For years, scientists have understood that the brain plays a role in the immune system, but the specifics have remained a mystery. Now, a recent discovery has shed light on this connection. Researchers have identified cells in the brainstem that detect immune signals from the body’s periphery, acting as key regulators of inflammation. Published in Nature, this research suggests that the brain carefully balances pro-inflammatory and anti-inflammatory signals, a finding with potential implications for treating autoimmune diseases and other conditions related to immune dysfunction.
Ruslan Medzhitov, an immunologist at Yale University, likened this discovery to a black swan event—unexpected yet coherent in hindsight. While the brainstem is known to control basic functions like breathing, this study reveals a previously unknown layer of biological complexity.
When the immune system detects a threat, it triggers an inflammatory response. However, this response must be finely tuned: too weak, and the body becomes vulnerable to infections; too strong, and it can harm the body’s own tissues. Previous studies showed that the vagus nerve, which links the body to the brain, influences immune responses. Yet, the specific neurons activated by immune signals were unknown.
To investigate, researchers monitored brain cell activity in mice injected with inflammatory triggers. They identified neurons in the brainstem that responded to these triggers. Stimulating these neurons reduced inflammatory molecules in the blood, while silencing them led to uncontrolled inflammation. These neurons act as a “rheostat,” maintaining the immune response at appropriate levels, according to Charles Zuker, a neuroscientist at Columbia University.
Further experiments revealed two groups of neurons in the vagus nerve: one responding to pro-inflammatory signals and another to anti-inflammatory signals. These neurons relay signals to the brain, allowing it to monitor the immune response. Stimulating anti-inflammatory neurons in mice with excessive inflammation reduced inflammation, suggesting a potential treatment approach.
While therapies targeting the vagus nerve have shown promise in diseases like multiple sclerosis and rheumatoid arthritis, much work remains. There could be other pathways through which the body communicates immune signals to the brain, and how the brain regulates inflammation back remains unclear.
This research opens new avenues for understanding the brain-immune system interaction, with implications for treating immune-related disorders.