Differential Replication of Pathogenic and Nonpathogenic Strains of West Nile Virus within Astrocytes

Abstract

The severity of West Nile virus (WNV) infection in immunocompetent animals is highly strain dependent, ranging from avirulent to highly neuropathogenic. Here, we investigate the nature of this strain-specific restriction by analyzing the replication of avirulent (WNV-MAD78) and highly virulent (WNV-NY) strains in neurons, astrocytes, and microvascular endothelial cells, which comprise the neurovascular unit within the central nervous system (CNS). We demonstrate that WNV-MAD78 replicated in and traversed brain microvascular endothelial cells as efficiently as WNV-NY. Likewise, similar levels of replication were detected in neurons. Thus, WNV-MAD78's nonneuropathogenic phenotype is not due to an intrinsic inability to replicate in key target cells within the CNS. In contrast, replication of WNV-MAD78 was delayed and reduced compared to that of WNV-NY in astrocytes. The reduced susceptibility of astrocytes to WNV-MAD78 was due to a delay in viral genome replication and an interferon-independent reduction in cell-to-cell spread. Together, our data suggest that astrocytes regulate WNV spread within the CNS and therefore are an attractive target for ameliorating WNV-induced neuropathology.

Investigation of neuropathogenesis and control of an equine-pathogenic Australian West Nile virus isolate in an established CD1 Swiss white mouse and a novel rabbit model

“…Instead, only chemokines CXCL10, CCL2 and CCL5 were induced, suggesting an important role for astrocytes in chemotaxis of leucocytes in infected brains, along with microglial cells [151]. Collectively, the findings from these three studies suggest the role of astrocytes in cytokine production may depend on the virus strain and the MOI used [64,151,193]. Further investigations into these aspects are required.…”

“…The UV-treated supernatant from these infected neurons was then able to mediate the activation of in vitro grown astrocytes, resulting in further pro-inflammatory cytokine production [64]. In a separate study, in vitro grown human brain cortical astrocytes were shown to produce IFNα/β after WNV infection at MOI of 0.01, but in a strain dependent manner [193]. In particular, the highly virulent WNV NY99 induced significantly higher levels of IFNα/β from the astrocytes than did the less virulent strain, WNV MAD78 [193].…”

“…In a separate study, in vitro grown human brain cortical astrocytes were shown to produce IFNα/β after WNV infection at MOI of 0.01, but in a strain dependent manner [193]. In particular, the highly virulent WNV NY99 induced significantly higher levels of IFNα/β from the astrocytes than did the less virulent strain, WNV MAD78 [193]. Interestingly, WNV NY99 infection of in vitro grown human astrocytes at the higher multiplicity of infection (MOI) of 1 yielded different results, in that it did not induce the production of IFN-I/II, IL1β, TNFα, IL6, and IL10 [151].…”

“…In the CNS, the role of neurons and astrocytes in WNV restriction has been investigated extensively in vitro [53,64,[149][150][151][192][193][194]. In modelling the responses of neurons to WNV infection, in vitro WNV-infection of neurons (human neuroblastoma cell line, SK-N-SH) have been shown to result in their expression of a range of pro-inflammatory cytokines, such as IL1β, IL6, IL8 and TNFα [64].…”

“…Non-leukocytic cells, such as fibroblasts, epithelial and neural cells, contribute to the early detection and mediation of cytokine and chemokine expression, as part of the antiviral defence mechanisms [53,64,[149][150][151][190][191][192][193][194]. In the skin of WNV-infected 6 week-old C3H mice, cells within the epidermis and adnexal glands (likely keratinocytes) were identified as targets for WNV replication, and may contribute to the persistence of virus in the skin, due to the slow turnover rate of keratinocytes (~ every 52 to 75 days for humans) [195].…”