Separation of subpopulations of in vitro colony forming cells from mouse marrow by equilibrium density centrifugation.

Equilibrium density centrifugation was used to characterise and separate subpopulations of mouse haemopoietic progenitor cells capable of producing colonies of granulocytes and macrophages in vitro. The material used to induce colony formation (CSF) was prepared from an extract of pregnant mouse uteri. This CSF preparation was found to be free of factors modifying the response. Under these culture conditions, in vitro colony forming cells (CFU-c) were found to be relatively homogeneous in their buoyant density. This homogeneity was independent of CSF concentration. A heterogeneous density profile of CFU-c was obtained when various cell fractions were cultured in the presence of CSF and rat blood lysate. The majority of the additional cells which responded to erythrocyte lysate were dense (modal density 1.080 g/cm3) compared to CFU-c which responded to CSF alone (modal density 1.074 g/cm3). It is concluded that in vitro colonies induced by CSF and in vitro colonies grown in the presence of CSF and erythrocyte lysate reflect two different populations of CFU-c.