Choroid plexus of the brain

The choroid plexus is the point where the cerebrospinal fluid is produced, essentially by partial filtration of the blood. The choroid plexus is the epithelial structure in the centre of this view. On left and right are brain parenchyma, in which the very fine processes of F4/80-positive microglial cells are just visible. At top left, there is a meningeal capillary. As elsewhere in the body, these vessels are surrounded by F4/80-positive macrophages, but they are particularly prominent in this location. Within the choroid plexus, F4/80-positive macrophages appear to underly the epithelial layers. It is not clear whether they are also intra-epithelial in this location.