In vitro infection with classical swine fever virus inhibits the transcription of immune response genes

A 1.6 Mb region on SSC2 is associated with antibody response to classical swine fever vaccination in a mixed pig population

Classical Swine Fever (CSF) is a contagious viral disease of pigs which is endemic in several parts of the world, including India. Prophylactic vaccination using live attenuated vaccine is the preferred method of control. However, there is significant inter-individual variation in the antibody response to vaccination. In this study, we measured the E2 antibody blocking percentage after 21 days of CSF vaccination in a mixed pig population consisting of Landrace, indigenous Ghurrah pigs, and their crossbreds. A Genome Wide Association Study (GWAS) carried out using single-SNP and haplotype based methods detected a 1.6 Mb region on SSC2 (28.92-30.52 Mb) as significantly associated with antibody response to CSF vaccination. The significant region and 1 Mb flanking sequences encompass 3 genes - EIF3M, DNAJC24 and ARL14EP, which code for proteins involved in Pestivirus replication and host immune response system. Our results combined with previous studies on immune response of pigs present this region as a suitable candidate for future functional investigations.

Expression of foot-and-mouth disease virus non-structural protein 3A upregulates the expression of autophagy and immune response genes in vitro

Foot-and-mouth disease (FMD) virus 3A protein regulates viral replication and virulence; thus, we generated BHK-Flp-In cell line expressing 3A protein because it can serve as helper cell line for infecting a replication defective FMDV to produce a live disabled vaccine. FMDV Asia1 3A was amplified, cloned in pcDNA vector and confirmed by sequencing. The 3A gene was subcloned in pcEF/FRT vector and transfected in BHK-Flp-In cells and transformed cells were selected by resistance to hygromycin and susceptibility to zeocin antibiotics. The BHK-Flp-In cells expressing 3A protein was designated as Flp-In3A. Western blot and immunofluorescence confirmed that Flp-In3A cells expressed FMDV3A protein. Absolute quantitation of 3A transcripts showed peak expression at 6 h in Flp-In3A cells followed by a sharp decrease and the cells showed growth retardation for 2 h post-seeding with cytoplasmic vacuolations with advancing time. Response to infection with FMDV Asia1 virus revealed smaller plaques in Flp-In3A cells. Then, we investigated the effect of FMDV3A expression on autophagy related genes by real time PCR. Most autophagy genes were upregulated by 9 h post-seeding of which, autophagosome marker LC3B-II was demonstrated by western blot. Transient expression of 3A in PK-15 cells upregulated both Th1 and Th2 genes. The study suggested that the expressed 3A protein of FMDV cannot be used for 3A trans-supplementation in helper cells; however, it acts as an endogenously processed antigen that has the potential to elicit immune response in vivo.

Genome-wide integrated analysis of miRNA and mRNA expression profiles to identify differentially expressed miR-22-5p and miR-27b-5p in response to classical swine fever vaccine virus

The present study was conducted to identify the differentially expressed miRNAs (DE miRNAs) in the peripheral blood mononuclear cells of crossbred pigs in response to CSF vaccination on 7 and 21 days of post vaccination as compared to unvaccinated control (0 dpv). Simultaneously, set of miRNA was predicted using mRNA seq data at same time point. The proportion of CD4^-CD8⁺ and CD4⁺CD8⁺ increased after vaccination, and the mean percentage inhibition was 86.89% at 21 dpv. It was observed that 22 miRNAs were commonly expressed on both the time points. Out of predicted DE miRNAs, it was found that 40 and 35 DE miRNAs were common, obtained from miRNA seq analysis and predicted using mRNA seq data on 7 dpv versus 0 dpv and 21 dpv versus 0 dpv respectively. Two DE miRNAs, ssc-miR-22-5p and ssc-miR-27b-5p, were selected based on their log₂ fold change and functions of their target genes in immune process/pathway of viral infections. The validations of DE miRNAs using qRT-PCR were in concordance with miRNA seq analysis. Two set of target genes, CD40 and SWAP70 (target gene of ssc-miR-22-5p) and TLR4 and Lyn (target gene of ssc-miR-27b-5p), were validated and were in concordance with results of RNA seq analysis at a particular time point (except TLR4). The first report of genome-wide identification of differentially expressed miRNA in response to live attenuated vaccine virus of classical swine fever revealed miR-22-5p and miR-27b-5p were differentially expressed at 7 dpv and 21 dpv.

