A critical role of IL-2 for the production and gene transcription of IL-5 in allergen-specific human T cell clones

The role of IL-2 in IL-5 synthesis of human helper T cells was investigated. All of the Der f II (a major allergen of house dust mite)-specific T cell clones established from atopic asthmatic patients produced both IL-2 and IL-4 upon activation (Th0 phenotypes). Recombinant IL-2 induced gene expression and protein synthesis of IL-5 in T cell clones that produced IL-5 upon antigenic stimulation. Human IL-5 promoter/enhancer-luciferase gene construct transfected to T cell clones was clearly transcribed in response to IL-2, indicating that the ~500 bp gene segment 5' upstream of the coding region was functionally sufficient for the gene transcription induced by IL-2. IL-2induced IL-5 synthesis as well as proliferation was dependent on tyrosine kinases. Moreover, IL-5 production by T cell clones stimulated with immobilized anti-CD3 antibody was completely abrogated by anti-IL-2 neutralizing antibody, suggesting that IL-5 (a Th2 cytokine) synthesis of human helper T cells is dependent on IL-2 (a Th1 cytokine). Our present findings clearly demonstrated that IL-2, known as a T cell growth factor, exerts a cytokine promoting activity on T cells. IL-2 produced at the site of allergic inflammation might facilitate eosinophilic inflammation by inducing IL-5 production in T cells.