Small lining cells along the border of the brain’s ventricles are the gateway and supervisor of the relationship between the brain and the rest of the body, including the immune system. The choroid plexus cells produce cerebral spinal fluid, which bathes the brain and provides a cushion. But, it, also, performs a vast amount of other much more complex functions. The fluid filled ventricles are a critical source of sophisticated communication between brain and immune cells.The