DNA vaccination against La Crosse virus

Differences in neuroinvasion and protective innate immune pathways between encephalitic California Serogroup orthobunyaviruses

The California serogroup (CSG) of Orthobunyaviruses comprises several members capable of causing neuroinvasive disease in humans, including La Crosse orthobunyavirus (LACV), Jamestown Canyon orthobunyavirus (JCV), and Inkoo orthobunyavirus (INKV). Despite being genetically and serologically closely related, their disease incidences and pathogenesis in humans and mice differ. We have previously shown that following intraperitoneal inoculation of weanling mice, LACV was highly pathogenic while JCV and INKV were not. To determine why there were differences, we examined the ability of these viruses to invade the CNS and compared the host innate immune responses that regulated viral pathogenesis. We found that LACV was always neuroinvasive, which correlated with its high level of neuroinvasive disease. Interestingly, JCV was not neuroinvasive in any mice, while INKV was neuroinvasive in most mice. The type I interferon (IFN) response was critical for protecting mice from both JCV and INKV disease, although in the periphery JCV induced little IFN expression, while INKV induced high IFN expression. Despite their differing neuroinvasive abilities, JCV and INKV shared innate signaling components required for protection. The presence of either cytoplasmic Rig-I-Like Receptor signaling or endosomal Toll-Like Receptor signaling was sufficient to protect mice from JCV or INKV, however, inhibition of both pathways rendered mice highly susceptible to neurological disease. Comparison of IFN and IFN-stimulated gene (ISG) responses to INKV in the brains of resistant wild type (WT) mice and susceptible immune knockout mice showed similar IFN responses in the brain, but WT mice had higher ISG responses, suggesting induction of key ISGs in the brain is critical for protection of mice from INKV. Overall, these results show that the CSG viruses differ in neuroinvasiveness, which can be independent from their neuropathogenicity. The type I IFN response was crucial for protecting mice from CSG virus-induced neurological disease, however, the exact correlates of protection appear to vary between CSG viruses.

Throw out the Map: Neuropathogenesis of the Globally Expanding California Serogroup of Orthobunyaviruses

The California serogroup (CSG) comprises 18 serologically and genetically related mosquito-borne orthobunyaviruses. Of these viruses, at least seven have been shown to cause neurological disease in humans, including the leading cause of pediatric arboviral encephalitis in the USA, La Crosse virus. Despite the disease burden from these viruses, much is still unknown about the CSG viruses. This review summarizes our current knowledge of the CSG viruses, including human disease and the mechanisms of neuropathogenesis.

The CARD9-Associated C-Type Lectin, Mincle, Recognizes La Crosse Virus (LACV) but Plays a Limited Role in Early Antiviral Responses against LACV

La Crosse virus (LACV) is a mosquito-transmitted arbovirus and the main cause of virus-mediated neurological diseases in children. To date, little is known about the role of C-type lectin receptors (CLRs)—an important class of pattern recognition receptors—in LACV recognition. DC-SIGN remains the only well-described CLR that recognizes LACV. In this study, we investigated the role of additional CLR/LACV interactions. To this end, we applied a flow-through chromatography method for the purification of LACV to perform an unbiased high-throughput screening of LACV with a CLR-hFc fusion protein library. Interestingly, the CARD9-associated CLRs Mincle, Dectin-1, and Dectin-2 were identified to strongly interact with LACV. Since CARD9 is a common adaptor protein for signaling via Mincle, Dectin-1, and Dectin-2, we performed LACV infection of Mincle^−/− and CARD9^−/− DCs. Mincle^−/− and CARD9^−/− DCs produced less amounts of proinflammatory cytokines, namely IL-6 and TNF-α, albeit no reduction of the LACV titer was observed. Together, novel CLR/LACV interactions were identified; however, the Mincle/CARD9 axis plays a limited role in early antiviral responses against LACV.

DNA vaccination regimes against Schmallenberg virus infection in IFNAR-/- mice suggest two targets for immunization

Schmallenberg virus (SBV) is an RNA virus of the Bunyaviridae family, genus Orthobunyavirus that infects wild and livestock species of ruminants. While inactivated and attenuated vaccines have been shown to prevent SBV infection, little is known about their mode of immunity; specifically, which components of the virus are responsible for inducing immunological responses in the host. As previous DNA vaccination experiments on other bunyaviruses have found that glycoproteins, as well as modified (i.e. ubiquitinated) nucleoproteins (N) can confer immunity against virulent viral challenge, constructs encoding for fragments of SBV glycoproteins G_N and G_C, as well as ubiquitinated and non-ubiquitinated N were cloned in mammalian expression vectors, and vaccinated intramuscularly in IFNAR^-/- mice. Upon viral challenge with virulent SBV, disease progression was monitored. Both the ubiquitinated and non-ubiquitinated nucleoprotein candidates elicited high titers of antibodies against SBV, but only the non-ubiquitinated candidate induced statistically significant protection of the vaccinated mice from viral challenge. Another construct encoding for a putative ectodomain of glycoprotein G_C (segment aa. 678-947) also reduced the SBV-viremia in mice after SBV challenge. When compared to other experimental groups, both the nucleoprotein and G_C-ectodomain vaccinated groups displayed significantly reduced viremia, as well as exhibiting no clinical signs of SBV infection. These results show that both the nucleoprotein and the putative G_C-ectodomain can serve as protective immunological targets against SBV infection, highlighting that viral glycoproteins, as well as nucleoproteins are potent targets in vaccination strategies against bunyaviruses.

