Detection of Differential Expression of Porcine IFN-αSubtypes by Reverse Transcription Polymerase Chain Reaction

Expression of porcine fusion protein IRF7/3(5D) efficiently controls foot-and-mouth disease virus replication

Several studies have demonstrated that the delivery of type I, II, or III interferons (IFNs) by inoculation of a replication-defective human adenovirus 5 (Ad5) vector expressing IFNs can effectively control foot-and-mouth disease (FMD) in cattle and swine during experimental infections. However, relatively high doses are required to achieve protection. In this study, we identified the functional properties of a porcine fusion protein, poIRF7/3(5D), as a biotherapeutic and enhancer of IFN activity against FMD virus (FMDV). We showed that poIRF7/3(5D) is a potent inducer of type I IFNs, including alpha IFN (IFN-α), IFN-β, and IFN-ω but not type III IFN (interleukin-28B), without inducing cytotoxicity. Expression of poIRF7/3(5D) significantly and steadily reduced FMDV titers by up to 6 log10 units in swine and bovine cell lines. Treatment with an IFN receptor inhibitor (B18R) combined with an anti-IFN-α antibody neutralized the antiviral activity in the supernatants of cells transduced with an Ad5 vector expressing poIRF7/3(5D) [Ad5-poIRF7/3(5D)]. However, several transcripts with known antiviral function, including type I IFNs, were still highly upregulated (range of increase, 8-fold to over 500-fold) by poIRF7/3(5D) in the presence of B18R. Furthermore, the sera of mice treated with Ad5-poIRF7/3(5D) showed antiviral activity that was associated with the induction of high levels of IFN-α and resulted in complete protection against FMDV challenge at 6, 24, or 48 h posttreatment. This study highlights for the first time the antiviral potential of Ad5-poIRF7/3(5D) in vitro and in vivo against FMDV.

IMPORTANCE

FMD remains one of the most devastating diseases that affect livestock worldwide. Effective vaccine formulations are available but are serotype specific and require approximately 7 days before they are able to elicit protective immunity. We have shown that vector-delivered IFN is an option to protect animals against many FMDV serotypes as soon as 24 h and for about 4 days postadministration. Here we demonstrate that delivery of a constitutively active transcription factor that induces the production of endogenous IFNs and potentially other antiviral genes is a viable strategy to protect against FMD.

Functional characterization of canine interferon-lambda

In this study, we provide the first comprehensive annotation of canine interferon-λ (CaIFN-λ, type III IFN). Phylogenetic analysis based on genomic sequences indicated that CaIFN-λ is located in the same branch with Swine IFN-λ1 (SwIFN-λ), Bat IFN-λ1 (BaIFN-λ), and human IFN-λ1 (HuIFN-λ1). CaIFN-λ was cloned, expressed in Escherichia coli, and purified to further investigate the biological activity in vitro. The recombinant CaIFN-λ (rCaIFN-λ) displayed potent antiviral activity on both homologous and heterologous animal cells in terms of inhibiting the replication of the New Jersey serotype of vesicular stomatitis virus (VSV), canine parvovirus, and influenza virus A/WSN/33 (H1N1), respectively. In addition, we also found that rCaIFN-λ exhibits a significant antiproliferative response against A72 canine tumor cells and MDCK cells in a dose-dependent manner. Furthermore, CaIFN-λ activated the JAK-STAT signaling pathway. To evaluate the expression of CaIFN-λ induced by virus and the expression of IFN-stimulated genes (ISGs) induced by rCaIFN-λ in the MDCK cells, we measured the relative mRNA level of CaIFN-λ and ISGs (ISG15, Mx1, and 2'5'-OAS) by quantitative real-time PCR and found that the mRNA level of CaIFN-λ and the ISGs significantly increased after treating the MDCK cells with viruses and rCaIFN-λ protein, respectively. Finally, to evaluate the binding activity of rCaIFN-λ to its receptor, we expressed the extracellular domain of the canine IFN-λ receptor 1 (CaIFN-λR1-EC) and determined the binding activity via ELISA. Our results demonstrated that rCaIFN-λ bound tightly to recombinant CaIFN-λR1-EC (rCaIFN-λR1-EC).

Reverse transcription real-time PCR for detection of porcine interferon α and β genes

A few studies provided convincing evidence of constitutive expression of type I interferons (IFNs) in humans and mice, and of the steady-state role of these cytokines under health conditions. These results were later confirmed in pigs, too. In line with this tenet, low levels of IFN-α/β can be detected in swine tissues in the absence of any specific inducer. These studies are compounded by the utmost complexity of type I IFNs (including among others 17 IFN-α genes in pigs), which demands proper research tools. This prompted us to analyse the available protocols and to develop a relevant, robust, reverse transcription (RT) real-time polymerase chain reaction (PCR) detection system for the amplification of porcine IFN-α/β genes. The adopted test procedure is user-friendly and provides the complete panel of gene expression of one subject in a microtitre plate. Also, a proper use of PCR fluorochromes (SYBR(®) versus EvaGreen(®) supermix) enables users to adopt proper test protocols in case of low-expression porcine IFN-α genes. This is accounted for by the much higher sensitivity of the test protocol with EvaGreen(®) supermix. Interestingly, IFN-β showed the highest frequency of constitutive expression, in agreement with its definition of 'immediate early' gene in both humans and mice. Results indicate that the outlined procedure can detect both constitutively expressed and virus-induced IFN-α/β genes, as well as the impact of environmental, non-infectious stressors on the previous profile of constitutive expression.

