T cell responses to the structural polypeptides of porcine reproductive and respiratory syndrome virus

Analysis of the genetic evolution and recombination of the PRRSV-2 GP2 protein in China from 1996 to 2023

Porcine reproductive and respiratory syndrome (PRRS) is among the most serious infectious diseases of pigs worldwide. It is caused by PRRSV and frequently mutates and recombines. To date, however, there have been relatively few studies that have analyzed the GP2 membrane protein of this virus. In this study, we compared 570 nucleotide sequences of the PRRSV-2 GP2 protein obtained from the NCBI GenBank database, which were subjected to phylogenetic analysis. We selected 64 representative strains to investigate the genetic evolution and recombination of the GP2 protein in China. Lineages 1 and 8 were the most prevalent, while lineages 5 and 8 showed closer genetic relationships. The nucleotide similarities of the 570 GP2 sequences ranged from 83.0% to 100%, with amino acid similarities from 80.2% to 100%. Recombinant analysis indicated lineage 1 strains had the highest recombination probability. Comparison of amino acid sequences showed substitutions without deletions or insertions, with lineage 1 exhibiting the most substitutions and lineage 8 the fewest. These findings enhance understanding of PRRSV-2 genetic variation and provide a foundation for further studies on GP2 and vaccine development.

IMPORTANCE

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant losses and posed threats to the swine breeding industry. To date, there have been comparatively few studies on the GP2 protein of PRRSV-2, and consequently, many unanswered questions remain regarding its pathogenicity-associated mechanisms and effects. We collected 570 nucleotide sequences of the GP2 protein of this virus and used these data to perform multifaceted analytical work in order to facilitate the understanding of the genetic evolution of this virus and recombinant mutations. These provide basic data for the follow-up study of GP2 and lay a foundation for further in-depth studies of this virus and vaccine development.

An attenuated herpesvirus vectored vaccine candidate induces T-cell responses against highly conserved porcine reproductive and respiratory syndrome virus M and NSP5 proteins that are unable to control infection

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a leading cause of economic loss in pig farming worldwide. Existing commercial vaccines, all based on modified live or inactivated PRRSV, fail to provide effective immunity against the highly diverse circulating strains of both PRRSV-1 and PRRSV-2. Therefore, there is an urgent need to develop more effective and broadly active PRRSV vaccines. In the absence of neutralizing antibodies, T cells are thought to play a central role in controlling PRRSV infection. Herpesvirus-based vectors are novel vaccine platforms capable of inducing high levels of T cells against encoded heterologous antigens. Therefore, the aim of this study was to assess the immunogenicity and efficacy of an attenuated herpesvirus-based vector (bovine herpesvirus-4; BoHV-4) expressing a fusion protein comprising two well-characterized PRRSV-1 T-cell antigens (M and NSP5). Prime-boost immunization of pigs with BoHV-4 expressing the M and NSP5 fusion protein (vector designated BoHV-4-M-NSP5) induced strong IFN-γ responses, as assessed by ELISpot assays of peripheral blood mononuclear cells (PBMC) stimulated with a pool of peptides representing PRRSV-1 M and NSP5. The responses were closely mirrored by spontaneous IFN-γ release from unstimulated cells, albeit at lower levels. A lower frequency of M and NSP5 specific IFN-γ responding cells was induced following a single dose of BoHV-4-M-NSP5 vector. Restimulation using M and NSP5 peptides from PRRSV-2 demonstrated a high level of cross-reactivity. Vaccination with BoHV-4-M-NSP5 did not affect viral loads in either the blood or lungs following challenge with the two heterologous PRRSV-1 strains. However, the BoHV-4-M-NSP5 prime-boost vaccination showed a marked trend toward reduced lung pathology following PRRSV-1 challenge. The limited effect of T cells on PRRSV-1 viral load was further examined by analyzing local and circulating T-cell responses using intracellular cytokine staining and proliferation assays. The results from this study suggest that vaccine-primed T-cell responses may have helped in the control of PRRSV-1 associated tissue damage, but had a minimal, if any, effect on controlling PRRSV-1 viral loads. Together, these results indicate that future efforts to develop effective PRRSV vaccines should focus on achieving a balanced T-cell and antibody response.

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.

The Construction and Immunogenicity Analyses of Recombinant Pseudorabies Virus With NADC30-Like Porcine Reproductive and Respiratory Syndrome Virus-Like Particles Co-expression

Porcine reproductive and respiratory syndrome (PRRS) and pseudorabies (PR) are highly infectious swine diseases and cause significant financial loss in China. The respiratory system and reproductive system are the main target systems. Previous studies showed that the existing PR virus (PRV) and PRRS virus (PRRSV) commercial vaccines could not provide complete protection against PRV variant strains and NADC30-like PRRSV strains in China. In this study, the PRV variant strain XJ and NADC30-like PRRSV strain CHSCDJY-2019 are used as the parent for constructing a recombinant pseudorabies virus (rPRV)-NC56 with gE/gI/TK gene deletion and co-expressing NADC30-like PRRSV GP5 and M protein. The rPRV-NC56 proliferated stably in BHK-21 cells, and it could stably express GP5 and M protein. Due to the introduction of the self-cleaving 2A peptide, GP5 and M protein were able to express independently and form virus-like particles (VLPs) of PRRSV in rPRV-NC56-infected BHK-21 cells. The rPRV-NC56 is safe for use in mice; it can colonize and express the target protein in mouse lungs for a long time. Vaccination with rPRV-NC56 induces PRV and NADC30-like PRRSV specific humoral and cellular immune responses in mice, and protects 100% of mice from virulent PRV XJ strain. Furthermore, the virus-neutralizing antibody (VNA) elicited by rPRV-NC56 showed significantly lower titer against SCNJ-2016 (HP-PRRSV) than that against CHSCDJY-2019 (NADC30-like PRRSV). Thus, rPRV-NC56 appears to be a promising candidate vaccine against NADC30-like PRRSV and PRV for the control and eradication of the variant PRV and NADC30-like PRRSV.

Intradermal co-inoculation of codon pair deoptimization (CPD)-attenuated chimeric porcine reproductive and respiratory syndrome virus (PRRSV) with Toll like receptor (TLR) agonists enhanced the protective effects in pigs against heterologous challenge

The objective of this study was to assess protective efficacy of vaccination using CPD-attenuated chimeric PRRSV and Toll like receptor (TLR) agonists (HSP70 c-terminal domain and HSPX) as adjuvants through different inoculation routes. In this study, a chimeric PRRSV composed of two field isolates was synthesized and attenuated by CPD in NSP1 as described in the previous study. The infection of the CPD-attenuated chimeric PRRSV to pigs of 3 weeks-old showed no clinical signs without pathological lesions in necropsy, while it induced improved cross immunity between its parent strains. The TLR agonists were expressed in E. coli and purified to be used. In challenge experiment, pigs of 3 weeks-old were vaccinated using the CPD-attenuated chimeric virus with the prepared TLR agonists through intramuscular or intradermal route, following heterologous challenge after 4 weeks of vaccination. In results, intramuscular or intradermal inoculation of the CPD-attenuated chimeric virus demonstrated excellent protective efficacy against heterologous challenges. Importantly, intradermal inoculation with the TLR agonists enhanced protective effects as shown in the significantly increased level of PRRSV-specific IFN-γ-SCs and cytokines in sera, and the significant reduction of pathological lesion and viral load in lung. This study suggested that the intradermal inoculation of CPD-attenuated chimeric PRRSV plus TLR agonists should be more effective for protection of pigs against diverse PRRS field viruses.

