The immune system seems to be governed by an internal clock that coordinates with our central biological clock.

The functioning of the human body, as well as that of plants and other animals, is regulated by an internal biological clock called the circadian rhythm that is synchronized with the night and day cycles.

It is formed by neurons of the suprachiasmatic nucleus, located at the base of the brain, which receive information directly from the cells responsible for capturing the light in the retina.

It has also been observed that cells, tissues and organs are also governed by their own biological clocks, which are coordinated with the central one.

That main circadian rhythm, whose discovery was recognized with the Nobel Prize in Medicine in 2017, is responsible for regulating critical functions of the organism such as sleep, body temperature, metabolism or the secretion of hormones.

Our Biological Clock is connected to our Immune Response

Recent studies have observed that the time of day can affect the severity of different diseases and their symptoms, from allergies to stroke.

“The immune system seems to be governed by an internal clock that coordinates with the central biological clock of the organism,” says immunologist Christophe Scheiermann, of the University of Geneva (Switzerland), co-author of an article published in the journal Trends in Immunology in which scientific studies on this issue are reviewed.

According to the study, if we understood better that relationship between time of day and the activity of defense cells, we could optimize the immune system to recover from disease and to be better prepared to respond when our body is attacked.

It would also be possible to administer treatments at a specific time to improve their effectiveness, or avoid side effects, as in the case of vaccines or chemotherapy.

The study examines the relationship between the behavior patterns of immune cells and the time of day under normal conditions, inflammation and disease.

Researchers have seen that, for example, the severity of the symptoms of allergies, which are caused by a mistake of the defense system that confuses something harmless with a pathogen, depend on the biological clock of the immune cells.

Lymphocytes secrete molecules to attack those supposed pathogens, some of which cause inflammation in the affected tissues. Such response helps fight infections, but also contributes to worsening allergy symptoms.

The point of activity of the inflammation occurs from midnight and until dawn, when we feel worse; later in the afternoon it is reduced, so it is not uncommon to notice improvement at that time.

Another example is strokes. They are related to the circadian rhythm of the immune system. They are more frequent at dawn or early in the morning and, in addition, some studies suggest that those occurring at those times are more serious.

The biological clock of the human body could also condition the effectiveness of medical treatments.

Apparently, our human biological clock also determines the generation of more antibodies. “The evidence is not entirely clear, although it could be a possibility.

In the case of cancer, for example, some animal studies suggest that chemotherapy might be improved if it were applied in the morning. However, most drugs used have half-lives in the human body that exceed the 24-hour cycles.

Unfortunately, at this point, almost 95% of the results obtained in the laboratory with experimental animals are not transferable to humans. At the moment scientists cannot modulate the treatment, although it would be very interesting, because they could increase the effectiveness of a drug and also reduce its toxicity.

The same happens with the drugs used in immunotherapy that precisely seek to facilitate the immune system’s attack on tumor.

They last a long time in the blood, so, for the moment, it is impossible to get them to exercise their function in only certain moments of the day.

That outcome could change with some of the current therapeutic strategies under study, such as the nanoparticles regulated with light, which allow activating and inhibiting the action of some drugs.

If this kind of approach could be developed, it would be a step forward in order to take advantage of the behavior pattern of the immune system.

Also in radiotherapy there are now some studies that seems to suggest that there may be some difference depending on the schedule, but at the moment they are very preliminary.

There are small clues that can lead us to investigate more in chronotherapies as well.

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