TLR3 and TLR7 are involved in expression of IL-23 subunits while TLR3 but not TLR7 is involved in expression of IFN-β by Theiler's virus-infected RAW264.7 cells

Theiler's murine encephalomyelitis virus (TMEV) infects macrophages and causes demyelinating disease (DD) in certain mouse strains. IL-23 p19/p40 and IFN-β, which are both expressed by macrophages in response to TMEV, could contribute to or prevent DD. Because TMEV may induce macrophages' cytokines through TLR3 and TLR7 (toll-like receptors), their role in TMEV-induced IL-23 and IFN-β expression by the RAW264.7 macrophage cell line was determined following infection with TMEV or stimulation with the poly (I:C) or loxoribine. TMEV infection or stimulation with poly (I:C), a TLR3 agonist, or loxoribine, a TLR7 agonist, induced expression of IL-23 and IFN-β in RAW264.7 cells. In addition, TMEV infection increased expression of TLR3 and TLR7 in RAW264.7 cells. Transfection of RAW264.7 cells with shRNA plasmid vectors expressing siRNA specific for TLR3 or TLR7 concomitantly decreased expression of TLR3 or TLR7, respectively, and TMEV-induced p19 mRNA, p19 protein, and IL-23 p19/p40. Transfection with TLR7-shRNA plasmids reduced expression of TMEV-induced p40 mRNA and p40 protein. However, transfection with TLR3-shRNA plasmids increased expression of TMEV-induced p40 mRNA but decreased p40 protein. In addition, transfection with TLR3-shRNA plasmids but not TLR7-shRNA plasmids decreased expression of TMEV-induced IFN-β mRNA. Thus TLR3 and TLR7 contribute to TMEV-induced IL-23 p19 and p40, while TLR3 contributes to TMEV-induced IFN-β.