Some types of immune messengers act on receptors in specific areas of the brain, promoting anxiety or pro-social behavior.
An ongoing infection could alter your behavior, and not only because you don’t feel in full form. Two new studies on a type of cytokinea molecule that acts as a chemical messenger between immune cells, strengthen the idea that the system that defends the body from infections can also influence the brainchanging our behaviors while we are sick. A discovery that has interesting implications both in evolutionary terms and for the hypothetical possibility of influencing some brain responses passing through the immune system.
Influences on the brain. In the two works, published on Cellthe scientists of MIT and Harvard Medical School have concentrated On a cytokine called Il-17 who – have found – in addition to his role of immune messenger he plays two types of very different effects on two brain regions: the amygdala and the somatosensory cortex. In the amygdala, this molecule can solicit a feeling of anxiety, while in the cortex it seems to promote prosocial behaviors.
Water on the fire. Gloria Choi, associate professor of neuroscience and cognitive sciences of the Picower Institute for learning and memory of Mit, and Jun Huh, associate professor of immunology at the Harvard Medical School, are responsible for both studies. The two have been interested in the role of this particular cytokine for some years. The molecule is involved In a phenomenon called “feverish effect”the temporary improvement of some behavioral manifestations typical of autistic spectrum disorders when children suffering from it have a fever.
In 2019, Choi and Huh showed that, in some cases, during an infection the release of the IL-17 suppresses the activity of the neurons of a small region of the cortex, whose hyperexcitation can produce autistic-like symptoms in mice.
Where does the cytokine act? In the new articles, scientists have mapped the IL-17 receptors, present in six different forms, in the various parts of the brain. Two cytokine receptors are found in the cortex, including the region that researchers had previously attached in the studies on the feverish effect. Not surprisingly, the receptors are found in a population of neurons involved in the control of behavior.
A disputed messenger. When a form of IL-17, called Il-17e, binds to these receptors, acts as a neuromodist: reduces the excitability of neurons And attenuates the controlled behaviors from this part of the brain. The authors suspect that cytokine It was originally a neuromodistand that later the immune system was appropriate to regulate cellular communications in immune responses.
In very simple creatures such as the nematode worm C. Elegansin fact, the IL -17 has no immune, but neural effects – promotes aggregation, a form of social communication.
More anxiety. The second study, on the other hand, explored other cytokine receptors present in the Amigdala, the agglomeration of nerve nuclei involved in the regulation of primitive emotions, such as fear and response to threats. In the Blatical Amigdala there are two types of receptors at AL-17 who work in pairs, and that when they bind to two forms of cytokine they become more excitable, increasing the feeling of anxiety. When the animals are treated with drugs that block one of these receptors – they discovered scientists – it happens counterintuctively that the levels of a form of these cytokines in the blood increase, causing adverse effects on mental health.
Stay at home! A hypothesis is that, during infections, anxiety can dissuade an individual sick from meeting other peoplethus arguing the spread of pathogens. Another type of cytokine would act on the same receptors in the brain to silence anxiety when the infection is resolved and this activation is no longer useful.
A phenomenon to be exploited. The two works suggest that the immune system can exercise multiple effects on the brain. An interesting idea also for therapeutic purposes: “Instead of thinking of acting directly on the brain, can we think of doing something about the immune system?” Choi wonders.
