Differential regulation of the IL-12 p40 promoter and of p40 secretion by CpG DNA and lipopolysaccharide

Challenge of macrophages with DNA containing an internal CpG moth results i n IL-12 p40 secretion. In the presence of IFN-gamma, CpG DNA induces more p 40 secretion than does LPS, In the RAW 264 macrophage cell line, both CpG D NA and LPS activate a p40 promoter-reporter construct, and the promoter res ponse to either agent is augmented 2- to 5-fold by IFN-gamma. While either LPS or CpG DNA induces p40 promoter activity, only CpG DNA induces an incre ase in p40 mRNA or protein secretion. Even though IFN-gamma augmented LPS-d riven p40 promoter activity in RAW 264 cells, the combination of IFN-gamma and LPS induced less p40 mRNA or protein Secretion than the combination of IFN-gamma and CpG DNA. The ability of IFN-gamma to augment LPS or CpG DNA-i nduced p40 promoter activation was observed with truncation mutants of the IL-12 promoter containing as few as 250 bp 5' of the TATA box. Although LPS alone is a poor inducer of p40 transcription, both LPS and CpG DNA induce similar nuclear translocation of NF-kappa B. This binding is not augmented by costimulation with IFN-gamma. Thus, CpG DNA induces p40 transcription by a mechanism that includes NF-kappa B translocation; however, CpG DNA appea rs to induce other factor(s) necessary for p40 transcription. These results illustrate fundamental differences between CpG DNA and LPS with respect to activation of IL-12 p40 secretion.