The immune system, an actor in the dialogue between peripheral tissues and brain

The majority of our organs accommodate in “permanent residence” of the cells of the immune system called T lymphocytes. However, As a function of the organ on which they watch, these sentries have specific characteristics. For example, Until about fifteen years ago. however. Nevertheless, this surveillance was not applied to the brain: indeed, a physical barrier at the vessels that irrigate it (known as hematoencalic barrier) was supposed to isolate the latter of the rest of the body, applying severe sorting on what is allowed to penetrate the brain fabric. In addition, The cells of the immune system not being part of the “VIPs”. Moreover, their presence in our brain was thus considered pathological. Meanwhile, The lymphocytes present in the immune system, actor dialogue between new meninges – membranes on the outskirts of our brain – were therefore the closest. Consequently, known to the brain fabric. Therefore. Moreover. Therefore, it immune system, actor dialogue between was admitted that the communication of peripheral tissues to the brain was mainly thanks to a multitude of substances in circulation in our body, capable of passing the cerebral barrier (hormones, neurotransmitters, cytokines …).

This vision has evolved in recent years, several teams that have identified the presence of certain lymphocytes in the brain. Furthermore, But the precise role of these cells, their origin and their function remained debated. However. Furthermore. Therefore, recently, Tomomi Yoshida and his colleagues, from the Immunobiology Department of the Faculty of Medicine of the Yale University, in the United States, raised a corner of the veil concerning the involvement of the immune system in the periphery-end dialogue.

However. it was at the start of deciding a simple question: is the healthy brain really virgin of any immune cell? To answer it. Tomomi immune system. actor dialogue between Yoshida and his colleagues first sought traces of T lymphocytes in the brain of adult mice and actually observed a signal inside the brain fabric. By leaning more carefully at the distribution of these cells. they highlighted that these cerebral lymphocytes were not distributed in a homogeneous manner. but that they were more present in certain structures, in particular the subnunical organ: a very small area located in the center of the brain, and involved in the regulation of water and food consumption. Thanks to fabrics from donors without neurological pathologies. they also highlighted that this presence in the subforming organ was not specific to mice, but also concerned humans. And after an analysis of immune system, actor dialogue between new the characteristics of these new cerebral lymphocytes. it appeared that the latter differ from those present in the nearby meninges. but presented a large resemblance to those of the adipose tissue – the cellular tissue immune system, actor dialogue between that stores fat.

An intriguing observation, which raised many questions among the team researchers: what functional link hid for this similarity? Could a modulation of the adipose tissue affect one or the other of these two populations of strangely identical lymphocytes? By submitting animals to a forty-eight hour fast. the American team observed a decrease in the fat mass of animals. associated with a decrease in the number of adipose lymphocytes and an increase in that of cerebral lymphocytes. In addition. after having specifically colored the lymphocytes of the adipose tissue. the researchers noted the appearance of lymphocytes similarly immune system, actor dialogue between new marked in the brain fabric, thus highlighting a migration of the adipose lymphocytes towards the brain. This migration begins when weaning babies mouse – age at which the population of brain lymphocytes is set up -. then continues, modulated by immune system, actor dialogue between the diet.

These revolutionary results immediately drawn attention to the intestinal microbiota. its role vis-à-vis these immune cells in residence in the brain. The microbiota is indeed the first system affected during a diet change. and it is also known to undergo drastic modifications when weaning. However, it appeared that the microbiota modulation by taking antibiotics caused a decrease in the number of cerebral lymphocytes. Even more: animals devoid of intestinal microbiota simply did not have them. These combined observations show that the microbiota is essential for the implementation of these immune cells in the brain. as well as their regulation.

It was then to solve the fundamental problem of the effective usefulness of these brain lymphocytes. Does their modulation by the microbiota and the adipose tissue cause changes in behavior, and in particular eating behavior? In immune system, actor dialogue between order to elucidate this question. Tomomi Yoshida. his colleagues have first modified different characteristics of the adipose lymphocytes, such as their ability to migrate to the subfornical organ or to express certain molecules that are specific to them on their surface. They then studied several behavioral parameters such as the quantity of food ingested by an animal following a fasting period.. the time taken to consume it, and arrived at a systematic conclusion: the alteration of adipose lymphocytes has a direct impact on eating behavior.

This work highlights a new communication mechanism between peripheral tissues. brains. which makes it possible to immune system, actor dialogue between new adapt behavior and maintain a certain physiological balance, a homeostasis of body weight, by playing on eating behavior. And it is probably only the beginning. If the study was essentially interested in the role of the immune system in the digestive-end system axis. it remains to explore the immune system. actor dialogue between axes associated with other brain structures where the team has detected lymphocytes. It is not excluded. thus, that such cells play an equivalent role of ambassadors in other functions such as sexual functions.