Co-expression of self-cleaved multiple proteins derived from Porcine Reproductive and Respiratory Syndrome Virus by bi-cistronic and tri-cistronic DNA vaccines

Porcine Reproductive and Respiratory Syndrome caused by Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) remains one of the important diseases in swine industry. A vaccine that is safe, effective and also elicit broad immune response against multiple antigens is desirable. In this study, we developed multi-cistronic DNA vaccines capable of co-expressing multiple structural proteins derived from PRRSV. To preserve the structure and function of each antigen protein, we employed self-cleaving 2A peptides to mediate separation of multiple proteins expressed by multi-cistronic genes. Six bi-cistronic genes encoding PRRSV GP5 and M proteins were generated, by which each construct contains different 2A sequences derived from Foot-and-mouth disease virus (F2A), porcine teschovirus-1 (P2A) and Thosea asigna virus (T2A) either with or without furin cleavage site (Fu). Vectored by the mammalian expression plasmid pTH, all six bi-cistronic genes co-expressed the proteins GP5 and M at comparable level. Importantly, all six types of 2A sequences could mediate a complete self-cleavage of the GP5 and M. We next generated tri-cistronic DNA vaccines co-expressing the PRRSV proteins GP5, M and N. All homologous and heterologous combinations of P2A and F2A in tri-cistronic genes yielded a complete self-cleavage of the GP5, M and N proteins. Our study reports a success in co-expression of multiple PRRSV structural proteins in discrete form from a single vaccine and confirms feasibility of developing one single vaccine that provides broad immune responses against PRRSV.

Pigs that recover from porcine reproduction and respiratory syndrome virus infection develop cytotoxic CD4+CD8+ and CD4+CD8- T-cells that kill virus infected cells

Porcine reproductive and respiratory syndrome virus (PRRSV) infection is difficult to control because the virus undergoes antigenic variation during infection and also modulates the protective host immune response. Although current vaccines do not provide full protection, they have provided insight into the mechanisms of protection. Live PRRSV vaccines induce partial protection before the appearance of neutralizing antibody, suggesting cell-mediated immunity or other mechanisms may be involved. Herein, we demonstrate recovery from infection is associated with development of cytotoxic T-lymphocytes (CTL) that can kill PRRSV-infected target cells. Initial experiments showed survival of PRRSV-infected monocyte derived macrophage (MDM) targets is reduced when overlaid with peripheral blood mononuclear cells (PBMC) from gilts that had recovered from PRRSV infection. Further studies with PBMC depleted of either CD4⁺ or CD8⁺ T-cells and positively selected subpopulations of CD4⁺ and CD8⁺ T-cells showed that both CD4⁺ and CD8⁺ T-cells were involved in killing. Examination of killing at different time points revealed killing was biphasic and mediated by CTL of different phenotypes. CD4⁺CD8^+high were associated with killing target cells infected for 3–6 hours. CD4⁺CD8^- CTL were associated with killing at 16–24 hours. Thus, all the anti-PRRSV CTL activity in pigs was attributed to two phenotypes of CD4⁺ cells which is different from the anti-viral CD4^-CD8⁺ CTL phenotype found in most other animals. These findings will be useful for evaluating CTL responses induced by current and future vaccines, guiding to a novel direction for future vaccine development.

Recognition of Highly Diverse Type-1 and -2 Porcine Reproductive and Respiratory Syndrome Viruses (PRRSVs) by T-Lymphocytes Induced in Pigs after Experimental Infection with a Type-2 PRRSV Strain

Background/Aim

Live attenuated vaccines confer partial protection in pigs before the appearance of neutralizing antibodies, suggesting the contribution of cell-mediated immunity (CMI). However, PRRSV-specific T-lymphocyte responses and protective mechanisms need to be further defined. To this end, the hypothesis was tested that PRRSV-specific T-lymphocytes induced by exposure to type-2 PRRSV can recognize diverse isolates.

Methods

An IFN-gamma ELISpot assay was used to enumerate PRRSV-specific T-lymphocytes from PRRSV_SD23983-infected gilts and piglets born after in utero infection against 12 serologically and genetically distinct type-1 and -2 PRRSV isolates. The IFN-gamma ELISpot assay using synthetic peptides spanning all open reading frames of PRRSV_SD23983 was utilized to localize epitopes recognized by T-lymphocytes. Virus neutralization tests were carried out using the challenge strain (type-2 PRRSV_SD23983) and another strain (type-2 PRRSV_VR2332) with high genetic similarity to evaluate cross-reactivity of neutralizing antibodies in gilts after PRRSV_SD23983 infection.

Results

At 72 days post infection, T-lymphocytes from one of three PRRSV_SD23983-infected gilts recognized all 12 diverse PRRSV isolates, while T-lymphocytes from the other two gilts recognized all but one isolate. Furthermore, five of nine 14-day-old piglets infected in utero with PRRSV_SD23983 had broadly reactive T-lymphocytes, including one piglet that recognized all 12 isolates. Overlapping peptides encompassing all open reading frames of PRRSV_SD23983 were used to identify ≥28 peptides with T-lymphocyte epitopes from 10 viral proteins. This included one peptide from the M protein that was recognized by T-lymphocytes from all three gilts representing two completely mismatched MHC haplotypes. In contrast to the broadly reactive T-lymphocytes, neutralizing antibody responses were specific to the infecting PRRSV_SD23983 isolate.

Conclusion

These results demonstrated that T-lymphocytes recognizing antigenically and genetically diverse isolates were induced by infection with a type 2 PRRSV strain (SD23983). If these reponses have cytotoxic or other protective functions, they may help overcome the suboptimal heterologous protection conferred by conventional vaccines.

The Non-structural Protein 5 and Matrix Protein Are Antigenic Targets of T Cell Immunity to Genotype 1 Porcine Reproductive and Respiratory Syndrome Viruses

The porcine reproductive and respiratory syndrome virus (PRRSV) is the cause of one of the most economically important diseases affecting swine worldwide. Efforts to develop a next-generation vaccine have largely focused on envelope glycoproteins to target virus-neutralizing antibody responses. However, these approaches have failed to demonstrate the necessary efficacy to progress toward market. T cells are crucial to the control of many viruses through cytolysis and cytokine secretion. Since control of PRRSV infection is not dependent on the development of neutralizing antibodies, it has been proposed that T cell-mediated immunity plays a key role. Therefore, we hypothesized that conserved T cell antigens represent prime candidates for the development a novel PRRS vaccine. Antigens were identified by screening a proteome-wide synthetic peptide library with T cells from cohorts of pigs rendered immune by experimental infections with a closely related (subtype 1) or divergent (subtype 3) PRRSV-1 strain. Dominant T cell IFN-γ responses were directed against the non-structural protein 5 (NSP5), and to a lesser extent, the matrix (M) protein. The majority of NSP5-specific CD8 T cells and M-specific CD4 T cells expressed a putative effector memory phenotype and were polyfunctional as assessed by coexpression of TNF-α and mobilization of the cytotoxic degranulation marker CD107a. Both antigens were generally well conserved among strains of both PRRSV genotypes. Thus, M and NSP5 represent attractive vaccine candidate T cell antigens, which should be evaluated further in the context of PRRSV vaccine development.

