The image was made possible by inserting a green fluorescent protein into the tissues that give rise to blood and lymph vessels in an embryonic zebrafish, which is otherwise transparent, and then photographing it under a light microscope. The sentry cells, called fluorescent granular perithelial cells (FGPs), are found only within blood vessels on the brain’s surface, and help protect the brain by engulfing and encasing toxins, cellular waste and microbes in sphere-like structures called vesicles.
The research, by scientists at the US National Institutes of Health and Japan’s National Institute of Genetics, challenges the hypothesis that FGPs were a type of immune cell, instead providing evidence they are produced by endothelial cells within the brain’s blood vessels. Understanding better how these cells work to protect the brain could lead to breakthroughs in preventing or treating age-related decline in human brain function.