CSF-responsive bone marrow cells in liquid culture: characterization and screening applications.

In a previous study, colony-stimulating factor (CSF) activity assayed in colony culture correlated closely with 3HTdR uptake by human marrow cells depleted of adherent cells. To use this assay for screening media for CSF and immunotoxins for marrow toxicity, cells growing in liquid culture were compared to conventional granulocyte/macrophage (CFU-gm) colony assays. CSF dose-response relationships for liquid and colony-forming assays were nearly identical. 3HTdR uptake by nonadherent marrow cells was CSF dose-related, and there was a linear relationship between number of cells cultured and 3HTdR uptake. Ricin cytotoxicity curves for liquid cultures and CFU-gm were identical on day 7 but showed some disparity with day 14 cultures. Results with all cultures showed 3HTdR uptake to be most closely correlated with CFU-gm colony, rather than cluster, growth. Myeloid cell differentiation in liquid culture was similar to colony cultures, producing mixtures of granulocytes, macrophages and eosinophils. By combining cell and differential counts, production of various myeloid cells could be quantitated. Cytotoxicity of anti-Ia for CFU-gm and liquid culture cells was compared and the majority of both cell populations expressed Ia-like antigens. Simultaneous staining for surface antigens and DNA content was used to characterize proliferating marrow cells, and the vast majority of cells expressed myeloid markers. Transferrin receptors were displayed by cells in S/G2/M and appeared after CSF stimulation on G0/G1 cells. We conclude liquid cultures can be used to screen conditioned media for human CSF and to screen for cytotoxicity to normal myeloid precursor cells. Behavior of CSF-responsive cells in liquid culture appears most closely related to that of CFU-gm colony-forming cells, and characterization of CSF-stimulated cells allows quantitative as well as qualitative estimates of myeloid cell production.