Influenza B virus causes annual epidemics and, along with influenza A virus, accounts for substantial disease and economic burden throughout the world. Influenza B virus infects only humans and some marine mammals and is not responsible for pandemics, possibly due to a very low frequency of reassortment and a lower evolutionary rate than that of influenza A virus. Influenza B virus has been less studied than influenza A virus, and thus, a comparison of influenza A and B virus infection mechanisms may provide new insight into virus-host interactions. Here we analyzed the early events in influenza B virus infection and interferon (IFN) gene expression in human monocyte-derived macrophages and dendritic cells. We show that influenza B virus induces IFN regulatory factor 3 (IRF3) activation and IFN-λ1 gene expression with faster kinetics than does influenza A virus, without a requirement for viral protein synthesis or replication. Influenza B virus-induced activation of IRF3 required the fusion of viral and endosomal membranes, and nuclear accumulation of IRF3 and viral NP occurred concurrently. In comparison, immediate early IRF3 activation was not observed in influenza A virus-infected macrophages. Experiments with RIG-I-, MDA5-, and RIG-I/MDA5-deficient mouse fibroblasts showed that RIG-I is the critical pattern recognition receptor needed for the influenza B virus-induced activation of IRF3. Our results show that innate immune mechanisms are activated immediately after influenza B virus entry through the endocytic pathway, whereas influenza A virus avoids early IRF3 activation and IFN gene induction.Recently, a great deal of interest has been paid to identifying the ligands for RIG-I under conditions of natural infection, as many previous studies have been based on transfection of cells with different types of viral or synthetic RNA structures. We shed light on this question by analyzing the earliest step in innate immune recognition of influenza B virus by human macrophages. We show that influenza B virus induces IRF3 activation, leading to IFN gene expression after viral RNPs (vRNPs) are released into the cytosol and are recognized by RIG-I receptor, meaning that the incoming influenza B virus is already able to activate IFN gene expression. In contrast, influenza A (H3N2) virus failed to activate IRF3 at very early times of infection, suggesting that there are differences in innate immune recognition between influenza A and B viruses.
Describes the development of performance indicators in the bibliographic records section since 1988. The timeliness of the section’s output was perceived to be more relevant from the user’s point of view than the number of books catalogued, so two key indicators were monitored: the length of time which books spend on the cataloguing shelves and the size of the backlog. The statistics in graphical form to assist planning the section’s work. Time analysis was introduced more recently, both to provide a more meaningful context for the performance indicators and also to put a cost on the section’s activities in the light of current trends towards greater financial accountability and the development of service‐level agreements. Discusses some problems inherent in the use of performance indicators and suggests greater integration between sections.
Abstract Given the rapid spread of flaviviruses such as West Nile virus (WNV) and Zika virus, it is critical that we develop a complete understanding of the key mediators of an effective anti-viral response. We previously demonstrated that WNV infection of mice deficient in mitochondrial antiviral-signaling protein (MAVS), the signaling adaptor for RNA helicases such as RIG-I, resulted in increased death and dysregulated immunity, which correlated with a failure of Treg expansion following infection. Thus, we sought to determine if intrinsic MAVS signaling is required for participation of Tregs in anti-WNV immunity. Despite evidence of increased Treg cell division, Foxp3 expression was not stably maintained after WNV infection in MAVS-deficient mice. However, intrinsic MAVS signaling was dispensable for Treg proliferation and suppressive capacity. Further, we observed generation of an effective anti-WNV immune response when Tregs lacked MAVS, thereby demonstrating that Treg detection of the presence of WNV through the MAVS signaling pathway is not required for generation of effective immunity. Together, these data suggest that while MAVS signaling has a considerable impact on Treg identity, this effect is not mediated by intrinsic MAVS signaling but rather is likely an effect of the overproduction of pro-inflammatory cytokines generated in MAVS-deficient mice after WNV infection.
