Eotaxin induced the proliferation and differentiation of Lin⁻ hematopoietic progenitors into granulocytes and macrophages. Thymidine incorporation (see the Materials and Methods; measured in counts per minute per well) induced by Eotaxin (A1), Eotaxin plus SCF and IL-3 (A2), Eotaxin plus IL-3 or GM-CSF (A3), and Eotaxin plus SCF (A4) is shown in (A). Proliferation of Lin⁻ cells (5 × 10³) stimulated with SCF, Eotaxin, or the combination of the two is shown in (B). The expression of the granulocyte and macrophage cell surface differentiation markers GR-1 and MAC-1 is shown in (C). Granulocytes that were double-stained for GR-1 and MAC-1 are marked by an arrow. The percentage of cells either not expressing MAC-1 and GR-1 or expressing MAC-1 or MAC-1 and GR-1 is shown at day 4 (C). Three different experiments were performed; the results shown are of one representative experiment. Each point is the mean of three to six determinations ± SD.