People who hang out in infertility forums will have heard about Natural Killer Cells.
For some they are a mysterious possible ‘cause’ of failed implantation or even miscarriage, for others they are ‘something that can be treated away with drugs’, and for others they are this unknown entity that might be ‘killing’ their fertility.
In fact, NK cells are protective, they are part of our defence system, they kill invaders, but they can also kill an embryo attempting to embed into the womb lining, if they sense it as an invader.
Why would they sense an embryo to be an invader? Well the simplest answer is - because it is an invader!
The real question is why is mom’s immune system not shutting down the NK cells? This is the normal way it works.
The immune activity of these NK cells is carried out by a bedazzling array of chemicals called cytokines, and just as in all aspects of happy human physiology the key factor here is ‘balance’.
When an embryo shows up in the womb it issues signals to the womb lining - sort of like “Hey mom, I made it, I’m here, feed me”.
An immune conversation takes place whereby the embryo begins to burrow into the endometrium using a series of inflammatory cytokines to assist it.
Once it settles in it needs to attract a blood supply - this also requires a series of inflammatory cytokines to be issues at the site.
So, all in all it is an inflammatory time for that portion of the womb.
This inflammation, mediated by various cytokines, which are messenger signals, result in the arrival at the site of implantation of a bunch of uterine Natural Killer Cells aka uNKC’s. Oh oh!
Well, no, this is all normal - uNKC’s are responsible for helping the embryo bed down and get settled in. Mainly they signal the local tissue to accept the embryo - or rather they provoke a response from the womb lining that sends a signal to somewhat suppress the local immune cells activity, so they don’t get too aggressive. In other words, a conversation takes place that invokes ‘immune tolerance’ of the invading embryo. Tolerance is the key word. Tolerance is another way of saying ‘balance’.
Incidentally, it is believed that all this inflammatory activity surrounding the embedding of the embryo is what causes the nausea in early pregnancy. This nausea may be unique in the world of women - it’s the only time nausea is wished for, welcomed and celebrated!
Once things settle down again in the womb, typically at the end of the first trimester, all this inflammation changes shape, moving from what we call a TH-1 state, to a TH-2 state. In simple terms this means it switches from being pro-inflammatory to being anti-inflammatory.
Interestingly it is this anti-inflammatory state that seems to be responsible for many of the positive effects’ pregnancy has on existing conditions, from endometriosis to various auto-immune conditions like Rheumatoid Arthritis.
The 2nd and 3rd trimesters typically take place with a Th-2 (anti-inflammatory) bias, and indeed baby is born with a heavily biased TH-2 immune system. This, by the way, is why breastmilk is really needed, it does what formula milk cannot do - provide the necessary bacterial colonisation to reactivate Th-1 immunity and thus bring balance to baby’s immature immune system. (Formula milk provides nutrition so baby can grow and not starve, which is fine, but it can’t provide the micro-biologically active component of breast-milk.)
So, let’s go back to these Natural Killer Cells in the womb. They are not the same as the NK cells in the blood, they have a different job. What does it mean then if your blood test shows elevated NK cells? What does it mean if a uterine swab shows elevated uNK cells?
Well, from a medical point of view it most likely means “Oh well, we don’t know why you have this going on, but to help you stop miscarrying, or to help you conceive, we are going to have to suppress your immune system so these things go away and you can get on with pregnancy.”
Now I can buy this, even as a natural fertility advocate I can see the point of using immune suppressing drugs to get the job done, so fair enough, this is an option, but my approach to it is to take steps to bring about balance earlier on - to remove or reduce the reasons why ones immune system may be ‘overactive’ in the first place. There are many different angles on this, with infection being only one, but there is always a common underlying factor and it is connected to the idea I mentioned above ‘tolerance’.
Specifically, in our gut we also have a system of tolerance, called oral tolerance, and this system concerns itself with informing the body about what foods to not reject mainly, and which foods to accept as harmless.
The key thing to understand here is that through a complex channel of communication from the gut to the brain, whatever state the gut is in gets reflected through out the body. If the gut’s system of oral tolerance is ‘lost’, i.e. of you have lost oral tolerance - then you will begin reacting to foods you should not ordinarily react to. Once this continues long enough the body wide systems of tolerance also begin to malfunction. In short uterine tolerance of the foetus is related to oral tolerance of food because the messengers that govern it are the same.
To close this out with an analogy that might allow for better understanding - imagine sleeping in a castle knowing the enemy is outside the gates but also knowing that the gates are well protected and have been for years. This allows you to sleep soundly. Now imagine the guards at the gates are missing or unable to guard properly - this would kinds affect your sleep wouldn’t it?
That’s the same for the body. A fully intact gut allows for a more secure feeling in the rest of the body - because the gut IS THE GATE, this is where most of the bad stuff can get in.
To stretch this analogy a bit more - if the gates have been unguarded for some time, then some enemy agents will get in and set up as sleeper agents inside the castle, ready to do damage. This is akin to infections. So even if you do beef up security at the gates, you then must go and seek out any sleeper agents.
This is the process of healing!
Everything is connected!