Evidence for phagocytosis of Aβ by AD microglia in vitro under the various experimental conditions. A) Twelve days after plating AD microglia with Aβ spots, diminution of the spots was visually apparent and microglia concurrently had become immunoreactive for Aβ even under vehicle control conditions, as shown here (anti-Aβ antibody 4G8 immunocytochemistry). B) In the absence of microglia, the Aβ spots remained visibly intact (phase contrast). C) Likewise, prior to exposure to Aβ spots the microglia exhibited little or no immunoreactivity for Aβ (anti-Aβ antibody 4G8 immunocytochemistry). D) Summary data illustrating the effects of indomethacin and 6E10 opsonization on Aβ spot thickness. Microglia in this model system carpet the top of Aβ spots (c.f., Fig. 2C) and therefore appear to clear the Aβ from the top down, resulting in progressive thinning of the spot, as measured here. With prolonged exposure, cracks and holes in the spot appear, as shown in Fig. 4A.