The smoke and mirrors behind HLA matching and NK cells activity assay – the “reason” and “cure” for unexplained implantation failure!

I was recently reading a blog post from Dr.Sher.  He discusses immunological implantation dysfunction and claims that it is a common cause of repeated, “unexplained” implantation failure. He says that due to immunological dysfunction the embryo will be destroyed by “malfunctional” NK cells and hence implantation failure ensues. He assures patients that such ruthless “killing” of your precious embryos by “crazy” NK cells can be prevented by some specific therapies.  I was startled to see the way that article is written without any sound scientific basis – a nicely concocted story without any evidence!

The link for that article is here: http://haveababy.com/fertility-information/ivf-authority/unexplained-infertility-and-ivf-failure

Before reading it, you must understand the meaning of two different words which are used frequently in that article – HLA and NK cells. HLA stands for Human Leucocyte Antigen. These are molecules which are present on the surface of almost all the cells of our body and help to protect us against infections.  They are also known as the major histocompatibility complex (MHC) . When our cells are infected by harmful microorganisms, their antigens are loaded on to the cell’s HLA molecules. These HLA molecules then carry the viral or bacterial fragments to the cell’s surface. Once they come to the surface of the cell, they present the microbial fragments to our body’s immune cells called cytotoxic T cells.  Cytotoxic T cells constantly scrutinize our body for foreign antigens (microbial fragments or any other protein which are not normally present in our body). They can recognize these foreign microbial fragments only when they are presented to them by the body’s own  HLA molecules. Once the cytotoxic T cells recognize that a particular cell is infected by a microorganism , it kills the cell , thus protecting our body from harmful microbes. Consider this analogy :  a thief (microbe) enters your home (cell). You need to tell the policemen (cytotocxic T cells) who are on surveillance duty that a thief is in your home. When the thief is not watching, you send one of your servants ( the HLA molecule) with information on a piece of paper (microbial fragment) outside your home , so that the police men gets notified about the thief and can protect you. This is the exact scenario but with a minute difference-our body’s policemen (cytotoxic T cells) destroy (sacrifice) the infected cell to save the nearby healthy cells – they burn the house down to kill the thief !

In order to evade our intelligent immune system some microbes prevent the HLA molecules from carrying the microbial fragments to the surface of the cell. This is analogous to the thief who prevents the servant from going out of the house with the piece of information about the thief. In such circumstances , Natural Killer (NK) cells come to the rescue. When an NK cell recognizes that a particular cell doesn’t express enough MHC molecules on its surface as it should, it just destroys the cell by suspecting a possible invasion. Amazing , right ?

In short,  HLA molecules and NK cells are components of our immune system which help to protect us against microbial invasion and other insults.  If this is so, how they are connected to implantation failure?

Our immune cells attack not only cells that express microbial antigens but all cells that express non-self antigens (proteins that are not normally present in our body). This is why transplanted organs from a non-compatible donor are attacked by our immune system , and this is why they are rejected. A donor is said to be compatible if he/she carries identical HLA molecules as that of the recipient. If the donor’s organ express non-identical HLA molecules , then cytotoxic T cells recognize these foreign HLA molecules and destroy the cells of the donated organ.  This is why HLA is also called Major Histocompatibility (Histo =tissue) Complex (MHC).  It is only after checking the HLA compatibility between the donor and the recipient that organ donations are performed.

If this is the case, how does a fetus which carries half of its genes from its father (and hence different HLA molecules on its cells’ surface) survive the maternal immune system attack? In order to explain this , a hypothesis was proposed: that the uterus is an immunologically privileged site, and for a fetus to be not rejected by the maternal immune system , it has to carry different HLA antigens on its surface , and this helps the maternal immune system to develop tolerance to the fetus. This is exactly the opposite of the organ transplantations scenario , where the donor and recipient’s HLAs should match. As a result , when husband and wife have excessive similarity in their HLA molecules ( a high degree of HLA matching) and suffer from infertility , they are treated with a variety of immune therapies , to try to stop the maternal immune system from rejecting the fetus!

