Prior Heterologous Flavivirus Exposure Results in Reduced Pathogenesis in a Mouse Model of Zika Virus Infection

Defining Parameters That Modulate Susceptibility and Protection to Respiratory Murine Coronavirus MHV1 Infection

Patients infected with SARS-CoV-2 experience variable disease susceptibility, and patients with comorbidities such as sepsis are often hospitalized for COVID-19 complications. However, the extent to which initial infectious inoculum dose determines disease outcomes and whether this can be used for immunological priming in a genetically susceptible host has not been completely defined. We used an established SARS-like murine model in which responses to primary and/or secondary challenges with murine hepatitis virus type 1 (MHV-1) were analyzed. We compared the response to infection in genetically susceptible C3H/HeJ mice, genetically resistant C57BL/6J mice, and genetically diverse, variably susceptible outbred Swiss Webster mice. Although defined as genetically susceptible to MHV-1, C3H/HeJ mice displayed decreasing dose-dependent pathological changes in disease severity and lung infiltrate/edema, as well as lymphopenia. Importantly, an asymptomatic dose (500 PFU) was identified that yielded no measurable morbidity/mortality postinfection in C3H/HeJ mice. Polymicrobial sepsis induced via cecal ligation and puncture converted asymptomatic infections in C3H/HeJ and C57BL/6J mice to more pronounced disease, modeling the impact of sepsis as a comorbidity to β-coronavirus infection. We then used low-dose infection as an immunological priming event in C3H/HeJ mice, which provided neutralizing Ab-dependent, but not circulating CD4/CD8 T cell-dependent, protection against a high-dose MHV-1 early rechallenge. Together, these data define how infection dose, immunological status, and comorbidities modulate outcomes of primary and secondary β-coronavirus infections in hosts with variable susceptibility.

T Cells in Tick-Borne Flavivirus Encephalitis: A Review of Current Paradigms in Protection and Disease Pathology

The family Flaviviridae is comprised of a diverse group of arthropod-borne viruses that are the etiological agents of globally relevant diseases in humans. Among these, infection with several of these flaviviruses-including West Nile virus (WNV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), tick-borne encephalitis virus (TBEV), and Powassan virus (POWV)-can result in neuroinvasive disease presenting as meningitis or encephalitis. Factors contributing to the development and resolution of tick-borne flavivirus (TBEV, POWV) infection and neuropathology remain unclear, though many recently undertaken studies have described the virus-host interactions underlying encephalitic disease. With access to neural tissues despite the selectively permeable blood-brain barrier, T cells have emerged as one notable contributor to neuroinflammation. The goal of this review is to summarize the recent advances in tick-borne flavivirus immunology-particularly with respect to T cells-as it pertains to the development of encephalitis. We found that although T cell responses are rarely evaluated in a clinical setting, they are integral in conjunction with antibody responses to restricting the entry of TBFV into the CNS. The extent and means by which they can drive immune pathology, however, merits further study. Understanding the role of the T cell compartment in tick-borne flavivirus encephalitis is instrumental for improving vaccine safety and efficacy, and has implications for treatments and interventions for human disease.

Immunization with Usutu virus and with a chimeric West Nile virus (WNV) harboring Usutu-E protein protects immunocompetent adult mice against lethal challenges with different WNV lineage 1 and 2 strains

West Nile virus (WNV) and Usutu virus (USUV), two antigenically related flaviviruses co-circulating in Europe, can cause severe neurological disease in animals and humans. The immune response against USUV and WNV and their immunopathogenesis are still poorly investigated. Here we present results upon sequential infections of adult immunocompetent CD-1 and BALB/c mice primed with two different doses (high dose, HD or low dose, LD) of an USUV isolate and challenged with HD or LD of three different WNV isolates. CD-1 and BALB/c LD USUV-primed mice, regardless of the dose, are largely protected from lethal WNV challenges despite showing no detectable neutralizing antibodies. Furthermore, mice immunized with a chimeric virus harboring the E protein of USUV within the WNV backbone (WNVE-USUV) are protected against a lethal challenge with WNV. We believe these findings could contribute to understanding the dynamics of the interaction during sequential infection of these two flaviviruses.

Novel Antiviral Efficacy of Hedyotis diffusa and Artemisia capillaris Extracts against Dengue Virus, Japanese Encephalitis Virus, and Zika Virus Infection and Immunoregulatory Cytokine Signatures

Currently, there are no specific therapeutics for flavivirus infections, including dengue virus (DENV) and Zika virus (ZIKV). In this study, we evaluated extracts from the plants Hedyotis diffusa (HD) and Artemisia capillaris (AC) to determine the antiviral activity against DENV, ZIKV, and Japanese encephalitis virus (JEV). HD and AC demonstrated inhibitory activity against JEV, ZIKV, and DENV replication and reduced viral RNA levels in a dose-responsive manner, with non-cytotoxic concentration ranging from 0.1 to 10 mg/mL. HD and AC had low cytotoxicity to Vero cells, with CC₅₀ values of 33.7 ± 1.6 and 30.3 ± 1.7 mg/mL (mean ± SD), respectively. The anti-flavivirus activity of HD and AC was also consistent in human cell lines, including human glioblastoma (T98G), human chronic myeloid leukemia (K562), and human embryonic kidney (HEK-293T) cells. Viral-infected, HD-treated cells demonstrated downregulation of cytokines including CCR1, CCL26, CCL15, CCL5, IL21, and IL17C. In contrast, CCR1, CCL26, and AIMP1 were elevated following AC treatment in viral-infected cells. Overall, HD and AC plant extracts demonstrated flavivirus replication inhibitory activity, and together with immunoregulatory cytokine signatures, these results suggest that HD and AC possess bioactive compounds that may further be refined as promising candidates for clinical applications.

Titration and neutralizing antibody quantification by focus forming assay for Powassan virus

The development of high-throughput assays measuring Powassan virus (POWV) lineage I and II represents an important step in virological and immunological studies. By adapting focus-forming assays previously optimized for West Nile virus and Zika virus, this protocol is able to determine viral load, evaluate antivirals, and measure neutralizing antibodies. Although limited by its requirement of a detection antibody, this protocol includes a rapid and high-throughput assay for measuring viral titer. By utilizing a baby hamster kidney cell line and a 96-well plate format, this protocol allows for more sensitivity in the detection of POWV lineage I.

For complete details on the use and execution of this protocol, please refer to Stone et al. (2022).

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Powassan virus focus forming assay for evaluation of antivirals

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Antibody focus reduction neutralization assay (FRNT) for Powassan virus

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Steps describing Powassan virus lineage I and II titration

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Balanced T and B cell responses are required for immune protection against Powassan virus in virus-like particle vaccination

Powassan virus (POWV) is a tick-borne pathogen for which humans are an incidental host. POWV infection can be fatal or result in long-term neurological sequelae; however, there are no approved vaccinations for POWV. Integral to efficacious vaccine development is the identification of correlates of protection, which we accomplished in this study by utilizing a murine model of POWV infection. Using POWV lethal and sub-lethal challenge models, we show that (1) robust B and T cell responses are necessary for immune protection, (2) POWV lethality can be attributed to both viral- and host-mediated drivers of disease, and (3) knowledge of the immune correlates of protection against POWV can be applied in a virus-like particle (VLP)-based vaccination approach that provides protection from lethal POWV challenge. Identification of these immune protection factors is significant as it will aid in the rational design of POWV vaccines.