Enhanced humoral and cellular immune responses to PRRS virus GP5 glycoprotein by DNA prime-adenovirus boost vaccination in mice

In order to investigate the induction of humoral and cellular immune responses against porcine reproductive and respiratory syndrome virus (PRRSV), BALB/c mice were immunized in a pcDNA3-GP5 prime-rAd-GP5 boost regimen. After humoral and cellular immune response detection, levels of PRRSV-specific antibodies, neutralizing antibodies, lymphocyte proliferation response, and cytotoxic T-lymphocyte response were significantly increased as compared to controls. The humoral immune response was induced more effectively by the DNA priming and recombinant adenovirus boosting regimen. Significant difference was observed between heterogeneous and homologous vaccination. Induction of anti-GP5 antibody response was higher in all heterogeneous combinations than those of the homologous combinations. In the induction of lymphocyte proliferation response and CTL response, the homologous combination of pcDNA3-GP5/pcDNA3-GP5/pcDNA3-GP5was significantly stronger than that of rAd-GP5/rAd-GP5/rAd-GP5, but was relatively weaker than the heterogeneous combination of pcDNA3-GP5/pcDNA3-GP5/rAd-GP5 and pcDNA3-GP5/rAd-GP5/rAd-GP5. This heterogeneous combination was a most efficient immunization regimen in induction of PRRSV-specific cellular immune response just as the antibody response. These results suggested that DNA immunization followed by recombinant adenovirus boosting could be used as a potential PRRSV vaccine.

Innate and adaptive immunity against Porcine Reproductive and Respiratory Syndrome Virus

Many highly effective vaccines have been produced against viruses whose virulent infection elicits strong and durable protective immunity. In these cases, characterization of immune effector mechanisms and identification of protective epitopes/immunogens has been informative for the development of successful vaccine programs. Diseases in which the immune system does not rapidly clear the acute infection and/or convalescent immunity does not provide highly effective protection against secondary challenge pose a major hurdle for clinicians and scientists. Porcine reproductive and respiratory syndrome virus (PRRSV) falls primarily into this category, though not entirely. PRRSV causes a prolonged infection, though the host eventually clears the virus. Neutralizing antibodies can provide passive protection when present prior to challenge, though infection can be controlled in the absence of detectable neutralizing antibodies. In addition, primed pigs (through natural exposure or vaccination with a modified-live vaccine) show some protection against secondary challenge. While peripheral PRRSV-specific T cell responses have been examined, their direct contribution to antibody-mediated immunity and viral clearance have not been fully elucidated. The innate immune response following PRRSV infection, particularly the antiviral type I interferon response, is meager, but when provided exogenously, IFN-α enhances PRRSV immunity and viral control. Overall, the quality of immunity induced by natural PRRSV infection is not ideal for informing vaccine development programs.

The epitopes necessary for protection may be identified through natural exposure or modified-live vaccines and subsequently applied to vaccine delivery platforms to accelerate induction of protective immunity following vaccination. Collectively, further work to identify protective B and T cell epitopes and mechanisms by which PRRSV eludes innate immunity will enhance our ability to develop more effective methods to control and eliminate PRRS disease.

Antigenic structures stably expressed by recombinant TGEV-derived vectors

Coronaviruses (CoVs) are positive-stranded RNA viruses with potential as immunization vectors, expressing high levels of heterologous genes and eliciting both secretory and systemic immune responses. Nevertheless, its high recombination rate may result in the loss of the full-length foreign gene, limiting their use as vectors. Transmissible gastroenteritis virus (TGEV) was engineered to express porcine reproductive and respiratory syndrome virus (PRRSV) small protein domains, as a strategy to improve heterologous gene stability. After serial passage in tissue cultures, stable expression of small PRRSV protein antigenic domains was achieved. Therefore, size reduction of the heterologous genes inserted in CoV-derived vectors led to the stable expression of antigenic domains. Immunization of piglets with these TGEV vectors led to partial protection against a challenge with a virulent PRRSV strain, as immunized animals showed reduced clinical signs and lung damage. Further improvement of TGEV-derived vectors will require the engineering of vectors with decreased recombination rate.

Expression of porcine respiratory and reproductive syndrome virus membrane-associated proteins in Listeria ivanovii via a genome site-specific integration and expression system

Listeria ivanovii (LI) possesses a facultative intracellular life cycle in macrophages and non-professional phagocytes thus making it a potential novel vaccine vector. We have developed a genome site-specific integration system as a universal tool for constructing the live LI-based vaccines. Using this system, the porcine reproductive and respiratory syndrome virus (PRRSV) orf5 and orf6 genes, coding for PRRSV membrane-associated protein GP5 and M, respectively, were integrated into the LI genome. Genome PCR and sequencing results showed that the orf5 or orf6 gene had been integrated into the LI genome downstream of orfXYZ or mpl gene. Western blot analysis of the non-secreted and secreted bacterial protein samples showed the expression and secretion of GP5 or M protein from the recombinant LI strains. The secretion of the heterologous proteins is a key step for bacterial vaccine vectors to deliver the antigens to the immune system to stimulate antigen-specific immune responses. Therefore, this integration system may be a potential tool for constructing novel vaccines using live LI as vector.

Maternal immunity enhances Mycoplasma hyopneumoniae vaccination induced cell-mediated immune responses in piglets

Background

Passively acquired maternal derived immunity (MDI) is a double-edged sword. Maternal derived antibody-mediated immunity (AMI) and cell-mediated immunity (CMI) are critical immediate defenses for the neonate; however, MDI may interfere with the induction of active immunity in the neonate, i.e. passive interference. The effect of antigen-specific MDI on vaccine-induced AMI and CMI responses to Mycoplasma hyopneumoniae (M. hyopneumoniae) was assessed in neonatal piglets. To determine whether CMI and AMI responses could be induced in piglets with MDI, piglets with high and low levels of maternal M. hyopneumoniae-specific immunity were vaccinated against M. hyopneumoniae at 7 d of age. Piglet M. hyopneumoniae-specific antibody, lymphoproliferation, and delayed type hypersensitivity (DTH) responses were measured 7 d and 14 d post vaccination.

Results

Piglets with M. hyopneumoniae-specific MDI failed to show vaccine-induced AMI responses; there was no rise in M. hyopneumoniae antibody levels following vaccination of piglets in the presence of M. hyopneumoniae-specific MDI. However, piglets with M. hyopneumoniae-specific MDI had primary (antigen-specific lymphoproliferation) and secondary (DTH) M. hyopneumoniae-specific CMI responses following vaccination.

Conclusions

In this study neonatal M. hyopneumoniae-specific CMI was not subject to passive interference by MDI. Further, it appears that both maternal derived and endogenous CMI contribute to M. hyopneumoniae-specific CMI responses in piglets vaccinated in the face of MDI.

