Maternal Immune

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Image of human conceptus fully implanted
Human conceptus fully implanted (Stage 5).
Circulating large granular lymphocyte
Circulating large granular lymphocyte
Uterine Leukemia Inhibitory Factor (LIF) Expression
Uterine Leukemia Inhibitory Factor (LIF) Expression[1]

How does the implanting conceptus avoid immune rejection by the maternal immune system? There are a number of maternal and embryonic mechanisms that are thought to act to prevent immune rejection of the implanting conceptus, though the complete mechanism(s) are unknown. This is particularly relevant to Assisted Reproductive Technologies involving donor eggs.

Recent studies have also identified innate lymphoid cells (ILCs) are present in the uterus during the first trimester.[2] Innate lymphoid cells form three main groups: ILC1, ILC2, and ILC3. The ILC1 group include natural killer (NK) cells and other interferon (IFN)γ-producing cells.

developmentally related hematopoietic cells, which contribute to host immune defenses.

Implantation Links: implantation | Week 2 | trophoblast | placenta | Lecture - Week 1 and 2 | Implantation Timeline | ectopic pregnancy | hydatidiform mole | placenta abnormalities | Category:Implantation

Some Recent Findings

  • Where and when should natural killer cells be tested in women with repeated implantation failure?[3] "Thirty-two of the 73 patients were considered to have idiopathic repeated implantation failure (RIF), and 17 fertile women with children were taken as controls. Immunohistochemical staining for endometrial CD56+ and blood CD56+ or CD16+ NK cells measured using flow cytometry were compared during the mid-luteal phase in both patients and controls. Seventeen out of the 32 patients with idiopathic RIF and only one of the controls had >250 CD56 cells per high power field 400× in endometrial biopsy (p<0.001). The percentage of blood NK cells out of the total lymphocyte population was higher in women with idiopathic RIF than in controls. There was a positive correlation between blood and endometrial CD56 cells (ρ=0.707; p<0.001). No significant differences were found between patients with other types of RIF and controls. This study suggested that testing for NK cells might be useful in women with idiopathic RIF during the mid-luteal phase."
  • Chemokine gene silencing in decidual stromal cells limits T cell access to the maternal-fetal interface[4] "The chemokine-mediated recruitment of effector T cells to sites of inflammation is a central feature of the immune response. The extent to which chemokine expression levels are limited by the intrinsic developmental characteristics of a tissue has remained unexplored. We show in mice that effector T cells cannot accumulate within the decidua, the specialized stromal tissue encapsulating the fetus and placenta. Impaired accumulation was in part attributable to the epigenetic silencing of key T cell-attracting inflammatory chemokine genes in decidual stromal cells, as evidenced by promoter accrual of repressive histone marks. These findings give insight into mechanisms of fetomaternal immune tolerance, as well as reveal the epigenetic modification of tissue stromal cells as a modality for limiting effector T cell trafficking."
  • Human Endometrial CD98 Is Essential for Blastocyst Adhesion[5] "These results indicate that CD98, a component of tetraspanin-enriched microdomains, appears to be an important determinant of human endometrial receptivity during the implantation window." OMIM CD98
  • Implantation failure: molecular mechanisms and clinical treatment.[6] "Implantation is a complex initial step in the establishment of a successful pregnancy. Although embryo quality is an important determinant of implantation, temporally coordinated differentiation of endometrial cells to attain uterine receptivity and a synchronized dialog between maternal and embryonic tissues are crucial. The exact mechanism of implantation failure is still poorly understood."
More recent papers
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Search term: Maternal Immune

<pubmed limit=5>Maternal Immune</pubmed>

Search term: Uterine natural killer

<pubmed limit=5>Uterine natural killer</pubmed>

Search term: decidual natural killer cells

<pubmed limit=5>decidual natural killer cells</pubmed>

Decidual Immune Cells

Decidual Macrophages (Mϕ) Decidual T cells Uterine Natural Killer cells
  • regulatory role at the fetal-maternal interface.
  • M2 macrophage phenotype involved in tissue remodeling and inhibit inflammation
  • maintenance of tolerance to the non-self semi-allogeneic fetus
  • activated by fetal HLA-C (expressed on extravillous trophoblast cells)
  • specific immune tolerance to fetal alloantigens
  • Killer Inhibitory Receptor (KIR) activation by fetal HLA-C (expressed on extravillous trophoblast cells)


  • second trimester decidual leukocytes[7]
    • expressed neutrophil activation markers and angiogenesis-related proteins - vascular endothelial growth factor-A, Arginase-1, and CCL2, similarly shown in tumor-associated neutrophils.

