Natural Killer Cells (NK Cells) and Pregnancy

Natural killer (NK) cells are a sub-type of white blood cells, which are crucial in our immune system. They play a key role in identifying and fighting foreign bodies, thereby preventing a woman’s body from falling prey to various diseases during pregnancy. However, elevated natural killer cells in pregnancy have been associated with unsuccessful pregnancy and recurrent miscarriages. Clinics now offer tests to check the activity and number of active NK cells at the time of pregnancy.

What Are Natural Killer Cells?

Natural killer cells are lymphocytes that quickly act in response to various pathological challenges. They play a crucial role in destroying virally infected cells and controlling tumour cells. Apart from fighting diseases, specialised NK cells found in placenta also play an essential role in establishing and maintaining pregnancy. These cells also help in providing blood to the growing foetus for its proper development and to protect it against infections and foreign bodies. Natural killer cells can kill infected cells without any prior activation, and that is why they are called natural killer cells.

What Are Its Types?

NK cells are of two types:

1. Uterine NK Cells

These immune cells are already present in the human uterus before the start of pregnancy. Their numbers significantly expand during the first trimester of pregnancy owing to increased progesterone levels and subsequently reduce as the pregnancy progresses. These innate immune cells shelter the embryo from severe infections and ensure its proper development.

2. Peripheral NK Cells

These cells flow in the bloodstream and safeguard the body against different viruses and malignancies.

Role and Importance of NK Cells in Pregnancy

The function of NK cells in pregnancy is not clearly established to date. But some key points concerning the role of NK cells in pregnancy are:

• NK cells existing in human endometrium dramatically increase in number due to the influence of progesterone during early gestation.
• The incursion of trophoblast cells is required for the successful implantation of an embryo in the uterus. NK cells are thought to support the spread of trophoblast cells, thus aiding in embryo implantation.
• NK cells produce many cytokines which have a cytotoxic effect against infected cells which in turn helps in keeping the embryo safe from virus infections and ascertaining its normal growth.
• NK cells are also an important source of angiogenic growth factors. They generate various angiogenic growth factors like angiopoietin (Ang-1, Ang-2), angiogenin, keratinocyte, fibroblast, a vascular endothelial growth factor, which help in supplying blood to the developing foetus.

What Causes Overproduction of Natural Killer Cells During Pregnancy?

High-stress levels or auto-immune disease can impact the NK cells activity. NK cells are disposed to enhance vigorously owing to an overactive immune system. In instances of some inflammation in the endometrial lining, pelvic cavity, or fallopian tubes, or polycystic ovarian syndrome, the immune system may react by sending NK cells moving in the bloodstream to attack and destroy the infected cells causing the problem. In such a scenario, the uterine NK cells, guarding the embryo, withdraw to allow the incoming peripheral NK cells to do their job. At times these cells tend to perceive the embryo as a foreign body thereby attacking and killing it, which leads to a miscarriage.

Can Excess NK Cells in the Bloodstream Cause Miscarriage?

Natural killer cells are often linked to miscarriage, which is not completely wrong. An overabundance of NK cells in the bloodstream can result in a miscarriage. The NK cells mistakenly start seeing the embryo as a foreign organism thus attacking and damaging it. Excessive production of NK cells can also negatively impact embryo implantation in the uterus, causing infertility in women.

How to Balance NK Cells During Pregnancy

Many couples wish to know what stops natural killer cells in pregnancy. You will be happy to know that natural killer cells can be controlled in pregnancy. Few ways to balance high NK cells to have a successful pregnancy are as follows:

• In case of inflammation in a woman’s pelvic cavity, a biopsy can be done to check the heightened levels of NK cell activity. The biopsy is usually performed between 24th and 28th days of the menstrual cycle. The procedure is an invasive one but not painful. It usually doesn’t require the use of anaesthesia.
• A comprehensive evaluation of T3, T4 and TSH (Thyroid Stimulating Hormone) levels to evaluate the working of the thyroid gland can also be done. It helps in assessing the presence of thyroid antibodies.
• An effective treatment to regulate excess NK cells brings into play the utilisation of steroids. Prednisone is a commonly used steroid administered in a dosage of about 10 mg to 20 mg every day. However, steroids during pregnancy can have serious side effects on both the mother and the unborn child. Steroids may not just suppress the NK cells activity but can also dampen the entire immune system leaving the pregnant woman more susceptible to common cold and flu.
• Some patients used certain natural products and herbal treatments and experienced positive results. These natural treatments can prove effective in controlling excess NK cells and reducing inflammation. However, it is advised that you consult your doctor before taking any such natural treatment during pregnancy to avoid any probable complications later on.

Nature killer cells may be a possible cause of unexplained infertility. The probability certainly increases in case a woman is prone to inflammatory conditions of the pelvic cavity or PCOS. Screening fertility patients, particularly, those who have undergone recurrent miscarriages for NK cells, can help in producing important results and finding out viable treatments for successful pregnancy in future.

Also Read: Epithelial Cells in Urine During Pregnancy