Colostral antibody-mediated and cell-mediated immunity contributes to innate and antigen-specific immunity in piglets

Immunoglobulins and immune cells are critical components of colostral immunity; however, their transfer to and function in the neonate, especially maternal lymphocytes, is unclear. Cell-mediated and antibody-mediated immunity in sow blood and colostrum and piglet blood before (PS) and after (AS) suckling were assessed to investigate transfer and function of maternal immunity in the piglet. CD4, CD8, and γδ lymphocytes were found in sow blood and colostrum and piglet blood PS and AS; each had a unique T lymphocyte profile. Immunoglobulins were detected in sow blood, colostrum, and in piglet blood AS; the immunoglobulin profile of piglet serum AS mimicked that of sow serum. These results suggest selectivity in lymphocyte concentration into colostrum and subsequent lymphocyte transfer into the neonate, but that immunoglobulin transfer is unimpeded. Assessment of colostral natural killer activity and antigen-specific proliferation revealed that colostral cells are capable of influencing the innate and specific immune response of neonatal pigs.

Immunogenic and protective properties of GP5 and M structural proteins of porcine reproductive and respiratory syndrome virus expressed from replicating but nondisseminating adenovectors

Porcine reproductive and respiratory syndrome virus (PRRSV) is responsible for significant economic losses in the porcine industry. Currently available commercial vaccines do not allow optimal and safe protection. In this study, replicating but nondisseminating adenovectors (rAdV) were used for the first time in pigs for vaccinal purposes. They were expressing the PRRSV matrix M protein in fusion with either the envelope GP5 wild-type protein (M-GP5) which carries the major neutralizing antibody (NAb)-inducing epitope or a mutant form of GP5 (M-GP5m) developed to theoretically increase the NAb immune response. Three groups of fourteen piglets were immunized both intramuscularly and intranasally at 3-week intervals with rAdV expressing the green fluorescent protein (GFP, used as a negative control), M-GP5 or M-GP5m. Two additional groups of pigs were primed with M-GP5m-expressing rAdV followed by a boost with bacterially-expressed recombinant wild-type GP5 or were immunized twice with a PRRSV inactivated commercial vaccine. The results show that the rAdV expressing the fusion proteins of interest induced systemic and mucosal PRRSV GP5-specific antibody response as determined in an ELISA. Moreover the prime with M-GP5m-expressing rAdV and boost with recombinant GP5 showed the highest antibody response against GP5. Following PRRSV experimental challenge, pigs immunized twice with rAdV expressing either M-GP5 or M-GP5m developed partial protection as shown by a decrease in viremia overtime. The lowest viremia levels and/or percentages of macroscopic lung lesions were obtained in pigs immunized twice with either the rAdV expressing M-GP5m or the PRRSV inactivated commercial vaccine.

Immune responses in pigs induced by recombinant DNA vaccine co-expressing swine IL-18 and membrane protein of porcine reproductive and respiratory syndrome virus

In this study, two DNA vaccines, which express the membrane (M) protein of porcine respiratory and reproductive syndrome virus (PRRSV) (pEGFP-M) and co-express both M and swine IL-18 (pEGFP-IL18-M), were constructed and their abilities to induce humoral and cellular responses in piglets were comparatively evaluated. Experimental results showed that both recombinant DNA vaccines could not elicit neutralizing antibodies in the immunized piglets. However, both DNA vaccines elicited Th1-biased cellular immune responses. Notably, pigs immunized with the plasmid pEGFP-IL18-M developed significantly higher levels of IFN-γ and IL-2 production response and stronger specific T-lymphocyte proliferation response than the pigs inoculated with the plasmids pEGFP-M and pEGFP-IL18 (P < 0.05). These results illustrated that co-expression of M and IL-18 proteins could significantly improve the potency of DNA vaccination on the activation of vaccine-induced virus-specific cell-mediated immune responses in pigs, which may be used as a strategy to develop a new generation of vaccines against highly pathogenic PRRSV.

Porcine reproductive and respiratory syndrome virus induces interleukin-15 through the NF-κB signaling pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) mainly infects macrophages/dendritic cells and modulates cytokine expression in these cells. Interleukin-15 (IL-15) is a pleiotropic cytokine involved in wide range of biological activities. It has been shown to be essential for the generation, activation, and proliferation of NK and NKT cells and for the survival and activation of CD8(+) effector and memory T cells. In this study, we discovered that PRRSV infection upregulated IL-15 production at both the mRNA and protein levels in porcine alveolar macrophages (PAMs), blood monocyte-derived macrophages (BMo), and monocyte-derived dendritic cells (DCs). We subsequently demonstrated that the NF-κB signaling pathway was essential for PRRSV infection-induced IL-15 production. First, addition of an NF-κB inhibitor drastically reduced PRRSV infection-induced IL-15 production. We then found that NF-κB was indeed activated upon PRRSV infection, as evidenced by IκB phosphorylation and degradation. Moreover, we revealed an NF-κB binding motif in the cloned porcine IL-15 (pIL-15) promoter, deletion of which abrogated the pIL-15 promoter activity in PRRSV-infected alveolar macrophages. In addition, we demonstrated that PRRSV nucleocapsid (N) protein had the ability to induce IL-15 production in porcine alveolar macrophage cell line CRL2843 by transient transfection, which was mediated by its multiple motifs, and it also activated NF-κB. These data indicated that PRRSV infection-induced IL-15 production was likely through PRRSV N protein-mediated NF-κB activation. Our findings provide new insights into the molecular mechanisms underling the IL-15 production induced by PRRSV infection.

Expression of the nucleocapsid protein of porcine reproductive and respiratory syndrome virus in soybean seed yields an immunogenic antigenic protein

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), is a serious disease of swine and contributes to severe worldwide economic losses in swine production. Current vaccines against PRRS rely on the use of an attenuated-live virus; however, these are unreliable. Thus, alternative effective vaccines against PRRS are needed. Plant-based subunit vaccines offer viable, safe, and environmentally friendly alternatives to conventional vaccines. In this study, efforts have been undertaken to develop a soybean-based vaccine against PRRSV. A construct carrying a synthesized PRRSV-ORF7 antigen, nucleocapsid N protein of PRRSV, has been introduced into soybean, Glycine max (L.) Merrill. cvs. Jack and Kunitz, using Agrobacterium-mediated transformation. Transgenic plants carrying the sORF7 transgene have been successfully generated. Molecular analyses of T(0) plants confirmed integration of the transgene and transcription of the PRRSV-ORF7. Presence of a 15-kDa protein in seeds of T(1) transgenic lines was confirmed by Western blot analysis using PRRSV-ORF7 antisera. The amount of the antigenic protein accumulating in seeds of these transgenic lines was up to 0.65% of the total soluble protein (TSP). A significant induction of a specific immune response, both humoral and mucosal, against PRRSV-ORF7 was observed following intragastric immunization of BALB/c female mice with transgenic soybean seeds. These findings provide a 'proof of concept', and serve as a critical step in the development of a subunit plant-based vaccine against PRRS.

