Basic Biology of Growth Factors
Hematopoietic cells are derived from self-renewing, pluripotent stem cells. Pluripotent stem cells are able to differentiate into committed progenitor cells. The most primitive form of committed progenitor is termed a colony-forming unit granu-locyte, erythrocyte, macrophage, and megakaryocyte (CFU-GEMM). This cell is capable of producing colonies containing neutrophils, macrophages, erythrocytes, megakary-ocytes, eosinophils, and basophils. CFU-GEMMs appear to have a limited capacity for self-renewal, and therefore, are not true "stem cells." The committed hematopoietic progenitors (erythroid burst-forming unit [BFU-E], erythroid colony-forming unit [CFU-E], granulocyte macrophage colony-forming unit [CFU-GM], granulocyte colony-forming unit [CFU-G], macrophage colony-forming unit [CFU-M], eosinophil colony-forming unit [CFU-Eo], basophil colony-forming unit [CFU-Baso], and megakaryocyte colony-forming unit [CFU-Meg]) are capable of giving rise to colonies containing cells of only one or two types.
The hematopoietic growth factors and interleukins are cytokines that regulate the growth, differentiation, and functional activities of progenitor cells in peripheral blood, bone marrow, and placental-cord blood. A second important action of many of these factors is augmentation of the function of mature cells. Some growth factors are specific for one type of progenitor, whereas others affect many types of progenitors. Figure 26-2 illustrates the hierarchy of hematopoietic progenitor cells and the sites of responsiveness of growth factors and interleukins. Table 26-13 lists the uses of hematopoietic growth factors.
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