Toll like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA), an intermediate product during viral replication for most viruses. TLR3 is expressed in various tissues and cells including cells of the central nervous system (CNS) (Bsibsi M et al. 2002). TLR3 activity in neurons and glial cells was found to be critical for controlling herpes simplex virus type 1 (HSV-1) infection in CNS (Lafaille FG et al. 2012). Children with inborn errors of TLR3-mediated immunity are prone to HSV-1 encephalitis (HSE), a rare life-threatening complication during HSV-1 infection (Casrouge A et al. 2006; Perez de Diego R et al. 2010; Zhang SY et al. 2007; Herman M et al. 2012; Lafaille FG et al. 2012). The functional defect in HSE patients with TLR3 deficiency is probably due to impaired induction of type I and III interferon (IFN) by cells of the CNS, which appears to be uniquely dependent upon TLR3 for protection against HSV1 (Zhang SY et al. 2007; Guo Y et al. 2011; Lafaille FG et al. 2012). Importantly, blood cells in the periphery produce normal amounts of interferons, even in TLR3-deficient patients, which perhaps can be explained by RIGI or MDA5-mediated antiviral responses

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