Relationships between Early Hemopoietic Progenitor Cells Determined by Correlation Analysis of Their Numbers in Individual Spleen Colonies

Abstract

Differentiation in the hemopoietic system is a complex process involving a progression of changes that extend through many cell divisions. In the most mature hemopoietic cells, the results of differentiation can be visualized directly and morphologic criteria can therefore be used to determine the relative positions of cells in the terminal stages of blood cell production. Detection of earlier cell types has relied on the development of assay procedures that exploit the capacity of primitive hemopoietic cells to give rise to colonies of mature progeny under appropriate conditions in vivo or in culture. A variety of such colony assays now exist (1, 3, 10, 11, 13, 14, 16, 17), and their use has led to a conceptual model of the hemopoietic system which makes a distinction between pluripotent stem cells or spleen colony-forming units (CFU-s), and secondary progenitor cell types still capable of extensive proliferation but committed to differentiation along a single pathway (9). Examples of this latter class of progenitor have been identified for bopth the granulopoietic and erythropoietic pathways. These are the progenitors of the granulopoietic colonies and the progenitors of the large erythroid bursts detected by established in vitro assay procedures (1, 3, 13), historically referred to as CFU-c (originally the only “colony-forming unit in culture”) and BFU-e (“erythropoietin-dependent burst-forming unit”), respectively.