A most interesting article from the Purdue University News Service: "an organ in the brain called the choroid plexus apparently plays a critical role in preventing the accumulation of a protein associated with Alzheimer's disease. The researchers found that the choroid plexus acts as a sort of 'fishnet' that captures the protein, called beta-amyloid, and prevents it from building up in the cerebrospinal fluid, which surrounds and bathes the brain and spinal cord. Moreover, tissue in the organ is able to soak up large amounts of the protein and may contain enzymes capable of digesting beta-amyloid. ... Future research may focus on efforts to isolate possible enzymes. ... the findings suggest that aging may degrade the organ's performance."
Link: http://news.uns.purdue.edu/html4ever/2006/060321.Zheng.Alzheimers.html