Host Cell Restriction Factors of Bunyaviruses and Viral Countermeasures

Conserved Antagonization of Type I Interferon Signaling by Arterivirus GP5 Proteins

Arteriviruses can establish persistent infections in animals such as equids, pigs, nonhuman primates, rodents, and possums. Some Arteriviruses can even cause overt and severe diseases such as Equine Arteritis in horses and Porcine Reproductive and Respiratory Syndrome in pigs, leading to huge economic losses. Arteriviruses have evolved viral proteins to antagonize the host cell's innate immune responses by inhibiting type I interferon (IFN) signaling, assisting viral evasion and persistent infection. So far, the role of the Arterivirus glycoprotein 5 (GP5) protein in IFN signaling inhibition remains unclear. Here, we investigated the inhibitory activity of 47 Arterivirus GP5 proteins derived from various hosts. We demonstrated that all GP5 proteins showed conserved activity for antagonizing TIR-domain-containing adapter proteins inducing interferon-β (TRIF)-mediated IFN-β signaling through TRIF degradation. In addition, Arterivirus GP5 proteins showed a conserved inhibitory activity against IFN-β signaling, induced by either pig or human TRIF. Furthermore, certain Arterivirus GP5 proteins could inhibit the induction of IFN-stimulated genes. These findings highlight the role of Arterivirus GP5 proteins in supporting persistent infection.

Analysis of Negative-Strand RNA Viruses by RT-qPCR: Rift Valley Fever Virus and Toscana Virus

RT-qPCR allows the detection of viruses and the monitoring of viral replication. This technique was extensively employed during the SARS-CoV-2 pandemic, where it demonstrated its efficiency and robustness. Here we describe the analysis of Rift Valley fever and Toscana virus infections over time, achieved through the RT-qPCR quantification of the viral genome. We further elaborate on the method to discriminate between genomic and antigenomic viral RNAs by using primers specific for each strand during the reverse transcription step.

Negative and ambisense RNA virus ribonucleocapsids: more than protective armor

SUMMARYNegative and ambisense RNA viruses are the causative agents of important human diseases such as influenza, measles, Lassa fever, and Ebola hemorrhagic fever. The viral genome of these RNA viruses consists of one or more single-stranded RNA molecules that are encapsidated by viral nucleocapsid proteins to form a ribonucleoprotein complex (RNP). This RNP acts as protection, as a scaffold for RNA folding, and as the context for viral replication and transcription by a viral RNA polymerase. However, the roles of the viral nucleoproteins extend beyond these functions during the viral infection cycle. Recent advances in structural biology techniques and analysis methods have provided new insights into the formation, function, dynamics, and evolution of negative sense virus nucleocapsid proteins, as well as the role that they play in host innate immune responses against viral infection. In this review, we discuss the various roles of nucleocapsid proteins, both in the context of RNPs and in RNA-free states, as well as the open questions that remain.

Generation of porcine PK-15 cells lacking the Ifnar1 or Stat2 gene to optimize the efficiency of viral isolation

Because pigs are intermediate or amplifying hosts for several zoonotic viruses, the pig-derived PK-15 cell line is an indispensable tool for studying viral pathogenicity and developing treatments, vaccines, and preventive measures to mitigate the risk of disease outbreaks. However, we must consider the possibility of contamination by type I interferons (IFNs), such as IFNα and IFNβ, or IFN-inducing substances, such as virus-derived double-stranded RNA or bacterial lipopolysaccharides, in clinical samples, leading to lower rates of viral isolation. In this study, we aimed to generate a PK-15 cell line that can be used to isolate viruses from clinical samples carrying a risk of contamination by IFN-inducing substances. To this end, we depleted the IFN alpha and beta receptor subunit 1 (Ifnar1) gene or signal transducer and activator of transcription 2 (Stat2) gene in PK-15 cells using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 method. Treatment of PK-15 cells lacking Ifnar1 or Stat2 with IFNβ or poly (I:C) resulted in no inhibitory effects on viral infection by a lentiviral vector, influenza virus, and Akabane virus. These results demonstrate that PK-15 cells lacking Ifnar1 or Stat2 could represent a valuable and promising tool for viral isolation, vaccine production, and virological investigations.

