Requirements for growth of human erythroid progenitors in nutrient agar.

Human erythroid bursts and neutrophil colonies from fetal liver, term cord blood, and adult bone marrow were grown in nutrient agar, and the colonies were scored using a fixed whole plate method. Human placental conditioned medium was shown to contain burst promoting activity, and low oxygen tension markedly enhanced growth of erythroid bursts. Morphological analysis of colonies showed that eosinophil colonies were more numerous in bone marrow than fetal liver and conversely macrophage and neutrophil-macrophage colonies were more numerous in fetal liver. Erythroid bursts were more numerous and larger in fetal liver. Human fetal liver cells do not produce endogenous colony-stimulating factor.