Age-dependent myeloid dendritic cell responses mediate resistance to la crosse virus-induced neurological disease

La Crosse virus (LACV) is the major cause of pediatric viral encephalitis in the United States; however, the mechanisms responsible for age-related susceptibility in the pediatric population are not well understood. Our current studies in a mouse model of LACV infection indicated that differences in myeloid dendritic cell (mDC) responses between weanling and adult mice accounted for susceptibility to LACV-induced neurological disease. We found that type I interferon (IFN) responses were significantly stronger in adult than in weanling mice. Production of these IFNs required both endosomal Toll-like receptors (TLRs) and cytoplasmic RIG-I-like receptors (RLRs). Surprisingly, IFN expression was not dependent on plasmacytoid DCs (pDCs) but rather was dependent on mDCs, which were found in greater number and induced stronger IFN responses in adults than in weanlings. Inhibition of these IFN responses in adults resulted in susceptibility to LACV-induced neurological disease, whereas postinfection treatment with type I IFN provided protection in young mice. These studies provide a definitive mechanism for age-related susceptibility to LACV encephalitis, where mDCs in young mice are insufficiently activated to control peripheral virus replication, thereby allowing virus to persist and eventually cause central nervous system (CNS) disease.

IMPORTANCE

La Crosse virus (LACV) is the primary cause of pediatric viral encephalitis in the United States. Although the virus infects both adults and children, over 80% of the reported neurological disease cases are in children. To understand why LACV causes neurological disease primarily in young animals, we used a mouse model where weanling mice, but not adult mice, develop neurological disease following virus infection. We found that an early immune response cell type, myeloid dendritic cells, was critical for protection in adult animals and that these cells were reduced in young animals. Activation of these cells during virus infection or after treatment with type I interferon in young animals provided protection from LACV. Thus, this study demonstrates a reason for susceptibility to LACV infection in young animals and shows that early therapeutic treatment in young animals can prevent neurological disease.

Interferon α/β receptor knockout mice as a model to study bluetongue virus infection

Bluetongue is an arthropod-borne disease caused by a virus of the genus Orbivirus, the bluetongue virus (BTV), which affects ruminant livestock such as cattle, sheep, and goats and wild ruminants such as deer, and camelids. Recently, adult mice with gene knockouts of the interferon α/β receptor (IFNAR-/-) have been described as a model of lethal BTV infection. IFNAR(-/-) mice are highly susceptible to BTV-1, BTV-4 and BTV-8 infection when the virus is administered intravenously or subcutaneosuly. Disease progression and pathogenesis closely mimics signs of bluetongue disease in ruminants. In the present paper we review the studies where IFNAR(-/-) mice have been used as an animal model to study BTV transmission, pathogenesis, virulence, and protective efficacy of inactivated and new recombinant marker BTV vaccines. Furthermore, we report new data on protective efficacy of different strategies of BTV vaccination and also on induction of interferon α/β and proinflammatory immune responses in IFNAR(-/-) mice infected with BTV.

Vaccines and animal models for arboviral encephalitides

Arthropod-borne viruses ("arboviruses") cause significant human illness ranging from mild, asymptomatic infection to fatal encephalitis or hemorrhagic fever. The most significant arboviruses causing human illness belong to genera in three viral families, Togaviridae, Flaviviridae, and Bunyaviridae. These viruses represent a significant public health threat to many parts of the world, and, as evidenced by the recent introduction of the West Nile virus (WNV) to the Western Hemisphere, they can no longer be considered specific to any one country or region of the world. Like most viral diseases, there are no specific therapies for the arboviral encephalitides; therefore, effective vaccines remain the front line of defense for these diseases. With this in mind, the development of new, more effective vaccines and the appropriate animal models in which to test them become paramount. In fact, for many important arboviruses (e.g. California serogroup and St. Louis encephalitis viruses), there are currently no approved vaccines available for human use. For others, such as the alphaviruses, human vaccines are available only as Investigational New Drugs, and thus are not in widespread use. On the other hand, safe and effective vaccines against tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JEV) have been in use for decades. New challenges in vaccine development have been met with new technologies in vaccine research. Many of the newer vaccines are now being developed by recombinant DNA technology. For example, chimeric virus vaccines have been developed using infectious clone technology for many of the arboviruses including, WNV, JEV, and TBEV. Other successful approaches have involved the use of naked DNA encoding and subsequently expressing the desired protective epitopes. Naked DNA vaccines have been used for TBEV and JEV and are currently under development for use against WNV. The development of less expensive, more authentic animal models to evaluate new vaccines against arboviral diseases will become increasingly important as these new approaches in vaccine research are realized. This article reviews the current status of vaccines, both approved for use and those in developmental stages, against the major arboviral encephalitides causing human disease. In addition, research on animal models, both past and present, for these diseases are discussed.

Antigenic drift, antigenic shift and interferon antagonists: how bunyaviruses counteract the immune system

Members of the Bunyaviridae family are amongst the most widespread viruses in the world. They can be found on every inhabited continent at virtually every latitude, and are able to infect a wide range of arthropods, plants and mammals including humans. More than 300 named viruses are contained within the family Bunyaviridae (Virus Taxonomy: Seventh Report of the International Committee on Taxonomy of Viruses (2000) 599), and several members cause significant disease in humans or domestic animals. Despite being recognised as an emerging threat, relatively little is known about their virulence mechanisms. Here, we try to summarise the current state of knowledge about how the viruses of the Bunyaviridae succeed in establishing infection in the face of a powerful immune system.