Microchimerism: cells of others living in our body

Most of us know that during pregnancy, the mother transmits different substances such as food and oxygen to the fetus. They allow the latter to nourish itself and survive. In this transmission, the fetus receives cells from the mother, which participate in its survival, growth and maturation.

But since the end of the 1990s it has been detected that the transmission of genetic information is not unidirectional, but it is possible to find that the baby's cells also pass through and interact with the mother's in the body of this. In other words, something called microchimerism occurs.

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Microchimerism: cells in a foreign body

The concept of microchimerism refers to that situation in which a person or creature has cells from other individuals in its body, having within it a small percentage of DNA different from its own. These cells establish a relationship with the genetically specific cells of the subject, being able to create a link between both types of cells, which gives rise to both positive and negative consequences.

Microchimerism occurs both in humans and in other animal species.such as rodents or dogs. It is a mechanism that has probably existed for millions of years, although it was discovered at the end of the last century.

Natural microchimerism

Although the first indications of this phenomenon were discovered through the performance of transplants in animals, the microchimerism that most frequently occurs in nature between two multicellular organisms is that which occurs during pregnancy.

During pregnancy, mother and child are connected by the umbilical cord and the placenta, and through this connection they exchange some cells that pass into the other's body and integrate into it. It is suspected that it has a higher incidence than thought and some experts even consider that it occurs in all pregnancies. Specifically, they have found that from the fourth week of gestation fetal cells can be found in the maternal body, and it is generally considered that from the seventh week it can be identified in all pregnancies.

This relationship between mother and child cells is not temporary and is lost after a few months or years after delivery: has observed the presence of the son's cells in the mother's body for more than twenty years after giving birth to light. These cells spread throughout the body, being found in the heart, liver or even brain and interacting with the subject's own cells.

Cells from the other organism become integrated into the structures and tissues themselves, including the nervous system. Different experts have wondered about the effect that these cells can have on behavior, and it may also be associated with the development of affection between mother and child. It could be speculated that the fact that part of one's own DNA is in the other may imply a greater protection rate at the behavioral level, generating a higher level of involvement and the perception of greater likeness.

It is relevant the fact that it is not even necessary for the pregnancy to come to fruition for said exchange of cells to take place: even in women who have lost the baby the existence of cells with a different DNA has been found, which seems to correspond to that of the baby.

The studies carried out so far have generally been carried out on mothers who have given birth to male children. It is not that microchimerism does not happen between mother and daughter, but it is much easier to locate cells with the Y sex chromosome in a female body instead of trying to differentiate two cells xx.

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Effects on the mother

It may be logical to think that in the interaction that occurs between mother and child, it will be the mother's cells that provide beneficial effects to the baby, as the mother's body is already formed and the baby's is in the process of training. But the truth is that the transmission of cells from the baby to her mother also can have big effects on your health.

It has been found, for example, that fetal cells often help heal wounds and internal injuries, as well as participate in the reduction of symptoms of disorders such as pain in osteoarthritis both during pregnancy and in the long term term. It also improves the immune system and facilitates the development of future pregnancies.

It has also been proposed that the presence of these cells may contribute to explaining why women have a greater ability to resistance and greater life expectancy, observing that many women who had given birth and possessed said microchimeric cells They usually have a better life expectancy (possibly due to an improvement in the autoimmune system, although this is mere speculation due to the moment). It has also been detected that it reduces the probability of cancer and that tend to participate in tissue regeneration, observing its involvement in the recovery of heart or liver diseases.

However, microchimerism can also have a negative effect. It has been observed that the immune system of some women reacts to these cells as if they were invaders, being linked to the emergence of some autoimmune diseases. These are more common in the mother than in the fetus. May also be linked to some types of cancer, despite the fact that its existence itself is a protective factor against this type of disease.

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Effects on the baby

The transmission of cells from the mother makes the body of the future baby has great importance for it. Curiously, this is the microchimerism that has received the least attention, focusing more on the effects of this transmission on the mother. A probable explanation for this is the difficulty of establishing differences between what the body itself and the subject's cells achieve per se and the specific influence of the maternal cells.

It has been detected that the presence of maternal cells in the body of the son or daughter helps, for example, diabetic children to fight his condition. On the other hand, said transmission has also been linked to the emergence of diseases such as severe immunodeficiency, neonatal lupus syndrome, dermatomyositis and biliary atresia.

acquired microchimerism

As we have indicated, microchimerism occurs naturally during pregnancy, this being the main form of existing microchimerism but in addition to during this process it is possible to find this phenomenon in another type of situations, being able to speak of an acquired microchimerism.

We are talking about organ and tissue transplants or blood transfusions, in which a part or a product of a certain organism is inserted into another. The donated organ or blood contains the donor's DNA, which enters and interacts with the body of the subject that receives said organ. In this case, the relationship is not symbiotic between individuals, since it is the person who receives the donation who receives the advantages and disadvantages of this phenomenon.

However, this type of microchimerism has its risks, since the body can recognize foreign DNA as something foreign invading it and react by attacking, which would lead to rejection of the organ, tissue or blood. That is why it is important to take into account the type of blood and the compatibility between donor and recipient, as well as the use of medication that prevents such rejection from occurring.

For this, the administration of drugs that reduce the role of alloreactive T cells (that is, the lymphocytes that react to the presence of DNA other than their own), so as to facilitate the emergence of tolerance to graft. A common way to do this is to inhibit the replication of these lymphocytes.

Bibliographic references:

• Briefcase. and Fuggle, S. (1999). Detection of microchimerism after blood transfusion and solid organ transplantation: A delicate balance between sensitivity and specificity. Transplantation Reviews, 13, 98-108.
• Khosrotehrani, K.; Johnson, K.L.; Cha, D.H.; Solomon, R.N. & Bianchi, D.W. (2004). Transfer of fetal cells with multilineage potential to maternal tissue. Journal of the American Medical Association 292(1): 75-80.
• Quiros, J.L. and Arce, I.C. (2010). Natural microchimerism Are there humans with several genomes? Bibliographic review. Legal Medicine of Costa Rica, 27 (1). Heredia, Costa Rica.
• Rodríguez-Barbosa, J.I.; Dominguez-Perles, R.; del Río, M.L.; Penuelas, G.; Valdor, R.; Source, C.; Munoz, A.; Ramírez, P.: Pons, J.A. & Grill, P. (2004). Tolerance induction in solid organ transplantation. Gastroenterology and Hepatology, 27 (Suppl. 4): 66-72. Elsevier.
• Rowland, K. (2018). We are multitudes. Aeon.