Detection of tryptase−, chymase+ cells in human CD34+ bone marrow progenitors

Summary 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.