[Role of interleukin-9 in asthma and allergic reactions].

Interleukin 9 (IL-9) is a cytokine produced by activated T lymphocytes and that activates in vitro mast cells as well as T and B lymphocytes. In vivo, transgenic mice overexpressing the gene encoding IL-9 show several of the hallmarks of human allergic asthma: increased IgE concentration, bronchial mastocytosis, eosinophilia, increased mucus production, as well as bronchial hyperresponsiveness. Whereas some of these features reflect direct IL-9 activities on target cells such as mast cells and B lymphocytes, increased mucus production and eosinophilia rather result from IL-13 and IL-5 production induced by IL-9 in T lymphocytes and mast cells. Preclinical studies in mice have shown that anti-IL-9 blocking antibodies interfere with the development of asthma-like reactions. In the human species, asthmatic patients produce large amounts of this cytokine and IL-9 production correlates nicely with species biological parameters of the disease. Phase 2 clinical trials are in progress to test the efficacy of anti-IL-9 antibodies in humans.