ADAM15 Participates in Tick-Borne Encephalitis Virus Replication

Farnesyltransferase inhibitor lonafarnib suppresses respiratory syncytial virus infection by blocking conformational change of fusion glycoprotein

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis and pneumonia in young children and the elderly. There are currently no approved RSV-specific therapeutic small molecules available. Using high-throughput antiviral screening, we identified an oral drug, the prenylation inhibitor lonafarnib, which showed potent inhibition of the RSV fusion process. Lonafarnib exhibited antiviral activity against both the RSV A and B genotypes and showed low cytotoxicity in HEp-2 and human primary bronchial epithelial cells (HBEC). Time-of-addition and pseudovirus assays demonstrated that lonafarnib inhibits RSV entry, but has farnesyltransferase-independent antiviral efficacy. Cryo-electron microscopy revealed that lonafarnib binds to a triple-symmetric pocket within the central cavity of the RSV F metastable pre-fusion conformation. Mutants at the RSV F sites interacting with lonafarnib showed resistance to lonafarnib but remained fully sensitive to the neutralizing monoclonal antibody palivizumab. Furthermore, lonafarnib dose-dependently reduced the replication of RSV in BALB/c mice. Collectively, lonafarnib could be a potential fusion inhibitor for RSV infection.

Development of a novel virus-like particle-based vaccine for preventing tick-borne encephalitis virus infection

Tick-borne encephalitis virus (TBEV) is an important tick-borne pathogen that poses as a serious public health concern. The coverage and immunogenicity of the currently available vaccines against TBEV are relatively low; therefore, it is crucial to develop novel and effective vaccines against TBEV. The present study describes a novel strategy for the assembly of virus-like particles (VLPs) by co-expressing the structural (core/prM/E) and non-structural (NS2B/NS3Pro) proteins of TBEV. The efficacy of the VLPs was subsequently evaluated in C57BL/6 mice, and the resultant IgG serum could neutralize both Far-Eastern and European subtypes of TBEV. These findings indicated that the VLP-based vaccine elicited the production of cross-subtype reactive antibodies. The VLPs provided protection to mice lacking the type I interferon receptor (IFNAR-/-) against lethal TBEV challenge, with undetectable viral load in brain and intestinal tissues. Furthermore, the group that received the VLP vaccine did not exhibit significant pathological changes and the inflammatory factors were significantly suppressed compared to the control group. Immunization with the VLP vaccine induced the production of multiple-cytokine-producing antiviral CD4+ T cells in vivo, including TNF-α+, IL-2+, and IFN-γ+ T cells. Altogether, the findings suggest that noninfectious VLPs can serve as a potentially safe and effective vaccine candidate against diverse subtypes of TBEV.

T-Cell Immunoglobulin and Mucin Domain 1 (TIM-1) Is a Functional Entry Factor for Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) is the causative agent of a potentially fatal neurological infection affecting humans. The host factors required for viral entry have yet to be described. Here, we found that T-cell immunoglobulin and mucin domain 1 (TIM-1) acted as the cellular entry factor for TBEV. Using a virus overlay protein binding assay, TIM-1 was identified as a virion-interacting protein. Cells that were relatively resistant to TBEV infection became highly susceptible to infection when TIM-1 was ectopically expressed. TIM-1 knockout and viral RNA bypass assays showed that TIM-1 functioned in the entry phase of TBEV infection. TIM-1 mediated TBEV uptake and was cointernalized with virus particles into the cell. Antibodies for TIM-1, soluble TIM-1, or TIM-1 knockdown significantly inhibited TBEV infection in permissive cells. Furthermore, in TIM-1 knockout mice, TIM-1 deficiency markedly lowered viral burden and reduced mortality and morbidity, highlighting the functional relevance of TIM-1 in vivo. With TIM-1, we have identified a key host factor for TBEV entry and a potential target for antiviral intervention. IMPORTANCE TBEV is a tick-transmitted flavivirus that causes serious diseases in the human central nervous system in Eurasia. The host determinants required for viral entry remain poorly understood. Here, we found that TIM-1 is a cellular entry factor for TBEV. Antibodies directed at TIM-1 or soluble TIM-1 treatment decreased virus infection in cell cultures. TIM-1 was cointernalized with virus particles into cells. TIM-1 deficiency significantly lowered viral burden and attenuated pathogenesis in the murine TBEV infection model. The demonstration of TIM-1 as a cellular entry factor for TBEV will improve understanding of virus infection and provide a target for antiviral development.

Selected Biomarkers of Tick-Borne Encephalitis: A Review

Tick-borne encephalitis (TBE) is an acute disease caused by the tick-borne encephalitis virus. Due to the viral nature of the condition, there is no effective causal treatment for full-blown disease. Current and nonspecific TBE treatments only relieve symptoms. Unfortunately, the first phase of TBE is characterized by flu-like symptoms, making diagnosis difficult during this period. The second phase is referred to as the neurological phase as it involves structures in the central nervous system-most commonly the meninges and, in more severe cases, the brain and the spinal cord. Therefore, it is important that early markers of TBE that will guide clinical decision-making and the choice of treatment are established. In this review, we performed an extensive search of literature reports relevant to biomarkers associated with TBE using the MEDLINE/PubMed database. We observed that apart from routinely determined specific immunoglobulins, free light chains may also be useful in the evaluation of intrathecal synthesis in the central nervous system (CNS) during TBEV infection. Moreover, selected metalloproteinases, chemokines, or cytokines appear to play an important role in the pathogenesis of TBE as a consequence of inflammatory reactions and recruitment of white blood cells into the CNS. Furthermore, we reported promising findings on tau protein or Toll-like receptors. It was also observed that some people may be predisposed to TBE. Therefore, to understand the role of selected tick-borne encephalitis biomarkers, we categorized these factors and discussed their potential application in the diagnosis, prognosis, monitoring, or management of TBE.