Immunity works according to the season 24.05.2015

When we talk about the biological clock, we usually mean the daily or circadian rhythms, which depend on the change of day and night. However, our biological clock is not limited to circadian rhythms alone. For example, there are physiological processes that follow the monthly cycle, and the most famous example is, of course, the menstrual cycle.

But there are clocks with an even longer period - in an article in Nature Communications, a group of researchers from Cambridge writes about the annual cycle of activity of some immune genes. In the laboratory of John Todd (John Todd) for some time they were engaged in the daily activity of the ARNTL gene, which suppresses inflammation, and as it turned out, at different times of the day it is "active" in different ways - at least in mice. At the same time, the researchers participated in an international project called BABYDIET, whose goal was to find out how the presence or absence of certain substances in the diet affects the development of children in the first year of life. For the project, blood samples were taken many times for a long time, so in the end the idea arose to check whether the activity of the ARNTL gene also changed depending on the season.

Indeed, in humans, ARNTL was most active in summer and least active in winter. Subsequently, it turned out that 23% of the genes have seasonal activity, and among them were those whose rhythmic activity has long been known, and those that have not yet been noticed in any "clockwork". (It is worth emphasizing that 23% do not refer to the full set of human genes in general, but only to some.) And just the inflammatory genes are most active in winter, that is, when the anti-inflammatory ARNTL falls asleep.

The results were compared with data from other large clinical trials in other countries. It turned out that the same genes in the inhabitants of Australia work the other way around, which is understandable - after all, in the southern hemisphere, compared to the northern hemisphere, winter and summer change places. On the other hand, seasonality in the activity of genes among the inhabitants of Iceland was disordered, irregular - perhaps due to the polar days and nights. But for those who live in the African Gambia, the annual cycle of genetic activity is tied to the rainy season.

Do immune genes and cells only sense the seasons? An analysis of adipose tissue biopsies (here, the authors of the work again used material from another independent study) showed that there are seasonal changes in genetic activity here too, so that the annual clock obviously works in a variety of tissues and organs.

Increased activity of inflammatory genes during autumn and winter may be a preventive measure against those pathogens that love cold seasons. On the other hand, the attack of infections here can be primary, and the immune system only reacts to them, so that the result is a kind of rhythm. Which of the explanations is correct and which is not remains to be seen. So far, we can confidently conclude that seasonal diseases are accompanied by seasonal rearrangements in our molecular genetic apparatus, and that this should be taken into account in everyday medical practice.

For example, the regular exacerbation of chronic diseases, including cardiovascular diseases, may well be the result of greater activity of inflammatory genes. Inflammation is known to have a bad effect on the state of blood vessels, and it turns out that the immune system, preparing for a seasonal infectious attack (or being provoked by such an attack), thereby harms other organs.

Of course, many people know from their own experience how well-being improves and worsens depending on the time of year, but now, at least, it is clear in which direction one should work in order to somehow smooth out such an unpleasant seasonality of our physiology.