So there is a lot of buzz about the recent discovery of lymphatic vessels that carry fluid away from the brain. There are a couple of reasonable questions: 1) Is this legit? 2) What does this really mean? See below for more details on my parsing of this study.
What is the journal?
Nature, cheap the gold standard of scientific journals.
What is the title of the original article?
Structural and functional features of central nervous system lymphatic vessels
Read the abstract here.
Who are the researchers?
What did they do?
The scientists investigated how T lymphocytes, a cell with immune functions, could pass through the membranes that cover the brain. Specifically, they used staining techniques to look for where the T lymphocytes were concentrated, since immune cells gather at the gateways into and out of tissues. They then tested the cells next to these areas of concentration to see what kind of tissue the vessels were made of. They used mice and humans. The brains of all mammals share many features, so it is completely reasonable to draw inferences from mouse brains to human brains, but there are some important differences as well, which is why while I enjoy peanut butter, I get bored after running on the wheel for only 3 minutes. The human samples were taken from 9 cadavers.
What did they find?
There is a tough covering over the brain called the dura mater, with channels called dural sinuses between layers of the covering. The team found that the T lymphocytes seemed to be lined up along vessel-like structures. There are blood vessels in the sinuses, and when the researchers used a dye to show where the blood vessels were, they were surprised to find that the lymphocytes were next to an as-of-yet unknown vessel. Additional dye staining confirmed that the new vessels did not belong to the cardiovascular system. The structure of these vessels has some similarities with the rest of the lymphatic system, and some differences. They only found the lymphatic structures in 2 of the 9 humans.
Importance of the study:
We used to think that the brain was largely separated from the rest of the body immunologically. Considering the results of this study, it is possible that certain neurological disorders could be linked to dysfunction of these vessels. Specifically, diseases like multiple sclerosis and Alzheimer’s disease, which seem to be related to changes in immune function, may have mechanisms- and hopefully treatments- different from those we originally thought.
Why we should be cautious:
The fact that only two human brains out of nine showed the structures should make us think twice. Still, there is the possibility that in the cadavers the vessels had collapsed or that t-cell function might not be as robust in dead people. Also, whole brains were used for the mice, and only samples of the dura mater were used for the humans, so those differences might change things too.
Grade on the reporting: C
The image of the location of the proposed vessels in humans that is widely being used is NOT from the study. There is in general too much speculation about what the study found, and not enough focus on the actual findings. There also needs to be more caution about these structures in humans.