Immunity system complexity: brain stem controls (Introduction)

by David Turell , Wednesday, June 19, 2024, 18:11 (157 days ago) @ David Turell

In the hypothalamus:

https://www.quantamagazine.org/the-brainstem-fine-tunes-inflammation-throughout-the-bod...

"Last month, researchers discovered cells in the brainstem that regulate inflammation throughout the body. In response to an injury, these nerve cells not only sense inflammatory molecules, but also dial their circulating levels up and down to keep infections from harming healthy tissues. The discovery adds control of the immune system to the brainstem’s core functions — a list that also includes monitoring heart rate, breathing and aspects of taste — and suggests new potential targets for treating inflammatory disorders like arthritis and inflammatory bowel disease.

"During an intense workout or high-stakes exam, your brain can sense the spike in your heart rate and help restore a normal rhythm. Likewise, the brain can help stabilize your blood pressure by triggering chemical signals that widen or constrict blood vessels. Such feats often go unnoticed, but they illustrate a fundamental concept of physiology known as homeostasis — the capacity of organisms to keep their internal systems working smoothly and stably amid shifting circumstances.

"Now, in a paper published on May 1 in Nature, researchers describe how homeostatic control extends even to the sprawl of cells and tissues that comprise our immune system.

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"These neurons operate like a “volume controller” that keeps the animals’ inflammatory responses within a physiological range, said paper author Hao Jin, a neuroimmunologist at the National Institute of Allergy and Infectious Diseases.

"The discovery may come as a surprise to immunologists who assume that the strength of an immune response is governed by the immune system’s own set of regulatory mechanisms, said the immunobiologist Ruslan Medzhitov of Yale University, who was not involved in the study. “We’ve never suspected that there will be something else on top of it, that we need an additional control. But clearly we do,” he said. “That’s what this work revealed: There are parts of the brainstem dedicated to this control.”

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"Such studies helped usher in a “transformation in the way we think about the brain,” Zuker said. Historically considered the seat of memory and emotion, the brain may devote far less energy to these higher-order functions than to monitoring the body’s organs, physiology and metabolism to maintain homeostasis. “Everyone in the lab began to think about that,” he said. “How far does the brain’s control over body biology go?”

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"He and his colleagues wanted to figure out which brain circuits were involved. In one experiment, they cut the vagus nerve and saw that, without its input, the brainstem neurons remained inert — demonstrating the vagus nerve’s central role in this brain-body immune circuit. Then they used genetic techniques to dial the brainstem neurons’ activity up or down. When dialed down, the mice experienced an out-of-control inflammatory response, with a corresponding rise in pro-inflammatory molecules and a dip in anti-inflammatory molecules. Dialing up the brainstem cells’ activity did the opposite: Anti-inflammatory molecules shot up, while levels of pro-inflammatory molecules plummeted, putting a damper on inflammation."

Comment: this is typical feedback system used throughout the body to maintain exact controls. It requires an appreciation of the necessity for control. Only design can accomplish this result.