Alternative codon usage of PRRS virus ORF5 gene increases eucaryotic expression of GP5 glycoprotein and improves immune response in challenged pigs

Evolutionary Patterns of Codon Usage in Major Lineages of Porcine Reproductive and Respiratory Syndrome Virus in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is economically important and characterized by its extensive variation. The codon usage patterns and their influence on viral evolution and host adaptation among different PRRSV strains remain largely unknown. Here, the codon usage of ORF5 genes from lineages 1, 3, 5, and 8, and MLV strains of type 2 PRRSV in China was analyzed. A compositional property analysis of ORF5 genes revealed that nucleotide C is most frequently used at the third position of codons, accompanied by rich GC3s. The effective number of codon (ENC) and codon pair bias (CPB) values indicate that all ORF5 genes have low codon bias and the differences in CPB scores among four lineages are almost not significant. When compared with host codon usage patterns, lineage 1 strains show higher CAI and SiD values, with a high similarity to pig, which might relate to its predominant epidemic propensity in the field. The CAI, RCDI, and SiD values of ORF5 genes from different passages of MLV JXA1R indicate no relation between attenuation and CPB or codon adaptation decrease during serial passage on non-host cells. These findings provide a novel way of understanding the PRRSV's evolution, related to viral survival, host adaptation, and virulence.

Plant synthetic GP4 and GP5 proteins from porcine reproductive and respiratory syndrome virus elicit immune responses in pigs

MAIN CONCLUSION

We demonstrated successful overexpression of porcine reproductive and respiratory syndrome virus (PRRSV)-derived GP4D and GP5D antigenic proteins in Arabidopsis. Pigs immunized with transgenic plants expressing GP4D and GP5D proteins generated both humoral and cellular immune responses to PRRSV. Porcine reproductive and respiratory syndrome virus (PRRSV) causes PRRS, the most economically significant disease affecting the swine industry worldwide. However, current commercial PRRSV vaccines (killed virus or modified live vaccines) show poor efficacy and safety due to concerns such as reversion of virus to wild type and lack of cross protection. To overcome these problems, plants are considered a promising alternative to conventional platforms and as a vehicle for large-scale production of recombinant proteins. Here, we demonstrate successful production of recombinant protein vaccine by expressing codon-optimized and transmembrane-deleted recombinant glycoproteins (GP4D and GP5D) from PRRSV in planta. We generated transgenic Arabidopsis plants expressing GP4D and GP5D proteins as candidate antigens. To examine immunogenicity, pigs were fed transgenic Arabidopsis leaves expressing the GP4D and GP5D antigens (three times at 2-week intervals) and then challenged with PRRSV at 6-week post-initial treatment. Immunized pigs showed significantly lower lung lesion scores and reduced viremia and viral loads in the lung than pigs fed Arabidopsis leaves expressing mYFP (control). Immunized pigs also had higher titers of PRRSV-specific antibodies and significantly higher levels of pro-inflammatory cytokines (TNF-α and IL-12). Furthermore, the numbers of IFN-γ+-producing cells were higher, and those of regulatory T cells were lower, in GP4D and GP5D immunized pigs than in control pigs. Thus, plant-derived GP4D and GP5D proteins provide an alternative platform for producing an effective subunit vaccine against PRRSV.

Recombinant Encephalomyocarditis Viruses Elicit Neutralizing Antibodies against PRRSV and CSFV in Mice

Encephalomyocarditis virus (EMCV) is capable of infecting a wide range of species and the infection can cause myocarditis and reproductive failure in pigs as well as febrile illness in human beings. In this study, we introduced the entire ORF5 of the porcine reproductive and respiratory syndrome virus (PRRSV) or the neutralization epitope regions in the E2 gene of the classical swine fever virus (CSFV), into the genome of a stably attenuated EMCV strain, T1100I. The resultant viable recombinant viruses, CvBJC3m/I-ΔGP5 and CvBJC3m/I-E2, respectively expressed partial PRRSV envelope protein GP5 or CSFV neutralization epitope A1A2 along with EMCV proteins. These heterologous proteins fused to the N-terminal of the nonstructural leader protein could be recognized by anti-GP5 or anti-E2 antibody. We also tested the immunogenicity of these fusion proteins by immunizing BALB/c mice with the recombinant viruses. The immunized animals elicited neutralizing antibodies against PRRSV and CSFV. Our results suggest that EMCV can be engineered as an expression vector and serve as a tool in the development of novel live vaccines in various animal species.

