Promoting effect of IFN-γ on the expression of LPS-induced IL-12 p40 and p35 mRNA in murine suppressor macrophages

We detected the expression of IL-12 p40/p35 mRNA by semi-quantitative RT-PCR and silver staining, and studied the molecular interaction between the IL-12 expression and the NF-kappaB activation induced by LPS and IFN-gamma /LPS in murine peritoneal suppressor macrophages (MPSMs). It was found that IFN-gamma strongly enhanced the LPS-induced IL-12 p40 and p35 mRNA expression. Both p40 and p35 mRNA levels were approximately equal. IFN-gamma also greatly promoted the LPS-induced secretion of IL-12 p70 in MPSMs. The Proteasome Inhibitor I (PSI) could block the expression of IL-12 p40 and p35 mRNA, and the degradation of I kappaB alpha induced by LPS or LPS/IFN-gamma. EMSA showed that LPS could augment the NF-kappaB binding activity to p40 promoter DNA. However, IFN-gamma could neither enhance the LPS-induced NF-kappaB activity nor promote the degradation of I kappaB alpha. Taken together, the data suggest: (i) IFN-gamma /LPS could strongly induce the expression of IL-12 p40 and p35 mRNA; both the expression levels were equal; this phenomenon coincided with the high-level secretion of IL-12 p70 induced by IFN-gamma /LPS; (ii) NF-kappaB signal pathway is essential for IFN-gamma /LPS to induce IL-12 mRNA expression; (iii) by blocking the degradation of I kappaB, the PSI suppresses the IL-12 p40/p35 mRNA expression induced by LPS and IFN-gamma /LPS; (iv) NF-kappaB signal may not be involved in the mechanism by which IFN-gamma enhanced the expression of the LPS-induced IL-12 p40/p35 mRNA.