New Type of Colony-forming Cell located in the Pleural Cavity

A semi-solid agar culture system has been developed which supports the clonal growth of granulocytic and/or macrophage colonies from their specific progenitor cells^1,2. In the course of studies on the level of these progenitor cells in the peripheral blood of mice, whole blood was cultured in agar-medium. Cultures were prepared in 35 mm plastic Petri dishes and each culture contained 1 ml. of 0.3% agar in modified Eagle's medium. The media and general technique of agar culture have been described elsewhere³. In these experiments, 0.2 ml. of whole, unheparinized blood was taken directly from the axilla of anaesthetized 3 months old C57BL mice and added to 5 ml. of agar-medium, held liquid at 37° C. One ml. portions of this mixture were pipetted into four replicate culture dishes, allowed to gel and incubated for 7 days at 37° C in a fully humidified atmosphere of 10% CO₂ in air. Each culture contained 0.1 ml. of a 1:6 dilution of pooled sera from C57BL mice injected 3 h previously with 5 µg endotoxin to provide an adequate concentration of the specific colony-stimulating factor (CSF), required for granulocytic and macrophage colony formation.