Porcine FcεRI Mediates Porcine Reproductive and Respiratory Syndrome Virus Multiplication and Regulates the Inflammatory Reaction

Non-infectious immune complexes downregulate the production of interferons and tumor necrosis factor-α in primary porcine alveolar macrophages in vitro

Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) has been harming the pig industry worldwide for nearly 40 years. Although scientific researchers have made substantial efforts to explore PRRSV pathogenesis, the immune factors influencing PRRSV infection still need to be better understood. Infectious virus-antibody immune complexes (ICs) formed by PRRSV and sub-or non-neutralizing antibodies specific for PRRSV may significantly promote the development of PRRS by enhancing PRRSV replication through antibody-dependent enhancement. However, nothing is known about whether PRRSV infection is affected by non-infectious ICs (NICs) formed by non-pathogenic/infectious antigens and corresponding specific antibodies. Here, we found that PRRSV significantly induced the transcripts and proteins of interferon-α (IFN-α), IFN-β, IFN-γ, IFN-λ1, and tumor necrosis factor-α (TNF-α) in vitro primary porcine alveolar macrophages (PAMs) in the early stage of infection. Our results showed that NICs formed by rabbit-negative IgG (RNI) and pig anti-RNI specific IgG significantly reduced the transcripts and proteins of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α in vitro PAMs and significantly elevated the transcripts and proteins of interleukine-10 (IL-10) and transforming growth factor-β1 (TGF-β1) in vitro PAMs. NICs-mediated PRRSV infection showed that NICs not only significantly decreased the induction of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α by PRRSV but also significantly increased the induction of IL-10 and TGF-β1 by PRRSV and considerably enhanced PRRSV replication in vitro PAMs. Our data suggested that NICs could downregulate the production of antiviral cytokines (IFN-α/β/γ/λ1 and TNF-α) during PRRSV infection in vitro and facilitated PRRSV proliferation in its host cells by inhibiting innate antiviral immune response. This study elucidated one novel immune response to PRRSV infection, which would enhance our understanding of the pathogenesis of PRRSV.

A Review: Understanding Molecular Mechanisms of Antibody-Dependent Enhancement in Viral Infections

Antibody Dependent Enhancement (ADE) of an infection has been of interest in the investigation of many viruses. It is associated with the severity of the infection. ADE is mediated by non-neutralizing antibodies, antibodies at sub-neutralizing concentrations, or cross-reactive non-neutralizing antibodies. Treatments like plasma therapy, B cell immunizations, and antibody therapies may trigger ADE. It is seen as an impediment to vaccine development as well. In viruses including the Dengue virus (DENV), severe acute respiratory syndrome (SARS) virus, Middle East respiratory syndrome (MERS) virus, human immunodeficiency virus (HIV), Ebola virus, Zika virus, and influenza virus, the likely mechanisms of ADE are postulated and described. ADE improves the likelihood of productively infecting cells that are expressing the complement receptor or the Fc receptor (FcR) rather than the viral receptors. ADE occurs when the FcR, particularly the Fc gamma receptor, and/or complement system, particularly Complement 1q (C1q), allow the entry of the virus-antibody complex into the cell. Moreover, ADE alters the innate immune pathways to escape from lysis, promoting viral replication inside the cell that produces viral particles. This review discusses the involvement of FcR and the downstream immunomodulatory pathways in ADE, the complement system, and innate antiviral signaling pathways modification in ADE and its impact on facilitating viral replication. Additionally, we have outlined the modes of ADE in the cases of different viruses reported until now.

Progress in PRRSV Infection and Adaptive Immune Response Mechanisms

Since its discovery, Porcine reproductive and respiratory syndrome (PRRS) has had a huge impact on the farming industry. The virus that causes PRRS is Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and because of its genetic diversity and the complexity of the immune response, the eradication of PRRS has been a challenge. To provide scientific references for PRRSV control and vaccine development, this study describes the processes of PRRSV-induced infection and escape, as well as the host adaptive immune response to PRRSV. It also discusses the relationship between PRRSV and the adaptive immune response.