Immunogenicity study of plant-made oral subunit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV)

Currently, killed-virus and modified-live PRRSV vaccines are used to control porcine reproductive and respiratory syndrome disease (PRRS). However, very limited efficacy of killed-virus vaccines and serious safety concerns for modified-live virus vaccines demand the development of novel PRRSV vaccines. In this report, we investigated the possibility of using transgenic plants as a cost-effective and scalable system for production and delivery of a viral protein as an oral subunit vaccine against PRRSV. Corn calli were genetically engineered to produce PRRSV viral envelope-associated M protein. Both serum and intestine mucosal antigen-specific antibodies were induced by oral administration of the transgenic plant tissues to mice. In addition, serum and mucosal antibodies showed virus neutralization activity. The neutralization antibody titers after the final boost reached 6.7 in serum and 3.7 in fecal extracts, respectively. A PRRSV-specific IFN-γ response was also detected in splenocytes of vaccinated animals. These results demonstrate that transgenic corn plants are an efficient subunit vaccine production and oral delivery system for generation of both systemic and mucosal immune responses against PRRSV.

Effect of dietary supplementation of oregano essential oils to sows on colostrum and milk composition, growth pattern and immune status of suckling pigs

This study evaluated the effects of supplementing sow diets with oregano essential oils (OEO) during gestation and lactation on sow colostrum and milk composition and on the growth pattern and immune status of suckling pigs. A total of 70 second-parity sows were randomly assigned to 1 of 2 gestation dietary treatments within 24 h after service: control (CON) or CON + 250 mg/kg of OEO (OREG). In lactation, sows were again assigned to either the CON or OREG dietary treatment. Thus, the lactation treatments were CON-CON, CON-OREG, OREG-CON, and OREG-OREG. Colostrum and blood samples were collected from 6 sows per lactation dietary treatment. Thymus lymphocyte (T lymphocyte) subpopulations (γδ, cluster of differentiation 8, and 32 cluster of differentiation 4) were enumerated in blood and mammary secretions along with IGF-1, IgG, and IgA concentrations. Piglet growth rate were determined from 18, 17, 17, and 18 litters from the CON-CON, CON-OREG, OREG-CON, and OREG-OREG lactation dietary treatments, respectively. Growth rates were determined in 630 piglets, and piglets were individually identified and weighed on 1, 5, 9, 12, 16, and 19 d of age. Oregano essential oil supplementation during gestation or lactation had no effect (P > 0.05) on GE, CP, GE:CP, GE:fat, and IGF-1 in sow milk. Reductions of the fat percentage in milk on d 7 (P < 0.05) and d 14 (P = 0.07) were found in sows supplemented with OEO during lactation compared with those in the CON treatment. Milk from sows supplemented with OEO during lactation had the greatest number of T lymphocytes compared with those in the lactation CON treatment on d 14 of lactation (P < 0.01). The number of T lymphocytes in milk was greater for sows in the CON-OREG treatment compared with those other treatments on d 14 of lactation (P < 0.05). Energy intake was greater on d 1 to 5 in piglets from sows fed OEO during gestation than those from sows in the CON treatment (P < 0.05). A trend (P = 0.10) for greater milk intake was observed in piglets from sows supplemented with OEO during gestation compared with those from sows in the CON treatment. Similarly, a tendency for an increase in ADG on d 1 to 5 was found in piglets from sows supplemented with OEO during gestation compared with those from sows in the CON treatment (P = 0.10). Insulin-like growth factor-1 at birth and on d 7 and 14 of lactation did not differ among piglets from sows assigned to the different dietary treatments. Oregano essential oil supplementation of sow diets did not affect (P > 0.05) immunoglobulin concentrations in piglets after suckling. Supplementing sow diets with OEO during gestation or lactation did not affect (P > 0.05) the T lymphocytes, percentage of T-lymphocyte subpopulations, and natural killer cell activity of piglets during lactation. Supplementing sow diets with 250 mg/kg of OEO during gestation and lactation did not affect the growth potential of and immune responses in suckling piglets.

Identification of CD8+ cytotoxic T lymphocyte epitopes from porcine reproductive and respiratory syndrome virus matrix protein in BALB/c mice

Twenty-seven nanopeptides derived from the matrix (M) protein of porcine reproductive and respiratory syndrome virus (PRRSV) were screened for their ability to elicit a recall interferon-γ (IFN-γ) response from the splenocytes of BALB/c mice following DNA vaccination and a booster vaccination with recombinant vaccinia virus rWR-PRRSV-M. We identified two peptides (amino acid residues K₉₃FITSRCRL and F₅₇GYMTFVHF) as CD8⁺ cytotoxic T lymphocyte (CTL) epitopes. These peptides elicited significant numbers of IFN-γ secreting cells, compared with other M nonapeptides and one irrelevant nonapeptide. Bioinformatics analysis showed that the former is an H-2K^d-restricted CTL epitope, and the latter is an H-2D^d-restricted CTL epitope. Multiple amino acid sequence alignment among different PRRSV M sequences submitted to GenBank indicated that these two CTL epitopes are strongly conserved, and they should therefore be considered for further research on the mechanisms of cellular immune responses to PRRSV.

Systemic and mucosal immunity induced by attenuated Salmonella enterica serovar Typhimurium expressing ORF7 of porcine reproductive and respiratory syndrome virus

Oral administration of attenuated Salmonella vaccine may provide valuable advantages such as low cost, easy preparation, and safety. Attenuated Salmonella vaccines also serve as carriers of foreign antigens and immunomodulatory cytokines. Presently, an attenuated Salmonella enterica serovar Typhimurium strain was used as a carrier for open reading frame 7 (ORF7) protein of porcine reproductive and respiratory syndrome virus (PRRSV), a swine pathogen of significant global economic importance. Initially, an attenuated S. enterica serovar Typhimurium expressing ORF7 gene derived from PRRSV Korean isolate was constructed. Following oral administration of a single dose of the attenuated Salmonella vaccine expressing PRRSV ORF7, humoral and cell-mediated immune responses specific for ORF7 were induced at both systemic and mucosal sites including spleen, mesenteric lymph node, Peyer's patch, and laminar propria, as evaluated by determining serum ORF7-specific IgG and mucosal IgA responses, as well as Th1- and Th2-type cytokine production from antigen-stimulated T cells. The induced humoral responses were sustained for at least 12weeks post-immunization. In particular, the immunized mice displayed immune responses to both the foreign ORF7 antigen and Salmonella itself. The results indicate the value of attenuated S. enterica serovar Typhimurium as an oral carrier of PRRSV antigenic proteins to induce effective systemic and mucosal immunity.

Porcine reproductive and respiratory syndrome virus: an update on an emerging and re-emerging viral disease of swine

Recognized in the late 1980s in North America and Europe the syndrome that caused reproductive and respiratory problems in swine was initially called "mystery swine disease" and is now termed "porcine reproductive and respiratory syndrome (PRRS)". In the early 1990 s an arterivirus, referred to as PRRS virus (PRRSV), was determined to be the etiologic agent of this disease. Since then research has progressed substantially. Most recently "porcine high fever disease" was reported in China starting in 2006 with PRRSV being a critical virus associated with high morbidity and mortality (20%) associated with this syndrome which in 2010 is still causing severe pathology in pigs in China, with spread to Vietnam and Cambodia. This volume contains a series of reviews that highlight the virus, its pathogenesis, epidemiology, immunology, vaccinology and host genetic control. This paper provides a brief historical review of PRRS and the associated PRRSV. It presents areas of research gaps that inhibit current progress towards PRRS elimination through production of effective vaccines and current plans for PRRS elimination or eradication programs. It is hoped that this discussion will stimulate further collaboration between researchers and swine veterinarians throughout the world to provide answers that enhance our understanding of PRRS and PRRSV in an effort to eliminate this economically important disease.

