The self-renewal process of murine hemopoietic stem cells supported by interleukin-3 and the synergistic factors and the probability of its occurrence.

: By use of the in vitro murine blast cell colony (Bl) assay system, Bl-constituting cells supported by interleukin-3 (IL-3), IL-3 + interleukin-6 (IL-6), IL-3 + granulocyte colony-stimulating factor (G-CSF) and IL-3 + interleukin-1 (IL-1) were replated and the frequencies of secondary (2nd) granulocyte/erythrocyte/macrophage/megakaryocyte (GEMM) colony and Bl progenitors were examined. According to the statistical method reported by Nakahata et al, the p values for the hemopoietic stem cells to self-renew were calculated and all cytokine groups produced similar p values ranging between 0.576 and 0.596. Further studies using IL-3-supported and IL-3 + G-CSF-supported Bl showed that the 2nd Bl progenitors could be produced even when there were more than 150 primary Bl-constituting cells per colony in the case of IL-3 + G-CSF, but no 2nd Bl progenitors were found in the case of IL-3. Their appearance was limited within the smaller primary Bl when supported by IL-3. Again there was a difference in the net product number of 2nd Bl progenitors, that is, the addition of G-CSF to the primary culture could produce around double the number of 2nd Bl progenitors. These data led us to hypothesize that synergistic factors could not modify the self-renewal probability, but maintained the self-renewal process for a longer period, in other words, for several cellular divisions.