2013-02-10 15:22:19
“Sleeping” viruses inserted into the genome are capable of reactivating.
From the very origin of life, organisms emerged capable of taking advantage of others, undesirable parasites that have accompanied us to this day and that cause a good number of diseases and miseries to animals and plants. One of the most successful parasites are viruses. Among them, one of the most problematic classes is retroviruses, a class to which AIDS viruses and some other leukemia-causing viruses belong.
The genome of retroviruses is made up of ribonucleic acid, RNA, instead of the more common deoxyribonucleic acid, or DNA, which we all store in our cells. To reproduce, once inside infected cells, these viruses need to copy their RNA genome into a DNA genome, which must then be inserted into the genome of a cell, at any location on one of its chromosomes. Once inserted, the virus genes produce RNA and proteins that are automatically assembled to give rise to new viral particles that will be expelled outside where they will spread and try to infect other cells.
If all goes well for the virus, the infected cell will eventually die. But if something goes wrong, and the virus’s genome doesn’t work entirely correctly, the virus’s genome will be permanently inserted into the cell’s. Sometimes, this can happen in germline cells, that is, in reproductive cells, which will mean that the virus genome becomes part of the genome of the infected species and reproduces with it as one of its genes. From that moment, the parasite becomes part of the very organism that it previously parasitized. The parasitism relationship becomes a symbiosis.
INHABITANTS OF THE GENOME
Sequencing and studying the genomes of several species, including humans and mice, has revealed that the genomes generally contain multiple retrovirus insertions. The genomes of these former parasites are in a “dormant” state, and do not normally produce infectious viral particles.
The genes of these retroviruses are not the only “sleeping” genes. About seven years ago, researchers managed to make chicken embryos grow teeth, “awakening” a gene that had been “in hibernation” since the lineage of birds separated from that of dinosaurs. It is possible, therefore, that retroviruses inserted into our genome can “wake up” in some circumstances, which could resurrect old infectious viruses and cause us problems. Is this possible?
In fact, recent research has shown that some of the retrovirus genes inserted into the mouse genome were activated if the animals suffered from cancer, autoimmune diseases, or bacterial infections. These three conditions have in common that they all affect the functioning of the immune system. Both infections, such as cancer, and, of course, autoimmune diseases, in which the immune system attacks the body itself, are characterized by an immunosuppressed state, which favors them. Could a more intensely immunocompromised state allow the resurrection of all retrovirus genes and produce infectious viral particles?
THEY LIVE!
To find out, a team of European and American researchers has used deeply immunosuppressed genetically modified mice in their studies; incapable of producing antibodies, necessary to bind to viruses and prevent their infection, and incapable of producing T lymphocytes, necessary to eliminate virus-infected cells. Researchers demonstrate that completely immunosuppressed mice are capable of producing infectious mouse leukemia viruses, which can reproduce perfectly in mouse cells and end up inducing leukemia. Likewise, other different retroviruses, also inserted into their genome, can appear in these animals.
Scientists are also studying whether other types of immunodeficiencies could stimulate the “resurrection” of retroviruses, and conclude that it is mainly the immunodeficiencies that prevent the generation of antibodies that stimulate it the most. As we know, antibodies are serum proteins produced by lymphocytes that are specialized in binding and neutralizing specific microorganisms, which also include retroviruses.
It is also known that the organisms of the intestinal flora have a modulating effect on the immune system, which tolerates them and allows symbiosis with them. Well, immunodeficient mice, but free of intestinal flora, which can be produced under sterile conditions in the laboratory, see their ability to resurrect their endogenous retroviruses diminished or prevented, which indicates that the intestinal flora can exert an important activating effect on these. virus in case of sudden immunosuppression.
These intriguing results, published in the journal Nature, suggest that our genomes are not just ours; They are infiltrated by potential retroviruses kept at bay thanks to the correct functioning of the immune system. Such retroviruses could “resurrect” (vade retro!) if the opportunity presented itself and cause serious health problems, including cancer. One more reason to take care of our immune system with a healthy diet and frequent physical exercise, which is the cheapest private healthcare (intimate, I would say) that can be found.
WORKS BY JORGE LABORDA.
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