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•Pseudorabies virus (PRV) variant strain XJ5 is more virulent than classical strain Ra in 12-week-old pigs.•Bartha-k61 vaccine was effective against both strains mentioned above upon experimental challenge.•Clinical outcome depended on virulence of challenge strains and age of pigs in PRV challenge model. Since late 2011, pseudorabies (PR) has resurfaced in many large pig farms, causing great economic loss for the swine industry in China. The PRV variant strain with high virulence and antigenic variation has been considered to be the main cause, and much attention has been focused on how to prevent and control the reoccurrence of this disease in China. In this study, two kinds of vaccination strategy were employed to evaluate the protective effects of Bartha-k61vaccine against both variant PRV (XJ5) and classical PRV (Ra) strain challenge. Humoral immunity response, clinical signs, survival rate, body weight, virus shedding and pathology were assessed in commercial pigs. The results showed that Bartha-k61vaccine, administered either once or twice, was effective against the PRV variant (XJ5) challenge, while no significant differences were observed between single and prime-boost vaccinated pigs. However, pigs vaccinated twice had better body weight gains than those vaccinated once, following challenge with the classical PRV strain (Ra) (p<0.01). Therefore, the Bartha-k61 vaccine appears to be an effective vaccine to control the spread of PRV variants in China in the absence of new powerful candidate vaccines specific to these PRV strains.

Alpha-herpesviruses, including pseudorabies virus (PRV) and herpes simplex virus type 1 (HSV-1), cause severe diseases in a wide range of hosts. However, the precise mechanisms of immune evasion by alpha-herpesviruses remains elusive, hindering the development of broad-spectrum antiviral vaccines and drugs. Here, we demonstrate that the immediate early protein US1, encoded by alpha-herpesviruses, directly interacts with cGAS, suppressing its dsDNA binding and enzymatic activity. Structural analysis using AlphaFold reveals a conserved overlapping region within PRV and HSV-1 US1 proteins. Deletion of these peptides leads to increased cGAS-mediated IFN-β production. Meanwhile, both synthetic and purified SUMO-fused US1 peptides significantly inhibit cGAS activity across species, with the SUMO-fused US1 peptides directly binding to the catalytic domain of cGAS. Both US1-deficient viruses (PRV-ΔUS1 and HSV-1-ΔUS1) exhibit higher IFN-β production and enhanced signaling through the cGAS-STING pathway. Importantly, mice infected with PRV-ΔUS1 or HSV-1-ΔUS1 show increased IFN-β secretion and reduced viral loads. In conclusion, overlapping peptides from US1 protein of alpha-herpesviruses antagonize cGAS-mediated innate immune responses, highlighting a promising target for the development of broad-spectrum inhibitors to counteract herpesvirus infections.

Porcine circovirus type 2 (PCV2), porcine circovirus type 3 (PCV3), and pseudorabies virus (PRV) are major pathogens posing significant threats to the swine industry. Viral evolution and mutations have limited the efficacy of current commercial vaccines, necessitating the development of more effective prophylactic strategies. In this study, a novel recombinant virus strain, designated as rPRV-ΔTK-PCV3(Cap)/ΔgIgE-PCV2(Cap), was generated using PRV SX-10 variant as the backbone. CRISPR/Cas9-mediated deletion of TK and gE/gI genes was performed, followed by insertion of PCV3 and PCV2 capsid protein genes into the respective loci. The engineered recombinant strain demonstrated stable proliferation in BHK-21 cells, efficiently expressed heterologous PCV3 and PCV2 capsid proteins, while maintaining biological properties comparable to its parental strain. The rPRV-ΔTK-PCV3(Cap)/ΔgIgE-PCV2(Cap) demonstrated favorable safety and immunogenicity profiles in mice and piglets, eliciting robust immune responses characterized by high titers of specific antibodies against PRV, PCV3, and PCV2, along with significantly elevated levels of cytokines (IFN-γ, IL-2, and IL-4). Histopathological analysis and viral load quantification demonstrated that rPRV-ΔTK-PCV3(Cap)/ΔgIgE-PCV2(Cap) immunization significantly attenuated tissue lesions and decreased viral copies of PRV and PCV in mice and piglets. Collectively, these findings suggest that rPRV-ΔTK-PCV3(Cap)/ΔgIgE-PCV2(Cap) serves as a promising candidate vaccine against PRV and PCV infections. •Generated novel recombinant virus rPRV-ΔTK-PCV3(Cap)/ΔgIgE-PCV2(Cap) via CRISPR/Cas9.•Demonstrated stable virus proliferation and efficient PCV3/PCV2 capsid protein expression.•Induced robust immune responses against PRV, PCV3, and PCV2.•Provided valuable insights for the development of trivalent vaccine candidates.

