The novel cytokine p43 induces IL-12 production in macrophages via NF-κB activation, leading to enhanced IFN-γ production in CD4 ⁺ T cells

Recently, we determined that p43, an auxiliary factor of mammalian multiaminoacyl-tRNA synthetases, is secreted, and functions as a novel pleiotropic cytokine. In this study, we have attempted to characterize the effects of p43 on the generation of IL-12 in mouse macrophages. p43 was determined to induce significant IL-12 production from mouse macrophages in a dose-dependent manner. The stimulatory effect of p43 on the activation of IL-12p40 promoter was mapped to a region harboring an NF-κB binding site. The nuclear extracts from the p43-stimulated macrophages exhibited profound NF-κB DNA-binding activity, as determined by the EMSA. In addition, the p43-stimulated IL-12 induction and NF-κB DNA-binding activity were significantly suppressed by caffeic acid phenethyl ester and BAY11-7082, both inhibitors of NF-κB activation, indicating that p43 induced the production of IL-12 in macrophages mainly via the activation of NF-κB. Importantly, p43 increased the level of IFN-γ production in the Ag-primed lymph node cells, but had no effect on IL-4 levels. The addition of a neutralizing anti-IL-12p40 mAb to the cell cultures resulted in a decrease of the production of p43-enhanced IFN-γ by the keyhole limpet hemocyanin-primed lymph node cells. Furthermore, coincubation with p43-pretreated macrophages enhanced the production of IFN-γ by the keyhole limpet hemocyanin-primed CD4 ⁺ T cells, thereby indicating that p43 may enhance IFN-γ expression in CD4⁺ T cells via the induction of IL-12 production in macrophages. These results indicate that p43 may play an essential role in the development of the Th1 immune responses associated with cancer immunotherapy and protective immunity against intracellular pathogens.