G-CSF–induced mobilization of neutrophils to the blood and induction of cell motility in the BM. (A) Percentage of Gr-1–expressing cells in the blood of animals 2 hours after injection of G-CSF or PBS. Data are representative of 1 of 5 independently performed experiments with 3-6 mice per group. (B) Injection of G-CSF leads to a rapid induction of neutrophil motility in vivo, as visible from kinetic overlays. The green channels of 3 time frames, each 1 minute apart, were overlaid to create one RGB image. White cells have not moved within 3 minutes; colored cells have moved. The respective videos are provided as supplemental Videos 2 and 3. (C) Percentage of migrating cells (activity) and velocity of mobilized neutrophils over time after G-CSF or 1 hour after PBS injection. Data shown in panel B are representative of 4 independently analyzed animals, and data in panel C show the combined results of all 4 mice imaged for 4 hours each (the time point 1 hour after G-CSF was measured in 3 mice). (D) Emigration of several neutrophils into the bloodstream (white arrowheads) observed in a G-CSF–treated animal, white arrow depicts direction of blood flow. The accompanying video is provided as supplemental Video 4. Similar events were seen in 2 independently analyzed animals. (E) Tracks of 40 cells each migrating in either a nonmobilized (blue track color, tracked for 40 minutes) or a G-CSF–mobilized animal (orange track color, tracked for only 10 minutes.), illustrated with a common starting point. Tracks are 1 representative of 4 animals measured independently. (F) Migratory activity or velocity of green cells in CX3CR1-EGFP mice 1 hour after injection of PBS or G-CSF. Three mice were measured independently for each condition; ns = nonsignificant. In panels A, C, and F, the horizontal bar indicates the mean value.