The anti–integrin α6 antibody inhibits homing of progenitors to BM, but does not enhance inhibition of homing mediated by the integrin α4 antibody. BM cells were incubated with function-blocking antibodies against integrin α6 (α6), integrin α4 (α4), both against integrins α6 and α4 (α6 + α4) or rat IgG2a control antibody (rIgG), and injected into lethally irradiated recipient mice. Three hours after injection, cells from BM, blood, and spleen were collected for CFU-GM assay. Data are pooled from 2 to 4 independent experiments. (A) The anti–integrin α6 antibody inhibited homing of CFU-GMs into BM, but not into spleen, and increased the number of CFU-GMs in blood. (B) The anti–integrin α4 antibody inhibited homing of CFU-GMs into BM. Incubation with both antibodies against integrin α6 and α4 chains did not further inhibit CFU-GM homing but resulted in retention of progenitors in blood. *P < .05; **P < .01; and ***P < .001, compared with results obtained with rIgG control antibody. ##P < .01 compared with results obtained with anti–integrin α4 antibody. (C) Incubation of BM cells with anti–integrin α6, anti–integrin α4, both antibodies, or control antibody did not affect growth of CFU-GMs, compared with cells not incubated with antibodies (no ab). The horizontal bars show mean values.