Eotaxin induced the differentiation and proliferation of hematopoietic progenitors into metamyelocytes and macrophages in a GM-CSF–independent pathway. (A) Eotaxin was either treated with 1:100 polyclonal antibodies to Eotaxin or 50 μg/mL neutralizing polyclonal antibodies to IL-3 or to IL-5. As a control, antibodies against Eotaxin were also mixed with GM-CSF. The treated and untreated Eotaxin and GM-CSF were then used to perform a GM-CFU assay using Lin⁻ cells that were purified from BM of wild-type (WT) BALB/c mice (▪). Eotaxin was used to stimulate GM colony formation using Lin⁻ cells that were purified from BM of GM-CSF–deficient mice (KO)3 or wild-type (WT) BALB/c mice (▧). The activity of Eotaxin was inactivated by treatment with 1 mmol/L DTT, acetonitrile (ACN), and boiling for 5 minutes (B). The results shown in (A) are the mean of three individual experiments ± SD.