The blood-brain barrier is a specialized layer of cells that wrap blood vessels passing through the central nervous system, ensuring that only certain molecules can pass in either direction. Thus the biochemistry of the central nervous system is kept distinct from that of the rest of the body. This separation is necessary for correct function, as illustrated by the point that the blood-brain barrier begins to break down with advancing age. This produces damage and dysfunction in the brain, as unwanted cells and molecules leak through the faulty blood-brain barrier. As noted here, however, the relative scope and size of this contribution to neurodegeneration, in comparison to other contributing factors, is far from fully determined.
Changes in the immune system have long been recognized to occur with aging, and it is now appreciated that neuroinflammation likely contributes to age-associated neurological diseases. However, it is less well understood how specific changes in the immune system with aging may affect central nervous system (CNS) functions and contribute to neurological disease. We posit that brain barriers, especially the blood-brain barrier (BBB) and blood-CSF barrier (BCSFB), are important interfaces between CNS and peripheral tissues that are affected by