Interleukin-4 promotes the development of tryptase and chymase double-positive human mast cells accompanied by cell maturation.

Human cultured mast cells (HCMCs) grown from cord blood mononuclear cells in the presence of stem cell factor (SCF) and interleukin-6 (IL-6) expressed tryptase but no or low chymase in their cytoplasm. The addition of IL-4 to these cells strikingly increased chymase expression. Consequently, the activity of chymase was significantly higher in IL-4-treated mast cells than that in IL-4-nontreated mast cells, whereas the activity of tryptase and histamine content were comparable in both cells. Electron microscopic immunocytochemistry also showed that secretary granules containing chymase increased in IL-4-treated mast cells. Interestingly, the IL-4-induced increase of chymase expression in HCMCs was accompanied by morphological maturation of the cells. Cytoplasmic projections were few in IL-4-nontreated HCMCs, and a small number of secretary granules were observed, most of which were empty or partially filled with discrete scrolls with rough particles showing immaturity. In contrast, IL-4-treated HCMCs had extremely abundant cytoplasmic projections and had many secretary granules filled with electron-dense crystal materials. Taken together, immature HCMCs grown only with SCF and IL-6 expressed tryptase with no or a low amount of chymase, and addition of IL-4 promoted cell maturation together with the expression of both tryptase and a high amount of chymase. Our findings will raise a possibility of a linear pathway of human mast cell development from tryptase single positive mast cells into tryptase and chymase double positive mast cells as the cells mature and will suggest that this maturation process is promoted by IL-4.