Eotaxin acts synergistically with SCF to induce colony formation, but not migration. (a) The total number of colonies (myeloid and erythroid) formed from fetal cells that migrated to either media alone (black bar), eotaxin (white bar), or MS5 supernatant (patterned bar) is shown. Standard error of the mean was determined, but in some cases was too small to be seen in the graph. No colonies were produced from the FBL output population in response to media alone. (b) As a control, eotaxin induced the migration of peritoneal eosinophils from IL-5 transgenic mice. (c through e) The cytospins are of cells harvested from 11 dpc FL colonies. The arrows identify erythrocytes. The total number of colonies (from the same experiment as the cytospins) and cells induced (in three separate experiments) is shown. (f) The total number of colonies generated from 11 dpc YS, FBL, and FL cells grown with SCF plus eotaxin is plotted for one representative experiment.