Exploration of New Sites in Adenovirus Hexon for Foreign Peptides Insertion

Adenoviral vectors are now being explored as vaccine carriers to prevent infectious diseases in humans and animals. There are two strategies aimed at the expression of a vaccine antigen by adenoviral vectors. The first includes an insertion of the foreign gene expression cassette into the E1 region. The second strategy is antigen incorporation into the viral capsid proteins. To extend this methodology, we have searched for new sites at the human adenovirus serotype 5 major capsid protein hexon for a vaccine antigen insertion. To this end, we utilized sites in the hexon hypervariable region (HVR) 7, 8 and 9 to display a 15-mer peptide containing the main neutralizing epitope of porcine reproductive and respiratory syndrome virus. However, we could not rescue the viruses with the insertions of the peptide into HVR 8 and 9, consistent with the viruses being unable to tolerate insertions at these sites. In contrast, the virus with the insertion of the peptide in HVR 7 was viable - growing well in cell culture and the inserted peptide was exposed on the virion surface.

The Cholera Toxin B Subunit (CTB) Fused to the Porcine Arterivirus Matrix M and GP5 Envelope Proteins Fails to Enhance the GP5-Specific Antibody Response in Pigs Immunized with Adenovectors

The porcine reproductive and respiratory syndrome virus (PRRSV) is an arterivirus of the Arteriviridae family. As the current commercial vaccines are incompletely protective effective against PRRSV infection, we developed a vaccine strategy using replicating but non-disseminating adenovectors (rAdVs) expressing the PRRSV M matrix protein in fusion with the neutralizing major epitope-carrying GP5 envelope protein (Roques et al. in Vet Res 44:17, 2013). Although production of GP5-specific antibodies (Abs) was observed, no PRRSV-specific neutralizing Abs (NAbs) were induced in pigs given the rAdVs expressing M-GP5 or M-GP5m (GP5m being a mutant form of GP5). Nevertheless, partial protection was observed in the M-GP5m-rAdV-inoculated pigs experimentally infected with PRRSV. Here, we determined the impact of the cholera toxin B subunit (CTB, known for its adjuvant effect) in fusion with the C-terminus of M-GP5m on the Ab response to PRRSV. Three-week-old pigs were immunized twice both intramuscularly and intranasally at 3-week intervals with rAdV-expressing the green fluorescent protein (rAdV-GFP), rAdV-M-GP5m, or rAdV-M-GP5m-CTB. Pigs immunized with rAdV-M-GP5m showed a high level of serum GP5-specific Abs (as determined by an indirect ELISA). In contrast, CTB in fusion with M-GP5m had an unexpected severe negative impact on GP5-specific Ab production. PRRSV-specific NAbs could not be detected in any pigs of all groups.

Actinobacillus pleuropneumoniae possesses an antiviral activity against porcine reproductive and respiratory syndrome virus

Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. This phenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) and porcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The main objective of this project was to study the in vitro interactions between these two pathogens and the host cells in the context of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolar macrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed by an infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV pre-infection did not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicity effect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPL and PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviral activity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (<1 kDa). The antiviral activity was also observed in SJPL cells infected with swine influenza virus but to a much lower extent compared to PRRSV. More importantly, the PRRSV antiviral activity of App was also seen with PAM, the cells targeted by the virus in vivo during infection in pigs. The antiviral activity might be due, at least in part, to the production of interferon γ. The use of in vitro experimental models to study viral and bacterial co-infections will lead to a better understanding of the interactions between pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools.