IRF1 up-regulates isg15 gene expression in dsRNA stimulation or CSFV infection by targeting nucleotides -487 to -325 in the 5' flanking region

Interferon (IFN)-stimulated gene 15 (ISG15) encodes a ubiquitin-like protein that is heavily involved in immune response elicitation. As an important member of interferon regulatory factor (IRF) family, IRF1 can activate the expression of multiple genes, including the human optineurin gene (Sudhakar et al., 2013). In this study, a sequence in the promoter region of the optineurin gene was compared to the 5' flanking region of the porcine isg15 gene. Porcine IRF1 also possesses antiviral activity against several swine viruses (Li et al., 2015), but the mechanism is not well understood. Herein, we report that porcine IRF1 and ISG15 were up-regulated in porcine kidney (PK-15) cells following stimulation with double-stranded RNA (dsRNA) or classical swine fever virus (CSFV) infection. We also found that siRNA-mediated knockdown of IRF1 expression resulted in lower ISG15 expression in response to polyinosinic:polycytidylic acid [poly(I:C)] or CSFV infection. The overexpression of IRF1 resulted in ISG15 up-regulation. IRF1 was shown to translocate to the nucleus in response to dsRNA stimulation. To further identify the functional domain of the isg15 gene that promotes IRF1 transcriptional activity, firefly luciferase and ISG15 reporter systems were constructed. The results of the firefly luciferase and ISG15 reporter assay suggested that IRF1 mediates the up-regulation of ISG15. Nucleotides -487 to -325, located in the 5' flanking region of the isg15 gene, constituted the promoter region of IRF1. ChIP assay indicated that IRF1 protein was able to interact with the DNA in the 5'fr of isg15 gene in cells. As an innate immune response protein with broad-spectrum antiviral activity, the up-regulation of ISG15 mediated by IRF1 in porcine cells is reported for the first time. These results warrant further investigation into the antiviral activity of porcine IRF1 against reported swine viruses.

Expression profiling of immune genes in classical swine fever vaccinated indigenous and crossbred piglets

Classical swine fever is a highly contagious disease of pigs which courses from life-threatening to asymptomatic, depending on the virulence of the virus strain and the immune-competence of the host. The present study was undertaken to investigate the expression of immunologically important genes, viz. IFNα, IFNβ, SLA, SLA-2, SLA-DR, Ii, SLA-DM, CSK and JUN and to ascertain genetic group differences on the basis of humoral immune response. Blood samples were collected from 5 indigenous and 6 crossbred piglets at pre-vaccination and after 28th day of classical swine fever (CSF) vaccination. On 28th day, the competitive Enzyme Linked Immunosorbent Assay (cELISA) revealed poor humoral immune response (E2 antibodies) in indigenous piglets (84.80%) as compared to crossbred piglets (98.33%) in response to CSF vaccination. The expression level of genes was analyzed in three ways, viz. indigenous 28th day post-vaccination (28dpv) versus pre-vaccination, crossbred 28th day post-vaccination versus pre-vaccination and crossbred 28th day post-vaccination versus indigenous 28th day post-vaccination. The study showed that IFNα, IFNβ, SLA, SLA-2, Ii, SLA-DM, CSK and JUN were significantly upregulated in crossbred piglets than indigenous piglets at 28th day post-vaccination. But the SLA-DR was significantly downregulated in CSF vaccinated crossbred over indigenous piglets.

Recombinant Swinepox Virus Expressing Glycoprotein E2 of Classical Swine Fever Virus Confers Complete Protection in Pigs upon Viral Challenge

