From the Canadian Institutes of Health Research, a potentially useful insight into existing defense mechanisms against Alzheimer's amyloid plaques: "Alzheimer's disease is characterized by the accumulation of amyloid proteins in the brain. These proteins form plaques around which microglia, the central nervous system's immune cells, aggregate. These microglia appear to be incapable of eliminating the plaques ... although the brain's resident microglia do appear to be poorly equipped for combating amyloid plaques, an entirely different case prevails for another type of microglia: those derived from bone marrow stem cells. ... bone marrow-derived microglia infiltrate amyloid plaques and succeed in destroying them most efficiently. These newly-recruited immune cells are specifically attracted by the amyloid proteins that are the most toxic to nerve cells."

Link: http://www.cihr-irsc.gc.ca/e/30601.html