The effects of thrombopoietin (TPO) and/or stem cell factor (SCF) on the development of human mast cells from CD34+ bone marrow (BM) cells were investigated using a serum-deprived liquid culture system. Mast cells were identified by measurement of intracellular histamine content, immunocytochemical staining, and flow cytometric analysis. Whereas SCF alone generated only a small number of tryptase+ cells, the addition of TPO to the culture containing SCF resulted in an apparent production of mast cells from 3 weeks until at least 15 weeks. Some of the cells reacted with an antichymase monoclonal antibody as well. Based on the effects of growth factor(s) on a later phase of the mast cell growth, TPO may stimulate an early stage of mast cell development in combination with SCF, whereas subsequent growth seems to be supported by SCF alone. Single-cell culture studies indicated that the CD34+CD38−c-kit+ cells and CD34+CD38+c-kit+ cells were responsible for the SCF + TPO–dependent mast cell production. Two-step culture assays clearly showed that mast cells originated from multilineage colony-forming cells that had potential to differentiate into neutrophil/mast cell lineages, neutrophil/macrophage/mast cell lineages, or neutrophil/macrophage/mast cell/erythroid lineages. These results suggest that TPO plays an important role in the development of human mast cells from CD34+ BM cells in concert with SCF, and provide direct evidence of the differentiation into the mast cell lineage of human multipotential BM-derived progenitors.
We examined the effects of retinoids on the human mast cell development using a serum-deprived culture system. When 10-week cultured mast cells derived from CD34+ cord blood cells were used as target cells, both all-trans retinoic acid (ATRA) and 9-cis RA inhibited the progeny generation under stimulation with stem cell factor (SCF) in a dose-dependent manner (the number of progeny grown by SCF plus RA at 10−7 mol/L was one tenth of the value obtained by SCF alone). The early steps in mast cell development appear to be less sensitive to RA according to the single CD34+c-kit+ cord blood cell culture study. The optimal concentration of RAs also reduced the histamine concentration in the cultured mast cells (3.00 ± 0.47 pg per cell in SCF alone, 1.44 ± 0.18 pg per cell in SCF+ATRA, and 1.41 ± 0.10 pg per cell in SCF+9-cis RA). RT-PCR analyses showed the expression of RAR, RARβ, RXR, and RXRβ messenger ribonucleic acid (mRNA) in 10-week cultured mast cells. The addition of an RAR-selective agonist at 10−10 mol/L to 10−7 mol/L decreased the number of mast cells grown in SCF, whereas an RXR-selective agonist at up to 10−8 mol/L was inactive. Among RAR subtype selective retinoids used at 10−9 mol/L to 10−7 mol/L, only the RAR agonist was equivalent to ATRA at 10−7 mol/L in its ability to inhibit mast cell growth. Conversely, the addition of excess concentrations of a RAR antagonist profoundly counteracted the retinoid-mediated suppressive effects. These results suggest that RA inhibits SCF-dependent differentiation of human mast cell progenitors through a specific receptor.
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