Cytokine receptor expression on hematopoietic stem and progenitor cells

Hematopoietic stem and progenitor cell populations were obtained by fluorescence activated cell sorting of murine bone marrow (BM) cells into Rhodamine-123io lineage-Ly6A/ E+ c-kit+ (primitive stem cells highly enriched for long-term BM repopulating activity), Rhodamine-123med/hl lineage- Ly6A/E+ c-kit+ (mature stem cells highly enriched for shortterm BM repopulating activity and day 13 spleen colony-forming activity) and lineage- Ly6A/E- c-kit+ (enriched for in vitro colony forming cells) populations. Neither stem cell population responds to single cytokines in vitro and each requires the synergistic action of two or more cytokines for proliferation, whereas the progenitor cell population proliferates in response to single cytokines. Since each of these cell populations was sorted as c-kit+, they express receptors for stem cell factor. Cell populations were also analyzed by autoradiography for their ability to specifically bind iodinated cytokines and this revealed that both stem cell populations expressed receptors for interleukin-1 alpha (IL-1 alpha), IL-3, IL-6, and granulocyte colony-stimulating factor (G-CSF), but lacked receptors for macrophage colony-stimulating factor (M-CSF), granulocyte-macrophage colony stimulating factor (GM-CSF), and leukemia inhibitory factor (LIF). Cells within the progenitor cell population specifically bound IL-3, GM-CSF, G-CSF, IL-6, and IL-1 alpha, whereas no receptors were detected for M-CSF and LIF. Within each cell population examined, heterogeneity was observed in the percentage of cells labeled and the number of receptors per cell. These results suggest that stem cell populations can be further subdivided according to their cytokine receptor profile and it will be of interest to determine if such subpopulations have distinctive functional properties.