06/03/2021

Isolation can affect defences and the brain

3 min
Barcelona's Via Laietana during last year's confinement: empty and with hotels, shops and restaurants closed.
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Pandemic management involves lockdowns, restrictions, and quarantines that lead to social isolation. We meet our friends and family much less often, and interpersonal distance, i.e. the space we leave with other people, has increased significantly. This distancing has been found to generate psychological discomfort and stress in many people, since we are a social species that instinctively seeks to be with other individuals. In addition, it has also been proposed that social isolation may indirectly influence many other biological processes. Benjamin M. Seitz and his collaborators, from several American universities and research centers, have theorized about the consequences that prolonged isolation can have on the functioning of the immune system and brain development, especially in children and adolescents.

As published in the journal Proceedings of the National Academy of Sciences of the United States, one of the multiple consequences of social isolation is the decrease in the contact we have with microorganisms in the environment, since we leave the house less and do not get as close to other people. This may lead to a decrease in the efficiency of the immune system, which would make us more susceptible to other infections, and could also alter brain development. The reasoning they put forward in their paper combines evolutionary and developmental aspects that, they explicitly say, need to be considered carefully, especially if this isolation is maintained for a longer period of time.

The maturation of the immune system

Regarding the immune system, they argue that we must take into account that people have been in contact with the microorganisms in the environment where we live since the beginning of our species. We share, therefore, a very long and intense history of coevolution with them. Coevolution is a phenomenon of mutual evolutionary adaptation that occurs between two or more species as a result of their reciprocal influence. In other words, the evolutionary changes that occur in one species act on the natural selection process of the other species with which it is in contact, and this selects processes of "counter-adaptation" that, in turn, also influence the first species. In the microorganisms that can affect us, natural selection favours the permanence of changes that allow them to better exploit the individuals they infect. In humans, on the other hand, as in all other mammals, this process has favoured the progressive maturation of the immune system in contact with microorganisms so that it can fight pathogens in the broadest and most effective way possible.

The immune system adapts throughout life to the pathogens in the environment, but the most important periods of maturation are childhood and adolescence. Contact with other children and adolescents, and also with adults who are not close family members, increases the repertoire of microorganisms with which they come into contact, most of the time without causing any disease. This prepares their immune system to cope efficiently in the future. Therefore, if social isolation is prolonged over time, we must be aware of the possibility of an increase in the incidence of other diseases due to a decrease in the efficiency of recognition of the immune system.

The nervous system and microbes

Similarly, it is known that the nervous system, and more specifically the brain, also matures influenced by certain microorganisms with which we have co-evolved, such as those that form part of the intestinal microbiota. It has been shown that a balanced intestinal microbiota favours a better functioning of the brain throughout life and a more ideal maturation of this organ during childhood and adolescence. Contact with other people promotes an enrichment of the intestinal microbiota through the microorganisms that we preconsciously exchange when we touch each other. In addition, this exchange promotes a more balanced development of the nervous system.

In this context, Seitz and his collaborators warn of the possible impact that reducing exposure to the outside microbial world may have on what they call "the quarantine generation", which will depend on the duration of social isolation due to lockdown and restrictions and on the developmental stage of each person. Still, as they say in the study, the ultimate impact, if any, will only be known for certain when comparative studies of the gut microbiota of infants, children and adolescents are made in relation to the time they have spent in lockdown or social isolation.

David Bueno is director of the UB-Edu1st Chair of Neuroeducation

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