BUOYANT DENSITY ANALYSIS OF MYELOID COLONY-FORMING CELLS IN GERMFREE AND CONVENTIONAL MICE

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Abstract
Granulocyte-macrophage colony-forming cells (CFUc), in the bone marrow of germ-free and conventional CBA mice, were compared quantitatively and qualitatively. Cells were separated on the basis of their buoyant density by equilibrium centrifugation in continuous albumin density gradients. CFUc in the density subpopulations were detected by culture in agar containing 3 different types of colony stimulating factor (CSF). The sources of the CSF were post-endotoxin mouse serum (CSFES), mouse lung conditioned medium (CSFMLCM) and human urine (CSFHU). Mice were removed from the germ-free environment and the buoyant density status of their CFUc was examined 1, 4 and 8 wk later. No difference was found between germ-free and conventional mice in the number of nucleated cells per femur or in their modal density, nor was the number of CFUc per femur different. The cell cycle status of CFUc, as determined by the thymidine suicide technique, was not significantly different. Functional heterogeneity was found among the density subpopulations for both groups of mice. This depended on the type of CSF. The density distribution of CFUc was significantly different in germ-free mice. There were proportionately more low density CFUc. The mean modal density of CFUc under CSFES stimulation was less by 0.0045 g/cm3 in germ-free mice. The removal of mice from the germ-free environment resulted in a shift of the distribution to higher densities. The trend was towards the conventional situation. The significance of the buoyant density status of CFUc was discussed.