Loss of osteomacs from endosteal surface during G-CSF–induced mobilization. Bone sections from mice treated with saline (A,B) or G-CSF for 2 (C), 6 (D), or for 6 days with G-CSF, followed by a recovery of 2 (E) or 4 days (F), were stained with a monoclonal antibody against the F4/80 antigen (B-F) or an isotype-matched nonimmune antibody (A). F4/80⁺ cells are stained brown. F4/80⁺ osteomacs forming a canopy over active osteoblasts at endosteal surfaces were detected in saline-treated animals (B, arrows) as well as 4 days following cessation of a 6-day G-CSF treatment (F). Clustering of F4/80⁺ cells around blood vessels was observed after 2 days of treatment (C, arrows). Pictures are representive of 1 mouse of 3 mice per time point.