Researchers have found that oral administration of rapamycin to an Alzheimer's disease mouse model causes an increase in beta (β)-amyloid protein plaques. β-amyloid buildup is a hallmark of Alzheimer's disease. Rapamycin is approved to treat transplant and cancer patients. Publicly available data suggest that the drug might also improve learning and memory in aged mice. However, the researchers observed that after rapamycin treatment, a protein called Trem2 (triggering receptor expressed on myeloid cells 2) is dramatically diminished. Trem2 is present in microglia, which are immune cells in the brain and spinal cord. "Trem2 is a receptor located on the surface...