Abstract
The colony-stimulating activity (CSA) of medium conditioned by phytohaemagglutinin (PHA)-stimulated blood mononuclear cells was tested using granulocyte-macrophage colony-forming cells (GM-CFC) from normal bone marrow. Low concentrations of the conditioned medium stimulated granulocytic colony-forming cells (CFC) which formed colonies by the seventh day of incubation; higher concentrations stimulated the formation of macrophage colonies which were not seen until the end of the second week in culture. The colony-stimulating activities could not be demonstrated in adherent cell-depleted bone marrow cultures. This dependence of activity on adherent cells was confirmed by incubating different concentrations of conditioned medium with isolated adherent cells and then testing for colony-stimulating activity in cultures of non-adherent bone marrow cells. The activities of conditioned media following exposure to adherent cells corresponded to the results seen when the conditioned medium from PHA-stimulated mononuclear cell cultures was used to stimulate agar cultures of unseparated marrow. The results suggest that PHA-responsive mononuclear cells (probably T lymphocytes) may modulate the regulation of colony-stimulating factor (CSF) production by adherent colony-stimulating cells (CSC).
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