Introducing the brain: immune protection from the skull (Introduction)

by David Turell , Sunday, May 08, 2022, 15:57 (713 days ago) @ David Turell

Tiny bone channels allow the marrow to monitor for trouble:

https://www.sciencealert.com/there-are-tiny-channels-in-the-human-skull-that-could-be-c...

"A shortcut between the skull and the brain could be a possible way for the human immune system to bypass the blood-brain barrier.

"Researchers recently discovered a series of tiny channels in mice and human skulls, and in mice at least, these little pathways represent an unexpected source of brain immunity.

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"Last year, researchers found a whole host of immune cells hidden in the bone marrow of the mouse cranium. When confronted with a virus or tumor in the brain, these cells traveled through the skull channels and into the cerebrospinal fluid.

"Now, it seems that this secret path is actually a two-way street.

"Not only can immune cells in the skull cap flow to the brain, researchers found that cerebrospinal fluid can also seep through to the skull.

"Experts think it works sort of like an immune pit stop.

"Last year, researchers found a whole host of immune cells hidden in the bone marrow of the mouse cranium. When confronted with a virus or tumor in the brain, these cells traveled through the skull channels and into the cerebrospinal fluid.

"Now, it seems that this secret path is actually a two-way street.

"Not only can immune cells in the skull cap flow to the brain, researchers found that cerebrospinal fluid can also seep through to the skull.

"Experts think it works sort of like an immune pit stop.

***

"'Now we know that the brain can signal to this hub of immunity – in other words, cry for help in case things go wrong, such as during infection and inflammation," says Matthias Nahrendorf, who works at Massachusetts General Hospital and Harvard University.

"'Cells in the skull's bone marrow are surveilling the cerebrospinal fluid that exits the brain through the skull channels we discovered earlier."

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"'Constant sampling of [cerebrospinal fluid] outflow suggests that the skull marrow state may reflect brain health and that the skull marrow has a prominent role in regulating [central nervous system] inflammation."

"A closer look with immunostaining revealed that bone marrow in the mouse skull had a slightly different composition of immune cells than bone marrow from the mouse tibia.

"In the skull, neutrophils, which are the immune system's first line of defense, and monocytes, which kill invaders or alert other blood cells to action, were significantly enriched after injecting the mouse brain with bacteria. These immune cells were also clustered near sinuses where cerebrospinal fluid flows and bone marrow is rich.

"The results suggest that cerebrospinal fluid has direct access to the skull bone marrow. What's more, immune cells can exit the skull bone marrow in response to cues from the cerebrospinal fluid.

"Most of the time, this pathway is helpful. By consistently checking cerebrospinal fluid for invaders and responding accordingly, the skull's immune system keeps the mammalian brain healthy.

***

"While the findings have not yet been replicated among humans, it's likely that our brains show a similar system that bypasses the blood-brain barrier. Using micro CT scans, the authors have already found similar tiny channels connecting the human skull to the brain's meninges, each about 1.5 millimeters in diameter.

"Whether white blood cells and cerebrospinal fluid also flow through these channels in our own species is unclear."

Comment: wow, design with obvious purpose. Our brain floats in a fluid layer to protect it from severe skull bumps. Now we see the fluid acting to protect it tied to bone marrow where fighting white cells are made.