TLR8 couples SOCS-1 and restrains TLR7-mediated antiviral immunity exacerbating West Nile virus infection in mice

Abstract

West Nile virus (WNV) is a neurotropic, single-stranded RNA (ssRNA) flavivirus that can cause encephalitis, meningitis, and death in humans and mice. Human Toll-like receptor (TLR) 7, 8, and mouse TLR7 recognize viral ssRNA motifs and induce antiviral immunity. However, the role of mouse TLR8 in antiviral immunity is poorly understood. Here, we report that TLR8 deficient ( Tlr8 ^−/− ) mice were resistant to WNV infection compared to wild-type (WT) controls. Efficient WNV clearance and moderate susceptibility to WNV-mediated neuronal death in Tlr8 ^−/− mice was attributed to overexpression of Tlr7 and an interferon-stimulated gene Isg-56 expression, while reduced expression of the pro-apoptotic gene coding Bcl2-associated X protein ( Bax) was observed. Interestingly, suppressor of cytokine signaling -1 (SOCS-1) directly associated with TLR8, but not with TLR7, indicating a novel role for TLR8 regulation of SOCS-1 function, while selective siRNA knockdown of Socs-1 resulted in induced Isg-56 and Tlr7 expression following WNV infection. Collectively, we report that TLR8 coupling with SOCS-1 inhibits TLR7-mediated antiviral immunity during WNV infection in mice.