Culture of human bone marrow in the teflon culture bag: identification of the human monoblast.

The proliferation of human bone marrow cells was studied in a liquid culture system without colony-stimulating factor. Bone marrow cells suspended in medium containing horse serum and fetal calf serum were incubated in the Teflon culture bag. During the first week there was an increase in the number of blast cells and early cells of the granulocytic series, both of which showed a high 3H-thymidine labeling index. The total number of mononuclear phagocytes increased during the first two weeks of culture. A number of characteristics of the cultured cells (alpha-naphthyl butyrate esterase, N-acetyl-DL-alanyl alpha-naphthyl esterase, Fc receptors, and phagocytosis) were determined. It was not feasible to recognize promonocytes and monoblasts with light microscopy, but with electron microscopy and the use of peroxidatic activity as marker, monoblasts and promonocytes were identified. The monoblast is a round cell with a few surface microextensions, a large nucleus, and few cytoplasmic granules. The nuclear envelope, the rough endoplasmic reticulum, and the granules show peroxidatic activity.