African Swine Fever Virus MGF505-7R Interacts with Interferon Regulatory Factor 9 to Evade the Type I Interferon Signaling Pathway and Promote Viral Replication

MGF505-7R and I267L Deletions Attenuate African Swine Fever Virus and Confer Protection Against the Virulent Pandemic Virus in Pigs

African swine fever virus (ASFV) poses a serious risk to wild boars and domestic pigs worldwide. Developing live-attenuated vaccines (LAVs) containing specific gene deletions is an effective approach to prevent and control African swine fever (ASF) epidemics. We created a novel ASFV mutant, ASFV-GS-Δ7R/ΔI267L, with deletions of genes MGF505-7R and I267L, using the highly pathogenic parental strain ASFV-GS/2018 (ASFV-GS). In vitro, the viral titer of ASFV-GS-Δ7R/ΔI267L was approximately 10 times lower than that of its parental strain. Pigs inoculated with 104 50% hemadsorption doses (HAD50) of this mutant did not exhibit the severe fever and sudden death that are characteristic of ASF. The viral load in the blood of vaccinated pigs remained low, and their body temperatures tended to revert to normal at the end of the immunization experiment. After being challenged with 102 HAD50 of virulent ASFV-GS, five of seven pigs in the immunization group remained disease-free, whereas seven pigs in the control group developed severe fever and died within 9 days after the challenge. Histological examination revealed that the protected pigs showed no visible pathological damage and had lower viral loads than the unprotected pigs. Furthermore, transcriptome analysis demonstrated that the host genes IL1B1 and CSF3 were significantly upregulated in ASFV mutant-infected porcine alveolar macrophages, but not in parental virus-infected macrophages. These findings provide important information for the development of ASF LAVs.

Safety and efficacy of a Vero-adapted live attenuated vaccine candidate for African swine fever

African swine fever (ASF) is a lethal disease that significantly affects the global swine industry owing to the high mortality rate of infected pigs. The causative agent, ASF virus (ASFV), is difficult to control; however, live attenuated vaccines have recently emerged as a promising solution. This study evaluated the safety and efficacy of a novel live attenuated ASFV strain (VaCln3 P13) derived from a Korean ASFV isolate adapted to Vero cells. VaCln3 P13 harbors 12 non-synonymous SNPs across multiple viral genes without large gene deletions, all of which may collectively contribute to its attenuated phenotype. Notably, mutations in MGF300-2R and MGF505-7R result in protein truncation potentially influencing its safety. Our evaluation in domestic pigs inoculated with varying doses of VaCln3 P13, demonstrated substantial attenuation and protective efficacy against a virulent ASFV challenge, with only transient clinical signs and no severe adverse effects. All vaccinated pigs developed robust humoral immune responses and overcame the virulent parental virus challenge and survived, whereas mock-inoculated pigs succumbed within 10 days post-challenge. Pathological assessments revealed limited histopathological lesions in vaccinated pigs, while unvaccinated controls displayed extensive hemorrhage, lymphoid depletion, and severe systemic lesions after the challenge. These findings underscore the potential of VaCln3 P13 as a vaccine candidate for ASF control and hold promise for further applications.

Advances in African swine fever virus molecular biology and host interactions contributing to new tools for control

African swine fever virus (ASFV) causes a frequently fatal hemorrhagic disease in domestic pigs and wild boar. The spread from Africa to Georgia in 2007 initiated a pandemic affecting many European and most Asian countries. This has had a very high socio-economic impact and threatens global food security. The virus is a large, complex, cytoplasmic DNA virus, the only member of the Asfarviridae family and codes for 170-190 proteins. Many of these have unknown functions and do not resemble other viruses or host proteins. This complexity has hindered the development of vaccines and other tools for control. The intensity of research has increased since the spread of ASFV in Europe and Asia, leading to rapid advances in knowledge. This review summarizes recent research, including the determination by cryogenic electron microscopy of the virus capsid structure and virion proteome. Novel information on the virus replication cycle, including mechanisms of virus entry into cells and the identification of host endosomal proteins important for entry, is summarized. Multiple, novel virus immune evasion proteins and their targets in the type I interferon response and inflammation pathways have been identified. The potential for the application of this knowledge to developing novel control tools, including modified live vaccines and other interventions targeting critical virus processes or host interactions, is discussed.

