Immunity system complexity: special brain coverage (Introduction)

by David Turell , Thursday, June 02, 2022, 00:26 (694 days ago) @ David Turell

Many new surprising findings:

https://www.nature.com/articles/d41586-022-01502-8?utm_source=Nature+Briefing&utm_c...

"A large body of evidence now shows that the brain and the immune system are tightly intertwined. Scientists already knew that the brain had its own resident immune cells, called microglia; recent discoveries are painting more-detailed pictures of their functions and revealing the characteristics of the other immune warriors housed in the regions around the brain. Some of these cells come from elsewhere in the body; others are produced locally, in the bone marrow of the skull. By studying these immune cells and mapping out how they interact with the brain, researchers are discovering that they play an important part in both healthy and diseased or damaged brains.

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"It’s now becoming clear that the brain’s margins are immunologically diverse: almost any type of immune cell in the body can also be found in the area surrounding the brain. The meninges — the fluid-filled membranes that wrap the brain — are an “immunological wonderland”, says Movahedi, whose work focuses on macrophages in the brain’s borders. “

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"Some residents are exclusive to the frontiers. In 2021, Jonathan Kipnis, a neuroimmunologist at Washington University in St. Louis, Missouri, and his colleagues reported7 that there is a local source of immune cells: the bone marrow of the skull.

"When they explored how the bone marrow mobilizes these cells, Kipnis and his colleagues demonstrated8 that, in response to an injury to the central nervous system or in the presence of a pathogen, signals carried in the cerebrospinal fluid were delivered to the skull bone marrow, prompting it to produce and release these cells.

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"His team has also detected a network of channels that snake and branch over the surface of the brain, and which swarm with immune cells, forming the brain’s own lymphatic system9. These vessels, which sit in the outermost part of the meninges, give immune cells a vantage point near the brain from where they can monitor any signs of infection or injury.

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"One big mystery is how exactly immune cells — particularly those around the borders — talk to the brain. Although there is some evidence that they might occasionally cross into the organ, most studies so far suggest that these cells communicate by sending in molecular messengers known as cytokines. These, in turn, influence behaviour.

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"Although these insights are tantalizing, much of the work on how immune cells, especially those in the borders, operate in the brain is still in its infancy. “We are very far away from understanding what’s happening in healthy brains,” Kipnis says.

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"Then, in 2021, her group pinpointed neurons in the insular cortex — a part of the brain involved in processing emotion and bodily sensations, among other things — that were active during inflammation in the colon, a condition also known as colitis.

"By activating these neurons artificially, the researchers were able to reawaken the intestinal immune response17. Just as Pavlov’s dogs learnt to associate the sound of a bell with food, causing the animals to salivate any time they heard the noise, these rodents’ neurons had captured a ‘memory’ of the immunological response that could be rebooted. “This showed that there is very intense crosstalk between neurons and immune cells,” says Movahedi, who wasn’t involved with this work.

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"Choi’s team is tracing out the specific neurons and circuits that modulate the immune response. One day, she hopes to be able to generate a comprehensive map of the interactions between the brain and immune system, outlining the cells, circuits and molecular messengers responsible for the communication in both directions — and connecting those to behavioural or physiological readouts."

Comment: the blood-brain-barrier is well known. it protects the brain from foreign proteins. However, design purpose can be seen in the emerging discovery of the complexity of brain immunity system. This most important organ must have tight protection.
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