Nitric oxide synthase-2 and expression of perforin in uterine NK cells

Uterine natural killer cells: supervisors of vasculature construction in early decidua basalis

Mammalian pregnancy involves tremendousde novomaternal vascular construction to adequately support conceptus development. In early mouse decidua basalis (DB), maternal uterine natural killer (uNK) cells oversee this process directing various aspects during the formation of supportive vascular networks. The uNK cells recruited to early implantation site DB secrete numerous factors that act in the construction of early decidual vessels (neoangiogenesis) as well as in the alteration of the structural components of newly developing and existing vessels (pruning and remodeling). Although decidual and placental development sufficient to support live births occur in the absence of normally functioning uNK cells, development and structure of implantation site are optimized through the presence of normally activated uNK cells. Human NK cells are also recruited to early decidua. Gestational complications including recurrent spontaneous abortion, fetal growth restriction, preeclampsia, and preterm labor are linked with the absence of human NK cell activation via paternally inherited conceptus transplantation antigens. This review summarizes the roles that mouse uNK cells normally play in decidual neoangiogenesis and spiral artery remodeling in mouse pregnancy and briefly discusses changes in early developmental angiogenesis due to placental growth factor deficiency.

Leukocyte driven-decidual angiogenesis in early pregnancy

Successful pregnancy and long-term, post-natal maternal and offspring cardiac, vascular and metabolic health require key maternal cardiovascular adaptations over gestation. Within the pregnant decidualizing uterus, coordinated vascular, immunological and stromal cell changes occur. Considerable attention has been given to the roles of uterine natural killer (uNK) cells in initiating decidual spiral arterial remodeling, a process normally completed by mid-gestation in mice and in humans. However, leukocyte roles in much earlier, region specific, decidual vascular remodeling are now being defined. Interest in immune cell-promoted vascular remodeling is driven by vascular aberrations that are reported in human gestational complications such as infertility, recurrent spontaneous abortion, preeclampsia (PE) and fetal growth restriction. Appropriate maternal cardiovascular responses during pregnancy protect mothers and their children from later cardiovascular disease risk elevation. One of the earliest uterine responses to pregnancy in species with hemochorial placentation is stromal cell decidualization, which creates unique niches for angiogenesis and leukocyte recruitment. In early decidua basalis, the aspect of the implantation site that will cradle the developing placenta and provide the major blood vessels to support mature placental functions, leukocytes are greatly enriched and display specialized properties. UNK cells, the most abundant leukocyte subset in early decidua basalis, have angiogenic abilities and are essential for normal early decidual angiogenesis. The regulation of uNK cells and their roles in determining maternal and progeny cardiovascular health over pregnancy and postpartum are discussed.

Granzyme B-dependent and perforin-independent DNA fragmentation in intestinal epithelial cells induced by anti-CD3 mAb-activated intra-epithelial lymphocytes

We previously found that an i.p. injection of anti-CD3 monoclonal antibody (mAb) into mice caused DNA fragmentation in the intestinal villous epithelial cells (IVECs) of the duodenum and the jejunum. In this study, in order to elucidate the mechanism of DNA fragmentation in IVECs, we searched for the inducer(s) of DNA fragmentation by using immunohistochemistry. The release of cytoplasmic granules from intraepithelial lymphocytes (IELs) and the formation of large gaps between IELs and IVECs were observed electron microscopically after antibody administration. The presence and distribution pattern of Granzyme B (GrB), a serine protease in cytolytic granules present in cytotoxic T lymphocytes and natural killer cells and considered to be the responsible molecule for DNA fragmentation in target cells, was examined in detail in intestinal villi by immunohistology. GrB was detected in cytoplasmic granules in nearly all IELs. The time-kinetics of granule release from IELs after mAb injection coincided not only with that of the extracellular diffusion of GrB, but also with that of DNA fragmentation in IVECs. On the other hand, perforin (Pfn), assumed to cooperate with GrB in DNA fragmentation, could not be detected in IELs, and its release was not confirmed after the anti-CD3 mAb injection. Anti-CD3 mAb injection also induced DNA fragmentation in IVECs in Pfn-knockout mice. These results support the notion that DNA fragmentation in IVECs by the stimulated IELs in the present study is induced by a mechanism involving GrB, but independent of Pfn.