Preparation of a new monoclonal antibody against D205R protein of African swine fever virus and identification of its linear antigenic epitope

African swine fever virus (ASFV), a highly contagious virus with a double-stranded DNA genome, is notorious for causing severe hemorrhagic fever in pigs, often leading to mortality rates as high as 100 %. First identified in Kenya in 1921, the virus has since spread globally, with a significant outbreak in China in 2018, causing extensive economic losses in the swine industry. The D205R protein (pD205R) of ASFV, classified as a non-structural protein, plays a role in the transcription of viral genes and is associated with ASFV RNA polymerase. However, the specific function of this protein remains unclear. To gain a deeper insight into the structure, function, and mechanisms of interaction between pD205R and the host, we successfully expressed the pD205R protein and generated a monoclonal antibody (mAb), designated 3G6G1, targeting this protein. The mAb 3G6G1 can be utilized for indirect immunofluorescence (IFA) and Western blotting (WB) detection of ASFV strains. Through the evaluation of the reactivity of antibodies against a series of truncated pD205R fragments, we identified the epitope recognized by mAb 3G6G1 as residing within the amino acid sequence 96 VLSKKNI 102. Bioinformatics analysis indicated that this antigenic epitope possesses a high antigenic index and is highly conserved. These findings will establish a foundation for further research into the function of the D205R protein and its role in the interaction between ASFV and its host.

The African swine fever virus B125R protein antagonizes JAK-STAT signalling by promoting the degradation of IFNAR2

African swine fever (ASF) is a highly contagious and severe hemorrhagic disease caused by African swine fever virus (ASFV). Currently, few safe and effective vaccines or antiviral drugs are available for its prevention. Interferon (IFN), a key component of innate antiviral immunity, induces interferon-stimulated genes (ISGs) by activating the JAK-STAT signalling pathway, resulting in antiviral effects. ASFV strains, including ASFV SY18, ASFV HLJ18, and ASFV BA71V, are highly sensitive to IFN-I treatment; however, the mechanisms by which ASFV antagonizes the host type I IFN response have not been fully elucidated. In this study, we identified the ASFV B125R protein (pB125R) as a negative regulator of the JAK-STAT pathway. We observed that ectopically expressed pB125R significantly suppressed the IFN-β-triggered activation of JAK-STAT signalling in HEK293T and PK-15 cells. Mechanistic studies revealed that pB125R binds to IFNAR2 and promotes its autophagic degradation, impairing the signal transduction of the IFN response at an early stage. This ultimately reduces the nuclear translocation of the ISGF3 complex and decreases ISG production. Our findings highlight the immunosuppressive activity of pB125R and reveal a novel mechanism by which ASFV evades the host IFN response, contributing to potential strategies for developing vaccines and therapeutics against ASF.

The alpha-coronavirus E protein inhibits the JAK-STAT pathway signaling by triggering STAT2 degradation through OPTN- and NBR1-mediated selective autophagy

