Selective stimulation of granulopoiesis in vitro by established bone marrow stromal cells

Bone marrow is a major granulopoietic organ whose hematopoietic microenvironment is comprised of stromal cells. In the present work, we examined the regulation of in vitro granulopoiesis with an established line of bone marrow stromal cells. In coculture of the progenitor cells on the particular stromal cell lines from bone marrow, large granulocyte (G) colonies consisting of over 200 cells were formed without G-CSF for 5 days. Stromal cells supported development of Gr-1 (granulocyte specific surface marker)-negative progenitors into Gr-1 and myeloperoxidase positive granulocytes. Seventy percent of the large G-colonies were formed on the stromal layers even in the presence of anti-G-CSF antibody, which indicates the G-CSF independent pathway of granulopoiesis. Inhibition of the large G-colony formation by the addition of anti-adhesion molecules, such as very late activation antigen-4 (VLA-4) and CD31 (PECAM-1), suggested the role of cell-to-cell adhesion in stroma-supported granulopoiesis.