Role of Toll-Like Receptor 3 Pathway Deficiencies in Children with Enterovirus Encephalitis

The spectrum of diseases caused by enterovirus is broad, ranging from asymptomatic infection, self-limited hand-foot-and-mouth diseases (HFMD) to life-threatening encephalitis or myocarditis. Enterovirus 71 (EV71), a type A enterovirus, causes HFMD in most affected children and is epidemic and a public threat in Taiwan and some Asia countries. Nevertheless, CNS-invasion and neurological complication account for the high mortality and neurological sequelae in few EV71 infected children. The molecular mechanisms underlying these different clinical presentations in enterovrial infection remain unknown. Pathogenesis of EV71-associated neurological disorders is not well-understood, due to the difficulty to study the EV71 infection in human central nerve system (CNS)-resident cells. Toll-Like Receptor (TLR) 3 is a double-strained RNA senor and expresses in some hematopoietic and in most non-hematopoietic cells, including CNS-resident neuron and glial cells. TLR3 could detect viral invasion and induce anti-viral response through the expression of anti-viral genes and Interferon (IFNs) in the IRF3-dependnet pathway. Human patients with inborn errors of TLR3 pathway have developed encephalitis in infection with Herpes simplex virus (HSV)-1. In 2012, Prof. Luigi Notarangelo from Harvard University and others applied induced pluripotent stem cells (iPSCs) to study the HSV-1 infection in TLR3- and TLR3 pathway-deficient (Unc-93B deficiency) CNS-residents cells which are not accessible from patients. TLR3 pathway-deficient neurons and oligodendrocytes are susceptible to HSV-1 and impaired TLR3-dependent IFN intrinsic immunity to HSV-1 in the CNS, in neurons and oligodendrocytes in particular, may underlie the pathogenesis of HSV encephalitis (HSE). This is the proof-of-concept to apply human genetic deficiency and iPSCs-derived cells to study infectious disease, particular for viral infection. We hypothesize that TLR3 pathway is critical for CNS against viral infection and CNS-involved infection might due to inborn error in TLR3 pathway in EV71-infected children. In our preliminary data, we have identified three deleterious TLR3 mutations, W769X, E211K and R867, in three patients with EV71 encephalitis. One patient’s fibroblasts have an impaired TLR3-dependent response and are susceptible to EV71 and HSV-1 . Moreover, we found a new IRF3 variant (R91C) in one CNS-involved EV71 infection child. In this proposal, we aim to validate the TLR3 mutations and the IRF3 variant we found as morbid genes in CNS-involved EV71 infection. In collaboration with Prof. Notarangelo, we plan use iPSCs to dissect the role of TLR3 pathway in CNS-resident cells against EV71 infection. We expect to archive several aims: AIM 1. Determine the functional impact of TLR3 W769X and E211K mutations. AIM 2. Validate the potential IRF3 mutation (R91C) as morbid gene to CNS-involved EV71 infection. AIM3. Study the role of TLR3 in enteroviral infection in iPSCs-derived CNS-resident cells Our study might demonstrate that, in the first time, CNS-involved EV71 infection is due to the defect in host genetic factor and TLR3 is non-redundant in CNS against not only HSV-1, but also EV71 infection. Moreover, we could acquire the genetic deficient iPSC model to study the host immunity against EV71 and this might be used for other infectious diseases. Our findings will open up the view of TLR3-mediated immunity and human susceptibility to enterovirus. Our concept and model might be helpful for Taiwan biomedical society to study not only EV71 but other for other immunological and infectious disease.

Project ID:PC10408-1516
External Project ID:MOST104-2320-B182-031