Background: Mast cells play a central role not only in the early phase of the allergic reaction, but also participate in the late phase of the allergic reaction through the allergen and IgE-dependent release of multifunctional cytokines.
Objective: Using the recently established culture system for human mast cells, we examined the expression of a variety of cytokines in cord blood-derived human cultured mast cells (HCMCs) in response to different stimuli.
Methods: HCMCs were grown from cord blood mononuclear cells in the presence of stem cell factor and IL-6 for 10 weeks. Cytokine mRNA expression in HCMCs by the different stimuli was examined by RT-PCR. Then taking 2 important cytokines, IL-13 and IL4, that share several functional properties and play important roles in allergic diseases, we examined protein as well as mRNA expression of both cytokines in HCMCs.
Results: HCMCs did not express either IL-13 or IL-4 spontaneously. Stimulation with PMA + A23187 induced the expression of IL4 protein, as well as IL-13 protein, in their cytoplasm, although IL-4 secreted in the supernatant was below detectable levels in contrast to a significant amount of IL-13. Stimulation of HCMCs by cross-linking of the high-affinity IgE receptor (Fc(epsilon)RI) induced the expression of IL-13 mRNA and protein, but not IL4. Although we previously found that IL-4 upregulates Fc(epsilon)RI expression on HCMCs, when HCMCs were first cultured in the presence of IL4 and then activated through FC(epsilon)RI cross-linking, remarkable increase was found in IL-13 production. Furthermore, although IL-4 was still undetectable at protein level, IL-4 mRNA expression was induced in the IL-4-primed HCMCs stimulating Fc(epsilon)RI cross-linking. In addition, we examined the effects of these cytokines on the surface molecule expression in HCMCs. Although IL4 remarkably upregulated lymphocyte function-associated antigen-1, intercellular adhesion molecule-1, and Fc(epsilon)RI expression and downregulated c-kit expression in HCMCs, IL-13 did not.
Conclusions: Our observation that HCMCs produce IL-13 on cross-linking of Fc(epsilon)RI, which was enhanced by IL-4 priming, supports an important role of mast cells in amplification of allergic reaction and further suggests one of the mechanisms enhancing mast cell function in the microenvironment.