Some studies have shown that the microglia secrete proteolytic enzymes, such as neprilysin, insulin-degrading enzyme (IDE), matrix metalloproteinase 9 (MMP-9) and plasminogen.24, 35, 36 This microglial behavior promotes Aβ clearance and may be helpful for inhibiting neurodegeneration in an AD brain. Here, PLG is linked to Alzheimer disease.