•PRV variant with defect in TK, gE and gI (rSMXΔgI/gEΔTK) is safe for newborn piglets and sheep.•rSMXΔgI/gEΔTK induced full protection in growing pigs against lethal challenge of PRV variant.•Bartha-K61vaccine failed to confer full protection in growing pigs against lethal PRV variant challenge.•rSMXΔgI/gEΔTK elicited higher neutralization antibody against PRV variant SMX than Bartha-K61 vaccine.•PRV variant with defect in TK, gE and gI is a DIVA (differentiating infected from vaccinated animals vaccine) candidate. One of the distinct features of the emerging Chinese pseudorabies virus (PRV) variant is its ability to cause severe neurological signs and high mortality in growing pigs in Bartha-K61-vaccinated pig farms. Either single- or multiple-gene-deleted live vaccine candidates have been developed; however, none was evaluated thoroughly in growing pigs. Here, we generated rSMXΔgI/gEΔTK, an attenuated PRV variant with defects in TK, gI and gE genes. The growth kinetics of the attenuated virus was similar to the wild type (wt) strain. It was safe for 1-day-old piglets. Twenty one-day-old weaned pigs were immunized intramuscularly either with 106.0 TCID50 of rSMXΔgI/gEΔTK or one dose of commercial Bartha-K61 vaccine, or with DMEM, and were challenged intranasally with 107.0 TCID50 wt virus at 28 days post vaccination. rSMXΔgI/gEΔTK elicited higher level neutralization antibody against both PRV variant SMX and Bartha-K61 strain, while Bartha-K61 vaccine elicited lower neutralization activity of antibody against SMX. After challenge, all pigs in rSMXΔgI/gEΔTK group survived without any clinical signs, while unvaccinated group showed 100% mortality, and Bartha-K61 group showed severe respiratory symptoms and 3 out of 5 pigs exhibited severe neurological signs. Pigs in rSMXΔgI/gEΔTK group gained significantly higher body weight and diminished viral excretion titer and period, compared with Bartha-K61 group. Furthermore, the safety and efficacy of rSMXΔgI/gEΔTK was also evaluated in sheep and compared with local vaccine in growing pigs. These data suggest that the attenuated strain rSMXΔgI/gEΔTK is a promising live marker vaccine candidate for PR control in the context of emerging PRV variants.

Cyclic GMP-AMP synthase (cGAS) is a pivotal DNA sensor that initiates antiviral responses, yet the mechanisms by which viruses evade cGAS-mediated innate immunity remain poorly understood. Here, we identified VP22, a tegument protein of pseudorabies virus (PRV), a member of the Alphaherpesvirinae subfamily, as a viral antagonist of the type I interferon (IFN-I) response through hijacking the host RNA helicase DDX21. Specifically, VP22 impairs 2’3’-cyclic GMP–AMP (cGAMP) synthesis by disrupting cGAS condensation. In vivo, cGAS restricts the replication of VP22-deficient PRV and attenuates its pathogenicity, an effect neutralized by VP22. Notably, DDX21 is essential for VP22-mediated inhibition of cGAS activity. Mechanistically, VP22 stabilizes DDX21 protein level and enhances its interaction with cGAS. Furthermore, VP22 promotes the translocation of DDX21 from the nucleus to the cytoplasm, a process required for inhibition of cGAS condensation and activation. Collectively, these findings reveal a previously unrecognized, host-dependent mechanism by which PRV subverts cGAS signaling, shedding light on viral strategies to subvert host DNA sensing and innate immunity.