Streptococcus suis contributes to inguinal lymph node lesions in piglets after highly pathogenic porcine reproductive and respiratory syndrome virus infection

The swine pathogens porcine reproductive and respiratory syndrome virus (PRRSV) and Streptococcus suis have both been reported to cause damage to the immune organs. Inguinal lymph node (ILN) injury has been reported in PRRSV-infected pigs with secondary S. suis infection, but not much is known about the mechanism. In this study, secondary S. suis infection after highly pathogenic (HP)-PRRSV infection caused more severe clinical symptoms, mortality, and ILN lesions. Histopathological lesions were seen in ILNs with a marked decrease in lymphocyte numbers. Terminal deoxynucleotidyl transferase (TdT)-mediated de-oxyuridine triphosphate (dUTP)-biotin nick end-labeling (TUNEL) assays revealed that HP-PRRSV strain HuN4 alone induced ILN apoptosis, but dual-infection with S. suis strain BM0806 induced greater levels of apoptosis. Besides, we found that some HP-PRRSV-infected cells underwent apoptosis. Furthermore, anti-caspase-3 antibody staining confirmed that ILN apoptosis was mainly induced by a caspase-dependent pathway. Pyroptosis was also observed in HP-PRRSV-infected cells, and there was more pyroptosis in piglets infected with HP-PRRSV alone compared with those with secondary S. suis infection, and HP-PRRSV-infected cells underwent pyroptosis. Altogether, this is the first report to identify pyroptosis in ILNs and which signaling pathway is related to ILN apoptosis in single or dual-infected piglets. These results contribute to a better understanding of the pathogenic mechanisms during secondary S. suis infection.

Proteomic Characterization of PAMs with PRRSV-ADE Infection

The antibody-dependent enhancement (ADE) effect of a PRRSV infection is that the preexisting sub- or non-neutralizing antibodies specific against PRRSV can facilitate the virus entry and replication, and it is likely to be a great obstacle for the selection of immune strategies and the development of high-efficiency PRRSV vaccines. However, the proteomic characterization of primary alveolar macrophages (PAMs) with a PRRSV-ADE infection has not yet been investigated so far. Therefore, we performed a tandem mass tag (TMT)-based quantitative proteomic analysis of PAMs with a PRRSV-ADE infection in this study. The results showed that a total of 3935 differentially expressed proteins (DEPs) were identified in the PAMs infected with PRRSV-ADE, including 2004 up-regulated proteins and 1931 down-regulated proteins. Further, the bioinformatics analysis for these DEPs revealed that a PRRSV-ADE infection might disturb the functions of ribosome, proteasome and mitochondria. Interestingly, we also found that the expression of the key molecules in the innate immune pathways and antiviral proteins were significantly down-regulated during a PRRSV-ADE infection. This study was the first attempt to analyze the proteomic characterization of PAMs with a PRRSV-ADE infection in vitro. Additionally, the findings will provide valuable information for a better understanding of the mechanism of virus-antibody-host interactions during a PRRSV-ADE infection.

Antibody-Dependent Enhancement: ″Evil″ Antibodies Favorable for Viral Infections

The pandemics caused by emerging viruses such as severe acute respiratory syndrome coronavirus 2 result in severe disruptions to public health. Vaccines and antibody drugs play essential roles in the control and prevention of emerging infectious diseases. However, in contrast with the neutralizing antibodies (NAbs), sub- or non-NAbs may facilitate the virus to enter the cells and enhance viral infection, which is termed antibody-dependent enhancement (ADE). The ADE of most virus infections is mediated by the Fc receptors (FcRs) expressed on the myeloid cells, while others are developed by other mechanisms, such as complement receptor-mediated ADE. In this review, we comprehensively analyzed the characteristics of the viruses inducing FcRs-mediated ADE and the new molecular mechanisms of ADE involved in the virus entry, immune response, and transcription modulation, which will provide insights into viral pathogenicity and the development of safer vaccines and effective antibody drugs against the emerging viruses inducing ADE.

