Regulation of chymase production in human mast cell progenitors.

BACKGROUND

Although mature tryptase-positive mast cells (MCs) and tryptase and chymase double-positive MCs are recognized using in situ staining and are preferentially distributed in different tissues, recent findings suggest that tryptase-positive MCs can give rise to tryptase and chymase double-positive MCs.

OBJECTIVE

We investigated the regulation of chymase production in developing MCs.

METHODS

Human cord blood or peripheral blood cells were cultured in the presence of stem cell factor and IL-6 with or without IL-4 in methylcellulose or liquid medium. Intracellular chymase and tryptase were determined with immunocytochemistry, flow cytometry, and ELISA. Chymase messenger RNA expression was examined with 3 different methods, such as Northern blotting.

RESULTS

Flow cytometric analysis always showed a unimodal histogram of chymase-positive, as well as tryptase-positive, cells in the presence of various cytokines, even when chymase was not detected in some MCs with immunocytochemistry. The chymase protein expression increased by culture duration and was enhanced by cytokines, such as a high concentration of stem cell factor or IL-4. Chymase messenger RNA was expressed higher in immature MCs than mature chymase protein-rich MCs. We generated macroscopic MC colonies in methylcellulose by culturing CD34(+) cells for 10 weeks and measured cellular chymase, tryptase, and histamine. The chymase/histamine ratio widely varied (0.07-1.01) depending on MC colony, even under the same culture conditions, including IL-4, whereas the tryptase/histamine ratio was relatively constant (1.02-1.89).

CONCLUSION

All human MCs in culture are capable of producing chymase, and the production is clonally regulated at their progenitors by cytokine-independent mechanisms, as well as being totally controlled by cytokine-dependent mechanisms accompanied by maturation.