Fig. 2

Phagocytosis of dead SH-SY5Ys and synaptosomes is reduced in TREM2 KO, but not R47H TREM2, relative to WT pMac. a After 3 h of phagocytosis of pHrodo-labelled dead SH-SY5Ys, immunofluorescence staining shows that TREM2 is highly recruited to the phagocytic cup (marked by white arrow) during engulfment of cells expressing the neuronal marker TUJ1, whereas in b TREM2 is lost before maturation to RAB9+ endosomes (marked by white arrow). c–f Phagocytosis is impaired in TREM2 KO pMac only. Representative images of phagocytosis of SH-SY5Ys (c) or synaptosomes (e) shown in yellow, by pMac (red cytoplasm and blue nucleus), taken at 3 h with INCell 6000. Inset is a section of the image magnified 3-fold. d, f Means were quantified for the parameters: number of spots per cell, sum of spot areas (μm²) per cell, percentage of cells containing phagocytosed particles per field. Data was normalised to mean for each genotype per experiment. Means ± SEM, for N = 3 harvests. Repeated-measures 2-way ANOVA, Dunnett’s post hoc test, pairwise comparisons to the WT for each time: *p < 0.05, **p < 0.01, ***p < 0.001. g, h Phagocytosis of dead SH-SY5Ys results in SYK phosphorylation, which is unaffected in R47H TREM2 cells but attenuated in TREM2 KO line, measured by Western blotting at 0.5, 1, and 2 h after phagocytosis initiation. h Means ± SEM, for N = 3 harvests. Repeated-measures 2-way ANOVA, with Dunnett’s post hoc test, pairwise comparisons to the WT for each time: p = 0.0008 at 0.5 h stimulation for KO versus WT (***)