Microchimerism: cells of others living in our body

This phenomenon occurs when several cells survive inside an organism to which they do not belong.

Most of us know that during pregnancy, the mother transmits different substances such as food and oxygen to the fetus. They allow the fetus 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 1990s it has been found that the transmission of genetic information is not unidirectional; it is possible to find that the baby's cells also pass and interact with the mother's cells in the mother's body. In other words, something called microchimerism occurs..

Microchimerism: cells in someone else's body

The concept of microchimerism refers to the situation in which a person or creature has in its organism cells of other individuals. has in its organism cells from other individualsThese cells establish a relationship with the subject's own genetic cells, creating a link between both types of cells. These cells establish a relationship with the genetically own 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 in humans as well as in other animal species, such as rodents or dogs.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 transplants in animals, the microchimerism that most frequently occurs in nature between two multicellular organisms is that which occurs during pregnancy.

During gestation, mother and child are connected by the umbilical cord and the placenta, and through this connection they exchange some cells that pass into each other's organism and are integrated into it. It is suspected to have a higher incidence than thought and some experts even consider that it occurs in all pregnancies. Specifically, it has been found that as early as the fourth week of gestation, fetal cells can already be found in the fetus. fetal cells can be found in the maternal organism, and it is generallyIt is generally 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 in the mother's body has been observed up to more than twenty years after giving birth. These cells spread throughout the organism, being found in the heart, liver or even the brain and interacting with the subject's own cells.

The cells coming from the other organism become integrated into one's own structures and tissues, including the nervous system.including the nervous system. Different experts have wondered about the effect that these cells may have on behavior, and it is possible that it is also associated with the emergence of affection between mother and child. One could speculate that the fact that part of one's own DNA is in the other may imply a higher rate of protection at the behavioral level, generating a higher level of bonding and the perception of greater similarity.

It is relevant that it is not even necessary for the pregnancy to come to fruition for such an exchange of cells to occur: even in women who have lost the baby cells with a different DNA, which seems to correspond to that of the baby, have been found.

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

Effects on the mother

It may be logical to think that in the interaction that takes place between mother and child it will be the mother's cells that provide beneficial effects to the baby, since the mother's body is already formed and the baby's is in the process of formation. But the fact is that the transmission of cells from the baby to the mother can also have great effects on the baby's health. can also have great effects on the baby's health.

It has been shown, for example, that fetal cells often help to heal wounds and internal injuries, as well as participate in the reduction of symptoms of disorders such as osteoarthritis pain 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, and it has been observed that many women who have given birth and have these microchimeric cells tend to have a better life expectancy (possibly due to an improvement in the autoimmune system, although this is mere speculation at the moment). They have also been found to reduce the likelihood of cancer and to tend to participate in tissue regenerationIt has been observed to be involved in the recovery of cardiac or hepatic diseases.

However, microchimerism can also have a negative effect. It has been observed that the immune system of some women react 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. They may also be linked to some types of canceralthough their existence in itself is a protective factor against this type of disease.

Effects on the baby

The transmission of cells from the mother to the organism of the future baby is of great importance for the baby. Curiously, this is the microchimerism that has received the least attention, focusing more on the effects that this transmission has on the mother. A probable explanation for this is the difficulty of differentiating between what the subject's own organism and cells achieve per se and the concrete influence of maternal cells.

It has been found that the presence of maternal cells in the son's or daughter's organism help, for example, diabetic children to fight their condition. fight against their condition. On the other hand, such 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, being this the main form of existing microchimerism, but in addition to this process it is possible to find this phenomenon in other types of situations, and it is possible to speak of acquired microchimerism..

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 into another. The donated organ or blood contains the donor's DNA, which enters and interacts with the body of the recipient. interacts with the body of the organ recipient.. 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 may recognize foreign DNA as something external that is invading it and react by attacking and react by attacking it, leading to rejection of the organ, tissue or blood. This 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 to prevent such rejection.

This should be done by administering drugs that reduce the role of alloreactive T cells (i.e. lymphocytes that react to the presence of DNA other than their own), so as to facilitate the emergence of tolerance to the graft. A common way to do this is to inhibit the replication of these lymphocytes.

Bibliographic references:

• Carter, A. 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.; 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. & Arce, I.C.. (2010). Natural microchimerism: Do humans with multiple genomes exist? Literature review. Medicina Legal de Costa Rica, 27 (1). Heredia, Costa Rica.
• Rodríguez-Barbosa, J.I.; Domínguez-Perles, R.; del Río, M.L.; Peñuelas, G.; Valdor, R.; Fuente, C.; Muñoz, A.; Ramírez, P.: Pons, J.A. & Parrilla, P. (2004). Tolerance induction in solid organ transplantation. Gastroenterology and Hepatology, 27 (Suppl. 4): 66-72. Elsevier.
• Rowland, K. (2018). We are multitudes. Aeon.