Figure 3. Changes in vesicle image area of DiD-labelled TBEV after internalization into astrocytes.

Panels A–C show distributions of image areas of labelled DiD-TBEV vesicles. Note that the fraction (shown as %) of small TBEV vesicles, with image areas <1 µm² (indicated by dashed lines), increased with the incubation time; from 41% after 2 h incubation (A), to 66% after 4 h incubation (B) and to 72% after 18 h incubation at 37°C (C). (D) The average vesicle area (in µm²) of TBEV vesicles significantly decreased with incubation time: 1.10±0.07 (4 h) and 0.97±0.03 (18 h) vs. 2.06±0.28 (2 h, **P<0.01, ***P<0.001). A similar decrease was observed in larger vesicles (L) with an image area >1 µm² (in µm²): 1.94±0.09 (4 h; **P<0.01) and 2.03±0.08 (18 h) vs. 3.06±0.39 (2 h). The average area (in µm²) of small vesicles (S) remained roughly the same throughout all examined incubation times: 0.61±0.04 (2 h), 0.63±0.02 (4 h) and 0.56±0.01 (18 h; P>0.05). The significant difference was observed only between 4 and 18 h (**P<0.01).