| Abstract: | Fractionated cell populations from haemopoietic tissues have been examined for their yield of stem cell proliferation inhibitory or stimulatory activities. These activities show marked concentration differences depending on the proliferative state of the stem cells in the haemopoietic tissues investigated. However, irrespective of whether haemopoietic tissue contains stem cells which are actively or minimally proliferating, inhibitory activity is produced by cells with a density of 1.052-1.060 gm/cm3, whilst cells with density 1.064-1.072 gm/cm3 elaborate stimulatory material. From inhibitor/stimulator dose response studies, it is concluded that the control of stem cell proliferation is mediated by an appropriate balance of stimulatory and inhibitory factors which, however, are unlikely to be produced by the stem cells themselves. |
