Neutrophil retention in the head is SDF1a dependent. (A-F) Sudan Black–stained WHIM-GFP larvae injected with either control (A-B), SDF1a (C-D), or SDF1b (E-F) MO. Lateral (A,C,E) or ventral (B,D,F) view of the head at 3 dpf; arrows point to neutrophil accumulation. (G) The mean velocity of tracked neutrophils from the ventral head of uninjected or SDF1a morphant MPO:GFP or WHIM-GFP larvae. **P < .001, *P < .01. (H-K) Neutrophil migration in the ventral head of MPO:GFP (H), SDF1a morphant MPO:GFP (I), WHIM-GFP (J), or SDF1a morphant WHIM-GFP (K) larvae was tracked in 3 dimensions. The tracks are plotted in 3-dimensional space and viewed in the xy-plane (left) or zy-plane (right). Units are in micrometers on each axis. Only tracks of neutrophils that lasted for ≥ 14 minutes and only the first 14 minutes of longer tracks are included. Tracks were taken from supplemental Video 1 with additional tracks in SDF1a morphant larvae from additional videos not shown. (L) WHIM-GFP larvae at 2 or 3 dpf injected with Tol2-CMV:SDF1a-2A-mCherry at the 1-cell stage. Three examples of WHIM-GFP neutrophils (green) in close association with cells expressing SDF1a-2A-mcherry (red) in the body (i), head (ii), and yolk sac (iii). Cells expressing mCherry alone did not recruit WHIM-GFP neutrophils. Bar = 200 μm (A-F); 25 μm (L).