Vectored vaccines to protect against PRRSV

PRRSV is the causative agent of the most important infectious disease affecting swine herds worldwide, producing great economic losses. Commercially available vaccines are only partially effective in protection against PRRSV. Moreover, modified live vaccines may allow virus shedding, and could revert generating virulent phenotypes. Therefore, new efficient vaccines are required. Vaccines based on recombinant virus genomes (virus vectored vaccines) against PRRSV could represent a safe alternative for the generation of modified live vaccines. In this paper, current vectored vaccines to protect against PRRSV are revised, including those based on pseudorabies virus, poxvirus, adenovirus, and virus replicons. Special attention has been provided to the use of transmissible gastroenteritis virus (TGEV) as vector for the expression of PRRSV antigens. This vector has the capability of expressing high levels of heterologous genes, is a potent interferon-α inducer, and presents antigens in mucosal surfaces, eliciting both secretory and systemic immunity. A TGEV derived vector (rTGEV) was generated, expressing PRRSV wild type or modified GP5 and M proteins, described as the main inducers of neutralizing antibodies and cellular immune response, respectively. Protection experiments showed that vaccinated animals developed a faster and stronger humoral immune response than the non-vaccinated ones. Partial protection in challenged animals was observed, as vaccinated pigs showed decreased lung damage when compared with the non-vaccinated ones. Nevertheless, the level of neutralizing antibodies was low, what may explain the limited protection observed. Several strategies are proposed to improve current rTGEV vectors expressing PRRSV antigens.

The immunogenicity of DNA constructs co-expressing GP5 and M proteins of porcine reproductive and respiratory syndrome virus conjugated by GPGP linker in pigs

The heterodimer of glycoprotein 5 (GP5) and non-glycosylated matrix protein (M) is the leading target for the development of new generation of vaccines against porcine reproductive and respiratory syndrome virus (PRRSV) infection. It has been demonstrated that DNA vaccine co-expressing GP5 and M proteins as a fusion protein aroused better immunogenicity than that expressing GP5 or M alone, but it was no better than the DNA vaccine co-expressing GP5 and M proteins with two different promoters. Altered natural conformation of the co-expressed GP5 and M fusion protein was considered as the major cause. Glycine-proline-glycine-proline (GPGP) linker can minimize the conformational changes in tertiary structure and provide flexibility of the peptide chain. The objective of this study was to evaluate whether the immunogenicity of DNA constructs co-expressing GP5 and M proteins linked by GPGP could be enhanced in pigs. Three recombinant DNA constructs expressing GP5/M fusion protein without GPGP linker (pcDNA-56), GP5/M fusion protein conjugated by GPGP linker (pcDNA-5L6), and M/GP5 fusion protein conjugated by GPGP linker (pcDNA-6L5) were established. Sixteen PRRSV-free pigs were randomly assigned to four groups and inoculated intramuscularly with 3 consecutive doses of 500 μg of empty vector pcDNA3.1, pcDNA-56, pcDNA-5L6 or pcDNA-6L5 each at a 2-week interval followed by challenge with 5 × 10(5) TCID(50) PRRSV at 3 weeks after the final inoculation. All pcDNA-56-, pcDNA-5L6-, and pcDNA-6L5- but not pcDNA-3.1-inoculated pigs developed neutralizing antibodies (NAs) 3 weeks after the final inoculation and a gradual increase in NA titers after PRRSV challenge, indicating that pigs inoculated with these DNA constructs could establish a sufficient immune memory. The pcDNA-5L6- and pcDNA-6L5-inoculated pigs displayed lower level and shorter period of viremia and lower tissue viral load following PRRSV challenge than did the pcDNA-56-inoculated pigs. The strategy of co-expressing GPGP-linked GP5 and M fusion protein may be a promising approach for future PRRSV vaccine development, possibly via the improvement of natural conformation of the target fusion protein.

Purification of porcine reproductive and respiratory syndrome virus from cell culture using ultrafiltration and heparin affinity chromatography

Porcine reproductive and respiratory syndrome (PRRS) virus is the causative agent of the most significant infectious disease currently affecting the swine industry worldwide. Density gradient ultracentrifugation remains the most commonly used method for porcine reproductive and respiratory syndrome virus (PRRSV) purification. However, this technique has notable drawbacks including long processing time and limited processing volume in each run. To overcome these limitations, a scalable process was developed. PRRSV propagated in MARC-145 was released by three freeze/thaw cycles. After a low speed centrifugation step, the virus particles in the supernatant were concentrated twice by an ultrafiltration step. The ultrafiltration step concentrated the virions effectively with no detectable loss while some cultural/cellular proteins were removed. The virions in the ultrafiltration retentate were then applied to a heparin affinity column on a fast performance liquid chromatography unit. The combined ultrafiltration and heparin affinity chromatography process removed more than 96% of cellular and medium proteins. During a stepwise elution strategy, the viral particles were eluted at two separate peaks recovering 27.5% and 25.4% of viral particles loaded onto the column with a purity of 194 and 3917 particles/microg protein, respectively.

Comparative measurement of cell-mediated immune responses of swine to the M and N proteins of porcine reproductive and respiratory syndrome virus

The principal objectives of this study were to develop autologous antigen-presenting cells (APCs) and to characterize the antigen-specific T-cell responses to the M and N proteins of porcine reproductive and respiratory syndrome virus (PRRSV) by using those APCs in outbred pigs. The orf6 and orf7 genes fused with porcine granulocyte-macrophage colony-stimulating factor (GM-CSF) were cloned into the mammalian expression vector to generate two plasmid DNAs, namely, pcDNA3.1-GM-CSF-PRRSV-M and pcDNA3.1-GM-CSF-PRRSV-N. Three of six pigs in two groups were repeatedly immunized with either plasmid DNA construct, and four pigs were used as controls. The recombinant M and N proteins fused with the protein transduction domain (PTD) of the human immunodeficiency virus type 1 transactivator of transcription protein were employed to generate major histocompatibility complex-matched autologous APCs from each pig. The levels of T-cell proliferation and gamma interferon (IFN-gamma) synthesis were compared between pigs immunized with the two plasmid DNAs after stimulation of the peripheral blood mononuclear cells (PBMCs) of each pig with the autologous antigen-presenting dendritic cells and PBMCs. Higher levels of T-cell proliferation and IFN-gamma synthesis were identified in PBMCs isolated from the pigs immunized with pcDNA3.1-GM-CSF-PRRSV-M than in those isolated from the pigs immunized with pcDNA3.1-GM-CSF-PRRSV-N. By way of contrast, serum antibodies were detected only in pigs immunized with pcDNA3.1-GM-CSF-PRRSV-N. However, no T-cell response or antibody production was detected in the control pigs. These results suggest that the M protein of PRRSV is a more potent T cell-stimulating antigen than the N protein. Nevertheless, it should be emphasized that the N protein substantially induces both cellular and humoral immune responses. The newly developed protocol for generating self APCs may prove effective in further efforts to characterize additional PRRSV proteins involved in the induction of cell-mediated immunity.