In his post , Dr. Sher writes:

“We diagnose alloimmune ID ( immunological dysfunction) by testing the male and female partners for the degree of sharing of genetic markers , known as of as DQa and HLA. A sufficient degree of matching clinches the diagnosis. We also test the embryo recipient for Nka in an attempt to measure the relative severity of the problem. This is because once the NK cells in the uterine lining are activated and the cytokine balance is disrupted, the situation is grave and will remain so (or worsen) unless the NKa cells are medically deactivated (down-regulated) at least 1 week in advance of the embryo(s) reaching the uterus”.

He obviously loves medical jargon , and talks about DQa and HLA, in order to impress patients ( and doctors !) as to how well-informed and erudite he is . DQa is just one sub-class of HLA. HLA is divided into class I and class II. Class I consists of HLA A, B, C and also HLA E, F, G. Class II consists of HLA DQ, DR and DB. Now what is the connection between HLA and NK ( natural killer) cells? How does HLA compatibility between the partners triggers NK cell activity which kills the embryo ?

 I have no clue – and neither does he, but he cloaks his ignorance in a lot of medical gobbledygook.

I need to explain here some scientifically proven facts about HLA expression in the human embryo,  and human NK cells:

Ø  The part of the human embryo which comes in contact with the maternal immune system is its trophoblast cells - more specifically , the external villus trophoblast (EVT).

Ø  These EVTs do not express class II HLA molecules (DR, DQ, DB) at all. They do not express highly antigenic class I HLA molecules (HLA A, HLA B). The EVT cells only express HLA G, E and C.

Ø  You must note that most of the HLA matching between you and your partner is done for HLA A, HLA B, HLA DQ.  Even if there is a high degree of matching between you and your partner for these molecules , this does not have any significance as regards your fertility, because of the simple fact that these molecules are not expressed at all in the cells of your embryos which come in contact with the maternal immune system!

Ø  It was believed (but never proved!) that if partners carry similar HLA molecules, the maternal immune system develop toxic T cells that might destroy the embryo . However, there is no proof that T cells attack human embryo.

The NK cell is another tall tale. I will enlist some facts about human NK cells below:

Ø  There are two types of NK cells: CD56 ^bright+ CD ¹⁶⁺ and CD56 ^dim+ CD¹⁶⁺. CD56 ^bright+ CD ¹⁶⁺ is the cell type predominantly present in the uterus.  This does not have significant cytotoxic activity.CD56 ^dim+ CD¹⁶⁺ is the NK cell type present in peripheral blood and has extensive cytotoxic activity.

Ø  The NK cell activity assay is mostly performed with the NK cells collected from the peripheral blood of infertile women . The NK cells present in peripheral blood do not reflect anything about the NK cell activity in the uterus. In other words, tests performed on peripheral blood NK cells cannot be used to draw conclusions about the uterus NK cells ! This testing is completely flawed.

Ø  NK cells activity assay is performed by measuring its ability to kill K562 cells. K562 cells are cancer cells , and they do not express the HLA molecules (HLA G, E and C.) that are expressed on the human embryo’s extravillous trophoblast. When K562 cells are scientifically manipulated to express HLA E or G, the  NK cells failed to kill the K562 cells!

Ø  When human trophoblast cells are grown in vitro (in laboratory environment) they do not express the same HLA molecules which they express in vivo (in the uterus). Also, even NK cells in vitro do not kill trophoblast cells!

The above scientifically proven facts I have painstakingly collected from the scientific literature emphasize only one thing – HLA compatibility between you and your partner and/or NK cell “malfunction” cannot kill your embryos It is wise to avoid tests used to “diagnose” them and therapies intended to “treat” and “cure” them. I sincerely wish that infertility specialists don’t make the vulnerable and desperate infertile patients’ condition even worse by making a mountain out of a mole hill. When a doctor meets a patient who suffers from unexplained infertility or repeated implantation failure, it is much more honest and humane to say ‘I do not know’ than to sell them false hope. 

Please read these articles for detailed info on this subject: 

http://myselfishgenes.blogspot.de/2013/03/does-hla-sharing-cause-miscarriage.html

http://myselfishgenes.blogspot.de/2014/07/tests-for-nk-cells-and-cures-for.html