A highly sensitive and specific assay using a novel human growth hormone cDNA reporter gene regulated by the human interleukin-4 inducible germline epsilon transcript promoter.

We have successfully developed a highly sensitive and specific assay system for human interleukin-4 (IL-4) regulated gene expression. It is based on a human Jijoye cell line with the germline epsilon transcript promoter joined to the human growth hormone (hGH) cDNA. The germline epsilon transcript promoter is responsive to IL-4 and involved in immunoglobulin heavy chain class switching. We cloned hGH complementary DNA (cDNA) as the reporter gene instead of using conventional hGH genomic DNA which failed to generate any IL-4 inducible clone in human Jijoye cells. The two IL-4 inducible cell lines with the hGH cDNA reporter show high signal/noise ratio for IL-4-mediated induction (60-90 fold). The response to IL-4 is dose-dependent with ED50 of 10 pM. As expected, there is no response to other human cytokines and growth factors, as well as mouse IL-4. The mutant hIL-4 antagonist hIL-4.Y124D inhibits the induction mediated by native hIL-4. These IL-4 inducible cell lines provide a sensitive, specific assay system to study IL-4-regulated gene expression, and in particular the regulation of the germline epsilon promoter.