Chemokine Gene Silencing

Remove the attraction of maternal immune cells.

A mouse study[4] has shown that the normal immune response to inflammation, accumulation of effector T cells in response to chemokine secretion does not occur during implantation. This is prevented locally by epigenetic silencing of chemokine expression in the decidual stromal cells.

Corticotropin-Releasing Hormone

Kill the maternal immune cells.

Both maternal and implanting conceptus release CRH at the embryo implantation site. This hormone then binds to receptors on the surface of trophoblast (extravillous trophoblast) cells leading to expression of a protein (Fas ligand, FasL) that activates the extrinsic cell death pathway on any local maternal immune cells ( T and B lymphocytes, natural killer cells, monocytes and macrophages).[8] This cannot be the only mechanism, as mice with dysfunctional FasL proteins are still fertile.

Links: Implantation

Uterine Natural Killer Cells

Uterine Natural Killer (uNK) or decidual NK (dNK) function to establishment of an immunosuppressive environment in comparison to circulating Natural Killer cells. There is a concentration of uNK cells in decidual tissue close to the invading conceptus trophoblast calls.

Circulating Natural Killer (NK) cells form part of the normal immune defence:

  1. have the ability to kill virus-infected cells and tumor cells
  2. release cytokines and chemokines involved in early inflammatory responses.
  3. regulated by inhibitory receptors and activating receptors
    1. inhibitory receptors - killer Ig-like receptors (KIRs) and CD94/NKG2A).
    2. activating receptors - (natural cytotoxicity receptors) NKp46, NKp30, and NKp44.

  • express large amounts of CD56 (different from peripheral blood NK cells) CD56bright
  • secrete angiogenic factors vascular endothelial growth factor (VEGF), placental growth factor, angiopoietin-2, matrix metalloproteinases and interferon γ


  • Neural cell adhesion molecule (NCAM)
  • adhesion glycoprotein with five extracellular immunoglobulin-like domains followed by two fibronectin type III repeats
  • some cells with the T cell markers CD3 and CD4 also express CD56.


  • mouse monoclonal primary anti-CD56 antibody (NCL-CD56-504; Novacastra Laboratories, Milton Keynes, UK)
  • rabbit polyclonal primary anti-CD56 antibody (Antibody #3606; Cell Signaling Technology)
  • antibodies-online

Implantation Factors

Implantation cartoon 01.jpg Implantation cartoon 02.jpg

Molecular Implantation and Decidualization[9]


In mice, endometrial secretion of two IL-6 family cytokines, leukemia inhibitory factor (LIF) and Interleukin-11 (IL-11), are key requirements for implantation. A recent human study suggests that there is a similar requirement for human conceptus implantation.[10]

Uterine Leukemia Inhibitory Factor (LIF) Expression[1]

Implantation LIF.jpg

a - At day 4 of pregnancy, oestrogen E2 induces LIF expression in the endometrial glands, leading to LIF secretion into the uterine lumen. There, LIF binds to its receptors on the surface of epithelial cells. b - This makes the uterus receptive to the blastocyst, which implants by day 5 of pregnancy. Hu et al. find that LIF expression in the endometrial glands also depends on the regulatory activity of p53. In the absence of p53, insufficient LIF is produced, the uterus does not become adequately receptive, and fewer blastocysts implant.


  1. 1.0 1.1 <pubmed>18046411</pubmed>
  2. <pubmed>25052762</pubmed>| Mucosal Immunol.
  3. <pubmed>25708533</pubmed>
  4. 4.0 4.1 <pubmed>22679098</pubmed>
  5. <pubmed>20976164</pubmed>| PMC2955532 | PLoS One
  6. <pubmed>20729534</pubmed>
  7. <pubmed>25135830</pubmed>
  8. <pubmed>11590404</pubmed>
  9. <pubmed>23223073</pubmed>| Nat Med
  10. <pubmed>19213836</pubmed>


<pubmed></pubmed> <pubmed></pubmed> <pubmed>25713505</pubmed> <pubmed>25342175</pubmed>


<pubmed></pubmed> <pubmed></pubmed> <pubmed>25310696</pubmed> <pubmed>25163504</pubmed> <pubmed>25135830</pubmed> <pubmed>25066422</pubmed> <pubmed>24954221</pubmed> <pubmed>24954224</pubmed> <pubmed></pubmed> <pubmed></pubmed>

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Cite this page: Hill, M.A. (2020, January 28) Embryology Maternal Immune. Retrieved from

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G