Figure 4: Light-guided migration and relocation of T cells in vivo.

(a–d) Uncaging of hCCL5** and directional T-cell migration in dermal tissues. (a) Time-lapse images (left) and time-coded tracks (right) of T cells migrating in dermal tissues of the ear injected with hCCL5** or PBS (control) before and after uncaging by raster-scanning with 720-nm light in the marked area (red circle). Cell tracks during the first 20 min immediately after the onset of uncaging. Scale bar, 50 μm. (b) Definition of the chemotactic index (CI) as the cosine of the angle θ between the velocity vector and the vector connecting the cell to the VOI centre. (c) Left, average CI of control and hCCL5** group 10 min before and after uncaging; right, CI distribution of cells starting from outside of the VOI during the first 10 min immediately after the onset of uncaging. (d) CIs plotted against distances away from the centre of the VOI as in a. (e, f) Directional T-cell migration in the lymph node after uncaging hCCL5** either by a light path patterned as a line (e) or as a circle (f) on all optical sections (3-μm step). Scale bar, 50 μm. Error bars indicate s.e.m.