Masking of the contribution of V protein to Sendai virus pathogenesis in an infection model with a highly virulent field isolate

Illumination of parainfluenza virus infection and transmission in living animals reveals a tissue-specific dichotomy

The parainfluenza viruses (PIVs) are highly contagious respiratory paramyxoviruses and a leading cause of lower respiratory tract (LRT) disease. Since no vaccines or antivirals exist, non-pharmaceutical interventions are the only means of control for these pathogens. Here we used bioluminescence imaging to visualize the spatial and temporal progression of murine PIV1 (Sendai virus) infection in living mice after intranasal inoculation or exposure by contact. A non-attenuated luciferase reporter virus (rSeV-luc(M-F*)) that expressed high levels of luciferase yet was phenotypically similar to wild-type Sendai virus in vitro and in vivo was generated to allow visualization. After direct intranasal inoculation, we unexpectedly observed that the upper respiratory tract (URT) and trachea supported robust infection under conditions that result in little infection or pathology in the lungs including a low inoculum of virus, an attenuated virus, and strains of mice genetically resistant to lung infection. The high permissivity of the URT and trachea to infection resulted in 100% transmission to naïve contact recipients, even after low-dose (70 PFU) inoculation of genetically resistant BALB/c donor mice. The timing of transmission was consistent with the timing of high viral titers in the URT and trachea of donor animals but was independent of the levels of infection in the lungs of donors. The data therefore reveals a disconnect between transmissibility, which is associated with infection in the URT, and pathogenesis, which arises from infection in the lungs and the immune response. Natural infection after transmission was universally robust in the URT and trachea yet limited in the lungs, inducing protective immunity without weight loss even in genetically susceptible 129/SvJ mice. Overall, these results reveal a dichotomy between PIV infection in the URT and trachea versus the lungs and define a new model for studies of pathogenesis, development of live virus vaccines, and testing of antiviral therapies.

Human parainfluenza viruses (HPIVs) are a leading cause of pediatric hospitalization for lower respiratory tract infection, yet it is unknown why primary infection typically induces immunity without causing severe pathology. To study the determinants of PIV spread within the respiratory tracts of living animals, we developed a model for non-invasive imaging of living mice infected with Sendai virus, the murine counterpart of HPIV1. This system allowed us to measure the temporal and spatial dynamics of paramyxovirus infection throughout the respiratory tracts of living animals after direct inoculation or transmission. We found that the upper respiratory tract and trachea were highly permissive to infection, even under conditions that limit lower respiratory infection and pathogenesis. The timing of transmission coincided with high virus growth in the upper respiratory tracts and trachea of donor mice independent of the extent of infection in the lungs. After transmission, infection spread preferentially in the upper respiratory tract and trachea, inducing protective immunity without weight loss. Our work reveals a disconnect between Sendai virus transmissibility and pathogenicity, and the experimental model developed here will be instrumental in studying PIV pathogenesis.

Paramyxovirus Sendai virus V protein counteracts innate virus clearance through IRF-3 activation, but not via interferon, in mice

The present study was undertaken to clarify the role of Sendai virus (SeV) V protein, which has been shown to downregulate IFN-beta induction through inhibition of IRF-3 activation, in viral pathogenesis. Mice infected with rSeV mutants, deficient in V expression or expressing V lacking the C-terminus, had several-fold higher IFN activity levels in the lungs than those in wild-type virus-infected mice, and the mutant viruses were rapidly excluded from the lung from the early phase of infection before induction of acquired immunity. In addition, the unique early clearance of the mutants did not occur in IRF-3 knockout (KO) mice. However, high titers of IFN were detected even in the infected KO mice. Furthermore, early clearance of the mutant viruses was also observed in IFN signaling-deficient mice, IFN-alpha/beta receptor KO mice and STAT1 KO mice. These results indicate that SeV V protein counteracts IRF-3-mediated innate antiviral immunity for efficient virus replication and pathogenesis in mice, but it is not IFN.

Sendai virus, the mouse parainfluenza type 1: a longstanding pathogen that remains up-to-date

Biologically speaking, Sendai virus (SeV), the murine parainfluenza virus type 1, is perceived as a common respiratory pathogen that is endemic in many rodent colonies throughout the world. Currently it is believed that SeV is the leading cause of pneumonia in mice and together with the mouse hepatitis viruses, is the most prevalent and important of the naturally occurring infections of mice. The scientific community also considers SeV as the archetype organism of the Paramyxoviridae family because most of the basic biochemical, molecular and biologic properties of the whole family were derived from its own characteristics. Recently, scientific interest for this old pathogen has re-emerged, this time because of its potential value as a vector for gene transfer. This review aimed at drawing an exhaustive picture of this multifaceted pathogen.

Accessory genes of the paramyxoviridae, a large family of nonsegmented negative-strand RNA viruses, as a focus of active investigation by reverse genetics

The Paramyxoviridae, a large family of nonsegmented negative-strand RNA viruses, comprises several genera each containing important human and animal pathogens. They possess in common six basal genes essential for viral replication and, in addition, a subset of accessory genes that are largely unique to each genus. These accessory genes are either encoded in one or more alternative overlapping frames of a basal gene, which are accessed transcriptionally or translationally, or inserted before or between the basal genes as one or more extra genes. However, the question of how the individual accessory genes contribute to actual viral replication and pathogenesis remained unanswered. It was not even established whether they are dispensable or indispensable for the viral life cycle. The plasmid-based reverse genetics of the full-length viral genome has now come into wide use to demonstrate that most, if not all, of these putative accessory genes can be disrupted without destroying viral infectivity, conclusively defining them as indeed dispensable accessory genes. Studies on the phenotypes of the resulting gene knockout viruses have revealed that the individual accessory genes greatly contribute specifically and additively to the overall viral fitness both in vitro and in vivo.