The zoonotic transmission of coronaviruses continues to pose a considerable threat to humans. Swine acute diarrhea syndrome coronavirus (SADS-CoV), a bat coronavirus related to HKU2, causes severe economic losses in the pig industry and has the potential to trigger outbreaks in humans. However, our understanding of how SADS-CoV evades the host's innate immunity remains limited, hindering effective responses to potential human outbreaks. In this study, we demonstrate that the SADS-CoV envelope protein (E) inhibits type I interferon (IFN-I) signaling by inducing the degradation of STAT2 via the macroautophagy/autophagy-lysosome pathway. Mechanistically, the E protein evades host innate immunity by promoting STAT2 degradation through autophagy, mediated by the NBR1 and OPTN receptors. Notably, ubiquitination of E protein is required for the autophagic degradation of STAT2. Additionally, lysine residue K61 of the E protein is crucial for its stable expression; however, it is not involved in its ubiquitination. In conclusion, our study reveals a novel mechanism by which the E protein disrupts IFN-I signaling by targeting STAT2 via autophagy, enhancing our understanding of SADS-CoV's immune evasion strategies and providing potential drug targets for controlling viral infections.Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; BafA1: bafilomycin A1; BSA: bovine serum albumin; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CC: coiled-coil; CHX: cycloheximide; Co-IP: co-immunoprecipitation; DAPI: 4',6-diamidino-2-phenylindole; DBD: DNA-binding domain; DMEM: Dulbecco's Modified Eagle's medium; DMSO: dimethyl sulfoxide; E, Envelope. FW: four-tryptophan; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HA: hemagglutinin; hpt: hours post-treatment; IF: indirect immunofluorescence; IFNB/IFN-β: interferon beta; IgG: immunoglobulin G; ISG: IFN-stimulated genes; ISRE: interferon-stimulated response element; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PBS: phosphate-buffered saline; PRRs: pattern recognition receptors; qPCR: quantitative polymerase chain reaction; SAR: selective autophagy receptor; SQSTM1/p62: sequestosome 1; STAT: signal transduction and activator of transcription; TBS-T: Tris-buffered saline with Tween 20; TCID50: 50% tissue culture infective dose; TOLLIP: toll interacting protein; Ub: ubiquitin; UBA: C-terminal ubiquitin-associated; VSV: vesicular stomatitis virus; WB: western blotting. WT: wild type.

Genetic and biological characterization of African swine fever virus clones selected at the early stages of adaptation in Vero cells

African swine fever is a highly contagious viral disease affecting domestic pigs and wild boars, caused by African swine fever virus (ASFV). ASFV exhibits highly restricted cell tropism, primarily targeting porcine macrophages for efficient and stable replication. This strict requirement for a specific cell type has posed significant challenges in ASFV research and remains a critical obstacle to vaccine development. Although several cell lines have been reported to support ASFV replication, significant genetic changes occur during passages in cell lines in unpredictable ways. In this study, we adapted a highly virulent Korean ASFV isolate to Vero cells, and plaque purification was employed during the early stages of cell adaptation to eliminate the competitive pressure between viral subpopulations. Three viral clones with distinct genetic properties were obtained and passaged independently up to 30 times. The three clones replicated efficiently in porcine alveolar macrophages (PAMs) and Vero cells even after 30 passages, while the parent virus did not grow in Vero cells. Genetic analysis revealed that the cell-adapted viral clones shared multiple single-nucleotide polymorphisms (SNPs) but also had unique SNPs and large deletions in their genome. This diversity of mutations in these clones could provide a valuable model for exploring gene functions and their effects on phenotypic properties. Future studies will focus on evaluating the phenotypic effects of these SNPs in vivo to support vaccine development.

The Strategies Used by Animal Viruses to Antagonize Host Antiviral Innate Immunity: New Clues for Developing Live Attenuated Vaccines (LAVs)

As an essential type of vaccine, live attenuated vaccines (LAVs) play a crucial role in animal disease prevention and control. Nevertheless, developing LAVs faces the challenge of balancing safety and efficacy. Understanding the mechanisms animal viruses use to antagonize host antiviral innate immunity may help to precisely regulate vaccine strains and maintain strong immunogenicity while reducing their pathogenicity. It may improve the safety and efficacy of LAVs, as well as provide a more reliable means for the prevention and control of infectious livestock diseases. Therefore, exploring viral antagonistic mechanisms is a significant clue for developing LAVs, which helps to explore more viral virulence factors (as new vaccine targets) and provides a vital theoretical basis and technical support for vaccine development. Among animal viruses, ASFV, PRRSV, PRV, CSFV, FMDV, PCV, PPV, and AIV are some typical representatives. It is crucial to conduct in-depth research and summarize the antagonistic strategies of these typical animal viruses. Studies have indicated that animal viruses may antagonize the antiviral innate immunity by directly or indirectly blocking the antiviral signaling pathways. In addition, viruses also do this by antagonizing host restriction factors targeting the viral replication cycle. Beyond that, viruses may antagonize via regulating apoptosis, metabolic pathways, and stress granule formation. A summary of viral antagonistic mechanisms might provide a new theoretical basis for understanding the pathogenic mechanism of animal viruses and developing LAVs based on antagonistic mechanisms and viral virulence factors.

