The brain’s connection to the immune system has long been a mystery. However, according to the findings of a new study, scientists have discovered neurons in the brainstem that play a key role in regulating immunity. These neurons receive signals from the immune system through the vagus nerve and maintain a balance between inflammatory and anti-inflammatory signals, thus controlling the body’s immune response. For instance, artificially activating anti-inflammatory neurons in mice reduced inflammation without any other intervention. This discovery could lead to the development of new treatment methods for autoimmune diseases, long COVID, and other conditions associated with an excessive immune response.
Upon detecting foreign elements, the immune system unleashes a cascade of immune cells and inflammatory substances. This inflammatory response must be finely regulated: if too weak, the body becomes more susceptible to infection; if too strong, it can damage its own tissues and organs. Previous studies have shown that the vagus nerve, an extensive network of nerve fibers connecting the body to the brain, influences the immune response. However, the specific neurons in the brainstem activated by immune stimuli have remained a mystery.
To investigate how the brain regulates the body’s immune response, scientists tracked the activity of brain cells after injecting mice with bacterial compounds that induce inflammation.
Researchers identified neurons in the brainstem that were activated in response to immune signals. Stimulating these neurons with a drug reduced the level of inflammatory molecules in the mice’s blood. Conversely, suppressing the activity of these neurons led to an uncontrolled immune reaction, resulting in a 300% increase in inflammatory molecules compared to mice with functioning brainstem neurons. Thus, these nerve cells maintained the inflammatory response at an appropriate level.
Further experiments revealed two distinct groups of neurons in the vagus nerve: one group responds to pro-inflammatory molecules of the immune system, while the other responds to anti-inflammatory ones. These neurons transmit their signals to the brain, allowing it to monitor the course of the immune response. In mice with conditions characterized by excessive immune reactions, artificial activation of neurons in the vagus nerve that transmit anti-inflammatory signals reduced inflammation.
The discovery of this new network of interaction between the body and the brain may offer a way to control the immune response in various diseases, such as autoimmune disorders or long COVID. There is evidence that treatments targeting the vagus nerve may be effective in multiple sclerosis and rheumatoid arthritis.
According to Stephen Liberles, a neurobiologist at Harvard Medical School, besides the neural network identified in this study, there may be other pathways through which the body transmits immune signals to the brain. Moreover, the mechanisms by which the brain sends signals back to the immune system to regulate inflammation remain unknown.
