HSV-1 activates NF-kappaB in mouse astrocytes and increases TNF-alpha and IL-6 expression via Toll-like receptor 3

Objective: To investigate the effect of HSV-1 infection via TLR3 on the transcriptional activity of NF-kappaB and the expression of cytokines TNF-alpha and IL-6 in astrocytes. Methods: HSV-1-infected primary astrocytes were cultured until the third passage and the mRNA and protein levels of TLR3, NF-kappaB, TNF-alpha, and IL-6 were assessed by immunofluorescence, RT-PCR, and Western blot. The effects of the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) and TLR3-neutralizing antibody on the expression of NF-kappaB, TNF-alpha, and IL-6 were investigated. Results: Uninfected astrocytes expressed TLR3 and NF-kappaB at the mRNA and protein levels. After infection with HSV-1, the TLR3 mRNA and protein levels were up-regulated and NF-kappaB protein was highly expressed. Also, the mRNA and protein levels of TNF-alpha and IL-6 were up-regulated. Pyrrolidine dithiocarbamate inhibited NF-kappaB activation, resulting in the down-regulation of nuclear NF-kappaB protein, which led to the down-regulation of the mRNA and protein levels of TNF-alpha and IL-6. After blocking astrocyte membrane TLR3, the nuclear NF-kappaB protein expression was down-regulated and the mRNA and protein levels of TNF-alpha and IL-6 were increased. The antiviral functions of astrocytes were weaker, as reflected by higher HSV-1 glycoprotein D (gD) mRNA expression and increased HSV-1 titers. Conclusion: Astrocytes infected with HSV-1 can activate NF-kappaB via TLR3 so as to up-regulate the expression of TNF-alpha and IL-6 that have antiviral functions.