Objective: IL-5 is strongly involved in the eosinophilic inflammation in bronchial asthma and atopic dermatitis. We have previously reported that IL-5 synthesis in atopic and nonatopic asthmatics is significantly enhanced compared to control subjects. T cell IL-5 synthesis is regulated through several transcriptional elements, one of which is the proximal human IL-5 promoter (-62 to -46). The present study was undertaken to delineate the transcriptional regulation through this element using nontransformed human T cells.
Methods: Con A blast lymphocytes which tolerate electroporation were derived from peripheral blood lymphocytes. Luciferase reporter analysis and gel shift analysis were performed.
Results: The proximal promoter element is the overlapping binding site for the constitutive binding factor, Oct-1, and the inducible one, AP-1. The transcriptional induction was ascribed to the inducible binding, while the constitutive binding was rather inhibitory. A mutant element which lost the constitutive binding but retained the inducible binding exerted 3 times more transcriptional activity compared to the wild type element. In contrast, another mutant element which lost the inducible binding and retained the constitutive binding exhibited no transcriptional induction. Gel shift analysis clarified that the inducible binding was more prominent and the constitutive binding was less in IL-5-producing T cells derived from asthma patients compared to IL-5-nonproducing cells derived from control subjects.
Conclusions: The ratio of the inducible/constitutive binding to the proximal promoter element may determine the capacity of human Th cells to transcribe IL-5 gene, and its regulation may control eosinophilic inflammation.