Long-term maintenance of multilineal hemopoiesis in collagen gel culture.

We examined the long-term maintenance of multilineal hemopoiesis in a collagen gel culture of mouse bone marrow cells. When cells were inoculated into the gel, stromal cells formed foci that were composed of sinusoidlike capillary structures, fibroblastic cells, adipocytes and macrophages. Many small hemopoietic foci similar to granulocyte-macrophage colonies (CFU-GM) appeared within a week and disappeared after two weeks. Several large hemopoietic foci appeared after two to three weeks of culture, without a second challenge of marrow cells. These large hemopoietic foci were composed mainly of myeloid cells. Megakaryocytes and mast cells were also observed. When erythropoietin (EPO) was added to the culture at the beginning, the erythroid focus appeared after 3 weeks and the number of megakaryocytes was greater than that in the culture without EPO. However, when EPO was added to the cultures after 6 or 12 weeks, erythroid cells appeared after 1 week and the number of megakaryocytes increased. This hemopoiesis lasted more than 6 months.