Fig. 2.

Aβ is phagocytized by microglia over time. Fluorescent confocal images of fAβ (circles) or sAβ (triangles) labeled with anti-Aβ were merged with confocal images of OX-42-immunoreactive microglia from the same tissue sections, allowing intracellular resolution and quantification of Aβ inside microglia. Microglia actively phagocytize fAβ over time, because 93% of microglia within 150 μm of the fAβ needle track contain material that is both Aβ-immunoreactive and Congo red-birefringent at 30 d after injection. In contrast, a relatively small percentage of microglia (10–20%) within 150 μm of the sAβ needle track contain Aβ immunoreactivity at the observed time points; this Aβ-immunofluorescent material is neither Congo red-birefringent nor thioflavin S-positive (data not shown) and thus lacks the characteristics of fAβ.