A characteristic feature of allergic asthma is the overexpression of the T helper type 2 (Th2) cytokines interleukin‐4 (IL‐4), IL‐5 and IL‐13 by T lymphocytes. Of these cytokines, IL‐5 is critical for the growth, survival and recruitment of eosinophils which are thought to be responsible for the tissue damage observed in asthmatic airways. The expression of human IL‐5 is primarily regulated at the transcriptional level; however, little is known about the mechanisms that control its transcription. Using nuclear extracts from allergen‐specific human T‐cell clones we have performed DNase I footprinting of the human IL‐5 promoter in order to establish sites occupied by transcription factors. We show footprints covering the conserved lymphokine element 0 [(CLE0) – 60 to – 44 base pairs (bp)] and GATA (– 73 to – 62 bp) elements, which have previously been identified to be important in the regulation of the murine IL‐5 promoter. We also describe a footprint covering a considerably extended Octamer binding site (– 249 to – 217 bp), which encompasses two hitherto unidentified CCAAT/enhancer binding protein consensus binding sites. We have also identified a previously unknown Ets binding site (– 274 to – 264 bp). These novel data on the regions of the human IL‐5 promoter that are bound by transcription factors should allow dissection of the regulatory mechanisms involved in the transcription of IL‐5 in the T‐helper lymphocytes of asthmatics
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