The human body is in constant relationship with the outside world. Through different systems, it establishes a continuous communication to maintain balance, development and protection against possible external aggressions of the organism. One of them is the immune system, which constantly analyzes the presence of foreign agents in the body in order to eliminate them, but in the case of the fetus something different happens.

In this context, science notes with astonishment an exceptional situation: the privileged relationship that the pregnant mother adopts with her child. Being genetically different from her, the mother’s body adapts its immune response selectively to protect it instead of rejecting it, which is what might be expected.

The pregnant woman’s immune system recognizes something external to her (the fetus) that has a different genome and proteome, and modifies its usual method of eliminating all external elements to allow its development. In the case of transplants, the opposite occurs, the organism reacts by rejecting the transplanted organ because it has different proteins from those identified as its own by the recipient.

Maternal-fetal communication is especially relevant given its enormous complexity, both biochemical and genetic. This dialogue begins from the introduction of the seminal fluid into the woman’s body, so the father is also part of this interaction.

The first signals emitted by the seminal fluid already promote the beginning of an immunological adaptation. Here, the antigens subsequently expressed by the fetus and the succession of humoral and cellular mechanisms that the mother will ultimately bring to the fore, will outline an environment of homeostatic equilibrium. It is in this environment that the processes of immuno-tolerance will develop in order to protect the new, fragile and incipient life.

As we explained in previous articles, the embryo communicates its presence to its mother from the moment of fertilization.

The embryo modifies the mother’s immune system by secreting interleukins that interact with specific receptors of the mother, provoking a biochemical response that releases growth factors, survival factors, and leukemia inhibitory factor, making it possible for its cells to form part of the immune system in pregnancy.

The responsible antigen that triggers this initial “biochemical dialogue” between mother and child is the histocompatibility antigen HLA-G that promotes the protection of the incipient and fragile human life, different from that of its mother.

This antigen, HLA-G, determines a specific response from maternal T lymphocytes, which will defend it from cytotoxic mechanisms, such as the mother’s natural killer (NK) cells, which can put its normal development at risk.

Likewise, the mother responds to this dialogue, firstly, by limiting the cellular response, mediated by T helper lymphocytes, which constitute the initial defense system against foreign elements or pathogens.

Secondly, by intensifying the activity of Treg lymphocytes, which are in charge of preserving the integrity of the tissues themselves, protecting them from the aggressive action of the immune response.

And finally, by attenuating the action of NK cells, which promote cell lysis and cytokine production, and by inhibiting their hormonal activity, through the PIBF molecule, which exerts an anti-abortion effect.

In this way, the mother and the fetus are, at the same time, protected from possible external aggressions, while the mother’s body respects the growth and development of the fetus inside her womb.

In vitro fertilization can modify this balance, by suppressing the phase of activation by the seminal fluid and the relationship of the blastocyst with its mother established in its journey through the Fallopian tubes, the pathway of the uterus.

This admirable design of nature, supported by science, which changes its standards to protect the life of the human embryo even before its conception, contrasts with the current alleged “right to abortion.” That is to say, to act exactly in the opposite direction that nature indicates for the initial relationship of a mother with her son, oriented towards his protection. Nature accompanies and protects nascent life, and our obligation is to respect and promote it. There is no right to extinguish it in any case.


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