Systemic administration of G-CSF promotes leukocyte trafficking in vivo and this response depends on G-CSFR expression by leukocytes. (A) Leukocyte trafficking in postcapillary venules of cremaster muscle in WT C57BL/6 mice 4 hours after intraperitoneal injection with saline or 10 μg G-CSF. n = 6 mice per group. *P < .05. (B) Leukocyte trafficking in postcapillary venules of cremaster muscle in WT mice reconstituted with WT bone marrow cells ([WT] → [WT]) 4 hours after intraperitoneal injection with saline or 10 μg G-CSF. n = 6 mice per group. *P < .01. (C) Leukocyte trafficking in postcapillary venules of cremaster muscle in bone marrow chimeric mice 4 hours after intraperitoneal injection with 10 μg G-CSF showing normal responses in G-CSFR^−/− mice reconstituted with WT bone marrow cells ([WT] → [G-CSFR^−/−]), but impaired G-CSF–induced leukocyte trafficking in WT mice reconstituted with G-CSFR^−/− bone marrow cells ([G-CSFR^−/−] → [WT]). n = 6 mice per group. *P < .05; **P < .005. Shown in panels A to C from left to right; leukocyte rolling flux, adhesion, and transendothelial migration. Data represent mean plus or minus SEM.