Regulation of Cytokine Gene Expression in T Helper Cell Subsets

We have examined the transcriptional regulation of the Th1-specific IL-2 gene and the Th2-specific IL-4 gene by transient transfection of promoter-chloramphenicol acetyl transferase (CAT) constructs into T cell clones and by electrophoretic mobility shift assays. Transfection of the Th2 clone D10.G4 with IL-4 promoter-CAT constructs demonstrated anti-CD3 inducible IL-4 promoter activity. In contrast, CAT constructs containing murine IL-2 promoter sequences were not inducible in D10.G4 cells. Transfection analyses in the Th1 clone D1.1 demonstrated inducible IL-2 promoter activity but no IL-4 promoter activity. Electrophoretic mobility shift assays using well-defined regulatory elements in the murine IL-2 gene promoter showed that anti-CD3 stimulation of Th2 clones failed to induce a characteristic increase in the ratio of p65-p50:p50-p50 NF-kappa B binding complexes in the nucleus that did occur in IL-2-producing clones. In addition, other protein complexes with NF-kappa B binding sequences were seen using lysates from Th1 and Th0 cells but not Th2 cells. Thus, expression of the promoter-CAT constructs directly correlates with endogenous IL-2 and IL-4 gene expression in Th1 and Th2 clones, confirming that the differential expression of IL-2 and IL-4 genes in these T cells is transcriptionally controlled. Furthermore, the lack of IL-2 transcription in activated Th2 cells is associated with the failure to generate required IL-2 gene promoter binding proteins, particularly NF-kappa B in the nucleus.