Pseudorabies virus (PRV) and porcine parvovirus type 1 (PPV1) are major pathogens that cause reproductive disorders in sows, and mixed infections are frequently detected on pig farms. In this study, a recombinant PRV (rPRV-VP2) based on a PRV variant (HLJ8) was constructed to express the PPV1 VP2 protein. To ensure safety, four virulence genes (TK, gE, gI, and UL39) of PRV HLJ8 were deleted, followed by further evaluation of safety and immunogenicity in piglets. The PPV1 VP2 expression cassette was inserted into the gE/gI deletion site, enabling successful expression of the VP2 protein, which exhibited hemagglutination activity with a titre of 1:64. Animal experiments demonstrated that rPRV-VP2 elicited robust antibody responses against both PRV and PPV1, providing complete protection in both mice and piglets. Compared with commercial PRV and PPV1 vaccines, rPRV-VP2 conferred comparable or superior protection, resulting in not only no clinical symptoms but also significantly reduced viral loads in tissues. The deletion of the gE gene can distinguish wild-type virus infection from vaccine immunity in clinical applications. Overall, rPRV-VP2 offers a safe and effective strategy for dual protection against PRV and PPV1, reducing vaccination costs in pig production.

Background Pseudorabies (PR) caused by the re-emerging of pseudorabies virus (PRV) variant has outbroken among PRV vaccine immunized swine in many pig farms, which has caused serious social and economic consequences since the end of 2011. The PRV UL49.5 protein can inactivate the transporter associated with antigen processing (TAP), thereby downregulating the cell surface expression of swine leukocyte antigen class I (SLA-I) to evade host immune surveillance. Methods In this study, based on the PRV ΔgE/TK strain, PRV ΔgE/TK/UL49.5 triple gene deletion strain was constructed through homologous recombination and deletion of the PRV UL49.5 gene by the Cre-LoxP system. Its growth curve and effect on SLA-I transcription level were determined. Preliminary studies were carried out on serum neutralizing antibody levels, IFN-γ and IL-4 cytokines levels in mice immunized with PRV ΔgE/TK/UL49.5, and the viral load and challenge protection in mice tissues after challenge. Results The growth characteristics of PRV ΔgE/TK/UL49.5 strain were similar to those of PRV ΔgE/TK strain. The level of SLA-I was returned to normal after the deletion of PRV UL49.5 gene. The immunization of PRV ΔgE/TK/UL49.5 did not affect the weight gain of mice. Immunized mice could induce high levels of serum neutralization antibodies and immune cytokines, including IFN-γ and IL-4, which could provide complete protection against virulent PRV challenge. No obvious pathological damage was observed in lung, brain and trigeminal ganglion of mice immunized with PRV ΔgE/TK/UL49.5, and the tissue viral load was the lowest. Conclusions PRV ΔgE/TK/UL49.5 strain can induce enhanced immunogenicity and had the potential to be used as a candidate strain.

