The time course of leucocyte colony-formation in cultures of bone-marrow progenitor cells from rats and dogs

The colony-forming units granulocyte and macrophage (CFU-GM) assay, using either rat or dog haematopoietic progenitor cells, assesses the toxicity of new compounds. To identify the characteristics of colony formation in this system, a time-course study of CFU-GM assays using rat and dog bone marrow cells was tested. Neutrophil colonies, macrophage colonies and mixed colonies of neutrophils and macrophages were formed in soft agar medium. Neutrophil colonies reached their maximum number on days 3–4 and decreased markedly thereafter. Macrophage colonies reached their maximum number on days 7–8 and remained steady thereafter. Only a small number of mixed colonies of neutrophils and macrophages were formed beginning around day 4. There were no significant differences between rat and dog bone marrow cells in the occurrence of these maxima, or in any other growth phenomenon. This result suggests that to evaluate the influence of compounds on neutrophil colonies and macrophage colonies, observations should be made on days 4 and 8, respectively.