Natural Killer Cells

Despite their fierce name, natural killer cells are actually a very important type of cell in the human body. Natural killer (NK) cells help to fight off various infections as well as cancer. In some women, though, NK cells can over react to a potential pregnancy, attacking the embryo. The end result is a miscarriage.

However, a simple test can determine whether NK cells are the culprits behind your multiple miscarriages.

Natural Killer Cells: What are They?

Natural killer cells are generally a helpful type of cell, which aids in protecting you from various infections and even cancer, as these cells target tumor cells. NK cells receive their name from the fact that are produced naturally by the body and their sole purpose is to search for and destroy harmful cells.

When a harmful cell is located, natural killer cells bind to the invader and produce a cytotoxic (meaning that it is deadly to cells) chemical. This chemical is called tumor necrosis factor (TNF) and is actually a type of chemotherapy drug.

Once the TNF has been excreted, holes begin to occur in the membrane of the invading cell. Because of the holes, fluids leak in, ultimately resulting in the cell bursting.

Why Natural Killer Cells Cause Miscarriage

In some women, the natural immune system response of the NK cells goes into overdrive. This means that the NK cells view the embryo as a cancer and decide to take action.

Once the embryo has been identified as an "invader," your NK cells will multiply in number in order to have more killing power. They will then attach to the embryo and kill it in the same way they would kill any other cell.

Because this is not a typical response of the immune system, it is likely that you will experience multiple miscarriages due to NK cells. However, with a proper diagnosis and treatment, it is possible to successfully achieve pregnancy.

Diagnosing NK Cells

To determine whether your multiple miscarriages are due to natural killer cells, a simple blood test will be performed. For this test, a sample of your blood will be taken and the NK cells isolated. These cells will then be cultured with various solutions to see how they react.

Embryonic cancer cells, which are similar to embryos and placentas, are used in combination with the NK cells to see how the NK cells react to a potential pregnancy. The embryonic cancer cells will have a special type of dye applied to them for easier identification by your fertility specialist.

After two to four hours, a second dye will be added to the solution. Only the dead cells will absorb this dye, not the living cells.

Next, the sample is placed into a flow cell cytometer, where all the cells are forced to pass by a laser in single file. The beam emitted from the laser causes the dye to fluoresce, thereby allowing the cells to be picked up by the computer and counted.

This process will give your fertility specialist an accurate measurement of the percentage of live cells to dead cells. If you are found to have more dead cells than live, it is likely that your miscarriages are due to over-active NK cells.


Useful treatment is available if you are found to have elevated levels of natural killer cells in your system. The main form of treatment tends to be IVIg infusions, a type of intravenous drug that helps to suppress the immune system. IVIg therapy has been shown to have an 80% success rate associated with it.

If you have been diagnosed with natural killer cells, it is important to also have regular monitoring of your thyroid performed. Approximately 5% of women with elevated natural killer cells will develop hypo- or hyperthyroidism. Therefore, it is necessary to have yearly thyroid testing done.




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