I thought this one was interesting, as a number of the neurological diseases are connected, and involve the BBB.
Interesting that this reference suggests MS is actually a disease of the BBB rather than the immune system.

http://en.wikipedia.org/wiki/Blood-b...ier#Meningitis
Multiple sclerosis (MS)
Multiple sclerosis (MS) is considered an auto-immune disorder in which the immune system attacks the myelin protecting the nerves in the central nervous system. Normally, a person's nervous system would be inaccessible for the white blood cells due to the blood-brain barrier. However, it has been shown using Magnetic Resonance Imaging that, when a person is undergoing an MS "attack," the blood-brain barrier has broken down in a section of his/her brain or spinal cord, allowing white blood cells called T lymphocytes to cross over and destroy the myelin. It has been suggested that, rather than being a disease of the immune system, MS is a disease of the blood-brain barrier"
Ron