Protective humoral immune response induced by an inactivated porcine reproductive and respiratory syndrome virus expressing the hypo-glycosylated glycoprotein 5

Porcine reproductive and respiratory syndrome (PRRS) causes significant economic losses to the swine industry worldwide. Although inactivated and live vaccines are commercially available for the control of PRRS, both types of vaccine have not always proven successful in terms of generating a protective immune response, particularly in the case of inactivated vaccines. In this study, we tested whether an inactivated vaccine could induce a humoral immune response to PRRS during a homologous challenge. Amino acid substitutions were introduced into glycoprotein (GP) 5 of the FL12 strain of the PRRS virus (PRRSV) using site-directed mutagenesis with a pFL12 infectious clone. The substitutions led to double deglycosylation in the putative glycosylation moieties on GP5. The mutant virus was subsequently inactivated with binary ethylenimine. The efficacy of the inactivated mutant virus was compared with that of the inactivated wild-type PRRSV. Only the inactivated mutant PRRSV induced serum neutralizing antibodies at six weeks post-vaccination. The group that was administered the inactivated mutant virus twice exhibited a significantly increased neutralizing antibody titer after a challenge with the virulent homologous strain and exhibited more rapid clearing of viremia compared to other groups, including the groups that were administered either the inactivated mutant or wild-type virus only once and the group that was administered the inactivated wild-type virus twice. Histopathological examination of lung tissue sections revealed that the group that was administered the inactivated mutant virus twice exhibited significantly thinner alveolar septa, whereas the thickness of the alveolar septa of the other groups were markedly increased due to lymphocyte infiltration. These results indicated that the deglycosylation of GP5 enhanced the immunogenicity of the inactivated mutant PRRSV and that twice administrations of the inactivated mutant virus conferred better protection against the homologous challenge. These findings suggest that the inactivated PRRSV that expresses a hypo-glycosylated GP5 is a potential inactivated vaccine candidate and a valuable tool for controlling PRRS for the swine industry.

Construction and immunogenicity of DNA vaccines encoding fusion protein of porcine IFN- λ 1 and GP5 gene of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has been mainly responsible for the catastrophic economic losses in pig industry worldwide. The commercial vaccines only provide a limited protection against PRRSV infection. Thus, the focus and direction is to develop safer and more effective vaccines in the research field of PRRS. The immune modulators are being considered to enhance the effectiveness of PRRSV vaccines. IFN-λ1 belongs to type III interferon, a new interferon family. IFN-λ1 is an important cytokine with multiple functions in innate and acquired immunity. In this study, porcine IFN-λ1 (PoIFN-λ1) was evaluated for its adjuvant effects on the immunity of a DNA vaccine carrying the GP5 gene of PRRSV. Groups of mice were immunized twice at 2-week interval with 100 μg of the plasmid DNA vaccine pcDNA3.1-SynORF5, pcDNA3.1-PoIFN-λ1-SynORF5, and the blank vector pcDNA3.1, respectively. The results showed that pcDNA3.1-PoIFN-λ1-SynORF5 can significantly enhance GP5-specific ELISA antibody, PRRSV-specific neutralizing antibody, IFN-γ level, and lymphocyte proliferation rather than the responses induced by pcDNA3.1-SynORF5. Therefore, type III interferon PoIFN-λ1 could enhance the immune responses of DNA vaccine of PRRSV, highlighting the potential value of PoIFN-λ1 as a molecular adjuvant in the prevention of PRRSV infection.

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.

A transgenic Marc-145 cell line of piggyBac transposon-derived targeting shRNA interference against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is now considered to be one of the most important diseases in countries with intensive swine industries. The two major membrane-associated proteins of porcine reproductive and respiratory syndrome virus (PRRSV), GP5 and M (encoded by ORF5 and ORF6 genes, respectively), are associated as disulfide-linked heterodimers (GP5/M) in the virus particle. In this study, we designed 5 of the small hairpin RNAs (shRNAs) targeting the GP5 and M gene of PRRSV respectively, and investigated their inhibition to the production of PRRSV. The highest activity displayed in shRNAs of the ORF6e sequence (nts 261-279), which the inhibition rate reached was 99.09%. The result suggests that RNAi technology might serve as a potential molecular strategy for PRRSV therapy. Furthermore, the transgenic Marc-145 cell line of piggyBac transposon-derived targeting shRNA interference against PRRS virus was established. It presented stable inhibition to the replication and amplification of PRRS. The work implied that shRNAs targeting the GP5 and M gene of PRRSV may be used as potential RNA vaccines in vivo, and supplied the screening methods of transformed pig embryonic fibroblast which are prerequisite for the disease-resistant transgenic pigs to PRRS.

