Mosquito Defensins Enhance Japanese Encephalitis Virus Infection by Facilitating Virus Adsorption and Entry within the Mosquito.

Japanese encephalitis virus (JEV) is a viral zoonosis that can cause viral encephalitis, death, and disability. Although the Culex mosquito is the primary vector of JEV, little is known about JEV transmission by this kind of mosquito. Here, we found that mosquito defensin facilitated the adsorption of JEV on target cells via the defensin/lipoprotein receptor-related protein 2 (LRP2) axis. Mosquito defensin bound the ED III domain of the viral envelope (E) protein and directly mediated efficient virus adsorption on the target cell surface; the receptor LRP2, which is expressed on the cell surface, affected defensin-dependent adsorption. As a result, mosquito defensin enhanced JEV infection in the salivary gland, increasing the possibility of viral transmission by mosquitoes. These findings demonstrate the novel role of mosquito defensin in JEV infection and the mechanisms through which the virus exploits mosquito defensin for infection and transmission.IMPORTANCE In this study, we observed the complex roles of mosquito defensin in JEV infection; mosquito defensin exhibited a weak antiviral effect but strongly enhanced binding. In the latter, defensin directly binds the ED III domain of the viral E protein and promotes the adsorption of JEV to target cells by interacting with lipoprotein receptor-related protein 2 (LRP2), thus accelerating virus entry. Together, our results indicate that mosquito defensin plays an important role in facilitating JEV infection and potential transmission.

Experimental Infection of Newly Hatched Domestic Ducklings via Japanese Encephalitis Virus-Infected Mosquitoes.

Japanese encephalitis virus (JEV) is a zoonotic pathogen that is maintained by mosquito vectors and vertebrate hosts including birds in a natural transmission cycle. Domestic ducklings are sensitive to JEV infection, but the clinical responses of domestic ducklings to natural JEV infection are unknown. In this study, we simulated the natural JEV infection of domestic ducklings via JEV-infected mosquito bites to evaluate the pathogenicity of JEV in domestic ducklings. Specific pathogen-free domestic ducklings were infected at day 2 post-hatching with JEV-infected Culex pipiens mosquito bites and monitored for clinical responses. Among 20 ducklings exposed to JEV-infected mosquitoes, six showed mild and non-characteristic clinical signs starting at two days post-infection, then died suddenly with neurological signs of opisthotonos (a condition of spasm of the back muscles causing the head and limbs to bend backward and the trunk to arch forward) between two and three days post-infection. The mortality of the affected ducklings was 30% (6/20). Multifocal lymphohistiocytic perivascular cuffs and lymphohistiocytic meningitis were macroscopically observed in the affected duckling brains. JEV was detected in the cytoplasm of neuronal cells in the affected duckling brains by immunohistochemical assays and was recovered from the affected duckling brains by viral isolation. These observations indicated that JEV infection via mosquito bites causes mortality associated with viral encephalitis in newly hatched domestic ducklings, thus demonstrating the potential pathogenicity of JEV in domestic ducklings under natural conditions.

Establishment and characterization of the pig tonsil epithelial (PT) cell line as a new model for persist infection of Japanese Encephalitis Virus.

Japanese encephalitis virus (JEV) causes a serious zoonotic disease worldwide, pig is the reservoir and amplifying host of JEV. JEV can persist infect tonsil in pig, but the relation between persist infection in tonsil and reservoir are not clear until now. A stable pig tonsil cell line is necessary for JEV persist infection research. In this study, we established a continuous epithelial cell line, named PT cell, from the pig tonsil. This cell is susceptible to JEV. We determined the growth characteristics, molecular properties, microstructure profiles of PT cell. JEV is easy to enter PT cell which may partly explain the reason of persist infection. We further determined that LMAN2L, a mannose lectin proteins, is the primary viral receptors for JEV entry in PT cell. IFITM3, an cellular surface antiviral factor, is underexpression in PT cell after JEV infection. All these results provide solid evidence that PT cell will promote additional research on JEV persist infection in pig tonsil.

Porcine reproductive and respiratory syndrome virus counteracts type I interferon-induced early antiviral state by interfering IRF7 activity.

Porcine reproductive and respiratory syndrome (PRRS) is an economically important disease with a significant impact on the pig industry. It is caused by PRRS virus (PRRSV), which predominantly infects and replicates in porcine pulmonary alveolar macrophages (PAMs). We pretreated PAMs with porcine interferon (IFN)-α to induce an antiviral state within the cells and subsequently infected them with highly pathogenic PRRSV. Changes in global gene expression in IFN-α-pretreated PAMs in response to PRRSV infection were determined by RNA-sequence analysis and confirmed by real-time PCR. We found that IRF7 and other antiviral interferon stimulating genes (ISG)s were suppressed by PRRSV infection. Further studies demonstrated that PRRSV could down-regulate the expression of IRF7 by the non-structure protein 7 (nsp7). In conclusion, PRRSV infection had a strong immunosuppressive effect of IFN. PRRSV nsp7 inhibits the expression of IRF7, thereby down-regulating the expression of IFN and downstream ISGs and facilitated the virus to replicate.