| Abstract: |
In hematopoietic cells, an ontogeny-dependent difference in telomere length has been reported, as has the shortening of telomeres when primitive hematopoietic cells were stimulated to proliferate extensively in vitro, following cytokine stimulation. Clonogenic assays for primitive progenitors require synergistic cytokine interaction and, consequently, ex vivo suspension cultures designed for expansion of such cells utilizing various cytokine combinations. Multiple cytokines with overlapping activities are implicated in proliferation and differentiation of primitive progenitors. In general, the hematopoietic growth factors are necessary for the expression of a pathway of differentiation but should be considered as permissive agents rather than instructive, since the “choice” of a differentiation pathway elected by a previously uncommitted cell is stochastically determined. Modulation of negative regulatory influences may also be important in the physiology of stem cells and primitive progenitors. A number of cytokines have been implicated in suppression of stem and progenitor cell proliferation. © 1998 Taylor & Francis. |