Abstract Background Appropriate diagnostic testing can be used to inform infection control measures and reduce SARS-CoV-2 transmission, yet the test kinetics, infectivity, and immunological responses during acute, non-severe SARS-CoV-2 infection need clarity. Methods We conducted a prospective cohort study between Nov 2020-July 2021 in Seattle, Washington of 95 unvaccinated, immunocompetent adults with no prior SARS-CoV-2 infection. Nasal swabs (nasopharyngeal and anterior) and blood serum samples were serially collected at six visits over two months. Viral RNA, N and S antigen concentrations, and viral growth/infectivity were measured from nasal samples. Anti-S total antibody and IgG assays were performed on serum. We fit loess curves to quantitative data corresponding to each testing modality by days since symptom onset (DSSO) and compared qualitative test results across time points to demonstrate time-dependent agreement of PCR, N antigen, and culture results. Generalized estimating equations were used to approximate relative risk of culture positivity (a proxy for infectiousness) for positive vs. negative test results (antigen and PCR), stratified by presence/absence of symptoms and DSSO. Sampling Schema Nasal swabs and venous blood were collected at visits 1-4; venous blood only at visits 5-6. All participants were enrolled within 14 days of symptom onset (median: 6) and 7 days of a positive test (median: 4). Results Infections in this cohort (median age: 29y) were mild (no hospitalization). Median (IQR) time to negative result was 11 (4), 13 (6), and 20 (7) DSSO for culture growth, N antigen, and PCR tests, respectively. Viral RNA quantities declined more slowly than antigen and culturable virus; antibody titers rose rapidly 5-15 DSSO and plateaued 20-30 DSSO. All culture-positive samples collected 0-5 DSSO were positive by PCR, but relative risk of culture positivity (infectiousness) for positive vs. negative PCR results declined 6-10 DSSO. Relative risk of culture positivity for positive vs. negative antigen results was consistently high 0-10 DSSO, with similar results when stratified by presence of symptoms. Diagnostic test kinetics and immunological responses Diagnostic test kinetics and immunological responses measured in adults with non-severe, symptomatic SARS-CoV-2 infection: loess trendlines and 95% confidence intervals are given for SARS-CoV-2 viral load (calculated from PCR Ct value using a calibration curve), TCID50 from viral culture, mean concentrations of nucleocapsid and spike antigen proteins, and anti-S total and IgG antibody concentrations. Conclusion The results reinforce the importance of molecular PCR testing as a highly sensitive diagnostic tool but with limited utility as an indicator of viral culturability and likely infectiousness. N antigen testing may be a preferable diagnostic test within two weeks of symptom onset, especially 6-10 DSSO, because it more closely correlates with culture growth over the course of infection. Disclosures Daphne Hamilton, BA, Roche (spouse is employed by Roche): Employee Alexander L. Greninger, MD, PhD, Abbott: Contract Testing|Cepheid: Contract Testing|Gilead: Grant/Research Support|Gilead: Contract Testing|Hologic: Contract Testing|Merck: Grant/Research Support|Novavax: Contract Testing|Pfizer: Contract Testing Geoffrey S. Gottlieb, MD, PhD, Abbott Molecular Diagnostics: Grant/Research Support|Alere Technologies: Grant/Research Support|BMGF: Grant/Research Support|BMS: Grant/Research Support|Cerus Corp.: Grant/Research Support|Gilead Sciences: Grant/Research Support|Janssen Pharmaceutica: Grant/Research Support|Merck & Co: Grant/Research Support|Roche Molecular Systems: Grant/Research Support|THERA Technologies/TaiMed Biologics: Grant/Research Support|ViiV Healthcare: Grant/Research Support.
Abstract The nonstructural (NS) proteins of West Nile virus (WNV) are important determinants of viral pathogenesis. WNV NS4B-P38G mutant, which has a P38G substitution in the NS4B protein is highly attenuated in mice, but induces stronger type 1 interferon (IFN) and T cell responses than the wild-type WNV. Here, we investigated mice lacking the RIG-I-like receptor adaptor gene Mavs, and found increased viremia and lethality following WNV NS4B-P38G infection. MAVS-/- mice had a reduced IFNβ production and impaired primary T cell response after infection. WNV NS4B-P38G also induced lower levels of type 1 IFNs and cell surface expression of MHC class II and co-stimulatory molecules on MAVS-/- dendritic cell (DC)s. IRF-3, -5, and -7 are the key transcription factors responsible for mediating the type I IFN and ISG response in mDCs during wild-type WNV infection. PCR array analysis showed a significantly decreased expression of IFNβ and most IFN stimulated gene (ISG)s, except IRF3 and IRF5 in WNV NS4B-P38G-infected MAVS-/- DCs compared to the wild-type group. Moreover, DCs of IRF3-/- x IRF7-/- double knockout or Irf3-/-×Irf5-/- ×Irf7-/- triple knockout mice had either unaffected or a higher IFNβ expression after WNV NS4B-P38G infection. Collectively, our results suggest that MAVS signaling is essential for the induction of type 1 IFN and T cell responses upon WNV NS4B-P38G mutant infection and this could occur through an IRF-3 and IRF-5-independent pathway.
Abstract Programmed necrosis coordinated by receptor-interacting kinase-3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL) is known to contribute to host immune responses to viral infections. However, the role of these proteins in host immunity during flavivirus infection remains poorly understood. Using a mouse model of West Nile virus encephalitis, we show that RIPK3 is required for the restriction of West Nile virus pathogenesis, independently of its role in programmed necrosis. While Ripk3−/− mice exhibited accelerated and enhanced mortality compared to WT controls, survival and clinical scores in mice lacking the executioner protein MLKL were unaffected. Moreover, cell death following WNV infection in primary cultures of myeloid and neuronal cells was unchanged in both Ripk3−/− and Mlkl−/− cultures. The enhanced susceptibility of Ripk3−/− mice arose, instead, from a failure to control infection within the central nervous system (CNS). While peripheral adaptive immune responses to WNV remained intact, Ripk3−/− mice exhibited decreased recruitment of inflammatory myeloid cells and lymphocytes to the CNS, despite higher CNS viral loads. RIP3 suppressed CNS viral burden via both CNS-intrinsic and –extrinsic mechanisms, as viral titers in the brain and spinal cord were higher in Ripk3−/− mice compared to controls following both subcutaneous and intracranial inoculation with WNV. Together, these data identify new roles for RIPK3 in the restriction of viral pathogenesis, and implicate RIPK3 as a key regulator of antiviral immunity within the CNS.
