CD68 and Alzheimer disease: Prior studies demonstrate that TREM2 knockout reduces CD68 (a lysosomal phagocytic marker) expression in aged or demyelinated mouse brains [67, 68], and impairs Aβ plaque clearance via dampened microglial engulfment [69, 70], whereas TREM2 activation enhances Aβ phagocytosis in AD models [65, 66].