Is NS1 the key to West Nile virus escaping immune detection?

Modulation of innate immune signaling by the secreted form of the West Nile virus NS1 glycoprotein

Read the full article on ScienceDirect.

West Nile virus (WNV) is a member of the family Flaviviridae and is known to employ several different strategies to escape immune detection. The innate immune response is the first line of defense against invading pathogens and one arm of this response involves pattern recognition receptors (PRRs) which recognize distinct pathogen associated molecular patterns (PAMPs). Recognition of these PAMPs by PRRs initiates a signaling cascade which results in an immune response aimed at eliminating the pathogen. Previously we demonstrated that one WNV protein, non-structural protein 1 (NS1) is able to inhibit immune signaling by the PRR, Toll-like receptor 3 (TLR3). TLR3 recognizes double-stranded RNA, formed during WNV replication. The NS1 protein is secreted to high levels during flavivirus infections and we investigated whether this secreted form of NS1 (sNS1) inhibits innate immune signaling pathways in naïve cells. Inhibition of the innate immune response in naïve cells makes those cells more susceptible to infection.

Previous research has demonstrated that sNS1 associates with naïve/uninfected cells and a number of other studies have shown immunomodulatory activity of sNS1. Given these previous findings, as well as our own data showing NS1-mediated TLR3 signaling inhibition we hypothesized that sNS1 would also inhibit TLR3 signaling. In addition, we were interested in determining if signaling by other TLRs could be inhibited by sNS1. To test these hypotheses, we initially used sNS1-containing supernatants from WNV replicon-bearing cells or cells engineered to secrete NS1. In agreement with our hypothesis, early experiments showed that the incubation of cells in the presence of sNS1-containing supernatants resulted in diminished TLR3 signaling ability. These results were reproduced when repeated using purified sNS1 protein. Additionally, we saw inhibition of signaling by TLRs 4 and 7 in our experiments using immunologically important cell types such as macrophages and dendritic cells.

It is our hope to directly study the impact of sNS1 on virus replication and viral spread in an animal model. Unfortunately, these studies are complicated by the multifunctional nature of NS1. For example, secreted NS1 has multiple effects on the lectin and alternative pathways of the complement system. Therefore, any observed effects of sNS1 on the pathogenesis of live virus infection could not be attributed directly to PRR inhibition. To circumvent this issue, we are currently generating a mutant WNV strain, incapable of inhibiting TLR signaling. Understanding the effects of innate immune modulation by NS1 will be useful in informing treatment and/or vaccination strategies.

Highlights blog Crook et al

Introducing the authors

Kristen R. Crook, Mindy Miller-Kittrell, Clayton R. Morrison, Frank Scholle
Department of Biological Sciences, North Carolina State University, Raleigh, USA

About the research

Modulation of innate immune signaling by the secreted form of the West Nile virus NS1 glycoprotein
Kristen R. Crook, Mindy Miller-Kittrell, Clayton R. Morrison, Frank Scholle
Virology, Volumes 458–459, June 2014, Pages 172–182

Read the full article on ScienceDirect.

 

Leave a Reply

Your email address will not be published. Required fields are marked *