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.

Construction and immunogenicity of DNA vaccines encoding fusion protein of murine complement C3d-p28 and GP5 gene of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has recently caused catastrophic losses in swine industry worldwide. The commercial vaccines only provide a limited protection against PRRSV infection. At present, DNA vaccine is the focus on the new vaccines. The gene fragment (p28) coding for the molecular adjuvants complement protein C3d (mC3d) from BALB/c mouse was cloned and expressed as a fusion protein for its application in the vaccine study of mice. Three potential vaccines construct units were engineered to contain two, four and six copies of mC3d-p28 coding gene linked to the GP5 gene of PRRSV and one vaccine expressing GP5 alone (pcDNA3.1-GP5) was constructed. Subsequently, the vaccines' abilities to elicit the humoral and cellular immune responses were investigated in mice. These results showed that significantly enhanced GP5-specific ELISA antibody, GP5-specific neutralizing antibody, IFN-γ level, and IL-4 level, could be induced in mice immunized with DNA construct units encoding the pcDNA3.1-C3d-p28.n-GP5 than those received DNA vaccine expressing GP5 alone (pcDNA3.1-GP5). Analysis of the immunogenicity of different repeats of mC3d-p28 revealed that mC3d-p28 had an enhancing effect on the immunogenicity of antigens, and that six or more repeats of mC3d-p28 may be necessary for efficient enhancement of antigen specific immune responses. This approach may provide a new strategy for the development of efficient vaccines against the PRRSV for pigs in the future.

The role of porcine reproductive and respiratory syndrome (PRRS) virus structural and non-structural proteins in virus pathogenesis

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating viral disease affecting the swine industry worldwide. The etiological agent, PRRS virus (PRRSV), possesses a RNA viral genome with nine open reading frames (ORFs). The ORF1a and ORF1b replicase-associated genes encode the polyproteins pp1a and pp1ab, respectively. The pp1a is processed in nine non-structural proteins (nsps): nsp1α, nsp1β, and nsp2 to nsp8. Proteolytic cleavage of pp1ab generates products nsp9 to nsp12. The proteolytic pp1a cleavage products process and cleave pp1a and pp1ab into nsp products. The nsp9 to nsp12 are involved in virus genome transcription and replication. The 3′ end of the viral genome encodes four minor and three major structural proteins. The GP2a, GP3and GP4(encoded by ORF2a, 3 and 4), are glycosylated membrane associated minor structural proteins. The fourth minor structural protein, the E protein (encoded by ORF2b), is an unglycosylated membrane associated protein. The viral envelope contains two major structural proteins: a glycosylated major envelope protein GP5(encoded by ORF5) and an unglycosylated membrane M protein (encoded by ORF6). The third major structural protein is the nucleocapsid N protein (encoded by ORF7). All PRRSV non-structural and structural proteins are essential for virus replication, and PRRSV infectivity is relatively intolerant to subtle changes within the structural proteins. PRRSV virulence is multigenic and resides in both the non-structural and structural viral proteins. This review discusses the molecular characteristics, biological and immunological functions of the PRRSV structural and nsps and their involvement in the virus pathogenesis.

