Recent Progress on Epidemiology and Pathobiology of Porcine Circovirus 3

The recently discovered porcine circovirus 3 (PCV3) belongs to the Circovirus genus of the Circoviridae family together with the other three PCVs, PCV1, PCV2, and PCV4. As reported, PCV3 can infect pig, wild boar, and several other intermediate hosts, resulting in single or multiple infections in the affected animal. The PCV3 infection can lead to respiratory diseases, digestive disorders, reproductive disorders, multisystemic inflammation, and immune responses. Up to now, PCV3 infection, as well as the disease caused by PCV3, has been reported in many swine farms worldwide with high positive rates, which indicates that the virus may be another important pathogen in the swine industry. Therefore, we reviewed the current progress on epidemiology and pathobiology of PCV3, which may provide the latest knowledge of the virus and PCV3-related diseases.     

Genetic Diversity of Porcine Circovirus 2 in Wild Boar and Domestic Pigs in Ukraine

Porcine circovirus type 2 (PCV2) is responsible for a number of porcine circovirus-associated diseases (PCVAD) that can severely impact domestic pig herds. For a non-enveloped virus with a small genome (1.7 kb ssDNA), PCV2 is remarkably diverse, with eight genotypes (a–h). New genotypes of PCV2 can spread through the migration of wild boar, which are thought to infect domestic pigs and spread further through the domestic pig trade. Despite a large swine population, the diversity of PCV2 genotypes in Ukraine has been under-sampled, with few PCV2 genome sequences reported in the past decade. To gain a deeper understanding of PCV2 genotype diversity in Ukraine, samples of blood serum were collected from wild boars (n = 107) that were hunted in Ukraine during the November–December 2012 hunting season. We found 34/107 (31.8%) prevalence of PCV2 by diagnostic PCR. For domestic pigs, liver samples (n = 16) were collected from a commercial market near Kharkiv in 2019, of which 6 out of 16 (37%) samples were positive for PCV2. We sequenced the genotyping locus ORF2, a gene encoding the PCV2 viral capsid (Cap), for 11 wild boar and six domestic pig samples in Ukraine using an Oxford Nanopore MinION device. Of 17 samples with resolved genotypes, the PCV2 genotype b was the most common in wild boar samples (10 out of 11, 91%), while the domestic pigs were infected with genotypes b and d. We also detected genotype b/d and b/a co-infections in wild boars and domestic pigs, respectively, and for the first time in Ukraine we detected genotype f in a wild boar from Poltava. Building a maximum-likelihood phylogeny, we identified a sublineage of PCV2 genotype b infections in both wild and domestic swine, suggesting a possible epizootic cluster and an ecological interaction between wild boar and domestic pig populations in northeastern Ukraine.     

The Role of the Host Ubiquitin System in Promoting Replication of Emergent Viruses

Ubiquitination of proteins is a post-translational modification process with many different cellular functions, including protein stability, immune signaling, antiviral functions and virus replication. While ubiquitination of viral proteins can be used by the host as a defense mechanism by destroying the incoming pathogen, viruses have adapted to take advantage of this cellular process. The ubiquitin system can be hijacked by viruses to enhance various steps of the replication cycle and increase pathogenesis. Emerging viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), flaviviruses like Zika and dengue, as well as highly pathogenic viruses like Ebola and Nipah, have the ability to directly use the ubiquitination process to enhance their viral-replication cycle, and evade immune responses. Some of these mechanisms are conserved among different virus families, especially early during virus entry, providing an opportunity to develop broad-spectrum antivirals. Here, we discuss the mechanisms used by emergent viruses to exploit the host ubiquitin system, with the main focus on the role of ubiquitin in enhancing virus replication.     

TGF-β from the Porcine Intestinal Cell Line IPEC-J2 Induced by Porcine Circovirus 2 Increases the Frequency of Treg Cells via the Activation of ERK (in CD4+ T Cells) and NF-κB (in IPEC-J2)

Porcine circovirus 2 (PCV2) causes immunosuppression. Piglets infected with PCV2 can develop enteritis. Given that the gut is the largest immune organ, however, the response of the gut’s immune system to PCV2 is still unclear. Here, IPEC-J2 cells with different treatments were co-cultured with PBMC or CD4⁺ T cells (Transwell). Flow cytometry and Western blotting revealed that PCV2-infected IPEC-J2 increased the frequency of CD4⁺ T cells among piglets’ peripheral blood mononuclear cells (PBMCs) and caused CD4⁺ T cells to undergo a transformation into Foxp3⁺ regulatory T cells (Treg cells) via activating CD4⁺ T ERK. Cytokines production and an inhibitor assay showed that the induction of Tregs by PCV2-infected IPEC-J2 was dependent on TGF-β induced by PCV2 in IPEC-J2, which was associated with the activation of NF-κB. Taken together, PCV2-infected IPEC-J2 activated NF-κB to stimulate the synthesis of TGF-β, which enhanced the differentiation of CD4⁺ T cells into Treg cells through the activation of ERK in CD4⁺ T cells. This information sheds light on PCV2′s function in the intestinal immune system and suggests a potential immunosuppressive mechanism for PCV2 infection.     