TRIM28 regulates the coagulation cascade inhibited by p72 of African swine fever virus

In 2018, African swine fever virus (ASFV) emerged in China, causing extremely serious economic losses to the domestic pig industry. Infection with ASFV can cause disseminated coagulation, leading to the consumption of platelets and coagulation factors and severe bleeding. However, the mechanism of virus-induced coagulation has yet to be established. In our study, ASFV downregulated the coagulation process, as detected by D-dimer (D2D) and Factor X (F10) expression in pigs challenged with ASFV HLJ/18. In vitro, ASFV infection increased Factor IX (F9) and Factor XII (F12) expression while downregulating F10 expression in porcine alveolar macrophages (PAMs). African swine fever virus induced both intrinsic and extrinsic coagulation cascades. In addition, several encoded proteins affect the expression of the crucial coagulation protein F10, and among the encoded proteins, p72 inhibits the activity and expression of F10. Proteomic analysis also revealed that p72 is involved in the coagulation cascade. p72 can interact with F10, and its inhibitory functional domains include amino acids 423-432 and amino acids 443-452. Finally, we found that F10 and p72 interact with tripartite motif-containing protein 28 (TRIM28). TRIM28 knockdown resulted in a decrease in F10 expression. Importantly, TRIM28 contributes to the reduction in F10 protein expression regulated by p72. Our findings revealed an inhibitory effect of the viral protein p72 on the ASFV infection-induced coagulation cascade and revealed a role of TRIM28 in reducing F10 expression, revealing a molecular mechanism of ASFV-associated coagulation.

How Does African Swine Fever Virus Evade the cGAS-STING Pathway?

African swine fever (ASF), a highly infectious and devastating disease affecting both domestic pigs and wild boars, is caused by the African swine fever virus (ASFV). ASF has resulted in rapid global spread of the disease, leading to significant economic losses within the swine industry. A significant obstacle to the creation of safe and effective ASF vaccines is the existing knowledge gap regarding the pathogenesis of ASFV and its mechanisms of immune evasion. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a major pathway mediating type I interferon (IFN) antiviral immune response against infections by diverse classes of pathogens that contain DNA or generate DNA in their life cycles. To evade the host's innate immune response, ASFV encodes many proteins that inhibit the production of type I IFN by antagonizing the cGAS-STING signaling pathway. Multiple proteins of ASFV are involved in promoting viral replication by protein-protein interaction during ASFV infection. The protein QP383R could impair the function of cGAS. The proteins EP364R, C129R and B175L could disturb the function of cyclic guanosine monophosphate-adenosine monophosphate (cGAMP). The proteins E248R, L83L, MGF505-11L, MGF505-7R, H240R, CD2v, E184L, B175L and p17 could interfere with the function of STING. The proteins MGF360-11L, MGF505-7R, I215L, DP96R, A151R and S273R could affect the function of TANK Binding Kinase 1 (TBK1) and IκB kinase ε (IKKε). The proteins MGF360-14L, M1249L, E120R, S273R, D129L, E301R, DP96R, MGF505-7R and I226R could inhibit the function of Interferon Regulatory Factor 3 (IRF3). The proteins MGF360-12L, MGF505-7R/A528R, UBCv1 and A238L could inhibit the function of nuclear factor kappa B (NF-Κb).

pK205R targets the proximal element of IFN-I signaling pathway to assist African swine fever virus to escape host innate immunity at the early stage of infection