Differences in Humoral Immune Response against the Type 2 Porcine Reproductive and Respiratory Syndrome Virus via Different Immune Pathways

The intramuscular vaccine is the principal strategy to protect pigs from porcine reproductive and respiratory syndrome virus (PRRSV), However, it is still difficult to control PRRSV effectively. This study infected piglets with PRRSV through intramuscular and intranasal inoculation. Subsequently, viral loads, anti-PRRSV antibody levels, and neutralizing antibodies (NAs) titers in both serum and saliva were monitored for 43 days. Meanwhile, tissues were obtained through necropsy at 43 days post-inoculation (dpi) to detect viral loads. The results indicated that viremia lasted from 3 to 31 dpi in both the inoculation groups, but the viruses survived in the lungs and lymph nodes after viremia clearance. The antibody response was detected from 11 dpi, but the response of NAs was delayed until 3–4 weeks. Furthermore, intranasal inoculation induced lower viral load levels than injection inoculation. In addition, positive SIgA and NAs levels were produced early, with higher levels through intranasal inoculation. Therefore, our data indicated that a more robust antibody response and lower virus loads could be induced by intranasal inoculation, and mucosal inoculation could be a suitable pathway for PRRSV vaccines.

Sophora subprostrate polysaccharide regulates histone acetylation to inhibit inflammation in PCV2-infected murine splenic lymphocytes in vitro and in vivo

Porcine circovirus type 2 (PCV2) has caused large economic losses in the swine industry worldwide; therefore, research on relevant therapeutic medicines is still urgently needed. To define the relationship between histone acetylation and inflammation induced by PCV2, we investigated whether traditional Chinese medicinal polysaccharides could alleviate viral infection by regulating histone acetylation. In this study, Sophora subprostrate polysaccharide (SSP)-treated PCV2-infected murine splenic lymphocytes in vitro and murine spleen in vivo were used to explore the regulatory effects of SSP on inflammation and histone acetylation caused by PCV2. SSP at different concentrations significantly reduced the secretion levels of the proinflammatory cytokines TNF-α and IL-6, the activity of COX-2, the mRNA expression levels of TNF-α, IL-6, iNOS and COX-2 and the protein expression levels of iNOS and COX-2 but promoted the secretion and mRNA expression levels of IL-10. Furthermore, the different concentrations of SSP significantly regulated the activity of histone acetylase (HAT) and the mRNA expression of HAT1, increased the activity of histone deacetylase (HDAC) and the mRNA expression of HDAC1 and reduced the protein expression levels of Ac-H3 and Ac-H4. Overall, SSP inhibited inflammation in PCV2-infected murine splenic lymphocytes by regulating histone acetylation in vitro and in vivo, thus playing an important role in PCV2 infection.

Effects of G-Rh2 on mast cell-mediated anaphylaxis via AKT-Nrf2/NF-κB and MAPK-Nrf2/NF-κB pathways

Background

The effect of ginsenoside Rh2 (G-Rh2) on mast cell-mediated anaphylaxis remains unclear. Herein, we investigated the effects of G-Rh2 on OVA-induced asthmatic mice and on mast cell-mediated anaphylaxis.

Methods

Asthma model was established for evaluating airway changes and ear allergy. RPMCs and RBL-2H3 were used for in vitro experiments. Calcium uptake, histamine release and degranulation were detected. ELISA and Western blot measured cytokine and protein levels, respectively.

