Detection of murine hemopoietin-1 in media conditioned by EMT6 cells

We have previously reported replating experiments which demonstrated the existence of subpopulations of murine high-proliferative-potential colony-forming cells (HPP-CFC). One population of HPP-CFC, termed HPP-CFC-1, is stimulated by the combination of macrophage colony-stimulating factor (CSF-1) plus hemopoietin-1 (H-1), and actively generate a second population of HPP-CFC, termed HPP-CFC-2, which is responsive to CSF-1 plus interleukin-3 (IL-3). These reclonal experiments represent an assay system that discriminates between the two types of synergistic factors, namely H-1 and IL-3. To date H-1 has only been detected in medium conditioned by human cells. In this paper we have utilized these recloning experiments to study the synergistic factor(s) present in media conditioned by the murine mammary carcinoma cell line EMT6. Colony formation in secondary cultures containing cells picked up from primary cultures incubated in CSF-1 plus EMT6-conditioned medium was identical to that seen in secondary cultures containing cells picked up from primary cultures incubated in CSF-1 plus a source of H-1. Both sets of cultures demonstrated the generation of HPP-CFC-2 in the primary cultures, indicating the presence of a molecule in EMT6-conditioned medium that is the murine equivalent of H-1.