Challenges for porcine reproductive and respiratory syndrome virus (PRRSV) vaccinology

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be a threat for the pig industry. Vaccines have been developed, but these failed to provide sustainable disease control, in particular against genetically unrelated strains. Here we give an overview of current knowledge and gaps in our knowledge that may be relevant for the development of a future generation of more effective vaccines. PRRSV replicates in cells of the monocyte/macrophage lineage, induces apoptosis and necrosis, interferes with the induction of a proinflammatory response, only slowly induces a specific antiviral response, and may cause persistent infections. The virus appears to use several evasion strategies to circumvent both innate and acquired immunity, including interference with antigen presentation, antibody-mediated enhancement, reduced cell surface expression of viral proteins, and shielding of neutralizing epitopes. In particular the downregulation of type I interferon-alpha production appears to interfere with the induction of acquired immunity. Current vaccines are ineffective because they suffer both from the immune evasion strategies of the virus and the antigenic heterogeneity of field strains. Future vaccines therefore must "uncouple" the immune evasion and apoptogenic/necrotic properties of the virus from its immunogenic properties, and they should induce a broad immune response covering the plasticity of its major antigenic sites. Alternatively, the composition of the vaccine should be changed regularly to reflect presently and locally circulating strains. Preferably new vaccines should also allow discriminating infected from vaccinated pigs to support a virus elimination strategy. Challenges in vaccine development are the incompletely known mechanisms of immune evasion and immunity, lack of knowledge of viral sequences that are responsible for the pathogenic and immunosuppressive properties of the virus, lack of knowledge of the forces that drive antigenic heterogeneity and its consequences for immunogenicity, and a viral genome that is relatively intolerant for subtle changes at functional sites.

Enhanced immune responses of mice inoculated recombinant adenoviruses expressing GP5 by fusion with GP3 and/or GP4 of PRRS virus

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important causes of economic losses of the swine industry. PRRS virus (PRRSV) infection poses a challenge to current vaccination strategies. In this study, three replication-defective adenovirus recombinants expressing fusion protein GP3-GP5, GP4-GP5, or GP3-GP4-GP5 were developed as potential vaccine against PRRSV in a mouse model. Six groups of BALB/c mice (24mice per group) were inoculated subcutaneously twice at 2-week intervals with above mentioned recombinants and other adenoviruses expressing single GP3, GP4, or GP5 protein. The results showed that the mice inoculated with recombinant adenoviruses developed PRRSV-specific antibodies, cellular immune response by 2 weeks post-boost-immunization. However, mice immunized with recombinant adenoviruses rAd-GP3-GP5, rAd-GP4-GP5, and rAd-GP3-GP4-GP5 developed significantly higher titers of neutralizing antibodies to PRRSV and produced stronger lymphocyte proliferation responses compared to mice immunized with rAd-GP3, rAd-GP4 or rAd-GP5 alone. It was also found that mice immunized with rAd-GP3-GP5 and rAd-GP3-GP4-GP5 were primed for significant higher levels of anti-PRRSV CTL responses than mice immunized with rAd-GP3 and rAd-GP5. These findings suggested that the recombinant adenoviruses expressing fusion proteins GP3-GP5 or GP3-GP4-GP5 might be an attractive candidate vaccine for preventing PRRSV infection.

Passive transfer of maternal Mycoplasma hyopneumoniae-specific cellular immunity to piglets

Immunity in the neonatal animal is primarily maternally derived, either by lymphocytes that pass into the newborn across the placenta or following colostrum ingestion. However, the effect of this passively transferred cellular maternal immunity on the newborn's immune repertoire is not clearly understood. Various studies have shown that colostral lymphocytes are activated and possess functional abilities; however, no studies have shown the transfer of colostral antigen-specific T-cell-specific responses in a newborn. In this study we examined the transfer of vaccine-induced Mycoplasma hyopneumoniae cellular immunity from immune dams to newborn piglets. Newborn piglets from vaccinated and nonvaccinated dams were assessed in two ways for cellular immune responses specific to M. hyopneumoniae: (i) delayed-type hypersensitivity (DTH) testing and (ii) in vitro lymphocyte proliferation, assayed on piglet blood lymphocytes and sow colostral lymphocytes. DTH responses to M. hyopneumoniae were detected only for offspring of vaccinated sows, whereas DTH responses to the nonspecific mitogen phytohemagglutinin were seen for all piglets. M. hyopneumoniae-specific proliferation was seen for colostral lymphocytes from vaccinated sows and for blood lymphocytes from neonatal piglets of vaccinated dams but not for blood lymphocytes from piglets of nonvaccinated sows. Functional antigen-specific T cells were transferred to offspring from vaccinated sows and participated in the neonatal immune response upon stimulation. These data have implications for defining disease intervention strategies.

Purification of the major envelop protein GP5 of porcine reproductive and respiratory syndrome virus (PRRSV) from native virions

Porcine reproductive and respiratory syndrome virus (PRRSV) is the cause of an economically important swine disease that has been devastating the global swine industry since the early 1990s. The current PRRSV vaccines are not very effective largely due to heterogeneic nature of the virus. The major envelope protein, GP5, exposes outside the virion, induces neutralizing antibodies, and thus is a primary target for developing a subunit vaccine. In this study, we report a process for purification of GP5 protein from native virions of PRRSV propagated in MARC-145 cells. PRRSV virions were first purified and concentrated through sucrose cushion ultracentrifugation. GP5 protein was subsequently solubilized with Triton X-100 detergent for further processing. Cation exchange chromatography (CEX) was utilized for partial fractionation of GP5, although the viral nucleocapsid protein (N) was a major impurity in CEX elution fractions. During a second chromatographic step, hydrophobic interaction chromatography (HIC) further purified GP5 protein by means of a two-stage elution scheme. Pure GP5 protein was eluted from the HIC resin in the second HIC elution stage by Triton X-100 displacement; however the protein is present as a homodimeric/tetrameric aggregate. This process may be useful in PRRSV subunit vaccine development.