Results

G-Rh2 inhibited OVA-induced airway remodeling, the production of TNF-α, IL-4, IL-8, IL-1β and the degranulation of mast cells of asthmatic mice. G-Rh2 inhibited the activation of Syk and Lyn in lung tissue of OVA-induced asthmatic mice. G-Rh2 inhibited serum IgE production in OVA induced asthmatic mice. Furthermore, G-Rh2 reduced the ear allergy in IgE-sensitized mice. G-Rh2 decreased the ear thickness. In vitro experiments G-Rh2 significantly reduced calcium uptake and inhibited histamine release and degranulation in RPMCs. In addition, G-Rh2 reduced the production of IL-1β, TNF-α, IL-8, and IL-4 in IgE-sensitized RBL-2H3 cells. Interestingly, G-Rh2 was involved in the FcεRI pathway activation of mast cells and the transduction of the Lyn/Syk signaling pathway. G-Rh2 inhibited PI3K activity in a dose-dependent manner. By blocking the antigen-induced phosphorylation of Lyn, Syk, LAT, PLCγ2, PI3K ERK1/2 and Raf-1 expression, G-Rh2 inhibited the NF-κB, AKT-Nrf2, and p38MAPK-Nrf2 pathways. However, G-Rh2 up-regulated Keap-1 expression. Meanwhile, G-Rh2 reduced the levels of p-AKT, p38MAPK and Nrf2 in RBL-2H3 sensitized IgE cells and inhibited NF-κB signaling pathway activation by activating the AKT-Nrf2 and p38MAPK-Nrf2 pathways.

Conclusion

G-Rh2 inhibits mast cell-induced allergic inflammation, which might be mediated by the AKT-Nrf2/NF-κB and p38MAPK-Nrf2/NF-κB signaling pathways.

Antibody dependent enhancement: Unavoidable problems in vaccine development

In some cases, antibodies can enhance virus entry and replication in cells. This phenomenon is called antibody-dependent infection enhancement (ADE). ADE not only promotes the virus to be recognized by the target cell and enters the target cell, but also affects the signal transmission in the target cell. Early formalin-inactivated virus vaccines such as aluminum adjuvants (RSV and measles) have been shown to induce ADE. Although there is no direct evidence that there is ADE in COVID-19, this potential risk is a huge challenge for prevention and vaccine development. This article focuses on the virus-induced ADE phenomenon and its molecular mechanism. It also summarizes various attempts in vaccine research and development to eliminate the ADE phenomenon, and proposes to avoid ADE in vaccine development from the perspective of antigens and adjuvants.

Porcine FcγRIIb mediated PRRSV ADE infection through inhibiting IFN-β by cytoplasmic inhibitory signal transduction

Antibody-dependent enhancement (ADE) in porcine reproductive and respiratory syndrome virus (PRRSV) infection is a significant obstacle to the development of effective vaccines for controlling PRRS. Our previous results have demonstrated that porcine FcγRIIb (poFcγRIIb) play an important role in mediating ADE of PRRSV infection in vitro. However, the underlying mechanisms involved in poFcγRIIb mediated-ADE are still not clear. In this study, MARC-145 cel1 lines stably expressing mutated poFcγRIIb (MARC-poFcγRIIb-T and MARC-poFcγRIIb-CT) in cytoplasm were established and the capacity of poFcγRIIb mutants in mediating ADE of PRRSV was investigated. Our results showed that removal of cytoplasmic domain or disruption the tyrosine residue within ITIM (immunoreceptor tyrosine-based inhibition motif) of the poFcγRIIb abolished the ability of poFcγRIIb to mediate ADE of PRRSV. Furthermore, we found that SHIP1 and TBK1 were involved in poFcγRIIb-mediated ADE of PRRSV infection. Taken together, our findings indicated that poFcγRIIb mediated the ADE pathway of PRRSV infection through recruiting SHIP-1, which further inhibited of TBK-1-IRF3-IFN-β signaling pathway to enhance PRRSV infection. These findings will contribute to the molecular mechanism of ADE infection and provide some implications for vaccine development.