Systems-level temporal immune-metabolic profile in Crimean-Congo hemorrhagic fever virus infection

Crimean-Congo hemorrhagic fever (CCHF) caused by CCHF virus (CCHFV) is one of the epidemic-prone diseases prioritized by the World Health Organisation as public health emergency with an urgent need for accelerated research. The trajectory of host response against CCHFV is multifarious and remains unknown. Here, we reported the temporal spectrum of pathogenesis following the CCHFV infection using genome-wide blood transcriptomics analysis followed by advanced systems biology analysis, temporal immune-pathogenic alterations, and context-specific progressive and postinfection genome-scale metabolic models (GSMM) on samples collected during the acute (T0), early convalescent (T1), and convalescent-phase (T2). The interplay between the retinoic acid-inducible gene-I-like/nucleotide-binding oligomerization domain-like receptor and tumor necrosis factor signaling governed the trajectory of antiviral immune responses. The rearrangement of intracellular metabolic fluxes toward the amino acid metabolism and metabolic shift toward oxidative phosphorylation and fatty acid oxidation during acute CCHFV infection determine the pathogenicity. The upregulation of the tricarboxylic acid cycle during CCHFV infection, compared to the noninfected healthy control and between the severity groups, indicated an increased energy demand and cellular stress. The upregulation of glycolysis and pyruvate metabolism potentiated energy generation through alternative pathways associated with the severity of the infection. The downregulation of metabolic processes at the convalescent phase identified by blood cell transcriptomics and single-cell type proteomics of five immune cells (CD4+ and CD8+ T cells, CD14+ monocytes, B cells, and NK cells) potentially leads to metabolic rewiring through the recovery due to hyperactivity during the acute phase leading to post-viral fatigue syndrome.

Rift Valley Fever vaccine strategies: Enhanced stability of RVF Clone 13

Rift Valley Fever virus (RVFV) causes the zoonotic RVF disease, which results in substantial economic losses in livestock industries. Regular vaccination of livestock against RVF is necessary to generate long-term immunity and avoid the loss of livestock. The live attenuated vaccine based on Clone 13 virus strain has been used to reduce the negative impact of RVF disease. The vaccine strain is heat labile and requires stringent conditions for storage and handling. This research evaluated lactose and sucrose-based stabilizers coupled with lyophilisation to enhance stability of the RVF Clone 13 vaccine strain. The glass transition temperature (Tg) of the sucrose-RVF vaccine was 97.0 °C with average residual moisture of below 2 %. The lactose formulation was characterised with Tg of 83.5 °C and residual moisture of above 2 %. The RVF Clone 13 sucrose-based formulation maintained higher antigen titres during lyophilisation compared to the lactose-formulated vaccine. Cellular-mediated and humoral immunity was evaluated and compared for the two newly formulated vaccines. Pheroid® technology was also investigated as a potential adjuvant and its ability to further enhance the immunogenicity conferred by the RVF Clone 13 vaccine formulations in Merino sheep. No adverse reactions were observed following injection of the vaccine formulations in mice, guinea pigs and Merino sheep. Comparable protective humoral immune responses against RVF were obtained for all animals vaccinated with the lactose and sucrose-based stabilisers with and without the Pheroid® adjuvant. No proliferation of CD8+ and CD4+ T-cells as well as expression of IFN-γ was observed for all animals group vaccinated with Pheroid® only. Specific CD8+ IFN-γ+T-cells were expressed at higher levels compared to the CD4+ IFN-γ+T-cells in the RVF Clone 13 vaccines, suggesting that cellular immunity against RVF is through the Class I antigen presentation pathway.

An Overview of the Infectious Cycle of Bunyaviruses

Bunyaviruses represent the largest group of RNA viruses and are the causative agent of a variety of febrile and hemorrhagic illnesses. Originally characterized as a single serotype in Africa, the number of described bunyaviruses now exceeds over 500, with its presence detected around the world. These predominantly tri-segmented, single-stranded RNA viruses are transmitted primarily through arthropod and rodent vectors and can infect a wide variety of animals and plants. Although encoding for a small number of proteins, these viruses can inflict potentially fatal disease outcomes and have even developed strategies to suppress the innate antiviral immune mechanisms of the infected host. This short review will attempt to provide an overall description of the order Bunyavirales, describing the mechanisms behind their infection, replication, and their evasion of the host immune response. Furthermore, the historical context of these viruses will be presented, starting from their original discovery almost 80 years ago to the most recent research pertaining to viral replication and host immune response.

