Microchimerism: other cells living in our body

Most of us know that during pregnancy, the mother is transmitting different substances such as food and oxygen to the fetus. They allow the latter to nourish and survive. In this transmission, the fetus receives cells from the mother, which participate in its survival, growth and maturation. But since the late nineties 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 and interact with those of the mother in the mother's body. 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 It has cells of other individuals in its organism , having in its interior a small percentage of DNA different from its own. These cells establish a relationship with the genetically characteristic of the subject, being able to create a link between both cell types, which leads to both positive and negative consequences.

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

The natural microchimerism

Although the first signs of this phenomenon were discovered through the performance of transplants in animals, the microchimerism that most often occurs in nature between two multicellular organisms is the one that 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 body of the other and become integrated into it. It is suspected that it has a greater incidence than thought and even some experts consider that it occurs in all pregnancies. Specifically, it has been found that from the fourth week of gestation and Fetal cells can be found in the maternal organism , and in general it is considered that from the seventh week it can be identified in all pregnancies.

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

The cells from the other organism come to be integrated into the structures and tissues , including the nervous system. Different experts have wondered about the effect that these cells can have on the behavior, being possible that it is also associated with the emergence of affection between mother and child. One could speculate on the fact that part of the DNA itself is in the other can imply a higher rate of protection at the behavioral level, generating a higher level of connection and the perception of greater similarity.

It is relevant the fact that it is not even necessary that the pregnancy comes to fruition for this cell exchange 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 with that of the baby.

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

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Effects on the mother

It can be logical to think that in the interaction that takes place between mother and child, it will be the cells of the mother that will provide beneficial effects to the baby, since the mother's organism is already formed and the baby's body is in the process of being trained. But the truth is that the transmission of cells by the baby to his mother also can have great effects on your health .

It has been proven, for example, that fetal cells usually contribute to healing wounds and internal injuries, as well as to participate in the reduction of symptoms of disorders such as pain in osteoarthritis both at the time of pregnancy and in the long 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 help to explain why women have a greater capacity for resistance and a longer life expectancy, noting that many women who had given birth and possessed these microchemical cells usually have a better hope of life. life (possibly due to an improvement of the autoimmune system, although this is mere speculation at the moment). It has also been detected that it reduces the likelihood of cancer and that tend to participate in tissue regeneration , observing its involvement in the recovery of cardiac or hepatic diseases.

However, microchimerism can also affect negatively.It has been observed that the immune system of some women react to these cells as if they were invasive, linked to the emergence of some autoimmune diseases. These are more common in the mother than in the fetus. They could also be linked to some types of cancer , although 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 organism of the future baby has a great importance for this. Interestingly, it is the microchimerism that has received less attention, focusing more on the effects of this transmission with the mother. A probable explanation for this is the difficulty of establishing differences between what the organism itself and the subject's cells achieve per se and the concrete influence of the maternal cells.

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

Acquired microquimerism

As we have indicated, microchimerism occurs naturally during pregnancy, this being the main form of existing microchimerism but also during this process it is possible to find this phenomenon in other types of situations, being able to talk about an acquired microquimerism .

We are talking about the performance of organ and tissue transplants or blood transfusions, in which a part or a product of a certain organism is inserted in another. The donated organ or blood contains the donor's DNA, which enters interacts with the body of the subject that receives it said organ . In this case the relationship is not symbiotic between individuals, since it is the one 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 the foreign DNA as something external that is invading and react by attacking, which would lead to the rejection of the organ, tissue or blood. That is why it is important to take into account the blood type and the compatibility between donor and recipient, as well as the use of medication that allows such rejection to not occur.

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

Bibliographic references:

• Carter, A. and Fuggle, S. (1999). Detection of microchimism 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 .; Salomon, 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.
• Quirós, J.L. and Arce, I.C. (2010). Natural microchimerism Is there a human with several genomes? Bibliographic review. Legal Medicine of Costa Rica, 27 (1). Heredia, Costa Rica.
• Rodríguez-Barbosa, J.I .; Domínguez-Perles, R .; del Río, M.L .; Peñuelas, G .; Valdor, R .; Source, C .; Muñoz, A .; Ramírez, P .: Pons, J.A. & Parrilla, P. (2004). Induction of tolerance in the transplant of solid organs. Gastroenterology and Hepatology, 27 (Suppl 4): 66-72. Elsevier
• Rowland, K. (2018). We are crowds. Aeon.