Abstract
The neurotropic Japanese encephalitis virus (JEV) is responsible for Japanese encephalitis, an uncontrolled inflammatory disease of the central nervous system. Microglia cells are the unique innate immune cell type populating the brain that cross-communicate with neurons via the CX3CR1-CX3CL1 axis. However, microglia may serve as a viral reservoir for JEV. Human microglia are able to transmit JEV infectivity to neighbouring cells in a cell-to-cell contact-dependent manner. Using JEV-treated human blood monocyte-derived microglia, the present study investigates molecular mechanisms behind cell-to-cell virus transmission by human microglia. For that purpose, JEV-associated microglia were co-cultured with JEV susceptible baby hamster kidney cells under various conditions. Here, we show that microglia hosting JEV for up to 10 days were able to transmit the virus to susceptible cells. Interestingly, neutralizing anti-JEV antibodies did not completely abrogate cell-to-cell virus transmission. Hence, intracellular viral RNA could be a contributing source of infectious virus material upon intercellular interactions. Importantly, the CX3CL1-CX3CR1 axis was a key regulator of cell-to-cell virus transmission from JEV-hosting human microglia. Our findings suggest that human microglia may be a source of infection for neuronal populations and sustain JEV brain pathogenesis in long-term infection. Moreover, the present work emphasizes on the critical role of the CX3CR1-CX3CL1 axis in JEV pathogenesis mediating transmission of infectious genomic JEV RNA.
Highlights
Japanese encephalitis (JE) is an uncontrolled inflammatory disease of the central nervous system (CNS) resulting from the infection by the neurotropic flavivirus, JE virus (JEV)
At later exposure periods of 6 and 8 days, observations under the light microscope demonstrated that both mock- and Japanese encephalitis virus (JEV)-treated human microglia were confluent with variable morphologies of flat and elongated or round cells and exerted equivalent granularity (Fig. 1a and b)
Human microglia were pre-treated with JEV for 6, 8, 10 and 12 days and subsequently co-cultured with susceptible target cells such as baby hamster kidney 21 (BHK-21) cells in cell-to-cell contact conditions for 2 additional days in the presence of control porcine serum (Ctrl serum)
Summary
Japanese encephalitis (JE) is an uncontrolled inflammatory disease of the central nervous system (CNS) resulting from the infection by the neurotropic flavivirus, JE virus (JEV). Microglia-associated virus remains infectious to susceptible cells under cell-to-cell contact conditions, allowing virus recovery[16]. The present study aims to understand and dissect the mechanisms behind virus transmission and recovery from JEV-associated human microglia. Our results demonstrate that virus recovery from the target cells occurred upon cell contact-mediated virus transmission from JEV-associated microglia up to 10 days after virus exposure. Viral RNA may be a contributing source of infectious virus material for cell-to-cell virus transmission. The latter virus transmission was dependent on CX3CR1-CX3CL1 interactions. The present study defines a novel function of human microglia as source of JEV virus infection via cell-to-cell virus transmission, independently of virus binding to its receptor on target cells
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