Natural killer (NK) cells are key players in the innate response to viruses, including herpesviruses. In particular, the variety of viral strategies to modulate the recognition of certain herpesviruses witnesses the importance of NK cells in the control of this group of viruses. Still, NK evasion strategies have remained largely elusive for the largest herpesvirus subfamily, the alphaherpesviruses. Here, we report that the gD glycoprotein of the alphaherpesviruses pseudorabies virus (PRV) and herpes simplex virus 2 (HSV-2) displays previously uncharacterized immune evasion properties toward NK cells. Expression of gD during infection or transfection led to degradation and consequent down-regulation of CD112, a ligand for the activating NK receptor DNAX accessory molecule 1 (DNAM-1). CD112 downregulation resulted in a reduced ability of DNAM-1 to bind to the surface of both virus-infected and gD-transfected cells. Consequently, expression of gD suppressed NK cell degranulation and NK cell-mediated lysis of PRV- or HSV-2–infected cells. These data identify an alphaherpesvirus evasion strategy from NK cells and point out that interactions between viral envelope proteins and host cell receptors can have biological consequences that stretch beyond virus entry. Significance Herpesviruses have developed fascinating mechanisms to evade elimination by key elements of the host immune system, allowing these pathogens to cause lifelong infections with periods of recurrent virus spread. Natural killer (NK) cells are central in the innate antiviral response. Here, we report that the gD glycoprotein of the alphaherpesviruses, pseudorabies virus and herpes simplex virus-2, displays previously uncharacterized immune evasion properties toward NK cells. Expression of the gD protein leads to degradation of CD112/nectin-2, a ligand for the NK-activating receptor DNAX accessory molecule 1 (DNAM-1). This impairs binding of DNAM-1 to the cell surface, thereby suppressing NK-mediated killing of virus-infected (or gD-transfected) cells. Identification of this previously unidentified immune evasion mechanism may contribute to the design of improved herpesvirus vaccines and herpesvirus-based therapeutic vectors.

•A TK/gE/gI triple gene-deleted Pseudorabies virus derived from current circulating field isolate HN1201 strain was generated by using bacterial artificial chromosome techniques.•Rescued virus showed reduced plaque size to its parent strain.•Efficacy study has been performed on 9 day-old piglets and results showed that vaccination can provide full protection to the virulent PRV HN1201 challenge. New-emerging variants of Pseudorabies virus (PRV) compromise the protection provided by current vaccines and cause the death of all ages of vaccinated pigs since 2011. New vaccines based on current circulating PRV strain are needed to control the spread of disease since the variants are antigenically different from classical strains of virus. In this study, a TK/gE/gI triple gene-deleted PRV derived from current circulating field isolate was generated by using bacterial artificial chromosome techniques, and the rescued virus showed similar growth properties in vitro to its parent strain but reduced plaque size. To evaluate it as vaccine candidate, 9 day-old pigs were vaccinated and challenged with a virulent PRV variant. The results showed that vaccination can generate high level of protective gB-specific antibodies after vaccination and provide complete protection to the viral challenge. By contrast, the unvaccinated piglets all died within 6 days after viral challenge. Therefore, the TK/gE/gI triple gene-deleted PRV could be a promising vaccine candidate to control the wide spreading of PR variants in China.

The respiratory mucosa serves as a primary entry point for numerous pathogenic microbes, and the respiratory mucosa secretes type I and III interferons (IFNs), the first generation of antiviral cytokines, in response to viral infection. The pseudorabies virus (PRV) causes serious illnesses in many domestic and wild animal species, particularly in pigs and cattle. However, more information is needed about the immunosuppressive properties and evolutionary history of emerging PRV field strains in China’s respiratory system. The PRV field strain JS2022, which was obtained from a cow farm for this investigation, is a spontaneous recombination of early PRV variant strains in the Jiangsu region and is similar to the PRV variations recovered in China in terms of its entire genome sequence. According to sequence analysis, JS2022 has a spontaneous deletion of 1,212 bp in the gE gene, 502 bp in the gI gene, and 192 bp in the glycoprotein (g) C gene. Pathogenicity analysis revealed that intranasal JS2022 causes severe neurological symptoms in calves, but this effect is different from that of ZJ01. In addition, a considerable number of viral antigens in the nasal mucosa were detected by immunohistochemical staining. Therefore, we constructed a bovine nasal mucosal explant model that maintained good cell morphology and activity even after 5 days. In bovine nasal mucosal explants, JS2022 and ZJ01 can cause infection, and the viral load increases dramatically over time. Quantitative research revealed that 24 hr after infection, JS2022 dramatically reduced the expression of downstream interferon‐stimulated genes and the innate immune factors IFN‐ β and IFN‐ λ 3 and bovine nasal mucosal explants. Overall, our results highlight the significance of PRV surveillance in cattle and offer a resource for learning more about the clinical traits and development of PRV.