The anti–integrin α6 antibody, in contrast to anti–integrin α4 antibody, does not mobilize progenitors or augment HSC or progenitor mobilization by G-CSF. CFU-GMs in blood were analyzed after injection of the anti–integrin α6 (α6), anti–integrin α4 (α4) antibody, and control rat IgG2a antibody (rIgG) without (A; left panel) or with simultaneous mobilization G-CSF (A; right panel). (B) Anti–integrin α4 but not anti–integrin α6 antibody enhanced G-CSF–stimulated mobilization of white blood cells (WBCs) and lymphocytes. (C) A synergistic effect of the anti–integrin α4 but not anti–integrin α6 antibody on mobilization by G-CSF of short-term HSCs analyzed by competitive repopulation assay. Reconstitution from CD45.1 mobilized blood cells expressed as percent of total nucleated cells; myeloid cell reconstitution from CD45.1 mobilized blood cells, as percent of total nucleated cells. *P < .05; ** P < .01; ***P < .001.