MYELOID DIFFERENTIATION IN CULTURES OF HUMAN HEMATOPOIETIC PRECURSOR CELLS

Culture conditions support the early phase of myeloid differentiation. Mechanisms of regulation can therefore be recognized in vitro by differential counts of neutrophil, macrophage, and eosinophil colonies under varying conditions. From such studies information of theoretical and clinical interest has emerged: Neutrophils and macrophages mature along a common pathway, from which the eosinophil line separates at an early stage of differentiation. Specific regulators exist for each of the three pathways. Colony-stimulating factors acting at the level of neutrophil, eosinophil, and macrophage precursor cells are detectable in vitro. They initiate maturation which is probably completed by other factors in vivo. An increase of macrophage and eosinophil colonies without monocytosis and eosinophilia in vivo is frequently observed in malignant disease. This phenomenon is likely to reflect a tumor defense mechanism. The relative frequency of various precursor cells in the circulation does not reflect their distribution in the bone marrow. There seems to be a prevalence of immature cells in peripheral blood. © 1979 Springer-Verlag.