PHENOTYPIC CHARACTERIZATION OF STEM-CELL FACTOR-DEPENDENT HUMAN FETALLIVER-DERIVED MAST-CELLS

Human foetal liver cells are an enriched source of mast cell progenito rs that complete their differentiation and mature in response to stem cell factor, the ligand for Kit, in liquid culture. These mast cells a re Kit+, metachromatic with toluidine blue+, tryptase+, histamine+ and show ultrastructure features of mast cells. Using a panel of monoclon al antibodies (mAb) against different cell-surface antigens (33 mAb we re used), the cell-surface phenotype of human stem cell factor-depende nt foetal liver-derived mast cells was examined by flow cytometry. Con sistent with previous reports on tissue-derived mast cells, those deri ved from foetal liver in vitro expressed HLA class I, CD9, CD29, CD33, CD43, CD45 and Kit. Unlike mast cells dispersed from tissue, a high e xpression of CD13 was found. Also, these in vitro-derived mast cells e xpress little, if any, high-affinity IgE receptor. However, small amou nts of mRNA for the alpha-chain in foetal liver-derived mast cells com pared to KU812 cells (a human basophil-like cell line) could be detect ed by Northern blotting. Full expression of FcepsilonRI may require ad ditional growth factor(s).