African swine fever virus (ASFV) is a nuclear cytoplasmic large DNA virus (NCLDV) that causes devastating hemorrhagic diseases in domestic pigs and wild boars, seriously threatening the development of the global pig industry. IFN-I plays an important role in the body's antiviral response. Similar to other DNA viruses, ASFV has evolved a variety of immune escape strategies to antagonize IFN-I signaling and maintain its proliferation. In this study, we showed that the ASFV early protein pK205R strongly inhibited interferon-stimulated genes (ISGs) as well as the promoter activity of IFN-stimulated regulatory elements (ISREs). Mechanistically, pK205R interacted with the intracellular domains of IFNAR1 and IFNAR2, thereby inhibiting the interaction of IFNAR1/2 with JAK1 and TYK2 and hindering the phosphorylation and nuclear translocation of STATs. Subsequently, we generated a recombinant strain of the ASFV-pK205R point mutation, ASFV-pK205R7PM. Notably, we detected higher levels of ISGs in porcine alveolar macrophages (PAMs) than in the parental strain during the early stages of ASFV-pK205R7PM infection. Moreover, ASFV-pK205R7PM attenuated the inhibitory effect on IFN-I signaling. In conclusion, we identified a new ASFV immunosuppressive protein that increases our understanding of ASFV immune escape mechanisms.

Multigenic family 110 (1 L-5-6 L) of African swine fever virus modulate cytokine genes expression in vitro

BACKGROUND

African swine fever (ASF) is a viral disease that affects pigs and wild boars providing economic burden in swine industry.

METHODS AND RESULTS

In this study, we investigated the effect of deleting the ASFV multigene family 110 (MGF110) fragment (1 L-5-6 L) on apoptosis modulation and the expression of proinflammatory cytokines. Gene expression in swine peripheral blood macrophages infected with either the parental "Volgograd/14c" strain or the gene-deleted "Volgograd/D(1L-5-6L) MGF110" strain was analyzed. Caspase-3 activity was 1.15 times higher in macrophages infected with the parental ASFV strain compared to the gene-deleted strain. Gene expression analysis of Caspase-3 (Cas-3), Interferon-A (IFN-A), Tumor Necrosis Factor A (TNF-A), B-cell Lymphoma-2 (Bcl-2), Nuclear Factor Kappa B (NF-kB), Interleukin-12 (IL-12), and Heat Shock Protein-70 (HSP-70) using RT-qPCR at various time points after infection revealed significant differences in expression profiles between the strains. The peak expression of cytokines (except NF-kB) occurred at 24 h post-infection with the "Volgograd/D(1L-5-6L) MGF110" strain. In samples infected with the ASFV "Volgograd/14c" strain, the most intense expression was observed at 72 and 96 h, except for Bcl-2 and NF-kB, which peaked at 6 h post-infection. The cytokine expression trend for the "Volgograd/D(1L-5-6L) MGF110" strain was more stable with higher expression values.

CONCLUSION

The expression trend for the parental strain increased over time, reaching maximum values at 72 and 96 h post-infection, but the overall expression level was lower than that of the gene-deleted strain. These findings suggest that deleting the multigene family 110 members (1 L-5-6 L) contributes to ASFV attenuation without affecting virus replication kinetics.

African swine fever virus pB475L evades host antiviral innate immunity via targeting STAT2 to inhibit IFN-I signaling

African swine fever virus (ASFV) causes severe disease in domestic pigs and wild boars, seriously threatening the development of the global pig industry. Type I interferon (IFN-I) is an important component of innate immunity, inducing the transcription and expression of antiviral cytokines by activating Janus-activated kinase-signal transducer and activator of transcription (STAT). However, the underlying molecular mechanisms by which ASFV antagonizes IFN-I signaling have not been fully elucidated. Therefore, using coimmunoprecipitation, confocal microscopy, and dual luciferase reporter assay methods, we investigated these mechanisms and identified a novel ASFV immunosuppressive protein, pB475L, which interacts with the C-terminal domain of STAT2. Consequently, pB475L inhibited IFN-I signaling by inhibiting STAT1 and STAT2 heterodimerization and nuclear translocation. Furthermore, we constructed an ASFV-B475L7PM mutant strain by homologous recombination, finding that ASFV-B475L7PM attenuated the inhibitory effects on IFN-I signaling compared to ASFV-WT. In summary, this study reveals a new mechanism by which ASFV impairs host innate immunity.