Regulation of lymphocytes by nitric oxide

Shortly after the identification of nitric oxide (NO) as a product of macrophages, it was discovered that NO generated by inducible NO synthase (iNOS) inhibits the proliferation of T lymphocytes. Since then, it has become clear that iNOS activity also regulates the development, differentiation, and/or function of various types of T cells and B cells and also affects NK cells. The three key mechanisms underlying the iNOS-dependent immunoregulation are (a) the modulation of signaling processes by NO, (b) the depletion of arginine, and (c) the alteration of accessory cell functions. This chapter highlights important principles of iNOS-dependent immunoregulation of lymphocytes and also reviews more recent evidence for an effect of endothelial or neuronal NO synthase in lymphocytes.

Uterine natural killer cells: a specialized differentiation regulated by ovarian hormones

In adult females of many species, a transient population of natural killer (NK) cells appears in cycles within the uterine endometrium (lining). Appearance of these lymphocytes coincides with specific phases of the ovarian hormone cycle and/or early pregnancy. Studies in rodents, women, and pigs dominate the literature and suggest the uterine (u)NK cells are an activated subset sharing many but not all features with circulating or lymphoid organ-residing NK cells. During successful murine pregnancy, uNK cells appear to regulate initiation of structural changes in the feed arterial systems that support maternal endometrial tissue at sites of implantation and subsequent placental development. These changes, which reverse after pregnancy, create a higher volume arterial bed with flaccid vessels unresponsive to vasoactive compounds. These unique pregnancy-associated arterial changes elevate the volume of low-pressure, nutrient-rich, maternal arterial blood available to conceptuses. Regulation of the differentiation, activation, and functions of uNK cells is only partially known, and there is lively debate regarding whether and how uNK cells participate in infertility or spontaneous abortion. This review highlights the biology of uNK cells during successful pregnancy.

Histological study of granulated metrial gland (GMG) cells in beige (DA-bg/bg) rats

To clarify the roles of granulated metrial gland (GMG) cells for successful pregnancy in rats, GMG cells in beige rats (genotype: DA-bg/bg), whose NK cells show lysosomal dysfunction because of abnormalities in cytoplasmic granules, were examined in mid- and late-pregnancy by light and electron microscopies. The GMG cells of beige rats were significantly less in number than those of the two controls (genotypes: DA-bg/+ and DA-+/+) in mid- and late-pregnancy, and this accompanied a low reproductive performance in the beige rats. The size of intracellular granules in the GMG cells of the beige rats was larger than for the two controls on each corresponding day of pregnancy. These results suggest that the activity of rat GMG cells and peripheral NK cells might be influenced by the beige gene, which is involved in reproductive performance.

Does nitric oxide play a role in maternal tolerance towards the foetus?

In pregnancy there occurs maternal tolerance to the foetus. Several mechanisms have been proposed to explain this phenomenon. The main immune population in the decidua are macrophages and natural killer cells, but with some "special" suppressor characteristics. There is also a predominant TH2 response. The non classical MCH type I HLA-G is expressed by trophoblasts and can suppress lymphomononuclear cytotoxicity. Other system to avoid the immune system is the expression of indoleamine-2,3-dioxygenase, that suppresses T cell activation by degrading tryptophan. Even though in the placenta there is a high production of nitric oxide, a well-known immune modulator, low attention has been paid to its role in maternal tolerance. There are many data showing that NO affects the IDO, CD95/CD95-L and the balance between TH1/TH2. Maybe NO could interact with several mechanisms at the same time, which could modify the tolerogenic activity depending on the concentration and the presence of other factors in the medium.

