G-CSF–induced hematopoietic cell mobilization is associated with a reduction of CXCR4 in myeloid cells. Bone marrow Gr1⁺ cells were purified from the bone marrow of groups of mice (C57/BL6) either untreated or treated for 5 days with G-CSF (5 μg/mouse, daily intraperitoneally for 5 days). (A) Gr1⁺ cells and Gr1^– cells were obtained from groups of mice treated for 5 days with G-CSF or buffer only. CXCR4 content in Gr1⁺ cells and Gr1^– cell lysates evaluated by immunoblotting with specific CXCR4 antibodies, and reprobing with anti–beta actin antibodies. (B) Western blot analysis of CXCR4 and actin content in cell lysates from 2 groups of mice treated with G-CSF and a control group of untreated mice.