Figure 8. Astrocytes are ineffective in degrading the engulfed cells.

Apoptotic cells were pre-labeled with pHrodo-dye and added to (A,C) control macrophage cultures and (B,D) neuronal cell cultures. Parallel neural and macrophage cell cultures were fixed after (A–B) 5 h or (C–D) 3 d. (A) After 5 h, macrophages had already started to degrade phagocytosed cells in the lysosomes (bright red intracellular compartments). (B,D) Astrocytes did not contain red fluorescing material at any time point, indicating that the engulfed cell corpses did not fuse with lysosomes. (C) Dead cells ingested by macrophages had been degraded after 3 days and only remnant pHrodo-dye was apparent intracellularly. (D) In contrast to the macrophages, astrocytes had accumulated more intact DAPI labeled nuclei at day 3, but did not fluoresces red, indicating that the ingested cells had not fused with lysosomes at this time. (E) BrdU labeled, apoptotic cells were added to neuronal cultures and parallel cultures were fixed after 1 and 3 days (1 d respective 3 d in graph) or were carefully washed after 1 or 3 days and incubated for an additional 2 days in medium without apoptotic cells (1 d+2 d respective 3 d+2 d in graph) prior to fixation. Counting of the ingested BrdU+ nuclei show that astrocytes continued to accumulate cell corpses during the 1 day to 3 days of incubation, but after 2 days in medium without dead cells the ingested dead cells had still not been degraded. Error bars represent SEM.