IL-9 increases the expression of several cytokines in activated mast cells, while the IL-9-induced IL-9 production is inhibited in mast cells of histamine-free transgenic mice.

Histamine and IL-9 are suspected to play an important role in the pathogenesis of asthmatic and allergic reactions. Mast cells store a large amount of histamine in their granules and are capable of producing different cytokines upon stimulation. In this study we show that mast cells stimulated by IL-9 and ionomycin or IL-9 and antigen-specific IgE/antigen express several cytokines at mRNA level, among them are IL-5, IL-4, IL-10, IL-9, IL-13, IL-1beta, IL-1Ra, IL-6 and MIF. Furthermore, both IL-9 and ionomycin are needed for the production of these cytokines in great quantities, which is mediated through the production of IL-1beta. Histamine-free mast cells respond by a markedly decreased IL-9 expression to this stimulation. Our results show that this IL-9-induced IL-9 production may result in a positive feedback loop in mast cells and the lack of histamine disturbs this loop, which may serve as an explanation for the reduced asthmatic symptoms, observed in histamine-free mice. Copyright 2004 Elsevier Ltd.