IL-12 is dysregulated in macrophages from IRF-1 and IRF-2 knockout mice

Macrophages derived from IFN-regulatory factor-1 (IRF-1) and IRF-2 knockout (-/-) and wild-type (+/+) mice were utilized to examine the role of these transcription factors in the regulation of IL-12 mRNA and protein expressio n, induction of IL-12 p40 mRNA by LPS was markedly diminished in both IRF-1 (-/-) and IRF-2(-/-) macrophages. In contrast, IRF-1(-/-), but not IRF-2(-/ -) macrophages exhibited impaired LPS-induced IL-12 p35 mRNA expression. Th e ability of IFN-gamma to augment LPS-induced IL-12 p40 mRNA further when b oth stimuli were present simultaneously was significantly diminished in bot h IRF-1(-/-) and IRF-2(-/-) macrophages, with the most profound impairment observed for IRF-1(-/-) macrophages. Reductions in IL-12 mRNA expression af ter stimulation with LPS or LPS plus IFN-gamma were accompanied by substant ial reductions in IL-12 p40 and IL-12 p70 protein in both IRF-1(-/-) and IR F-2(-/-) macrophages. Priming IRF-1(-/-) and IRF-2(-/-) macrophages with IF N-gamma for 24 h before LPS treatment partially restored impaired IL-12 mRN A and protein production in both IRF-1(-/-) and IRF-2-/- macrophages. Depre ssed IL-12 levels were paralleled by significant reductions in IFN-gamma mR NA expression in IRF-1(-/-) and IRF-2(-/-) macrophages. These results indic ate that both IRF-1 and IRF-2 are critical transcription factors in the reg ulation of macrophage IL-12 and consequently IFN-gamma production.