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Viruses trick the immune system by using friendly bacteria as a disguise
Last reviewed: 30.06.2025
Gut bacteria maintain peaceful relations with our immune system. Some viruses have managed to turn this to their advantage: they fly under the immune system’s radar, literally riding on friendly bacteria and using them as camouflage.
It is no secret that without bacterial microflora, a person would not survive a day. Most microorganisms that constantly "rent" living space in our body pay for it with services that are not at first glance unnoticeable, but irreplaceable. For example, the largest bacterial diaspora - gastrointestinal microflora - helps us digest food, supplies us with important nutritional components of its own production. In addition, microflora helps repel attacks of pathogenic bacteria and helps cleanse the body of harmful substances.
It is clear that friendly bacteria must be able to negotiate with the immune system so that it does not attack them. Over thousands of years of cohabitation, our immune system has learned to distinguish friendly bacteria from enemy bacteria. It turned out that some viruses decided to take advantage of this. One of the two articles published in the journal Science talks about the polio virus, which enters the body with the help of gastrointestinal bacteria; the second article “blames” the mouse breast cancer virus (MMTV) for the same thing. In both cases, scientists eradicated the bacterial microflora in mice with antibiotics, and then looked at how this affected the infectious properties of the viruses.
In the first case, poliovirus infected animals twice as badly as in the presence of bacteria. The same was shown for MMTV. Moreover, the researchers checked how the transmission of the mammary cancer virus from mother to child would occur. This virus is transmitted with mother's milk, but if the mother and child did not have any intestinal microflora, the child showed resistance to the virus. However, as soon as bacteria appeared in the child's intestines, the body was open to the virus.
The cell wall of bacteria is made up of lipopolysaccharide molecules, which act as a kind of ID card for friendly microorganisms. The bacteria show their “credentials” to immune cells, which triggers a chain of reactions that suppress the immune response to the presence of these bacteria. So, according to the authors of the articles, viruses literally sit on top of bacteria: covered with bacterial lipopolysaccharide, they evade the immune attack.
It is possible that the polio virus penetrates the human body in a similar way. However, it is unclear what to do in this regard: it is not necessary to eradicate intestinal microflora as a preventive measure, so as not to suddenly get the poliovirus!