Fig. 2.
APOE particles require opsonins to exhibit APOE isoform-dependent phagocytosis of astrocytes. (A and B) Representative FACS analysis with apoE2/3/4 particles and pHrodo-conjugated synaptosomes in the absence (A) and presence (B) of Protein S (1 μg/mL). (A) Without Protein S, apoE2/3/4 particles failed to show the difference in astrocyte-mediated phagocytosis. (B) With Protein S, apoE2 particles show an increase and apoE4 particles show a decrease in the number of astrocytes with high pHrodo intensity (>5 × 102 in pHrodo intensity) compared with apoE3 particles. (C) Quantification of FACS data. Note that high concentration (400 nM) of apoE particles actually reduced overall phagocytosis by astrocytes. (D) apoE2/3/4 particles alone do not induce significant phagocytosis compared with Protein S. Phagocytic index was calculated by measuring the area of pHrodo-positive synaptosomes normalized by area of astrocytes labeled by CFDA SE cell tracer kit. Representative data are from three independent experiments. **P < 0.01; ***P < 0.001; ****P < 0.0001 (one-way ANOVA). Results are quantified and graphed ±SEM.