Classical swine fever (CSF) is a highly contagious and serious viral disease that affects the pig industry worldwide. The glycoprotein E2 of the classical swine fever virus (CSFV) can induce neutralizing antibodies, and it is widely used for novel vaccine development. To explore the development of a vaccine against CSFV infections, the gene of glycoprotein E2 was inserted into the swinepox virus (SPV) genome by homologous recombination. The culture titers of rSPV-E2 remained at about 4.3 × 10⁶ TCID₅₀ for more than 60 passages in PK15 and swine testis cell lines. The rSPV-E2 could not be replicated in Vero, MDBK or other non-porcine cell lines. After two to three passages, the SPV specific gene of rSPV-E2 could not been detected in the non-porcine cell culture. To evaluate the immunogenicity of rSPV-E2, 20 CSFV seronegative minipigs were immunized with rSPV-E2, a commercial C-strain vaccine, wild-type SPV (wtSPV; negative control), or PBS (a no-challenge control). After challenge with CSFV, pigs in the rSPV-E2-immunized group showed significantly shorter fever duration compared with the wtSPV-treated group (P < 0.05). E2-specific antibodies in the rSPV-E2-immunized group increased dramatically after vaccination and increased continuously over time. CSFV genomic copies in the serum of rSPV-E2-immunized pigs were significantly less compared with the wtSPV-treated group at all time points after challenge (P < 0.01). Significant reduction in gross lung lesion scores, histopathological liver, spleen, lung, and kidney lesion scores were noted in the rSPV-E2-immunized group compared with the wtSPV-treated group (P < 0.01). The results suggested that the recombinant rSPV-E2 provided pigs with significant protection from CSFV infections; thus, rSPV-E2 offers proof of principle for the development of a vaccine for the prevention of CSFV infections in pigs.

Viperin inhibits rabies virus replication via reduced cholesterol and sphingomyelin and is regulated upstream by TLR4

Viperin (virus inhibitory protein, endoplasmic reticulum-associated, IFN-inducible) is an interferon-inducible protein that mediates antiviral activity. Generally, rabies virus (RABV) multiplies extremely well in susceptible cells, leading to high virus titres. In this study, we found that viperin was significantly up-regulated in macrophage RAW264.7 cells but not in NA, BHK-21 or BSR cells. Transient viperin overexpression in BSR cells and stable expression in BHK-21 cells could inhibit RABV replication, including both attenuated and street RABV. Furthermore, the inhibitory function of viperin was related to reduce cholesterol/sphingomyelin on the membranes of RAW264.7 cells. We explored the up-stream regulation pathway of viperin in macrophage RAW264.7 cells in the context of RABV infection. An experiment confirmed that a specific Toll-like receptor 4 (TLR4) inhibitor, TAK-242, could inhibit viperin expression in RABV-infected RAW264.7 cells. These results support a regulatory role for TLR4. Geldanamycin, a specific inhibitor of interferon regulatory factor 3 (IRF3) (by inhibiting heat-shock protein 90 (Hsp90) of the IRF3 phosphorylation chaperone), significantly delayed and reduced viperin expression, indicating that IRF3 is involved in viperin induction in RAW264.7 cells. Taken together, our data support the therapeutic potential for viperin to inhibit RABV replication, which appears to involve upstream regulation by TLR4.

Classical swine fever in pigs: recent developments and future perspectives

Classical swine fever (CSF) is one of the most devastating epizootic diseases of pigs, causing high morbidity and mortality worldwide. The diversity of clinical signs and similarity in disease manifestations to other diseases make CSF difficult to diagnose with certainty. The disease is further complicated by the presence of a number of different strains belonging to three phylogenetic groups. Advanced diagnostic techniques allow detection of antigens or antibodies in clinical samples, leading to implementation of proper and effective control programs. Polymerase chain reaction (PCR)-based methods, including portable real-time PCR, provide diagnosis in a few hours with precision and accuracy, even at the point of care. The disease is controlled by following a stamping out policy in countries where vaccination is not practiced, whereas immunization with live attenuated vaccines containing the 'C' strain is effectively used to control the disease in endemic countries. To overcome the problem of differentiation of infected from vaccinated animals, different types of marker vaccines, with variable degrees of efficacy, along with companion diagnostic assays have been developed and may be useful in controlling and even eradicating the disease in the foreseeable future. The present review aims to provide an overview and status of CSF as a whole with special reference to swine husbandry in India.

