REVISED CYTOKINE NETWORK IN THE EARLY STAGES OF HEMATOPOIESIS

The production of various blood cells is regulated by many hematopoietic cytokines. Granulocyte colony-stimulating factor(G-CSF)/granulocyte-macrophage colony-stimulating factor(GM-CSF), erythropoietin(EPO), and thrombopoietin(TPO) are cytokines in granulocyte/macrophage, erythrocyte, and platelet lineages, respectively. EPO acts on erythroid lineage, while TPO acts on hematopoietic stem and progenitor cell(HSPC). How G-CSF and GM-CSF regulate HSPC is poorly understood. Here we clarified the effect of G-CSF and GM-CSF, compared with that of TPO. Methods:Single HSC1(LTHSC), HSC2(ST-HSC), HPC1(CMP), HPC2(MPP1,2), HPC3(MPP3), and HPC4(LMPP) cells were cultured for 7 days. For transplantation, freshly isolated cells and cultured cells were transplanted.Results:SCF supported the in vitro survival of HSC1, HPC1,2,3, but not of HSC2 and HPC4. SCF+G-CSF did not significantly induce division of HSC1, but induced HSC2 and HPC1 a few times, and induced HPC2,3,4 many times. SCF+GM-CSF did not significantly induce division of HSC1,2, HPC1,2, but induced HPC3,4 many times. SCF+TPO induced division of HSC1,2, HPC1,2,3, but not of HPC4. SCF-cultured HSC1 displayed stable reconstitution, and SCF+G-CSF or SCF+GM-CSF-cultured cells displayed comparable levels of reconstitution. However, SCF+TPO-cultured cells displayed gradually decreased level of reconstitution after secondary transplantation. SCF+G-CSF-cultured HSC2 maintained higher level of reconstitution than did SCF or SCF+TPO-cultured cells. Clonal cell transplantation showed that the frequency of HSC in SCF culture was similar to that of SCF+G-CSF culture, but was greater than that of SCF+TPO culture. Conclusion:Neither G-CSF nor GM-SCF directly effected on LT-HSC. G-CSF acted on ST-HSC and MPP, while GM-CSF acted on LMPP. TPO acted on LT-and ST-HSC, but leading to substantial loss of HSC activity.Key words:HSPC,G-CSF,GM-CSF,TPO