Fc gamma RII-dependent sensitisation of natural interferon-producing cells for viral infection and interferon-alpha responses

Natural interferon-producing cells (NIPC), also called plasmacytoid dendritic cells, are the most potent producers of IFN-alpha in response to viral and bacterial components, serving an important function in innate immune defences. The present work demonstrates that NIPC responsiveness can be primed by immunisation, increasing their capacity to produce IFN-alpha after viral infection. NIPC isolated from pigs immunised against classical swine fever virus (CSFV), a member of the Flaviviridae, were more receptive to viral infection and produced higher levels of IFN-alpha than NIPC from immunologically naive animals. This sensitisation of NIPC was maintained for at least 8 months after immunisation. IFN-alpha production was dependent on live virus and required replication, and the "immune" NIPC responded to lower infectious doses of virus. Co-localisation of the virus with Fc(gamma)RII (CD32) in polarised structures was observed with "immune" NIPC only. This Fc(gamma)RII-dependent virus capture and sensitisation of NIPC, evidently mediated through cytophilic CSFV-specific antibodies, was inhibited by non-specifically aggregated immunoglobulin as well as by pre-formed virus-antibody complexes. In conclusion, these results demonstrate that NIPC not only represent a major player in innate immunity but are also functionally linked to the immunological memory of the adaptive immune system.

Identification of classical swine fever virus protein E2 as a target for cytotoxic T cells by using mRNA-transfected antigen-presenting cells

Vaccination of pigs against Classical swine fever virus (CSFV) by using live-virus vaccines induces early protection before detectable humoral immune responses. Immunological analyses indicate that this is associated with T-cell activation, underlining the importance of targeting cytotoxic T-lymphocyte (CTL) responses for vaccine improvement. Antigen-presenting cells (APCs) transfected with mRNA encoding structural protein E2 or non-structural viral proteins NS3-NS4A were used to identify viral genes encoding CTL epitopes. Monocyte-derived dendritic cells (DCs) and fibrocytes served as the APCs. In vitro translation of the mRNA and microscopic analysis of transfected cells demonstrated that E2 and NS3-NS4A could be identified. APCs transfected with either of the mRNA molecules restimulated CSFV-specific T cells to produce gamma interferon and specific cytotoxic activity against CSFV-infected target cells. The presence of CTL epitopes on E2 was confirmed by using d/d-haplotype MAX cells expressing E2 constitutively as target cells in d/d-haplotype CTL assays. A potent CTL activity against E2 was detected early (1-3 weeks) after CSFV challenge. This work corroborates the existence of CTL epitopes within the non-structural protein domain NS3-NS4A of CSFV. Furthermore, epitopes on the E2 protein can also now be classified as targets for CTLs, having important implications for vaccine design, especially subunit vaccines. As for the use of mRNA-transfected APCs, this represents a simple and efficient method to identify viral genes encoding CTL epitopes in outbred populations.

Susceptibility of in vivo- and in vitro-produced porcine embryos to classical swine fever virus

The objective of this study was to investigate the susceptibility of in vivo- and in vitro-produced (IVP) porcine embryos to classical swine fever virus (CSFV). IVP zona pellucida (ZP)-intact porcine embryos (n = 721) were co-cultured with CSFV for 120 h. After washing according to the International Embryo Transfer Society guidelines (without trypsin) and transferring embryos to CSFV-susceptible porcine kidney cells (PK15 cell line), no virus was isolated. However, when 88 IVP ZP-intact porcine embryos were co-cultured with CSFV for only 48 h before being transferred to PK15 cells, virus was isolated in three of six replicates. Similarly, 603 in vivo-produced porcine embryos were co-cultured with CSFV for 120 h. Subsequently, CSFV was isolated in eight of 50 groups (16%) and the ability of these to form a blastocyst was significantly reduced when compared with the control group (68.2 +/- 19.9% vs 81.9 +/- 9.7%; p < or = 0.001). In contrast, the development of CSFV-exposed IVP porcine embryos was not affected when compared with control embryos (19.1 +/- 10.8% vs 18.9 +/- 10.6%; p > or = 0.05). After removal of the ZP of IVP embryos and subsequent co-culture with CSFV, the virus was isolated from all groups of embryos. These data suggest that virus replication had occurred in the embryonic cells. In conclusion, data indicate that in vivo- and in vitro-produced ZP-intact porcine embryos differ in their susceptibility to CSFV. Hatched or micro-manipulated embryos may increase the risk of transmission of CSFV by embryo transfer, which has to be confirmed by in vivo tests under isolation conditions.

Estimating the probability of freedom of classical swine fever virus of the East-Belgium wild-boar population

A report of the Scientific Committee on Animal Health and Animal Welfare of the European Commission (CEC, 1999.) includes recommendations for setting up monitoring programmes for classical swine fever (CSF) infection in a wild-boar population, based on the assumption that one would detect at least 5% prevalence in a CSF-infected wild-boar population. This assumption, however, is not science based. We propose an alternative method to provide evidence for a wild-boar population being free of CSF and evaluate the efficiency of a surveillance programme that was implemented in Belgium in 1998. In our study, the probability of freedom of CSF-virus was estimated based on 789 samples; these were collected from wild-boars within the surveillance programme (within the three provinces which include 95% of the Belgian wild-boar population) and examined by three diagnostics methods (antibody detection, virus detection and virus RNA detection). A Bayesian framework was used for the estimation, accounting for the diagnostic test characteristics without the assumption of the presence of a gold standard. The median probability of freedom of CSF-virus was estimated at 0.970, with a 95% credibility interval of 0.149-1.000. Independent on the choice of the prior information, the posterior distributions for the probability of freedom of CSF-virus were always skewed close to the upper boundary of 1. This represents a big gain of knowledge since we did not use any prior information for the probability of freedom of CSF-virus and took the uncertainty about the accuracy of the diagnostic methods into account.