Genetic analysis of reproductive traits and antibody response in a PRRS outbreak herd

Porcine reproductive and respiratory syndrome (PRRS) is the most economically significant disease impacting pig production in North America, Europe, and Asia, causing reproductive losses such as increased rates of stillbirth and mummified piglets. The objective of this study was to explore the genetic basis of host response to the PRRS virus (PRRSV) in a commercial multiplier sow herd before and after a PRRS outbreak, using antibody response and reproductive traits. Reproductive data comprising number born alive (NBA), number alive at 24 h (NA24), number stillborn (NSB), number born mummified (NBM), proportion born dead (PBD), number born dead (NBD), number weaned (NW), and number of mortalities through weaning (MW) of 5,227 litters from 1,967 purebred Landrace sows were used along with a pedigree comprising 2,995 pigs. The PRRS outbreak date was estimated from rolling averages of farrowing traits and was used to split the data into a pre-PRRS phase and a PRRS phase. All 641 sows in the herd during the outbreak were blood sampled 46 d after the estimated outbreak date and were tested for anti-PRRSV IgG using ELISA (sample-to-positive [S/P] ratio). Genetic parameters of traits were estimated separately for the pre-PRRS and PRRS phase data sets. Sows were genotyped using the PorcineSNP60 BeadChip, and genome-wide association studies (GWAS) were performed using method Bayes B. Heritability estimates for reproductive traits ranged from 0.01 (NBM) to 0.12 (NSB) and from 0.01 (MW) to 0.12 (NBD) for the pre-PRRS and PRRS phases, respectively. S/P ratio had heritability (0.45) and strong genetic correlations with most traits, ranging from -0.72 (NBM) to 0.73 (NBA). In the pre-PRRS phase, regions associated with NSB and PBD explained 1.6% and 3% of the genetic variance, respectively. In the PRRS phase, regions associated with NBD, NSB, and S/P ratio explained 0.8%, 11%, and 50.6% of the genetic variance, respectively. For S/P ratio, 2 regions on SSC 7 (SSC7) separated by 100 Mb explained 40% of the genetic variation, including a region encompassing the major histocompatibility complex, which explained 25% of the genetic variance. These results indicate a significant genomic component associated with PRRSV antibody response and NSB in this data set. Also, the high heritability and genetic correlation estimates for S/P ratio during the PRRS phase suggest that S/P ratio could be used as an indicator of the impact of PRRS on reproductive traits.

Interaction of CSFV E2 protein with swine host factors as detected by yeast two-hybrid system

E2 is one of the envelope glycoproteins of pestiviruses, including classical swine fever virus (CSFV) and bovine viral diarrhea virus (BVDV). E2 is involved in several critical functions, including virus entry into target cells, induction of a protective immune response and virulence in swine. However, there is no information regarding any host binding partners for the E2 proteins. Here, we utilized the yeast two-hybrid system and identified fifty-seven host proteins as positive binding partners which bound E2 from both CSFV and BVDV with the exception of two proteins that were found to be positive for binding only to CSFV E2. Alanine scanning of CSFV E2 demonstrated that the binding sites for these cellular proteins on E2 are likely non-linear binding sites. The possible roles of the identified host proteins are discussed as the results presented here will be important for future studies to elucidate mechanisms of host protein-virus interactions during pestivirus infection. However, due to the limitations of the yeast two hybrid system, the proteins identified is not exhaustive and each interaction identified needs to be confirmed by independent experimental approaches in the context of virus-infected cells before any definitive conclusion can be drawn on relevance for the virus life cycle.

Porcine circovirus type 2 decreases the infection and replication of attenuated classical swine fever virus in porcine alveolar macrophages

Recently, it has been noted that porcine circovirus type 2 (PCV2) infection adversely affects the protective efficacy of Lapinized Philippines Coronel (LPC) vaccine, an attenuated strain of classical swine fever virus (CSFV), in pigs. In order to investigate the possible mechanisms of the PCV2-derived interference, an in vitro model was established to study the interaction of LPC virus (LPCV) and PCV2 in porcine alveolar macrophages (AMs). The results showed that PCV2 reduced the LPCV infection in AMs and the levels of PCV2-derived interference were dose-dependent. The PCV2-derived interference also reduced the replication level of LPCV in AMs. The full-length PCV2 DNA and its fragment DNA C9 CpG-ODN were involved in the reduction of LPCV infection in AMs, whereas UV-inactivated PCV2 was not. In addition, a moderate negative correlation between the LPCV antigen-containing rate and IFN-γ production was observed, and had a dose-dependent trend with the level of PCV2-inoculation. The results of the present study may partially explain how PCV2 infection interferes with the efficacy of LPC vaccine.