Immunogenicity of the highly pathogenic porcine reproductive and respiratory syndrome virus GP5 protein encoded by a synthetic ORF5 gene

Since May 2006, a highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV), which causes continuous high fever and a high proportion of deaths in vaccinated pigs of all ages, has emerged and prevailed in Mainland China. Huge efforts should be made towards the development of an efficient vaccine against the highly pathogenic PRRSV. Although the ORF5-encoded GP5 is the most important immunogenic protein, accumulating evidences have demonstrated that incomplete protection conferred by GP5-based vaccines. The inability to induce robust protective immunity has been postulated to be associated with the presence of a non-neutralizing decoy epitope and heavy glycosylation in close to its neutralizing epitope. In this study, a synthetic ORF5 gene (SynORF5) was engineered with the codon usage optimized for mammalian cell expression based on the native ORF5 gene of highly pathogenic PRRSV strain WUH3. Additional modifications, i.e., inserting a Pan DR T-helper cell epitope (PADRE) between the neutralizing epitope and the non-neutralizing decoy epitope, and mutating four potential N-glycosylation sites (N30, N34, N35 and N51) were also included in the synthetic ORF5 gene. The immunogenicity of the SynORF5-encoded GP5 was evaluated by DNA vaccination in mice and piglets. Results showed that significantly enhanced GP5-specific ELISA antibody, PRRSV-specific neutralizing antibody, IFN-gamma level, as well as lymphocyte proliferation response, could be induced in mice and piglets immunized with DNA construct encoding the modified GP5 than those received DNA vaccine expressing the native GP5. The enhanced immunogenicity of the modified GP5 will be useful to facilitate the development of efficient vaccines against the highly pathogenic PRRSV in the future.

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.

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.

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.

Recombinant adenovirus expressing GP5 and M fusion proteins of porcine reproductive and respiratory syndrome virus induce both humoral and cell-mediated immune responses in mice

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important contagious agents of swine in the world. PRRSV infection poses a challenge to current vaccination strategies. In this study, three replication-defective adenovirus recombinants were developed as potential vaccine against PRRSV in a mouse model. Three groups of BALB/c mice (24 mice per group) were inoculated subcutaneously twice at 2-week intervals with the recombinants expressing PRRSV GP5 (rAd-GP5), M (rAd-M), and M-GP5 fusion protein (rAd-M-GP5). Two additional groups were injected with wild-type adenovirus (wtAd) or PBS as control. The results showed that the mice inoculated with recombinant adenoviruses developed PRRSV-specific antibodies, cellular immune response by 2 weeks post second inoculation. However, only mice immunized with recombinant adenovirus rAd-M-GP5 developed significantly higher titers of neutralizing antibodies to PRRSV and produced stronger lymphocyte proliferation responses compared to mice immunized with rAd-M or rAd-GP5 alone. It was also found that mice immunized with rAd-M-GP5 were primed for significant higher levels of anti-PRRSV CTL responses than mice immunized with rAd-M. Mice receiving rAd-GP5 also mounted PRRSV-specific response, but levels were lower. It suggested that the recombinant adenovirus expressing M-GP5 fusion protein might be an attractive candidate vaccine to be tested for preventing PRRSV infection.

Evolution of ORF5 of Spanish porcine reproductive and respiratory syndrome virus strains from 1991 to 2005

ORF5 sequences of porcine reproductive and respiratory syndrome virus (PRRSV) were analysed to determine genetic diversity, codon usage, positive and negative selection sites and potential changes in the predicted glycoprotein 5 (GP5). A hypothetical GP5 containing all selected sites was constructed to determine its characteristics. These sequences corresponded to isolates obtained 10 years apart (1991–1995, 18 strains) and a second set (n = 46) from 2000 to 2005. Similarity to Lelystad virus (LV) decreased from 95.5% in 1991–1995 to 89.5% in 2000–2005. Three highly variable regions were found in ORF5. Codon usage was different in both sets for leucine, glutamine, serine and proline. Thus, 2000–2005 sequences used codons more similar to those present in highly expressed pig genes compared to the 1991–1995 set. Twenty four sites of positive selection and 20 sites of negative selection were found in GP5, most of them in transmembrane regions. Additional glycosylation in N37 of GP5 was common in 2000–2005 but some sequences lack a glycosylation site in N46. The hypothetical GP5 was only 88.1% similar to LV and was less hydrophobic. Taking together these results suggest that PRRSV is still adapting to pig cells.