Interleukins, Chemokines, and Tumor Necrosis Factor Superfamily Ligands in the Pathogenesis of West Nile Virus Infection

Engagement of AKT and ERK signaling pathways facilitates infection of human neuronal cells with West Nile virus

West Nile virus (WNV) is an important neurotropic virus that accounts for the emergence of human arboviral encephalitis and meningitis. The interaction of WNV with signaling pathways plays a key role in controlling WNV infection. We have investigated the roles of the AKT and ERK pathways in supporting WNV propagation and modulating the inflammatory response following WNV infection. WNV established a productive infection in neuronal cell lines originated from human and mouse. Expression of IL-11 and TNF-α was markedly up-regulated in the infected human neuronal cells, indicating elicitation of inflammation response upon WNV infection. WNV incubation rapidly activated signaling cascades of AKT (AKT-S6-4E-BP1) and ERK (MEK-ERK-p90RSK) pathways. Treatment with AKT inhibitor MK-2206 or MEK inhibitor U0126 abrogated WNV-induced AKT or ERK activation. Strong activation of AKT and ERK signaling pathways could be detectable at 24 h after WNV infection, while such activation was abolished at 48 h post infection. U0126 treatment or knockdown of ERK expression significantly increased WNV RNA levels and viral titers and efficiently decreased IL-11 production induced by WNV, suggesting the involvement of ERK pathway in WNV propagation and IL-11 induction. MK-2206 treatment enhanced WNV RNA replication accompanied with a moderate decrease in IL-11 production. These results demonstrate that engagement of AKT and ERK signaling pathways facilitates viral infection and may be implicated in WNV pathogenesis.

Skin tropism during Usutu virus and West Nile virus infection: an amplifying and immunological role

Usutu virus (USUV) and West Nile virus (WNV) are closely related emerging arboviruses belonging to the Flavivirus genus and posing global public health concerns. Although human infection by these viruses is mainly asymptomatic, both have been associated with neurological disorders such as encephalitis and meningoencephalitis. Since USUV and WNV are transmitted through the bite of an infected mosquito, the skin represents the initial site of virus inoculation and provides the first line of host defense. Although some data on the early stages of WNV skin infection are available, very little is known about USUV. Herein, USUV-skin resident cell interactions were characterized. Using primary human keratinocytes and fibroblasts, an early replication of USUV during the first 24 hours was shown in both skin cells. In human skin explants, a high viral tropism for keratinocytes was observed. USUV infection of these models induced type I and III interferon responses associated with upregulated expression of various interferon-stimulated genes as well as pro-inflammatory cytokine and chemokine genes. Among the four USUV lineages studied, the Europe 2 strain replicated more efficiently in skin cells and induced a higher innate immune response. In vivo, USUV and WNV disseminated quickly from the inoculation site to distal cutaneous tissues. In addition, viral replication and persistence in skin cells were associated with an antiviral response. Taken together, these results provide a better understanding of the pathophysiology of the early steps of USUV infection and suggest that the skin constitutes a major amplifying organ for USUV and WNV infection.IMPORTANCEUsutu virus (USUV) and West Nile virus (WNV) are closely related emerging Flaviviruses transmitted through the bite of an infected mosquito. Since they are directly inoculated within the upper skin layers, the interactions between the virus and skin cells are critical in the pathophysiology of USUV and WNV infection. Here, during the early steps of infection, we showed that USUV can efficiently infect two human resident skin cell types at the inoculation site: the epidermal keratinocytes and the dermal fibroblasts, leading to the induction of an antiviral innate immune response. Moreover, following cutaneous inoculation, we demonstrated that both viruses can rapidly spread, replicate, and persist in all distal cutaneous tissues in mice, a phenomenon associated with a generalized skin inflammatory response. These results highlight the key amplifying and immunological role of the skin during USUV and WNV infection.

Fast-response electrochemical biosensor based on a truncated aptamer and MXene heterolayer for West Nile virus detection in human serum

West Nile virus (WNV) is a mosquito-borne flavivirus that can cause West Nile fever, meningitis, encephalitis, and polio. Early detection of WNV is important to prevent infection spread on the field. To commercialize the electrochemical biosensor for WNV, rapid target detection with the cheap manufacture cost is essential. Here, we developed a fast-response electrochemical biosensor consisting of a truncated WNV aptamer/MXene (Ti3C2Tx) bilayer on round-type micro gap. To reduce the target binding time, the application of the alternating current electrothermal flow (ACEF) technology reduced the target detection time to within 10 min, providing a rapid biosensor platform. The MXene nanosheet improved electrochemical signal amplification, and the aptamer produced through systematic evolution of ligands by exponential enrichment process eliminated unnecessary base sequences via truncation and lowered the manufacturing cost. Under optimized conditions, the WNV limit of detection (LOD) and selectivity were measured using electrochemical measurement methods, including cyclic voltammetry and square wave voltammetry. The LOD was 2.57 pM for WNV diluted in deionized water and 1.06 pM for WNV diluted in 10% human serum. The fabricated electrochemical biosensor has high selectivity and allows rapid detection, suggesting the possibility of future application in the diagnosis of flaviviridae virus.

Special Issue: "Innate Immunity to Virus Infection, 1st Edition"

Frequent outbreaks of emerging and re-emerging pathogenic viruses have become one of the major challenges for global public health [...].