A recombinant pseudorabies virus surface - displaying the classical swine fever E2 protein induces specific antibodies rapidly.

Pseudorabies virus (PRV) and classical swine fever virus (CSFV) are both economically important pathogens threatening the pig industry in many countries. The triple-gene-deleted variant of PRV, herein referred to as rPRVTJ-delgE/gI/TK, has exhibited pronounced efficacy and safety profiles. This underscores its viability as a prospective vaccine vector. However, the generation of specific anti-E2 antibodies necessitates elevated immunization doses and extended durations when the extracellular domain of the E2 protein of CSFV is secreted via the recombinant rPRVTJ-delgE/gI/TK vector. To enhance the presentation of exogenous antigens by antigen-presenting cells (APCs), we engineered the E2 protein expressed on the surface of PRV particles in this study. The recombinant virus expressing the E2 protein with a heterogonous transmembrane domain was generated in the backbone of rPRVTJ-delgE/gI/TK and designated as rPRVTJ-UL44-E2. The E2 gene was fused to the 3' terminus of the UL44 gene utilizing P2A, a self-cleaving peptide sequence. The electron microscopy showed that the E2 protein was anchored on the surface of the viral particles of rPRVTJ-delgE/gI/TK-E2. The insertion of the E2 gene did not alter the native biological characteristics of the viral vector. Rabbits immunized with 107 median tissue culture infective doses (TCID50) of rPRVTJ-UL44-E2 exhibited a rapid seroconversion to anti-E2 specific antibodies within 7 days post-immunization (dpi). All the rabbits immunized with the rPRVTJ-UL44-E2 had generated antibodies specific to E2 prior to the administration of the booster immunization. However, the immunized rabbits were not protected from the CSFV C-strain challenge. Nevertheless, this strategy has notably achieved rapid induction of E2-specific non-neutralizing antibodies. These findings provide insights that the design of rPRVTJ-UL44-E2 requires optimization, thereby indicating a promising avenue for augmenting vaccine-induced immune responses.

African Swine Fever Virus Modulates the Endoplasmic Reticulum Stress-ATF6-Calcium Axis to Facilitate Viral Replication.

ABSTRACTAfrican swine fever (ASF), caused by African swine fever virus (ASFV), is a devastating infectious disease of domestic pigs and wild boar, which threatens the global pig industry. The endoplasmic reticulum (ER) is a multifunctional signaling organelle in eukaryotic cells that is involved in protein synthesis, processing, posttranslational modification and quality control. As intracellular parasitic organisms, viruses have evolved several strategies to modulate ER functions to favor their life cycles. We have previously demonstrated that the differentially expressed genes associated with the unfolded protein response (UPR) (downstream the ER stress) are significantly enriched upon ASFV infection. However, the correlation between the ER stress or UPR and ASFV replication has not been illuminated yet. Here, we demonstrated that ASFV infection induces ER stress both in target cells and in vivo, and subsequently activates the activating transcription factor 6 (ATF6) branch of the UPR to facilitate viral replication. Mechanistically, ASFV infection disrupts intracellular calcium (Ca2+) homeostasis, while the ATF6 pathway facilitates ASFV replication by increasing the cytoplasmic Ca2+ level. More specifically, we demonstrated that ASFV infection triggers ER-dependent Ca2+ release via the inositol triphosphate receptor (IP3R) channel. Notably, we showed that the ASFV B117L protein plays crucial roles in ER stress and the downstream activation of the ATF6 branch, as well as the disruption of Ca2+ homeostasis. Taken together, our findings reveal for the first time that ASFV modulates the ER stress-ATF6-Ca2+ axis to facilitate viral replication, which provides novel insights into the development of antiviral strategies for ASFV.

Immune Responses Induced by a Recombinant Lactiplantibacillus plantarum Surface-Displaying the gD Protein of Pseudorabies Virus.

Pseudorabies virus (PRV) is one of the herpes viruses that can infect a wide range of animals including pigs, cattle, sheep, mice, and wild animals. PRV is a neurotropic alphaherpesvirus capable of infecting a variety of mammals. There is a rising interest in the targeted application of probiotic bacteria to prevent viral diseases, including PRV. In this study, the surface expression of enhanced green fluorescent protein (EGFP) on recombinant Lactiplantibacillus plantarum NC8 (rNC8) through the LP3065 LPxTG motif of Lactobacillus plantarum WCFS1 was generated. The surface expression was observed through confocal microscopy. Dendritic cell targeting peptides (DCpep) were also fused with LPxTG that help to bind with mouse DCs. The PRV-gD was cloned in LP3065 LPxTG, resulting in the generation of rNC8-LP3065-gD. Inactivated rNC8-LP3065-gD was administered intravenously in mice on days 1 and 7 at a dose of 200 µL (109 CFU/mouse) for monitoring immunogenicity. Subsequently, a challenge dose of PRV TJ (104 TCID50) was administered intramuscularly at 14 days post-immunization. The survival rate of the immunized mice reached 80% (4/5) with no significant signs of illness. A significant rise in anti-gD antibodies was detected in the immunized mice by ELISA. Quantitative PCR (qPCR) results showed decreased viral loading in different body tissues. Flow cytometry of lymphocytes derived from mice spleen indicated an increase in CD3+CD4+ T cells, but CD3+CD8+ T cells were not detected. Moreover, it offers a model to delineate immune correlates with rNC8-induced immunity against swine viral diseases.

Ferritin Nanoparticle Delivery of the E2 Protein of Classical Swine Fever Virus Completely Protects Pigs from Lethal Challenge.

Classical swine fever (CSF), caused by the classical swine fever virus (CSFV), results in significant economic losses to the swine industry in many countries. Vaccination represents the primary strategy to control CSF and the CSFV E2 protein is known as the major protective antigen. However, the E2 protein expressed or presented by different systems elicits distinct immune responses. In this study, we established a stable CHO cell line to express the E2 protein and delivered it using self-assembled ferritin nanoparticles (NPs). Subsequently, we compared the adaptive immune responses induced by the E2-ferritin NPs and the monomeric E2 protein produced by the CHO cells or a baculovirus expression system. The results revealed that the NP-delivered E2 protein elicited higher titers of neutralizing antibodies than did the monomeric E2 protein in pigs. Importantly, only the NP-delivered E2 protein significantly induced CSFV-specific IFN-γ-secreting cells. Furthermore, all the pigs inoculated with the E2-ferritin NPs were completely protected from a lethal CSFV challenge infection. These findings demonstrate the ability of the E2-ferritin NPs to protect pigs against the lethal CSFV challenge by eliciting robust humoral and cellular immune responses.

Antiviral Effects and Underlying Mechanisms of Probiotics as Promising Antivirals.

Probiotics exert a variety of beneficial effects, including maintaining homeostasis and the balance of intestinal microorganisms, activating the immune system, and regulating immune responses. Due to the beneficial effects of probiotics, a wide range of probiotics have been developed as probiotic agents for animal and human health. Viral diseases cause serious economic losses to the livestock every year and remain a great challenge for animals. Moreover, strategies for the prevention and control of viral diseases are limited. Viruses enter the host through the skin and mucosal surface, in which are colonized by hundreds of millions of microorganisms. The antiviral effects of probiotics have been proved, including modulation of chemical, microbial, physical, and immune barriers through various probiotics, probiotic metabolites, and host signaling pathways. It is of great significance yet far from enough to elucidate the antiviral mechanisms of probiotics. The major interest of this review is to discuss the antiviral effects and underlying mechanisms of probiotics and to provide targets for the development of novel antivirals.