恶性疟原虫富组氨酸蛋白2重组蛋白与真核表达质粒免疫特性的比较

目的　探讨以恶性疟原虫富组氨酸蛋白 2 (PfHRP2 )为基础的不同形式的侯选疫苗诱导小鼠免疫应答的特性 ,为包含HRP2的恶性疟红内期疫苗的研制提供实验依据。方法　用重组蛋白TP HRP2及真核表达质粒pcDNA3 1(- ) HRP2免疫BALB c小鼠 ,对抗体应答的动力学及特异性进行分析 ,取脾细胞进行体外增殖实验 ,用免疫血清进行P f.体外生长抑制实验。结果　重组蛋白TP HRP2加福氏佐剂诱导BALB c小鼠产生了高水平的抗体 ,其抗体产生快、持续时间久 ,并具较高的特异性 ,细胞应答被同期激活 ,免疫血清可明显抑制红细胞内发育期疟原虫。重组真核表达质粒pcDNA3 1(- ) HRP2诱导BALB c小鼠产生了较高水平和具有一定特异性的抗体 ,其抗体的产生需要多次免疫和较长时间 ,初始化的脾细胞对抗原再刺激的回忆应答显著 ,但免疫血清对疟原虫的体外生长没有抑制作用。结论　HRP2重组蛋白与真核表达质粒在小鼠具有较为不同的免疫特性 ,HRP2重组蛋白疫苗具有潜在的应用前景     

DEAD-Box RNA Helicase 21 (DDX21) Positively Regulates the Replication of Porcine Reproductive and Respiratory Syndrome Virus via Multiple Mechanisms

The porcine reproductive and respiratory syndrome virus (PRRSV) remains a persistent hazard in the global pig industry. DEAD (Glu-Asp-Ala-Glu) box helicase 21 (DDX21) is a member of the DDX family. In addition to its function of regulating cellular RNA metabolism, DDX21 also regulates innate immunity and is involved in the replication cycle of some viruses. However, the relationship between DDX21 and PRRSV has not yet been explored. Here, we found that a DDX21 overexpression promoted PRRSV replication, whereas knockdown of DDX21 reduced PRRSV proliferation. Mechanistically, DDX21 promoted PRRSV replication independently of its ATPase, RNA helicase, and foldase activities. Furthermore, overexpression of DDX21 stabilized the expressions of PRRSV nsp1α, nsp1β, and nucleocapsid proteins, three known antagonists of interferon β (IFN-β). Knockdown of DDX21 activated the IFN-β signaling pathway in PRRSV-infected cells, suggesting that the effect of DDX21 on PRRSV-encoded IFN-β antagonists may be a driving factor for its contribution to viral proliferation. We also found that PRRSV infection enhanced DDX21 expression and promoted its nucleus-to-cytoplasm translocation. Screening PRRSV-encoded proteins showed that nsp1β interacted with the C-terminus of DDX21 and enhanced the expression of DDX21. Taken together, these findings reveal that DDX21 plays an important role in regulating PRRSV proliferation through multiple mechanisms.     

Induction of Innate Immune Response by TLR3 Agonist Protects Mice against SARS-CoV-2 Infection

SARS-CoV-2, a member of the coronavirus family, is the causative agent of the COVID-19 pandemic. Currently, there is still an urgent need in developing an efficient therapeutic intervention. In this study, we aimed at evaluating the therapeutic effect of a single intranasal treatment of the TLR3/MDA5 synthetic agonist Poly(I:C) against a lethal dose of SARS-CoV-2 in K18-hACE2 transgenic mice. We demonstrate here that early Poly(I:C) treatment acts synergistically with SARS-CoV-2 to induce an intense, immediate and transient upregulation of innate immunity-related genes in lungs. This effect is accompanied by viral load reduction, lung and brain cytokine storms prevention and increased levels of macrophages and NK cells, resulting in 83% mice survival, concomitantly with long-term immunization. Thus, priming the lung innate immunity by Poly(I:C) or alike may provide an immediate, efficient and safe protective measure against SARS-CoV-2 infection.     

First Survey of SNPs in TMEM154, TLR9, MYD88 and CCR5 Genes in Sheep Reared in Italy and Their Association with Resistance to SRLVs Infection

Maedi-visna virus (MVV) and caprine arthritis encephalitis virus (CAEV), referred to as small ruminant lentiviruses (SRLVs), belong to the genus Lentivirus of the Retroviridae family. SRLVs infect both sheep and goats, causing significant economic losses and animal welfare damage. Recent findings suggest an association between serological status and allelic variants of different genes such as TMEM154, TLR9, MYD88 and CCR5. The aim of this work was to investigate the role of specific polymorphisms of these genes in SRLVs infection in some sheep flocks in Italy. In addition to those already known, novel variants in the TMEM154 (P7H, I74V, I105V) gene were detected in this study. The risk of infection was determined finding an association between the serological status and polymorphisms P7H, E35K, N70I, I74V, I105V of TMEM154, R447Q, A462S and G520R in TLR9 gene, H176H* and K190K* in MYD88 genes, while no statistical association was observed for the 4-bp deletion of the CCR5 gene. Since no vaccines or treatments have been developed, a genetically based approach could be an innovative strategy to prevent and to control SRLVs infection. Our findings are an important starting point in order to define the genetic resistance profile towards SRLVs infection.