Eotaxin is a GM-CSF for Lin⁻ hematopoietic progenitors and can synergize with SCF to stimulate the production of granulocytes and macrophages. The concentration-dependent colony-stimulating activity of Eotaxin is shown in (A). The ability of Eotaxin (100 ng/mL) to stimulate colony formation in Lin⁻cells seeded in the concentration of 1 to 5,000 cells/plate is shown in (A1; see the Materials and Methods). Macrophages (M) and granulocyte-neutrophils (N) types of colonies stimulated by Eotaxin are shown in (A2). The colony-stimulating activities of Eotaxin, IL-3, MIP-1α, GM-CSF, SCF, and IL-5 and their combinations are shown (▪). The number of cells per plate collected from the GM-CFU assay (see the Materials and Methods) is shown (▧). (C) The pictures of colonies stimulated by either SCF, Eotaxin, or both were taken at an original magnification of ×200. Five different experiments were performed. The results shown are of one representative experiment. Each point is the mean of three determinations ± SD.