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Natural Killer Cells: What are they and How do they Affect Fertility Treatment?

Many women who have auto-immune, hyper-allergenic sensitivities, and/or conditions that cause excessive inflammation may have an hyper-active immune system-- causing them to experience implantation failures, chemical pregnancies, and even miscarriages. Natural killer (NK) cells are a symptom of this hyper-active immune system.

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Hello, I'm Dr. Norbert Gleicher. I'm the medical director chief scientist at the Center for Human Reproduction. Today's topic is an immunological one. I want to talk to you a little bit about so-called "NK" or natural killer cells. And the reason I want to talk to you about the subject is because it has kind of become a little bit overblown or maybe I should say quite a lot overblown in its importance in our field. And let me explain to you why we think that to be the case. Immunology, as we have been presenting in our video library and in our newsletter and in many publications from scientists here at the center, immunology is very important for reproductive success. The reason for that is that the little embryo that is trying to implant is really like a little organ transplant from the partner( from the male partner) and if a woman were to receive such an organ transplant from her partner, she would automatically reject a mini kidney transplant for example, yet a woman who has a normally functioning immune system will not reject that little embryo that is trying to implant. And though we still do not completely understand why that is, it in recent years has become quite clear that the principal reason why that little embryo, in most cases, succeeds in implanting and in growing without being attacked by the maternal immune system as she would if she got from her partner kidney transplant or a liver transplant, the reason is that apparently the embryo communicates once it enters the endometrial cavity with the maternal immune system and says two things. It first of all says,"Hey, hi, I'm here!" and secondly, it says, "Please let me in!" And in response, the maternal immune system (if it is a normally functioning immune system) kind of feels that embryo out to determine whether it's a good a healthy embryo and if it is, the immune system lets that embryo in--allows that embryo to implant by reprogramming itself from "rejection" to "tolerance." In other words, a specific (what is called, "tolerance pathway") is induced by the mother's immune system that allows that one embryo to pass the controls that otherwise reject invaders and allows it to implant. Now, that reprogramming of the maternal immune system does not work well in women whose immune system is already running a little hyperactive-- meaning in women who have autoimmune problems, in women who are hyper allergenic (who are kind of allergic to everything that's around them), in women who have evidence of inflammation. In all of these conditions, the immune system works already a little bit over time. And immune systems that are hyperactive don't reprogram themselves very well. And so if that embryo is not trying to implant, that immune system still sees it as "foreign" and still attacks it and often rejects it. And there's consequences in those women we find more frequently: what is called implantation failure, early pregnancy losses, so-called chemical pregnancies, and even miscarriages at later stages. Now why is all of this important since I just want to talk to you about NK cells? Well, the answer is that many of our colleagues. in our opinion, put too much emphasis on NK cells or for that matter even an antiphospholipid antibodies or other supposedly reliable markers of immune problems. And let me explain what I mean by that. If a woman has increased in NK cells, that is a sign of a hyperactive immune system. If a woman has abnormal autoimmune findings and testing that too is a sign of a hyperactive immune system. If a woman has elevated inflammatory markers, that, as I already said before, is also a sign of a hyperactive immune system. The difference between how we view these findings and how many of our colleagues view these findings is that we do not believe that NK cells make pregnancies be miscarried or that antiphospholipid antibodies are the cause for miscarriages. What we believe is that they are all just markers of a hyper active immune system and women who have a hyperactive immune system then have difficulty with implantation and with pregnancy maintenance. So we are not looking for one sign, like NK cells or another sign like antiphospholipid antibodies, we are looking for a panel of tests which all indicate that the woman has a hyperactive immune system. And if she does, we assume that she will attack that embryo that is trying to implant and that we need to calm down her immune system. And therefore we do not put special emphasis on NK cells versus some other findings. We are looking on a much broader scale for evidence of hyperactive immune systems and intervene in that regard. Thank you.

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