Background Mast cells (MCs) arise from haematopoietic stem cells. We have recently reported that CD34+ progenitors derived from human bone marrow (BM) develop into tryptase+, chymase+ MCs when cultured in the presence of recombinant human stem cell factor (rhSCF) and recombinant human IL-6 (rhIL-6). In an experiment for the expression of chymase during differentiation, chymase+ cells were detected in human BM, but tryptase+ cells were not found.
Objective The purpose of this study was to show the appearance of chymase+ cells in CD34+ cells with an origin different from MC differentiation.
Methods CD34+ cells from human BM were sorted with anti-CD117 monoclonal antibody (mAb), and cytospins of CD34+, CD34+CD117+, or CD34+CD117− were prepared. These cells were cultured with rhSCF+rhIL-6 for 12 weeks. Some of the cells were subjected to either histological stain with Wright–Giemsa or immunocytochemistry with anti-chymase mAb. Real-time RT-PCR was also performed to compare the transcriptional level of chymase from each cell preparation.
Results Chymase was expressed in CD34+ cells as well as human MCs by immunocytochemistry. Substantial CD34+CD117− cells, but not CD34+CD117+ cells, were stained immunocytochemically with anti-chymase mAb. For 1 week culture with rhSCF+rhIL-6, no cells expressed chymase in any preparation. Real-time RT-PCR revealed positivity for chymase mRNA in CD34+ cells, but it reduced at 1 week of culture, and increased as cells developed into MCs. Chymase mRNA in CD34+CD117+ cells was negligible compared with that in CD34+CD117−. Tryptase mRNA was below the detectable level in CD34+ cells, and increased along with MC differentiation. After 12 weeks of culture, CD34+CD117+ developed predominantly into MCs, whereas CD34+CD117− developed into monocytes/macrophages.
Conclusion Our findings suggested that chymase is present not only in MCs but also in CD34+CD117− BM progenitors, but that its origin is different from the MC lineage.