6 and 12, the interval of uNK cell expansion. Percentages of uNK cells expressing AT1 or AT2 changed between gd6 and gd10. Atrial natriuretic peptide did not localize to uNK cells at gd6 or 8, but did colocalize to uNK cells at gd10 and 12, times immediately after spiral arterial modification. This is the first report of AT1, AT2, and ANP expression in uterine immune cells. Expression of these molecules suggests that uNK cells have the potential to contribute to the changes in blood pressure that occur between days 5 and 12 of pregnancy in mice.

Hormonal regulation of uterine natural killer cells in mouse preimplantation uterus

Uterine Natural Killer (uNK) cells are the most abundant lymphocyte population recruited in the uteri during murine and human pregnancy. Previous investigation on uNK cells during mouse pregnancy focused more on its accumulation in postimplantation periods, which were believed to play important roles in regulating trophoblast invasion and angiogenesis towards successful placentation. However, by using recently developed methods of Dolichos biflorus agglutinin (DBA) lectin, a closer examination during mouse preimplantation revealed that there were also dynamic regulations of uNK cell, suggesting a major regulation by steroid hormones. Here we provide a detailed examination of uNK cells distribution during mouse early pregnancy by DBA lectin reactivity, with emphasis on preimplantation period and its hormonal regulation profiles. Our results showed that uNK precursor cells or its cell membrane specific components could be recruited in the uterus by estrogen or/and progesterone, and the effects could be completely abolished by specific antagonists of their nuclear receptors (estrogen and progesterone receptor). These results suggested that the preimplantation uterus, through concerted hormone regulation, could recruit uNK precursor cell or its specific cellular component, which might be conducive for uterine receptivity and further uNK construction/function during postimplantation.

Uterine NK cells, spiral artery modification and the regulation of blood pressure during mouse pregnancy

Reproductive success in mammals involves coordinated changes in the immune and cardiovascular as well as in the neuroendocrine and reproductive systems. This review addresses studies that identify potential links for NK cells and T cells with the local and systemic cardiovascular adaptations of pregnancy. The studies reviewed have utilized immunohistochemisty and in vivo analyses of vascular parameters by ultrasound, chronic monitoring of hemodynamics via radiotelemetric recording and intravital microscopy. At the uterine level, functional subsets of uterine natural killer cells were identified. These included subsets expressing molecules important for vasoregulation, in addition to those previously identified for angiogenesis. Spiral arteries showed conducted responses that could account for conceptus control of vasoactivity and mouse gestational blood pressure 5-phase pattern. Vascular immunology is an emerging transdisciplinary field, critical for both reproductive immunology and cardiovascular disease.

Analysis of uterine natural killer cells in mice

The term uterine natural killer (uNK) cell is applied in mice to an abundant but transient NK cell population that undergoes unique, terminal differentiation within embryo implantation sites during endometrial decidualization and pregnancy. In mice, decidualization is induced by attachment and implantation of hatched, blastocyst-stage embryos. Within each implantation site, uNK cells proliferate and rapidly differentiate into highly restricted regions called decidua basalis and the mesometrial lymphoid aggregate of pregnancy (MLAp). uNK cells begin to die within healthy decidua basalis by day 8 of the 19-20 day pregnancy of mice. By gestation day 12, uNK cell numbers have peaked and most uNK cells show in situ nuclear fragmentation indicative of disintegration. Morphological studies (standard histology, ultrastructure, immunohistochemistry, in situ hybridization, and RNA analyses from laser capture microdissected uNK cells) have provided most of the current understanding regarding this cell lineage. These approaches identified the special angiogenic properties of uNK cells and their regulatory relationships with normal physiological changes to the uterine (endometrial) arterial tree that accompany successful pregnancy. This chapter highlights key information needed for successful dissection of the dynamically changing decidua basalis that is enriched in uNK cells and special morphological procedures used for uNK cell study. Preparation of viable mouse uNK cell suspensions is difficult but can be achieved. This chapter includes techniques for isolation of uterine leukocyte suspensions and their enrichment for uNK cells that permit immediate downstream applications such as culture, isolation of high quality RNA, or flow cytometry.

Murine endometrial and decidual NK1.1+ natural killer cells display a B220+CD11c+ cell surface phenotype

Uterine natural killer (uNK) cells accumulate at the maternal-fetal interface during gestation and are thought to have an important role during pregnancy in both mice and humans. While the cell surface phenotype of human uNK cells is increasingly well defined, less is known regarding the cell surface expression profile of murine uNK cells both before and during gestation. Herein, we demonstrate that murine NK1.1(+) (KLRB1C) endometrial NK (eNK) cells, derived from virgin mice, and NK1.1(+) decidual NK (dNK) cells, obtained from pregnant mice, belong to the B220(+) (PTPRC) CD11c(+) (ITGAX) subset of NK cells. While B220 expression was low on NK1.1(+) eNK cells, it was increased on a subset of NK1.1(+) dNK cells at Embryonic Day 10.5. Endometrial NK and dNK cells also differed somewhat in their expression patterns of two activation markers, namely, CD69 and inducible costimulator (ICOS). The eNK cells acquired a B220(hi)ICOS(+) dNK cell surface phenotype when cultured in vitro in the presence of uterine cells and murine interleukin 15. Thus, the cell surface profiles generated for both NK1.1(+) eNK cells and dNK cells demonstrate that they belong to the recently described B220(+)CD11c(+) subset of NK cells, which are potent cytokine producers.