Internalization and processing of the Tau protein (15 µg; A,B) and its highly phosphorylated form (1.5 µg; C,D) by cortical cells. Following 24 h (A,C) or 48 h (B,D) of incubation with protein, cells were immunostained with a mouse anti-His-tag antibody targeted by an AlexaFluor® 594 antibody (red) and with a rabbit anti-MAP2 antibody targeted by an AlexaFluor® 488 antibody (green). Nuclei were stained with DAPI. The protein was sometimes detected outside cells where it was probably attached to the extracellular matrix. Different digital zooms were applied to the 60× optical zoom: A: 2.6×, B: 2.8×, C: 2.1×, D: 3×. All scale bars correspond to 5 µm.