Figure 5.

A subpopulation of activated microglia is MHC class II-positive. A: IA (MHC class II protein)-positive microglia are closely associated with amyloid plaques as well as capillary endothelium, as shown in a neocortex section of a 23-month-old APP23 transgenic mouse. B: Double-labeling of amyloid (purple reaction product) and IA (brown reaction product) reveals MHC class II protein reactivity within and around the compact amyloid deposits. Although MHC class II staining is also visible at a blood vessel and an amyloid plaque, it was not detected at diffuse, nonfibrillary amyloid as present in the center of the picture. Scale bar, 50 μm.