The Emerging Role of the Serine Incorporator Protein Family in Regulating Viral Infection

Serine incorporator (SERINC) proteins 1–5 (SERINC1-5) are involved in the progression of several diseases. SERINC2-4 are carrier proteins that incorporate the polar amino acid serine into membranes to facilitate the synthesis of phosphatidylserine and sphingolipids. SERINC genes are also differentially expressed in tumors. Abnormal expression of SERINC proteins occurs in human cancers of the breast, lung, colon, liver, and various glands, as well as in mouse testes. SERINC proteins also affect cleft lip and palate and nerve-related diseases, such as seizure Parkinsonism and borderline personality. Moreover, SERINC proteins have garnered significant interest as retroviral restriction factors, spurring efforts to define their function and elucidate the mechanisms through which they operate when associated with viruses. Human SERINC proteins possess antiviral potential against human immunodeficiency virus (HIV), SARS-COV-2, murine leukemia virus (MLV), equine infectious anemia virus (EIAV), and hepatitis B virus (HBV). Furthermore, the crystal structure is known, and the critical residues of SERINC5 that act against HIV have been identified. In this review, we discuss the most prevalent mechanisms by which SERINC3 and SERINC5 antagonize viruses and focus on the potential therapeutic applications of SERINC5/3 against HIV.

NSG-Mice Reveal the Importance of a Functional Innate and Adaptive Immune Response to Overcome RVFV Infection

Rift Valley fever (RVF) is a zoonotic disease caused by RVF Phlebovirus (RVFV). The RVFV MP-12 vaccine strain is known to exhibit residual virulence in the case of a deficient interferon type 1 response. The hypothesis of this study is that virus replication and severity of lesions induced by the MP-12 strain in immunocompromised mice depend on the specific function of the disturbed pathway. Therefore, 10 strains of mice with deficient innate immunity (B6-IFNARtmAgt, C.129S7(B6)-Ifngtm1Ts/J, B6-TLR3tm1Flv, B6-TLR7tm1Aki, NOD/ShiLtJ), helper T-cell- (CD4tm1Mak), cytotoxic T-cell- (CD8atm1Mak), B-cell- (Igh-Jtm1DhuN?+N2), combined T- and B-cell- (NU/J) and combined T-, B-, natural killer (NK) cell- and macrophage-mediated immunity (NOD.Cg-PrkdcscidIl2rgtm1WjI/SzJ (NSG) mice) were subcutaneously infected with RVFV MP-12. B6-IFNARtmAgt mice were the only strain to develop fatal disease due to RVFV-induced severe hepatocellular necrosis and apoptosis. Notably, no clinical disease and only mild multifocal hepatocellular necrosis and apoptosis were observed in NSG mice, while immunohistochemistry detected the RVFV antigen in the liver and the brain. No or low virus expression and no lesions were observed in the other mouse strains. Conclusively, the interferon type 1 response is essential for early control of RVFV replication and disease, whereas functional NK cells, macrophages and lymphocytes are essential for virus clearance.

Epidemiological study of Kabuto Mountain virus, a novel uukuvirus, in Japan

Kabuto Mountain virus (KAMV), the new member of the genus Uukuvirus, was isolated from the tick Haemaphysalis flava in 2018 in Japan. To date, there is no information on KAMV infection in human and animals. Therefore, serological surveillance of the infection among humans and wild mammals was conducted by virus-neutralization (VN) test and indirect immunofluorescence assay (IFA). Sera of 24 humans, 59 monkeys, 171 wild boars, 233 Sika deer, 7 bears, and 27 nutria in Yamaguchi Prefecture were analyzed by VN test. The positive ratio of humans, monkeys, wild boars, and Sika deer were 20.8%, 3.4%, 33.9% and 4.7%, respectively. No positive samples were detected in bears and nutria. The correlation coefficients between VN test and IFA in human, monkey, wild boar, and Sika deer sera were 0.5745, 0.7198, 0.9967 and 0.9525, respectively. In addition, KAMV was detected in one pool of Haemaphysalis formosensis ticks in Wakayama Prefecture. These results indicated that KAMV or KAMV-like virus is circulating among many wildlife and ticks, and that this virus incidentally infects humans.