Comparative cytokine gene expression: regulation and release by human mast cells

Since data on the ability of human mast cells to produce various cytokines are scanty, we examined the mRNA expression, its modulation and the resulting protein expression of a number of well-characterized cytokines, using semi-quantitative reverse transcription-polymerase chain reaction of cell extracts and enzyme-linked immunosorbent assays for analysis of cell supernatants. One million cells/ml of the human mast cell line HMC-1 were stimulated with 25 ng/ml phorbol myristate acetate (PMA), 5 x 10(-7) M calcium ionophore A 23187 (ionophore) or both stimuli combined for various time periods. Constitutive expression in unstimulated cells was found for interleukin-1 beta (IL-1 beta) -3, -4, -8, tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta). Maximal mRNA up-regulation was observed by 2-4 hr, with a second peak for TNF-alpha at 24 hr. After a 4-hr stimulation, IL-13 expression was detectable as well, whereas for IL-12, only the p35 but not the p40 chain was found, and IL-2, -5, -7 and interferon-gamma (IFN-gamma) were not expressed at all. Large quantities of IL-8, TNF-alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-3 were secreted time-dependently over a 72-hr period, with lower levels of IL-1 beta, -6, -10 and TGF-beta and no detectable IL-2, -4 and IFN-gamma protein. When IL-6 and IL-8 expression was compared in more detail, IL-6 mRNA was found to be up-regulated only with ionophore but not PMA, whereas both stimuli alone or combined increased IL-8 mRNA expression. Preincubation with cycloheximide inhibited IL-6 but not IL-8 transcription, and incubation of stimulated cells with actinomycin D stabilized IL-8 and also IL-6 mRNA. These data suggest a selective regulation of distinct cytokines in human mast cells at the transcriptional and post-transcriptional levels. Furthermore, the spectrum of cytokines produced by HMC-1 cells supports the well-recognized role of mast cells in immediate-type hypersensitivity reactions as well as their potential colony-stimulating and tissue-remodelling abilities.