A way for the human immune system to get around the blood-brain barrier could be a shortcut between the skull and the brain.
A series of tiny channels in mice and human skulls are an unexpected source of brain immunity.
Scientists used to think that the immune system could connect with the brain through a neurological customs gate.
It seems that there is no need to go the long way around. Immune cells inside the brain's bone appear to have a different path.
The immune cells were found in the bone marrow of the mouse. The cells traveled through the skull channels and into the fluid of the brain.
It seems that this secret path is a two-way street.
The immune cells in the skull cap can travel to the brain.
It works like an immune pit stop according to experts.
The human skull has a channel in it. Herisson et al. are from Nature Neuroscience.
Cells in the bone marrow watch for threats as the clear liquid that soaks the brain flows through cracks in the skull.
Immune cells are produced by the bone marrow if a pathogen is detected.
The fluorescent tracers show that the fluid traveled through the skull cap to the bone marrow.
When researchers injected the brains of mice with the bacterium that causes meninges, it caused inflammation in the brain.
The fluid and the bacteria entered the skull through these small channels and stimulated the immune system.
The mouse brain has a skull channel. Herisson et al. are from Nature Neuroscience.
99 percent of the stem cells in the skull bone marrow were labeled with a specific antibody an hour after they were injected into the mouse brain.
In other words, cry for help in case things go wrong, as we know that the brain can signal to this hub of immunity.
The cells in the skull are surveilling the fluid that leaves the brain through the skull channels.
The bone marrow in the skull is connected to the meninges via small channels in the bone.
Since then, it has become clear that the skull is an overlooked source of immunity. It was thought that the brain's health was monitored by immune sites in other parts of the body.
The new research shows that the other sites are not as involved initially. After researchers injected mice with an intracerebral pathogen, peripheral bone marrow in a mouse leg bone did not show any cells. The skull bone marrow did.
The immune system is embedded in the skull.
The authors write that the skull marrow warrants closer scrutiny due to its proximity to the meninges and the central nervous system.
The skull marrow has a role to play in regulating inflammation in the central nervous system, and constant sampling of the outflow suggests that.
The bone marrow from the mouse skull had a slightly different composition of immune cells than the bone marrow from the mouse tibia.
The immune system's first line of defense, monocytes, were enriched in the skull after injecting the mouse brain. The immune cells were clustered near the sinuses.
The results show that the fluid in the brain has access to the bone marrow. Immune cells can leave the skull bone marrow in response to the fluid in the brain.
This pathway is helpful most of the time. The immune system of the skull keeps the brain healthy.
What happens if the immune system goes into full gear?
This likely has huge implications for conditions like dementia and Alzheimer's disease because they have an inflammatory component.
It is likely that our brains show the same system that was found in the study. The authors have found similar tiny channels connecting the human skull to the brain using microCT scans.
It's not clear if white blood cells and cerebrospinal fluid also flow through these channels.
Multiple Sclerosis, myasthenia gravis, and Guillain-Barr syndrome are all marked by an immune response, but how this response is jumpstarted is still being figured out.
When the immune response is harmful, such as when skull bone marrow-derived immune cells damage the brain and surrounding nerves, our work may be helpful.
Understanding what fuels neuro-inflammation is the first step to successfully modifying it.
Nature Neuroscience published the study.
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