Scientists find 'dial' in brain that controls immune system, hope for autoimmune disease treatment

Their study showed that the brain maintains a balance between molecular immune system signals that induce inflammation and increase it on the one hand, and those that temper and reduce it on the other, to ensure only a necessary amount of safe inflammation in the body.

The findings have been described by others in the field as a "black-swan event" — occurring out of the blue but making perfect sense.

The discovery has implications for the treatment of autoimmune disorders — which are caused by an excessive immune response by the body to naturally occurring molecules — and adds to the increasing research being published about the brain and the body.

One of the most important nerves in our body is the vagus nerve, a large network of nerve cells that connect the body and the brain, running from our brain to the groin. It also connects to the other organs around it, such as the lungs, heart, liver, intestines, and so on.

The vagus nerve plays a role in relaying immune system signals, previous research has shown. However, scientists hadn't figured out which specific brain neurons are activated by the immune system.

To get the answers, the team from Columbia University monitored the activity of brain cells in mice after injecting them with bacteria that triggered infection and inflammation.

Inflammation is the body's natural response to an infection, causing swelling and pain in a certain area or all over the body. This occurs because the body fills the region around any pathogen with white blood cells to kill it. Inflammation also occurs around organs and other parts of the body in autoimmune diseases.

As the experiment progressed, the neuroimmunologists, led by Dr Hao Jin, identified the neurons that switched on in the mice's brains in response to the immune triggers.

The team then messed with these cells to see what would happen. They found that when these neurons were activated with a drug, they reduced the levels of inflammation. On the other hand, when they were silenced, the bodies of the mice went into an uncontrolled immune response, increasing inflammation by 300 percent.

Additional investigation through more experiments revealed two groups of nerve fibres and neurons in the vagus nerve. One group was found to be responsive to pro-inflammatory immune response while the other responded to anti-inflammatory molecules. These neurons on the vagus nerve relayed a feedback signal back to the brain, which the brain used to monitor the unfolding immune response event.

The team also found in their experiments with mice that when there was an excessive immune response, artificially activating the vagus nerve cells that carry anti-inflammatory signals reduced the levels of inflammation.

These findings hold promise for the treatment of autoimmune diseases such as lupus and multiple sclerosis (MS).

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Glimpse into body-brain network

The Columbia University team's research adds a new context to understanding the body-brain network and offers a glimpse of hope for autoimmune disease therapeutics outside of steroids, which dampen the immune system.

The authors of the study state that the data can also help in treating the varying but debilitating Long Covid syndrome that manifests through various symptoms in people and persists for years after infection.

The study shows that there is a "whole layer of biology that we haven't even anticipated", said Yale University immunologist Ruslan Medzhitov to Nature in an accompanying commentary.

There is more work to be done before therapeutics can be invented to treat autoimmune diseases using vagus nerve activation, said the authors.

Previously, electrical shock signals have been used in studies to activate the giant nerve network and change immune response.

More studies conducted on the body-brain axis are expected to emerge over the next few years, with the promise of treating many on steroids around the world in the near future.

(Edited by Nida Fatima Siddiqui)

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