The baby came out - but his cells may have remained in the body

It turns out that many women carry fetal cells in their body from the period of pregnancy and that these cells can help restore tissues, but also incite the immune system against the body. It all started when doctors were trying to understand how a drug addict's liver regenerated itself without help

In 2002, Mrs. C (full name is not saved in the system) was on the verge of death. After a long life of hard drug use, she accidentally infected herself with the hepatitis C virus. The virus invaded C's liver, destroying a significant portion of it. Since the liver is responsible for treating a large part of the toxins in the blood, the medical predictions regarding the woman's future were grim. Her days, the doctors said, were numbered. C chose to refuse medical treatment, and waited for her death in battle. and waited. and waited. and waited.

But death was coming, and as the days passed, the sick woman began to feel better. This development shocked doctors, as the woman's liver cells were not supposed to be able to regenerate the liver. But this first surprise was marginal compared to the surprise provided by the in-depth examination, which showed that the new liver cells did not belong to the woman at all. The most obvious clue to this was that a large part of them were - male, with a small but prominent Y chromosome.

How do male cells reach one of the most important organs in a woman's body? And if they have already invaded the body, why would they choose to repair the damaged organ? And how can one explain the fact that the immune system did not attack them, as it was supposed to do with any other cell of foreign origin? The answers to these questions were only found when the doctors realized that these were not cells that invaded the body from the outside, but from the inside: these were the cells of the fetus that C carried in her womb almost twenty years ago.

How could the fetal cells leave the uterus and the placenta and reach the bloodstream? The answer is not entirely clear even today. Until the end of the twentieth century, it was common to think that the placenta was an impassable barrier - a wall in shape - to all cells in the body. On the one hand, it protects the fetus from the maternal immune system, which sees the infant as an invader and as a foreign body to everything. On the other hand, it also does not allow the embryonic cells to reach the mother's blood circulation and start creating small embryos in any tissue where they settle. Only towards the end of the century was the understanding reached that the placenta is actually very permeable to some of the fetal cells, which are able to leave the fetus and the placenta and spread in the mother's body.

The initial evidence came in 1996, when researchers were able to discover fetal cells in the body tissues of several mothers, even decades after pregnancy and birth. These cells were able to cross the placental barrier, reach the blood circulation and settle in the various tissues - the liver, the skin and more. After finding a suitable niche, the embryonic cells differentiated to adapt to their environment, thus becoming liver cells, skin cells, or any other type of cell suitable for the tissue in which they settled. The same thing happened to the body of Mrs. C, who experienced five pregnancies during her lifetime. The cells of one of the fetuses she carried managed to reach the blood circulation, and survive nineteen years after the pregnancy. The fetus, the researchers determined, saved the life of the one who gave it life in the first place!

In retrospect, it turns out that this gift is not unusual. In two studies conducted in 2002, fetal cells were found in the blood circulation of 30-50 percent of the women tested. According to these studies, almost half of the readers of this list, if they were pregnant, still carry the fetal cells in their bodies. And to the same extent, many of the readers of the list left several orphaned cells in their mother's body, before leaving it forever. According to the theory, these cells are ready to be called into action and repair the damaged tissues in times of need.

But, as with every subject and discovery, embryonic cells also have a good side and a bad side. The good thing is that the cells are apparently able to colonize different tissues and repair them when needed. This feature, preserved for many years in the mother's body, can explain why women live longer than men. The downside is that the fetal cells do not really belong to the mother's body, and as a result, the immune system may act against them.

The human immune system is similar to a wild guard dog - it attacks any intruder that enters its living space, without harming the owner himself. But, as in the old folk tales, if you let a dog taste human flesh even once, he will never obey again. Similarly, if the immune system recognizes human cells from an extracorporeal source and attacks them, it may go into a bad culture and attack the body that is consuming it: billions of killer cells will try to neutralize and destroy billions of other cells in the body, which are unable to defend themselves. This type of disease, in which the immune system rebels against the body, is called autoimmunity - an immune action against the self.

This idea, according to which the fetal cells provide the immune system with a motive to attack the body, fits well with the fact that women suffer from autoimmune diseases at a higher frequency than men - more than three times. Until now, it was thought that the women's immune system was simply more 'nervous', prone to severe paranoia attacks and occasionally rebelling and harming the body itself. Now they are beginning to understand that it is possible that the fetal cells that remain in the body after pregnancy stimulate the immune system to attack them, and from the moment it experiences the taste of human flesh, it may also attack the body that hosts it.

What is the moral? Is it better to avoid having children, and get rid of the danger of autoimmune diseases? of course not. Autoimmune diseases exist in men even without connection to fetal cells, and the whole theory linking autoimmune diseases and tissue repair to fetal cells has not yet been unequivocally proven.