Natural Killer Cells (NK Cells)

Definition - What does Natural Killer Cells (NK Cells) mean?

Natural Killer (NK) cells are a type of white blood cells, an important part of the body's immune system, that kills abnormal cells in the body such as cells infected with viruses or bacteria and tumor cells. These cells can make up to 30% of the total cell population in the inner lining of the pregnant or non-pregnant uterus. NK cells undergo significant changes as a response to the variations of hormones during menstruation and fertilization. The presence of high levels of NK cells in the blood has been noted in some infertile women and women who develop recurrent miscarriages suggesting to some that they may play a role in female fertility. Research is underway to identify an exact relationship between NK cells and fertility.

FertilitySmarts explains Natural Killer Cells (NK Cells)

Natural killer cells are produced in the bone marrow, spleen and lymph nodes. They contain receptors on their cell membranes which act like sensors to detect abnormal cells. When a NK cell detects an abnormal cell, it releases enzymes and proteins that kill and dissolve the abnormal cell. Their response is rapid and can detect and kill viral infected cells within 3 days of infection.

Despite their compelling name, there is no evidence that these cells might harm the fetus or the placenta. In fact, some research suggests that these cells might actually help make the implantation and survival of the embryo successful. NK cells are abundantly present around the site of the implantation of the embryo. This has led some researchers to believe that these cells might release certain chemicals, called cytokines, which help in the development of arteries that would nourish the developing fetus.

There is limited evidence that links NK cells with female infertility. In a study conducted at the King's College London, researchers found that infertile females had a significantly higher amount of NK cells when compared to a group of fertile females. How this higher level of NK cells is linked to infertility is largely unknown. It has also been suggested that there is no scientific basis for NK cell testing for women who experience infertility or recurrent miscarriage.

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