Dual Regulation of Host TRAIP Post-translation and Nuclear/Plasma Distribution by Porcine Reproductive and Respiratory Syndrome Virus Non-structural Protein 1α Promotes Viral Proliferation

In this study, we show that porcine reproductive and respiratory syndrome virus (PRRSV) non-structural protein 1α (nsp1α) facilitates PRRSV escape from innate immune by modulating nuclear to cytoplasmic translocation and distribution ratio of TRAIP to promote virus proliferation. Mechanistically, TRAIP interacts with PRRSV nsp1α via its K205 site, while NSP1α decreases the SUMOylation and K48 ubiquitination independent of the TRAIP interaction K205 site. Modulation of the dual modification of TRAIP by PRRSV nsp1α results in over-enrichment of TRAIP in the cytoplasm. Enrichment of nsp1α-induced cytoplasmic TRAIP in turn leads to excessive K48 ubiquitination and degradation of serine/threonine-protein kinase (TBK1), thereby antagonizing TBK1-IRF3-IFN signaling. This study proposes a novel mechanism by which PRRSV utilizes host proteins to regulate innate immunity. Findings from this study provides novel perspective to advance our understanding in the pathogenesis of PRRSV.

Protective effect of polysaccharide peptide on cerebral ischemia‑reperfusion injury in rats

In the present study, the protective effects and regulatory mechanism of polysaccharide peptide (PSP) were investigated in rats with cerebral ischemia-reperfusion (IR) injury. Neuroblastoma N2a cells were divided into five groups: Negative control; IR injury; PSP low dose treatment; PSP middle dose treatment; and PSP high dose treatment. In vitro, the cell viability was detected by an MTT assay. ELISA was performed to determine the activity of lactate dehydrogenase (LDH) and caspase-3. A cerebral IR injury model in vivo was established, and hematoxylin and eosin (H&E) staining, western blotting, neurological deficit score and cerebral infarction were assessed. The cell viability was markedly improved following treatment with PSP and the activity of LDH and caspase-3 was decreased following PSP administration (P<0.05). The in vivo studies determined that the neurological deficit score and cerebral infarction volume were reduced with the concentration of PSP increasing between 150 and 250 mg/kg. The H&E staining indicated that PSP was able to protect the nerve cells against the cerebral IR injury. In addition, PSP upregulated the decreased silent information regulator protein 1, peroxisome proliferator-activated receptor γ coactivator-1α and apoptosis regulator B-cell lymphoma 2 expression induced by cerebral IR injury. The protein expression level of caspase-3 and apoptosis regulator apoptosis regulator Bcl-2-like protein 4 was downregulated following PSP administration. These results suggested that PSP may improve nerve cell viability, enhance the neuroprotective role in cerebral IR injury and provide a novel approach for the treatment of cerebral IR injury.

Response of the cDC1 and cDC2 subtypes of tracheal dendritic cells to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is the most important disease affecting the swine industry worldwide. Although monocytes and macrophages, especially tissue-resident and alveolar macrophages, are the primary target of PRRSV, monocyte- and bone marrow-derived dendritic cells (DCs) are also susceptible to PRRSV infection. It has been shown that lung DCs cannot be infected with PRRSV, but the response and susceptibility of bona fide conventional DC subtypes (cDCs; cDC1 and cDC2) is unknown. In this work, evaluation of the response of tracheal cDC1 and cDC2 subsets to PRRSV revealed differential cytokine expression, whereby cDC1 subsets expressed higher levels of IFN-α and cDC2 subsets more IL-10. Toll-like receptors (TLRs) were also affected: cDC2 cells induced greater upregulation of TLR2 and TLR4, and CD163⁺ cells showed TLR3 upregulation. However, we could not demonstrate under our experimental conditions that cDC1 and cCD2 subsets are susceptible to PRRSV infection. Our findings show the effects of PRRSV on cDC1 and cDC2 subsets and that these cells were not infected by PRRSV.