Differentiation restriction in the neutrophil-granulocyte, macrophage, eosinophil-granulocyte pathway: Analysis by equilibrium density centrifugation

Bone marrow culture techniques and equilibrium density centrifugation of human bone marrow cells were used to analyse the neutrophil-granulocyte, macrophage and eosinophilgranulocyte progenitor hierarchy. The buoyant density of progenitor cells changes as cells differentiate down the granulocyte-macrophage pathway and this allows the construction of a density ‘map’ of the points at which differentiation decisions are made. Unipotent progenitors, neutrophil-granulocyte (G), monocyte-macrophage (M), eosinophil-granulocyte (Eo), are more dense than bi- and tripotent progenitors (GM and EoGM) and have a lower 7-day proliferative capacity (assessed as the clone size achieved in maximally stimulated agar cultures). Experiments in which marrow cells were separated on a basis of their density and either cultured in agar immediately or after an interval of 6 days in suspension culture, were performed to establish the density of the cells which give rise to each type of progenitor, i.e. to investigate parent-progeny relationships. In each case the patent cells were of lower density than the unipotent or bipotent progenitor in question. The ability to separate, at least partially, unipotent, bipotent and multipotent cells of closely related lineages is important since it facilitates studies of the intracellular events taking place as restriction of the cell's differentiation options takes place.