Differential response of porcine immature monocyte-derived dendritic cells to virulent and inactivated transmissible gastroenteritis virus

TGEV nonstructural protein ORF3b upregulates the expression of SLA-DR at the transcriptional level in monocyte-derived porcine dendritic cells

Transmissible gastroenteritis virus (TGEV) is a porcine intestinal pathogenic coronavirus that can cause acute intestinal diseases in pigs, especially in suckling piglets under two weeks of age, with a mortality rate of 100 %. Dendritic cells (DCs) are important antigen-presenting cells (APCs) that are essential for the initiation and modulation of immune responses in animals. In this study, we used monocyte-derived porcine DCs as an in vitro model of APCs to further study the pathogenic mechanism of TGEV. Our results demonstrated that TGEV successfully replicates in monocyte-derived porcine DCs, whereas UV-inactivated TGEV failed to infect these cells. Importantly, TGEV infection of DCs led to significant upregulation of swine leukocyte antigen II DR (SLA-DR), a key molecule in the major histocompatibility complex class II (MHC-II) family. We further demonstrated that the ORF3b nonstructural protein of TGEV significantly enhances SLA-DR expression at the transcriptional level in porcine DCs. This study provides new insights into the pathogenic mechanisms of TGEV.

HSP90AB1 Is a Host Factor Required for Transmissible Gastroenteritis Virus Infection

Transmissible gastroenteritis virus (TGEV) is an important swine enteric coronavirus causing viral diarrhea in pigs of all ages. Currently, the development of antiviral agents targeting host proteins to combat viral infection has received great attention. The heat shock protein 90 (HSP90) is a critical host factor and has important regulatory effects on the infection of various viruses. However, its roles in porcine coronavirus infection remain unclear. In this study, the effect of HSP90 on TGEV infection was evaluated. In addition, the influence of its inhibitor VER-82576 on proinflammatory cytokine (IL-6, IL-12, TNF-α, CXCL10, and CXCL11) production induced by TGEV infection was further analyzed. The results showed that the knockdown of HSP90AB1 and HSP90 inhibitor VER-82576 treatment resulted in a reduction in TGEV M gene mRNA levels, the N protein level, and virus titers in a dose-dependent manner, while the knockdown of HSP90AA1 and KW-2478 treatment had no significant effect on TGEV infection. A time-of-addition assay indicated that the inhibitory effect of VER-82576 on TGEV infection mainly occurred at the early stage of viral replication. Moreover, the TGEV-induced upregulation of proinflammatory cytokine (IL-6, IL-12, TNF-α, CXCL10, and CXCL11) expression was significantly inhibited by VER-82576. In summary, these findings indicated that HSP90AB1 is a host factor enhancing TGEV infection, and the HSP90 inhibitor VER-82576 could reduce TGEV infection and proinflammatory cytokine production, providing a new perspective for TGEV antiviral drug target design.

Transmissible Gastroenteritis Virus: An Update Review and Perspective

Transmissible gastroenteritis virus (TGEV) is a member of the alphacoronavirus genus, which has caused huge threats and losses to pig husbandry with a 100% mortality in infected piglets. TGEV is observed to be recombining and evolving unstoppably in recent years, with some of these recombinant strains spreading across species, which makes the detection and prevention of TGEV more complex. This paper reviews and discusses the basic biological properties of TGEV, factors affecting virulence, viral receptors, and the latest research advances in TGEV infection-induced apoptosis and autophagy to improve understanding of the current status of TGEV and related research processes. We also highlight a possible risk of TGEV being zoonotic, which could be evidenced by the detection of CCoV-HuPn-2018 in humans.

H9N2 avian influenza virus enhances the immune responses of BMDCs by down-regulating miR29c

Avian influenza virus (AIV) of the subtypes H9 and N2 is well recognised and caused outbreaks-due to its high genetic variability and high rate of recombination with other influenza virus subtypes. The pathogenicity of H9N2 AIV depends on the host immune response. Dendritic cells (DCs) are major antigen presenting cells that can significantly inhibit H9N2 AIV replication. MicroRNAs (miRNAs) influence the ability of DCs to present antigens, as well as the ability of AIVs to infect host cells and replicate. Here, we studied the molecular mechanism underlying the miRNA-mediated regulation of immune function of mouse DCs. We first screened for and verified the induction of miRNAs in DCs after H9N2 AIVstimulation. We also constructed miR29c, miR339 and miR222 over-expression vector and showed that only the induction of miR29c lead to a hugely increased expression of surface marker MHCII and CD40. Whilst the inhibition of miR29c, miR339 and miR222 in mouse DCs would repressed the expression of DCs surface markers. Moreover, we found that miR29c stimulation not only up-regulate MHCII and CD40, but also enhance the ability of DCs to activate lymphocytes and secrete cytokines IL-6 or TNF-a. Furthermore, we found that Tarbp1 and Rfx7 were targeted and repressed by miR29c. Finally, we revealed that the inhibition of miR29c marvelously accelerated virus replication. Together, our data shed new light on the roles and mechanisms of miR29c in regulating DC function and suggest new strategies for combating AIVs.

Review of immunological responses to porcine coronaviruses and implications on population based control strategies in epidemic and endemic infections

Five major porcine coronaviruses (COVs) have been identified which cause severe gastrointestinal (GI) and respiratory disease in pigs. They include transmissible gastroenteritis (TGEV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus, porcine respiratory coronavirus, and porcine hemagglutinating encephalomyelitis. These diseases, especially TGEV and PEDV, have caused epidemics in Europe, Asia, and the Americas over the past 50 years, causing significant economic losses to swine producers. As pigs are a major protein source worldwide there is great interest in understanding, controlling, and preventing these diseases. These diseases have no cure, and current vaccines are not fully protective. On-farm prevention and biosecurity are difficult to enforce and have not stopped the spread of these diseases between herds. Recent advances in the immunology of porcine COVs has revealed that the immune response to porcine COVs shares many similarities with the response to human COVs, leading to increased interest in pigs as models for human disease. Highlights of these advances include the key role of local antigen presenting cells in the gastrointestinal tract in stimulating a protective immune response. This understanding has lead to new proposed vaccines. Advances in the understanding of the ways the viruses evade and degrade the host immune system have also lead to novel proposed therapies. Many of these therapies are in the early development stages, as researchers attempt to create efficacious, cost-effective, and practical therapies for these diseases.