Identification of Splenic Progenitors for CD11b High Myeloid Cells in the Long-Term Culture with GM-CSF

Abstract Granulocyte macrophage-colony stimulating factor (GM-CSF) is a key hematopoietic cytokine for the development of immune cells from progenitors in bone marrow (BM). However, the role of GM-CSF in hematopoiesis outside of BM has been less well understood. In a recent report, we discovered that significant proliferation of CD11bhi myeloid cells, including CD11chi dendritic cells (DCs) and CD11clo macrophages, were detected in the culture of splenocytes with GM-CSF between 1 and 3 weeks. To further characterize this slow myelopoiesis of CD11bhi cells in vitro, we set out to find their progenitors in spleen. We have identified and isolated the distinct splenic populations of myeloid progenitors based on the established cell-surface markers of hematopoietic progenitors in BM. When those isolated splenic progenitors were cultured with GM-CSF, lineage− CD117+CD115−CD16/32+ splenic cells were effective to produce CD11bhi myeloid cells. Our current study indicates that splenic progenitors comparable to BM granulocyte-macrophage progenitor (GMP) are responsible for generating CD11bhi DCs and macrophages in the long-term culture with GM-CSF.