The close interconnection between the gut and the central nervous system is already well described, what is new is the possibility of some of the brain’s defense systems originating in the gut.
New research 1 in mice published in the journal Nature found that immune cells are first trained in the gut and then migrate to the brain, where they exert their protective effects.
The blood brain barrier (BBB) stands in the way of pathogens trying to access the central nervous system, and in this barrier there are immune cells trained to detect and combat possible pathogens present in the blood.
Since most pathogens access the bloodstream through the gut, it seems pretty logical that immune cells are placed there that learn to detect them, and are trained to initiate an immune response if need be.
The researchers found plasma cells which produce antibodies of the type IgA in the BBB of mice, and since these cells are usually found either in the lungs or the gut, they wondered if the above was true.
Indeed, that was the case. When they took germ-free mice, who have a bacteria free intestine, there were no observable plasma cells in their brains. However, a microbiome –poop– transplant from either mice or humans was capable of reverting this finding, showing this connection between the BBB and the gut.
How the gut can protect the brain from infection
Further, when they prompt the brain’s immune response by infecting the mice with a common intestinal pathogenic fungus, the researchers could observe how the antibodies released by the plasma cells located in blood vessels in the BBB attacked the fungi and impeded the progression of the infection to the brain.
This study is the first showing the presence of this type of immune cells in the brain –in health– but there are still many unanswered questions like: what brings these cells to travel from the gut to the brain since they are present even without need of an attacker?
Further research is needed, also to see whether these results are generalizable to other animals, including humans, but it is yet another example of the intricate crosstalk among biological systems. Isn’t it awesome?