Genetic Variations of African Swine Fever Virus: Major Challenges and Prospects

African swine fever (ASF) is a contagious viral disease affecting pigs and wild boars. It typically presents as a hemorrhagic fever but can also manifest in various forms, ranging from acute to asymptomatic. ASF has spread extensively globally, significantly impacting the swine industry. The complex and highly variable character of the ASFV genome makes vaccine development and disease surveillance extremely difficult. The overall trend in ASFV evolution is towards decreased virulence and increased transmissibility. Factors such as gene mutation, viral recombination, and the strain-specificity of virulence-associated genes facilitate viral variations. This review deeply discusses the influence of these factors on viral immune evasion, pathogenicity, and the ensuing complexities encountered in vaccine development, disease detection, and surveillance. The ultimate goal of this review is to thoroughly explore the genetic evolution patterns and variation mechanisms of ASFV, providing a theoretical foundation for advancement in vaccine and diagnostic technologies.

Interferon regulatory factors inhibit TiLV replication by activating interferon-a3 in tilapia (Oreochromis niloticus)

Tilapia lake virus (TiLV) is an emerging virus that seriously threatens the tilapia industries worldwide. Interferon regulatory factors (IRFs), which are the crucial mediators regulating the response of interferon (IFN) to combat invading viruses, have not yet been reported in tilapia during TiLV infection. Here, six IRF (IRF1, IRF2, IRF4, IRF7, IRF8, and IRF9) homologs from tilapia were characterized and analyzed. These IRFs typically shared the conserved domains and phylogenetic relationship with IRF homologs of other species. Tissue distribution analysis showed that all six IRF genes were expressed in various tissues, with the highest expression in immune-related tissues. Furthermore, overexpression of IRFs in tilapia brain (TiB) cells significantly inhibited TiLV propagation, as evidenced by decreased viral segment 8 gene transcripts and copy numbers of viral segment 1. More importantly, all six IRF genes significantly enhanced the promoter activity of type I interferon-a3 (IFNa3) in TiB cells, suggesting that tilapia IRF genes serve as positive regulators in activating IFNa3. Surprisingly, the promoter activity of IFNa3 mediated by IRF genes was markedly inhibited post-TiLV infection, indicating that TiLV antagonized IRF-mediated IFN immune response. Taken together, six IRF genes of tilapia are highly conserved transcription factors that inhibit TiLV infection by activating the promoter of IFNa3, which is in turn restrained by TiLV. These findings broaden our knowledge about the functionality of IRF-mediated antiviral immunity in tilapia against TiLV infection and host-TiLV interaction, which lays a foundation for developing antiviral strategies in tilapia cultural industries.

Deletion of MGF505-2R Gene Activates the cGAS-STING Pathway Leading to Attenuation and Protection against Virulent African Swine Fever Virus

African swine fever virus (ASFV) is the etiological agent causing African swine fever (ASF), affecting domestic pigs and wild boar, which is currently the biggest animal epidemic in the world and a major threat to the swine sector. At present, some safety concerns about using LAVs against ASFV still exist despite a commercial vaccine licensed in Vietnam. Therefore, the efforts to identify virulence factors and their mechanisms, as well as to generate new vaccine prototypes, are of major interest. In this work, we have identified the MGF505-2R gene product as an inhibitor of the cGAS/STING pathway, specifically through its interaction with STING protein, controlling IFN-β production. In addition, immunization of a recombinant virus lacking this gene, Arm/07-ΔMGF505-2R, resulted in complete attenuation, demonstrating its involvement in ASFV virulence. Finally, immunization with Arm/07-ΔMGF505-2R induced the generation of antibodies and proved to be partially protective against virulent ASFV strains. These results identify MGF505-2R, as well as its mechanism of action, as a gene contributing to understanding the molecular mechanisms of ASFV virulence, which will be of great value in the design of future vaccine prototypes.

