crofty asked: So theres a few of you out there getting an NK Biopsy - I have no idea what that is or what it's for??? can someone fill me in??
Here's an overview of immunology and NK cells. The immune system does go on to be much more fascinating than this account of the highlights.
There are many different types of white blood cells that participate in your immune system. Each has its own particular way of patrolling the body and of responding to nasties. Although they're called white blood cells, many get permission to leave the blood****** and patrol through the rest of your body looking for trouble. The three most popular white blood cells are:
* Macrophages (big eaters) wander around your tissues eating rubbish (bacteria and damaged bits of cells). Their keep things looking clean and tidy. They can often deal with little problems without needing specialist T or B cells to wade into the fight.
* B cells make antibodies to fight things that are found outside the cells of your body. Mostly this involves killing or neutralising things that are in the blood******. Other body locations that are not inside cells include breast milk and the inside of your intestines. B cells make antibodies that are secreted into these locations too. (B stands for Bursa of Fabricius, which is the location of B cell kindergarten in birds. In people and other mammals B cells grow up in the Bone marrow. Handy that it also begins with a B.) But some nasty things prefer to live inside your body's cells which generally puts them out of a B cell's reach.
* T cells attack things that are inside your cells. Mostly this involves destroying cells that have been hijacked by viruses that have taken up residence inside them. (T stands for Thymus. The thymus is T cell kindergarten and is located on top of your heart. It is not related to the thyroid which is at the front of your throat/neck.)
Every cell in your body holds up a flag identifying itself as part of you (these are tissue-type markers that need to be matched for some transplants, they are also called MHC proteins). T cells inspect these flags for ones which aren't quite right which identifies that the cell has gone bad (eg. virus infection makes a slightly wrong flag and a mismatched transplant has a completely wrong flag). If T cells find something wrong then they seek permission to become armed and to fight/kill whatever they have found. But some viruses realise that if they make their hijacked cells hide their flags then they're completely hidden from T cells. To stop things hiding this way we need another white blood cell - NK cells.
NK cells patrol the body looking for cells that aren't showing enough of the right flags. They go about armed and ready to kill, which is why they were named Natural Killer cells. Your healthy cells have to quickly show their flags and give the secret handshake in order to cancel the NK cell attack. The NK cell then moves on to challenge the next cell it finds.
If your embryo was a clone of you (an identical twin), then the immune system wouldn't care about it. But your embryo is only half like you, and half like the genetic father. This means that if any of your T or B cells were to see it they would probably like to attack it for looking like the father. This is the issue for blood-type positive (Rh+) babies with blood-type negative (Rh-) mothers. The first such baby remains hidden from the mother's immune system during the pregnancy, but events during birth usually immunise the mother against that blood type, so any subsequent Rh+ babies will be attacked by the mother's immune system while in utero.
Another consequence of the embryo only being genetically half-like you means that it might be a bit too slow at cancelling an NK cell attack, by having not enough of the preferred flags, and by being a bit clumsy at the handshake.
It's reasonable to suppose that one reason why embryos don't implant is because the immune system is actively fighting it. The immune system isn't supposed to examine embryos, but sometimes cells like to go over and above their job description. In the uterus, NK cells are more common than T and B cells. Their numbers and activity seem to be greatest right when an embryo would like to implant, so NK cells are the prime suspects for this type of implantation failure. They have motive (genetic half-likeness), means (NK cell activity) and opportunity (right place at the right time).
Uterine biopsies for NK cells are usually done at CD21 so as to get a picture of what's likely to be happening at implantation time. Both the number and activity (how good they are at killing) of the NK cells can be assessed. Activity might be more important than number. Some places offer a blood test, also done on or around CD21, to assess NK cell activity.
If the tests indicate that NK cells are being overenthusiastic the treatment is to take drugs to suppress your immune system to give the embryo a chance to implant. Suppression continues through the first trimester. After that the embryo should be more robust to surviving little attacks and the pregnancy itself should be doing its own immunosuppression. This natural immunosuppression is why many autoimmune diseases go away during pregnancy - but they return afterwards.
Treatment also includes blood thinners (e.g. aspirin or Clexane/heparin). I'm not sure of the reason for including this in NK cell protocols, but following are a couple of possibilities.
* If a couple of really eager white blood cells decide to have a go at the embryo despite the immunosuppression, the resulting inflammation may recruit platelets and start causing blood clots, which isn't good for the developing bub, so blood thinners will minimise that potential for damage.
* IVF for women with anti-phospholipid antibodies is more successful when treated this way. Women with NK cell issues are more likely to have anti-phospholipid antibodies. Phospholipids form part of the outside of every cell in the body (and they make some of the insides too).
Even if specialists are right about the immune system being involved in rejecting the embryo, but wrong about the particular cells responsible, the treatments they use basically covers all the bases.