In vitro proliferation of haemopoietic cells in the presence of adherent cell layers. II. Differential effect of adherent cell layers derived from various organs.

Mouse bone marrow-derived adherent cell populations promoted proliferation of haemopoietic cells in vitro in a liquid culture system for at least 4 weeks. Adherent cell layers derived from other haemopoietic organs (foetal liver, adult spleen) and fibroblasts from embryonic tissues did not maintain haemopoietic cells in this system. Medium, conditioned by adherent cells derived from foetal liver, spleen and embryonic tissues displayed a considerable colony stimulating activity (CSA). Marrow-derived adherent cells produced no detectable CSA. A possible relationship between the in vitro expression of a growth-promoting activity of an adherent cell population on haemopoietic cells, and its endogenous CSA production, is discussed.