Interleukin-11 signaling is required for the differentiation of natural killer cells at the maternal-fetal interface

Interleukin-11 (IL-11) is a multifunctional hematopoietic growth factor that has been implicated in the control of reproduction. Studies on IL-11 receptor-alpha (IL-11R alpha)-deficient mice showed that female mice are infertile due to defective decidualization. In this report, we evaluated the development of decidual cells, immune cells, and the vasculature associated with the implantation site of IL-11R alpha-deficient mice; with the aim of better understanding the nature of the fertility defect. Messenger RNAs for decidual differentiation, such as decidual prolactin-related protein and prolactin-like protein-J are expressed in the IL-11R alpha mutant. However, the number of decidual cells expressing these genes is decreased in the mutant compared with the wild-type control. Although, trophoblast cells differentiate and express placental lactogen-I in the IL-11R alpha-deficient uterine environment, they fail to progress and expand in number. Defects in the organization of the decidual vasculature were also apparent in the IL-11R alpha mutant uterus. The most dramatic effect of IL-11 signaling was on the hematopoietic environment of the uterine decidua. Differentiated/perforin-expressing uterine natural killer (NK) cells were virtually absent from implantation sites of IL-11R alpha mutant mice. NK cell precursors were capable of homing to the IL-11R alpha-deficient uterus and a known regulator of NK cell differentiation; IL-15 was expressed in the IL-11R alpha mutant uterus. Splenic NK cells from IL-11R alpha mutant mice were also able to respond to IL-15 in vitro. Thus, the defect in NK precursor cell maturation was not intrinsic to the NK precursor cells but was dependent upon the tissue environment. In summary, IL-11 signaling is required for decidual-specific maturation of NK cells.

IGF-I Overexpression causes fetal loss during placentation in mice

To understand the role of IGF-I in murine pregnancy, we studied the reproductive performance of IGF-I overexpressed mice. Fetal loss occurred only in the transfected uterine horn during day 10-15 of pregnancy. The placenta appeared healthy until Day 10 of pregnancy. From day 12, the decidua basalis of the transfected horn increased in thickness. The vascular lumen was expanded, and most of embryos were dead. Uterine natural killer cells did not undergo apoptosis from day 10 to day 15 when they usually go through apoptosis. Thus, it is likely that IGF-I plays a role in the decidual formation through regulation of uNK cells. This is the first report to demonstrate that IGF-I overexpression can cause fetal loss during murine placentation.

Nitric oxide and the immune response

During the past two decades, nitric oxide (NO) has been recognized as one of the most versatile players in the immune system. It is involved in the pathogenesis and control of infectious diseases, tumors, autoimmune processes and chronic degenerative diseases. Because of its variety of reaction partners (DNA, proteins, low-molecular weight thiols, prosthetic groups, reactive oxygen intermediates), its widespread production (by three different NO synthases (NOS) and the fact that its activity is strongly influenced by its concentration, NO continues to surprise and perplex immunologists. Today, there is no simple, uniform picture of the function of NO in the immune system. Protective and toxic effects of NO are frequently seen in parallel. Its striking inter- and intracellular signaling capacity makes it extremely difficult to predict the effect of NOS inhibitors and NO donors, which still hampers therapeutic applications.

Natural killer cells and nitric oxide

Natural killer (NK) cells and nitric oxide (NO) are both important components of the natural or innate immune response. NK cells are large granular lymphocytes capable of destroying cells infected by virus or bacteria and susceptible tumor cells without prior sensitization and restriction by MHC antigens. They are abundant in blood, spleen, liver and lungs and are distinct from both T and B lymphocytes in their circulation patterns, profile of surface antigens, receptor repertoire and the way in which they discriminate between self and non-self. Uniquely, NK cells express receptors that can recognize and discriminate between normal and altered MHC class I determinants. NK cell cytotoxic activity is strongly induced by cytokines such as IL-2 and IL-12, and this activation is associated with synthesis of NO. Inhibitors of NO synthesis impair NK cell-mediated target cell killing, demonstrating a role for NO in NK cell function. Furthermore, NO itself can regulate NK cell activation. In this article, evidence that NO is a mediator of NK cell-mediated target cell killing, and that NO is a regulator of NK cell activation will be reviewed. Results of NO synthase gene deletion studies will be discussed, and rodent and human NK cells will be compared.