biology

Uterine natural killer cells

Uterine natural killer cells is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Uterine natural killer cells rather than just read about it. In short: Uterine natural killer cells make up approximately 70% of maternal lymphocytes during pregnancy, occupying both the decidua basalis of the endometrium at the implantation site and the mesometrial lymphoid aggregate of pregnancy (MLAp) that surrounds the blood vessels supplying the placenta. This number is at its peak in early pregnancy but declines at parturition.

Key takeaways

Uterine natural killer cells belongs to biology; place it in that map before memorising details.
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Reproduce the core statement of Uterine natural killer cells from memory before moving on to harder problems.

Reference excerpt

Uterine natural killer cells make up approximately 70% of maternal lymphocytes during pregnancy, occupying both the decidua basalis of the endometrium at the implantation site and the mesometrial lymphoid aggregate of pregnancy (MLAp) that surrounds the blood vessels supplying the placenta. This number is at its peak in early pregnancy but declines at parturition.

Morphology

General Most studies of uterine natural killer cells use murine cells to model the human equivalent: unless stated otherwise, this section focuses on murine uterine natural killer cells. Uterine natural killer cells are large, granular, rounded or oval lymphocytes. On microscopic examination, they may have one or more cytoplasmic projections and/or be binucleate. Characteristically they contain eosinophilic granules that stain darkly with PAS, indicating the presence of glycoproteins. These granules usually appear regular (but some can be irregularly shaped), and they grow in size and number until approximately 2 weeks of gestation. Granules differ between species, with rat uterine natural killer cells displaying an increased number of small granules than murine cells. Rat uterine natural killer cell morphology also differs from the mouse due to the common occurrence of myelin within the granules. In all species, as active cells, they have numerous prominent organelles including mitochondria, well-developed golgi apparatus, free ribosomes and rough endoplasmic reticulum.

Receptors and surface proteins Human uterine natural killer cells share many of the surface receptors and proteins of circulating natural killer cells, exhibiting high levels of CD94 and CD56. However, they possess a unique expression profile of certain proteins, specifically CD9, CD103 (an integrin) and killer immunoglobulin-like receptors. Notably, mouse models suggest that they lack CD16 and L-selectin, proteins that are prominent on pNKs (peripheral NK cells). There are also integrin families present in the membrane of uterine natural killer cells (α5β1, α4β1 and α6β1), the binding of which (by ligands fibronectin, vascular cell adhesion molecule 1, and laminin) induces certain uterine natural killer cell-specific effects (see 'Functions of uNK cells'). As with circulating natural killer cells, uterine natural killer cells also express immunoglobulin-like transcripts and natural cytotoxicity receptors.

Origin In humans, the Uterine natural killer cell population is low during the proliferative phase of the menstrual cycle. The number increases after ovulation by the migration of circulating natural killer cells, as well as differentiation of haematopoietic stem cells. The population of natural killer cells in the uterine tissue will only persist if pregnancy occurs. CD34(+) are stem cells that act as Natural Killer cell precursors. They have the capacity to develop into mature Uterine Natural Killer cells. An increase in CD34(+) in the endometrium results in increased chance of pregnancy and decreased chance on infertility. In implantation, endometrial CD34+ hematopoietic stem cell population increased (3.97% vs 0.69% P < 0.0004).

Origin of uterine natural killer cells during pregnancy Based on studies using mouse models, both tissue resident natural killer cells and circulating natural killer cells are thought to contribute to the Uterine natural killer cell population during pregnancy. The origin of Uterine natural killer cells has been suggested to occur in two phases dependent on the stage of uterine tissue remodelling. At the onset of decidualisation, local proliferation of tissue resident natural killer cells occurs with little involvement from circulating natural killer cells. During the formation of the placenta, circulating natural killer cells are recruited.

Functions Uterine natural killer cells have an important role during pregnancy in both, humans and in mice. However, unlike natural killer cells, Uterine natural killer cells do not have a fundamental role in the innate immune system and therefore, are not cytotoxic. Throughout pregnancy, there is adaptation of the uterus to allow the growth of the foetus to occur. Studies in mice have shown that uterine natural killer cells have a key role in this remodelling. During the remodelling, spiral arteries undergo structural changes to allow adequate nutritional substances to supply the growing foetus. In mice, uterine natural killer cells were also found to produce growth-promoting factors which are important in early development before the placenta is fully formed.

Localisation Uterine natural killer cells accumulate during pregnancy, and this is thought to be the result of a two-wave process, beginning with proliferation of tissue resident natural killer cells in the decidua basalis, with minimal contribution to this pool from circulating natural killer cells from the blood stream. Later during placentation, circulating natural killer cells are thought to be recruited to aid with vascular remodelling. These cells are attracted to the uterus during pregnancy independent of chemokine receptors CCR-2 and CCR-5 in spite of these being important in recruitment of other inflammatory responses, and the exact method of their homing is yet to be understood.

Role in disease Uterine natural killer cells secrete trophoblast invasion promoting cytokines (IL-8 and IP-10) and various angiogenic factors required for remodelling maternal spinal arteries in order to support sufficient perfusion of the placenta in later pregnancy. Failure of this to occur can lead to miscarriage or pre-eclampsia.

References

Illustrations

Worked examples

Example 1 — a first encounter with Uterine natural killer cells

Start with the simplest possible case. Write down what Uterine natural killer cells claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Uterine natural killer cells before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Uterine natural killer cells ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Uterine natural killer cells

In research: Uterine natural killer cells appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Uterine natural killer cells in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Uterine natural killer cells is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human cells, Lymphocytes, so understanding it makes those chapters shorter.
In everyday life: Look for Uterine natural killer cells outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Uterine natural killer cells in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Uterine natural killer cells means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Uterine natural killer cells out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Uterine natural killer cells in simple terms?

Why does Uterine natural killer cells matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Uterine natural killer cells?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Uterine natural killer cells.