DEXAMETHASONE SUPPRESSES GENE-EXPRESSION AND PRODUCTION OF IL-13 BY HUMAN MAST-CELL LINE AND LUNG MAST-CELLS

Background: IL-13 has been shown to induce IgE production in B cells b y promoting class switching to IgE. Mast cells are known to play an im portant role in the pathogenesis of allergic diseases. We evaluated th e ability of human mast cells to produce IL-13 using human mast cell l ine HMC-1 and freshly isolated lung mast cells and then examined the e ffect of dexamethasone on the gene expression and production of IL-13 by these cells. Methods: HMC-1 cells and lung mast cells were cultured with 10 ng/ml phorbol l2-myristate U-acetate (PMA) and 1 mu mol/L ion omycin and with 5 mu g/ml phytohemagglutinin (PHA) and 10 ng/ml PMA, r espectively, in the presence of dexamethasone. The gene expression of IL-13 at 3 hours (HMC-1 cells) or 12 hours (human lung mast cells) aft er stimulation was assessed semiquantitatively by sequential reverse t ranscription-polymerase chain reaction and Southern blot analysis. IL- 13 production at 12 hours after stimulation was assayed by ELISA. Resu lts: The gene expression of IL-13 by HMC-1 cells and human lung mast c ells, which was detected at a low level in an unstimulated condition, was increased by PMA/ionomycin and suppressed by dexamethasone. The su pernatant of HMC-1 cells and human lung mast cells showed a low level of IL-13, which was increased by the stimulation and suppressed by dex amethasone, Conclusion: These findings indicate that HMC-1 cells and h uman lung mast cells produce IL-13 and that dexamethasone suppresses t he production of IL-13 by these cells through an inhibitory action on the gene expression.