Co-expressing GP5 and M proteins under different promoters in recombinant modified vaccinia virus ankara (rMVA)-based vaccine vector enhanced the humoral and cellular immune responses of porcine reproductive and respiratory syndrome virus (PRRSV)

The porcine reproductive and respiratory syndrome virus (PRRSV) has three major structural proteins which designated as GP5, M, and N. Protein GP5 and M have been considered very important to arouse the humoral and cellular immune responses against PRRSV infection and proposed to be the excellent candidate proteins in the design of PRRS bioengineering vaccine. There were some attempts on expressing GP5 or M in DNA vaccine and adenovirus to arouse humoral and cellular immune responses, but few papers have been reported on that the immune response can be difference because of the expression patterns of GP5 and M proteins in the recombinant virus. In this article, four recombinant viruses that expressed GP5 and M proteins of PRRSV in the modified vaccinia virus ankara (MVA) with different expression patterns were made. In these recombinant virus (rMVAs), GP5 and M proteins were expressed in MVA in the same virus but under the control of two promoters (rMVA-GP5/M), or as a fusion protein under one promoter (rMVA-GP5-M), or separately (rMVA-GP5 and rMVA-M). The humoral and cellular immune responses for the four recombinant viruses were evaluated with mouse model. Every mouse was inoculated with 5 x 10(5) TCID50 of the different rMVAs and boosted 3 weeks later. Neutralizing antibody titers for each group were detected with virus neutralization test assay weekly after the primary inoculation for 13 weeks to evaluate the humoral immune response. The production of gamma interferon (IFN-gamma), interleukin-2 (IL-2), and interleukin-4 (IL-4) was detected in splenocytes of rMVA-inoculated mice at 30, 60, and 90 days post inoculation to evaluate the cellular immune response. Results showed that rMVA-GP5 and rMVA-M cannot induce obvious humoral and cellular immune responses; rMVA-GP5-M inoculated group developed better immune responses than rMVA-GP5 and rMVA-M inoculated groups; however, mice inoculated with rMVA-GP5/M maintained the strongest cellular response against PRRS and consistently enhanced the anti-PRRSV humoral responses. The strategy of co-expressing PRRSV GP5 and M protein in MVA under the control of different promoters might be an attractive method for future PRRSV vaccine design.

Influence of porcine reproductive and respiratory syndrome virus GP5 glycoprotein N-linked glycans on immune responses in mice

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically significant viral diseases in the swine industry. Infection with PRRSV following vaccination is common, since protection is incomplete. Persistent infection may be one of the biggest obstacles to control of the disease. "Glycan shielding" was postulated to be a primary mechanism to explain evasion from neutralizing immune response, ensuring in vivo persistence of virus, such as HIV, SIV, and HBV. The objective of this study was to construct recombinant adenoviruses expressing single or multiple N-linked glycosylation site (NGS) mutant GP5 of PRRSV, and evaluate the expression in cell culture, and potential to induce immune responses in BALB/c mice. Six recombinant adenoviruses were constructed each expressing wild-type GP5 and 1-4 NGS mutants: N44S, N44/51S, N30/44/51S, N30/33/44/51S and N30/33S. Inoculation of BALB/c mice with all five recombinants expressing NGS mutant GP5 resulted in a significant neutralizing antibody responses which were significantly higher than that of recombinant adenovirus expressing wild-type GP5. But there were no significant difference in lymphocyte proliferation responses induced by wild type and NGS mutant GP5. It indicated that glycosylations of GP5 at residues N30, N33, N44 and N51 are critical for induction of neutralizing antibodies. These NGS mutant PRRSV GP5 will be useful to characterize the effects of glycosylation on immunogenicity in the natural host, and may lead to a new approach for the generation of PRRSV vaccines.

Analysis of immunogenicity of minor envelope protein GP3 of porcine reproductive and respiratory syndrome virus in mice

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically significant viral diseases in swine industry. Though the minor envelope protein GP3 is associated with protective immunity, its immunogenicity and protective mechanism are poorly known. In this study, two recombinant adenoviruses, rAd-GP3 expressing complete GP3 and rAd-tGP3 expressing truncated GP3 in which aa2-64 were deleted, were constructed and the immunogenicity were tested in a mouse model. Four groups of BALB/c mice were immunized subcutaneously twice at 2-week internals with the recombinants rAd-GP3 and rAd-tGP3 or with wild type adenovirus (wtAd) and PBS as control. The results showed that the mice immunized with recombinant adenoviruses developed PRRSV-specific neutralizing antibodies and cellular immune response, including T-cell proliferation responses and cytotoxic T responses, by 2 weeks post-primary immunization. Moreover, the levels of immune responses of mice immunized with rAd-tGP3 were significantly higher than that of mice with rAd-GP3. It indicated that the first 64aa fragment of GP3 might affect the conformation of the antigen structures of GP3 protein. GP3 protein should be one of candidate molecules for developing a new safer effective vaccine.

The challenge of PRRS immunology

Porcine reproductive and respiratory syndrome (PRRS) is one of the most challenging subjects of research in veterinary viral immunology, and the immune response against PRRS virus (PRRSV) still is poorly understood. Infected pigs develop a strong and rapid humoral response but these initial antibodies do not confer protection and can even be harmful by mediating an antibody-dependent enhancement of disease. In contrast, development of neutralising antibodies (NAs) is delayed and generation of cell-mediated immune responses, such as PRRSV-specific interferon (IFN)-γ secreting cells, is initially erratic. In spite of this, induction of strong and rapid NAs and IFN-γ responses seem to be required for effective vaccination. PRRSV strongly modulates the host’s immune responses. The virus inhibits key cytokines, such as IFN-α, and may induce regulatory cytokines, such as interleukin (IL)-10. Development of NAs seems to be impaired by the existence of a decoy epitope close to the main neutralisation epitope in glycoprotein 5. This ability to modulate the host immune response probably varies among strains or isolates. The genetic diversity of the virus is very high and it has been shown that this diversity can have serious implications for the development of vaccines, since the immunity induced by one strain may be only partial against a different strain, even within the same genotype. With this panorama, the development of newer and universally efficacious PRRSV vaccines is challenging, but the present state of knowledge allows optimism if collaborative efforts are undertaken in the scientific community.

Morphine modulates gammadelta lymphocytes cytolytic activity following BCG vaccination

Chronic opioid administration modulates lymphocytes' functional capabilities increasing susceptibility to infectious diseases. Bacille-Calmette-Guérin (BCG) vaccination initiates a non-specific and specific cell-mediated immunity orchestrated by T lymphocytes including gammadelta T lymphocytes. gammadelta T lymphocytes increase in natural killer and antigen-directed cytolytic response following BCG vaccination. The objective of this study was to determine morphine effects on gammadelta T lymphocytes' cytolytic activity. Pigs were chronically administered morphine and subsequently vaccinated with Mycobacterium bovis BCG. By administering morphine prior to BCG vaccination, natural killer response was significantly suppressed (p=.034). Furthermore, innate cytolytic response against M. bovis-infected monocytes (p=.002) as well as antigen specific cytolytic functions (p=.04) were significantly altered due to morphine administration. It was concluded that administering morphine prior to BCG vaccination significantly altered gammadelta T lymphocyte cytolytic responses.

Construction of a multiprobe for the simultaneous detection of viroids infecting citrus trees

Infections with different viroid species are common among cultivated fruit trees and grapevines, and many old-clone citrus varieties contain up to five citrus viroids (CVds) within a single tree. This paper describes the construction of a CVd-Multiprobe consisting of full-length clones of Hop stunt viroid, Citrus exocortis viroid, Citrus bent leaf viroid and CVd-III. The CVd-Multiprobe was tested against RNA transcripts of the four viroids and RNA extracts from plants singly infected with CEVd or HSVd or multiply infected with different CVds. The viroids were effectively diagnosed with the DIG labeled CVd-Multiprobe when tested by Northern hybridization or dot blot analyses. The CVd-Multiprobe does not provide information on the specific viroid resulting in a positive signal. However, this should not be considered as a problem, since most citrus certification programs will discard budwood source trees infected with any of the known CVds.