Differential expression and activity of the porcine type I interferon family

Type I interferons (IFNs) are central to innate and adaptive immunity, and many have unique developmental and physiological functions. However, in most species, only two subtypes, IFN-alpha and IFN-beta, have been well studied. Because of the increasing importance of zoonotic viral diseases and the use of pigs to address human research questions, it is important to know the complete repertoire and activity of porcine type I IFNs. Here we show that porcine type I IFNs comprise at least 39 functional genes distributed along draft genomic sequences of chromosomes 1 and 10. These functional IFN genes are classified into 17 IFN-alpha subtypes, 11 IFN-delta subtypes, 7 IFN-omega subtypes, and single-subtype subclasses of IFN-alphaomega, IFN-beta, IFN-epsilon, and IFN-kappa. We found that porcine type I IFNs have diverse expression profiles and antiviral activities against porcine reproductive and respiratory syndrome virus (PRRSV) and vesicular stomatitis virus (VSV), with activity ranging from 0 to >10(5) U.ng(-1).ml(-1). Whereas most IFN-alpha subtypes retained the greatest antiviral activity against both PRRSV and VSV in porcine and MARC-145 cells, some IFN-delta and IFN-omega subtypes, IFN-beta, and IFN-alphaomega differed in their antiviral activity based on target cells and viruses. Several IFNs, including IFN-alpha7/11, IFN-delta2/7, and IFN-omega4, exhibited minimal or no antiviral activity in the tested target cell-virus systems. Thus comparative studies showed that antiviral activity of porcine type I IFNs is virus- and cell-dependent, and IFN-alphas are positively correlated with induction of MxA, an IFN-stimulated gene. Collectively, these data provide fundamental genomic information for porcine type I IFNs, information that is necessary for understanding porcine physiological and antiviral responses.

Characterization and virus-induced expression profiles of the porcine interferon-omega multigene family

Interferon-omega is a member of the type I interferon family. In this work, 8 functional porcine interferon-omega genes and 4 pseudogenes present on porcine chromosome 1 were identified in the porcine genome database by BLAST scanning. Their genetic and genomic characteristics were investigated using bioinformatics tools. Then the PoIFN-omega functional subtype genes were isolated and expressed in BHK-21 cells. The PoIFN-omega subtypes possessed about 10(4) to 10(5) units of antiviral activity per milliliter. PoIFN-omega 7 had the highest antiviral activity, about 20 times that of PoIFN-omega 4, which had the lowest antiviral activity. Differential expression of the subtypes was detected in PK15 cells and porcine peripheral blood mononuclear cells (PBMCs) in response to pseudorabies virus and poly(I).poly(C). Expression of PoIFN-omega 2/-omega 6 was up-regulated to the greatest extent by virus infection.

Sequence and expression analyses of porcine ISG15 and ISG43 genes

The coding sequences of porcine interferon-stimulated gene 15 (ISG15) and the interferon-stimulated gene (ISG43) were cloned from swine spleen mRNA. The amino acid sequences deduced from porcine ISG15 and ISG43 genes coding sequence shared 24-75% and 29-83% similarity with ISG15s and ISG43s from other vertebrates, respectively. Structural analyses revealed that porcine ISG15 comprises two ubiquitin homologues motifs (UBQ) domain and a conserved C-terminal LRLRGG conjugating motif. Porcine ISG43 contains an ubiquitin-processing proteases-like domain. Phylogenetic analyses showed that porcine ISG15 and ISG43 were mostly related to rat ISG15 and cattle ISG43, respectively. Using quantitative real-time PCR assay, significant increased expression levels of porcine ISG15 and ISG43 genes were detected in porcine kidney endothelial cells (PK15) cells treated with poly I:C. We also observed the enhanced mRNA expression of three members of dsRNA pattern-recognition receptors (PRR), TLR3, DDX58 and IFIH1, which have been reported to act as critical receptors in inducing the mRNA expression of ISG15 and ISG43 genes. However, we did not detect any induced mRNA expression of IFNalpha and IFNbeta, suggesting that transcriptional activations of ISG15 and ISG43 were mediated through IFN-independent signaling pathway in the poly I:C treated PK15 cells. Association analyses in a Landrace pig population revealed that ISG15 c.347T>C (BstUI) polymorphism and the ISG43 c.953T>G (BccI) polymorphism were significantly associated with hematological parameters and immune-related traits.