Pathological modeling of TBEV infection reveals differential innate immune responses in human neurons and astrocytes that correlate with their susceptibility to infection

Abstract

Background: Tick-borne encephalitis virus (TBEV) is a member of the Flaviviridae family, Flavivirus genus, which includes several important human pathogens. It is responsible for neurological symptoms that may cause permanent disability or death, and, from a medical point of view, is the major arbovirus in Central/Northern Europe and North-Eastern Asia. TBEV tropism is critical for neuropathogenesis, yet little is known about the molecular mechanisms that govern the susceptibility of human brain cells to the virus. In this study, we sought to establish and characterize a new in vitro model of TBEV infection in the human brain and to decipher cell type-specific innate immunity and its relation to TBEV tropism and neuropathogenesis.Method: Human neuronal/glial cells were differentiated from neural progenitor cells and infected with the TBEV-Hypr strain. Kinetics of infection, cellular tropism, and cellular responses, including innate immune responses, were characterized by measuring viral genome and viral titer, performing immunofluorescence, enumerating the different cellular types, and determining their rate of infection and by performing PCR array and qRT-PCR. The specific response of neurons and astrocytes was analyzed using the same approaches after enrichment of the neuronal/glial cultures for each cellular subtype. Results: We showed that infection of human neuronal/glial cells mimicked three major hallmarks of TBEV infection in the human brain, namely, preferential neuronal tropism, neuronal death, and astrogliosis. We further showed that these cells conserved their capacity to mount an antiviral response against TBEV. TBEV-infected neuronal/glial cells, therefore, represented a highly relevant pathological model. By enriching the cultures for either neurons or astrocytes, we further demonstrated qualitative and quantitative differential innate immune responses in the two cell types that correlated with their particular susceptibility to TBEV. Conclusion:Our results thus reveal that cell type-specific innate immunity is likely to contribute to shaping TBEV tropism for human brain cells. They describe a new in vitro model for in-depth study of TBEV-induced neuropathogenesis and improve our understanding of the mechanisms by which neurotropic viruses target and damage human brain cells.

Low-pathogenic virus induced immunity against TBEV protects mice from disease but not from virus entry into the CNS

“…Immunofluorescence staining for TBEV antigen of brain sections from control, TBEV-Hypr-infected mice revealed high numbers of infected cells across different brain regions. Based on location and morphology, most of the infected cells appeared to be neurons (Figure 3A-B), as has been reported previously (22,23). However, to further investigate whether major glial cell types such as microglia and astrocytes could also constitute a target of TBEV, double labeling of brain sections using antibodies targeting TBEV antigen and microglia/macrophages (Iba-1 + ) or astrocytes (GFAP + ) was performed.…”

“…Neuronal cells are regarded as primary targets of TBEV (22,23). Accordingly, in the absence of vaccine-induced protective immunity, high numbers of infected neurons were detected by immunostaining in TBEV-Hypr infected mice.…”

“…This hypothesis is furthermore supported by the presence of inflammatory (PVI) and reactive (gliosis) changes within the CNS of vaccinated mice, which both constitute frequent findings during and after neuroinfection (18). Besides neurons, some studies have demonstrated TBEV infection of astrocytes (23,26,27). Furthermore, it has been shown that TBEV can infect and survive in rat and human astrocytes for several days without affecting each other’s viability (26,27).…”

Sleep architecture, obstructive sleep apnea and functional outcomes in adults with a history of Tick-borne encephalitis

“…We hypothesize that persons with a history of TBE are more prone to experience symptoms from a mild degree of OSA, probably a consequence of the brain infection with its immunopathological reactions and effect on brain cells [ 35 , 36 ] The potential mechanisms for the origin of fatigue in TBE might be related to neurotransmitter dysfunctions as proposed for fatigue observed in multiple sclerosis [ 37 ]. Furthermore, the areas of the brain involved in TBE might be of importance to explain fatigue and sleep disturbances as TBE sequelae.…”

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

“…Some non-structural proteins of TBEV, such as NS1, NS2A, NS4A, NS4B or NS5, display antagonistic functions, thus, interfering with components of the innate immune response (reviewed in [ 3 , 69 , 70 , 71 , 72 ]; [ 73 ]). In addition, TBEV infection modulates expression patterns of many antiviral genes which are involved in the innate immune response such as genes for PRRs, cytokines or chemokines [ 74 ]. Besides TBEV itself, tick-derived saliva was shown to modulate the host innate immune response by influencing pathways, such as increasing the activation of the Akt pathway in TBEV-infected dendritic cells [ 75 ], and innate immune cells (reviewed in [ 76 ]).…”