African Swine Fever Virus pF778R Attenuates Type I Interferon Response by Impeding STAT1 Nuclear Translocation

African swine fever virus (ASFV) is an extensive and intricate double-stranded DNA virus with approximately 100% lethality in domestic swine. There is no effective vaccine to combat this virus, and this has led to substantial economic losses in the swine industry. ASFV encodes various proteins that impede interferon-based immune defenses in the host by employing diverse mechanisms. However, the roles of most of these proteins remain unknown. Therefore, understanding the immune evasion mechanisms employed by ASFV may facilitate the development of effective measures against the virus. In this study, we discovered a negative regulation of the type I interferon (IFN) response by the ASFV ribonuclease reductase large subunit pF778R. This novel type Ⅰ IFN response antagonist significantly inhibits IFN-α-induced interferon-stimulated response element promoter activation, precludes the upregulation of various interferon-stimulated genes, and prevents STAT1 nuclear translocation. Mechanistically, pF778R did not affect the protein levels of crucial molecules in the JAK/STAT signaling pathway or engage in direct interactions. However, pF778R expression impedes type I IFN responses mediated by the JAK/STAT signaling pathway. Further investigations revealed that pF778R did not interfere with STAT1 phosphorylation or dimerization, but it inhibited IFN signaling by weakening the nuclear accumulation of activated STAT1. The critical role of the ASFV protein pF778R in evading IFN-I-mediated innate immunity highlights a unique mode of ASFV evasion and provides insights into the pathogenic mechanism of the virus.

The MGF300-2R protein of African swine fever virus is associated with viral pathogenicity by promoting the autophagic degradation of IKKα and IKKβ through the recruitment of TOLLIP

The multigene family genes (MGFs) in the left variable region (LVR) of the African swine fever virus (ASFV) genome have been reported to be involved in viral replication in primary porcine alveolar macrophages (PAMs) and virulence in pigs. However, the exact functions of key MGFs in the LVR that regulate the replication and virulence of ASFV remain unclear. In this study, we identified the MGF300-2R gene to be critical for viral replication in PAMs by deleting different sets of MGFs in the LVR from the highly virulent strain ASFV HLJ/18 (ASFV-WT). The ASFV mutant lacking the MGF300-2R gene (Del2R) showed a 1-log reduction in viral titer, and induced higher IL-1β and TNF-α production in PAMs than did ASFV-WT. Mechanistically, the MGF300-2R protein was found to interact with and degrade IKKα and IKKβ via the selective autophagy pathway. Furthermore, we showed that MGF300-2R promoted the K27-linked polyubiquitination of IKKα and IKKβ, which subsequently served as a recognition signal for the cargo receptor TOLLIP-mediated selective autophagic degradation. Importantly, Del2R exhibited a significant reduction in both replication and virulence compared with ASFV-WT in pigs, likely due to the increased IL-1β and TNF-α, indicating that MGF300-2R is a virulence determinant. These findings reveal that MGF300-2R suppresses host innate immune responses by mediating the degradation of IKKα and IKKβ, which provides clues to paving the way for the rational design of live attenuated vaccines to control ASF.

Functional Landscape of African Swine Fever Virus-Host and Virus-Virus Protein Interactions

Viral replication fully relies on the host cell machinery, and physical interactions between viral and host proteins mediate key steps of the viral life cycle. Therefore, identifying virus-host protein-protein interactions (PPIs) provides insights into the molecular mechanisms governing virus infection and is crucial for designing novel antiviral strategies. In the case of the African swine fever virus (ASFV), a large DNA virus that causes a deadly panzootic disease in pigs, the limited understanding of host and viral targets hinders the development of effective vaccines and treatments. This review summarizes the current knowledge of virus-host and virus-virus PPIs by collecting and analyzing studies of individual viral proteins. We have compiled a dataset of experimentally determined host and virus protein targets, the molecular mechanisms involved, and the biological functions of the identified virus-host and virus-virus protein interactions during infection. Ultimately, this work provides a comprehensive and systematic overview of ASFV interactome, identifies knowledge gaps, and proposes future research directions.