Natural cell killers (NKC): influence in reproduction and in the embryo’s implantation failure

Natural cell killers - Instituto Bernabeu

Embryo implantation in the mother’s uterus is a very important phenomenon in the human survival and evolution. Many of its regulating processes have been already described but we still have a long way to understand it all.

Genetically speaking, the human embryo is the result of a chromosomal combination between the egg and the sperm. Hence is a “new” person. It’s very interesting how this “new person” with different genetic charge (at least 50%) can, successfully, adhere and implant on a tissue (maternal uterus), and the mother’s defence mechanisms (immunological system) don’t act to reject it, as it happens with organs transplants. This phenomenon is known as “pregnancy immunologic tolerance”.

Basing on this biological premise, is normal to think that patients who have not chieved pregnancy after several in vitro fertilization treatments with Repeated Implantation Failure (RIF), a posible cause might be the mother’s immunological action, which increases against the embryo and prevents it from implantation.

Indeed, studies done on patients with RIF (Implantation failure and Recurrent Miscarriage), show an increase in cells responsible for immunological rejections, called Natural Killer Cells (NKC). They are present on both, the mother’s blood and in the endometrium (where implantation takes place). So, the study of the NK cells in blood and/or endometrium (biopsy) could be useful to rule out this phenomenon as the cause of reproduction failures. More recently, it’s been proposed as useful and, furthermore, evaluates the NK cell’s “activation” degree. This means its inclination to reject, and it would be achieved by measuring the colled NK CD69+ cells levels.

Natural killer cells (NKC) determination

Instituto Bernabeu’s RIF Unit, along the specialized IB Biotech technical support, has the necessary technology to determine the NK cells. These values determination is part of the specific and personalized protocol applied to our patients with repeated implantation failures and recurrent miscarriages.


Dr. Juan Carlos Castillogineacologist at Instituto Bernabeu.

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