Characterization of epitopes for neutralizing monoclonal antibodies to classical swine fever virus E2 and Erns using phage-displayed random peptide library

Infection of cells with classical swine fever virus (CSFV) is mediated by the interaction of envelope glycoproteins E2 and Erns with receptor molecules on the cell surface. These proteins are also the major antigens for eliciting neutralizing antibodies and conferring protective immunity. Here we report the identification of multiple neutralizing epitopes on these proteins by screening a phage-displayed random peptide library with CSFV-specific neutralizing monoclonal antibodies. Two different E2-specific neutralizing mAbs (a18 and 24/10) were found to bind to a common motif SPTxL, which is similar to the sequence SPTTL of the E2 protein (aa 289-293), indicating that this is likely to be an immunodominant epitope. Similarly, an immunodominant epitope corresponding to the sequence DKN of Erns (aa 117-119) was identified for two independent Erns-specific neutralizing antibodies, b4-22 and 24/16, respectively. Another binding motif, CxNNxTC, was identified for mAb 24/16, but not for b4-22. Sequencing analysis of the genes coding for the light chain of these mAbs was conducted to ensure that all mAbs were derived from different hybridomas, rather than from different subclones of a common parent line. Inhibition studies using immunofluorescent antibody assay and virus neutralization test demonstrated that the mimotope peptides truly mimicked the antibody binding determinants on the viral proteins. The detailed mapping data for these neutralizing epitopes will be useful for development of improved diagnostic tests and perhaps a peptide-based vaccine for this important swine disease.

Immunomodulatory effect of plasmids co-expressing cytokines in classical swine fever virus subunit gp55/E2-DNA vaccination

The aim of this study was to determine the immunomodulatory effects of IL-12, IL-18 and CD154 (CD40 ligand, CD40L) in DNA-vaccination against the classical swine fever virus. Four recombinant plasmids were constructed including the CSFV coding region for the glycoprotein gp55/E2 alone or together with porcine IL-12, IL-18 or CD154 genes. Five groups of four pigs each were immunized intramuscularly (i.m.) three times with the respective constructs. The control group was inoculated with empty plasmid DNA. Eighteen days after the final immunization, the pigs were challenged with a lethal dose of CSFV strain Eystrup and monitored for a further 16 days. This study showed that co-delivery of IL-18 and CD154 induced an earlier appearance of serum antibodies, reduced B-cell deficiency after infection and protected pigs against a lethal CSFV infection. In contrast, co-delivery of IL-12 led to a reduced titer of neutralizing antibodies and protection against a lethal CSFV challenge in comparison to the other pigs and to pigs that were immunized with a gp55/E2 plasmid alone.

Porcine adenovirus as a delivery system for swine vaccines and immunotherapeutics

Porcine adenovirus (PAdV) has many qualities which make it an ideal choice for use as a delivery vector in swine. It is a low grade pathogen, present almost world-wide in a number of serotypes varying in their virulence and tissue tropism, which may allow for serotype specific vaccine targeting. PAdV is species specific having only been isolated from swine, reducing the possibility of its spread to other animals or man following administration. When engineered to contain a foreign gene, recombinant PAdV (rPAdV) can be grown to high titres in tissue culture cells making it cheap to produce. Knowledge of the complete nucleotide sequence of the PAdV genome has enabled rationally directed insertions of foreign genes which remain stably inserted in the genome and can be expressed at high levels following delivery to the target host. Importantly, recombinant PAdV can be administered by injection or by the oral route in feed or drinking water. We have delivered a range of antigens and immunomodulatory molecules to commercially available pigs using rPAdV and found it to be a very effective delivery system. Significantly, recombinant PAdV serotype 3 is highly effective as a delivery vehicle even when administered in the face of high levels of artificially induced serotype specific neutralising antibody to the vector.

Oronasal vaccination with classical swine fever virus (CSFV) replicon particles with either partial or complete deletion of the E2 gene induces partial protection against lethal challenge with highly virulent CSFV

A cDNA clone of the classical swine fever virus (CSFV) strain Alfort/187 [Ruggli N, Tratschin JD, Mittelholzer C, Hofmann MA. Nucleotide sequence of classical swine fever virus strain Alfort/187 and transcription of infectious RNA from stably cloned full-length cDNA. J Virol 1996;70(6):3478-87] was used to construct two E2 deletion mutants lacking either the complete E2 gene or, alternatively, a stretch of 204 nucleotides encoding 68 amino acids located in the C-terminal region of the E2 glycoprotein. The respective in vitro synthesized mutant RNAs replicated in SK-6 cells but no infectious virus was generated. Both replicons could be packaged into virus particles in SK-6 cells constitutively expressing E2 of CSFV. For the resulting CSF virus replicon particles (CSF-VRP) A187-E2del373 and A187-E2del68 titers of 10(6) and 10(7) TCID(50)/ml, respectively, were obtained. Oronasal vaccination with 10(7) TCID(50) of either of the two CSF-VRP protected pigs against a challenge with a lethal dose of CSFV strain Eystrup. In contrast, after intradermal vaccination VRP A187-E2del68 but not VRP A187-E2del373 lacking the complete E2 gene induced a protective immune response. We conclude that E2-complemented CSF-VRP have the potential to be used as live-attenuated non-transmissible oral vaccines for pigs. In addition, our data suggest that E2 of CSFV is dispensable for the induction of mucosal but not of parenteral immunity.

A DNA vaccine expressing the E2 protein of classical swine fever virus elicits T cell responses that can prime for rapid antibody production and confer total protection upon viral challenge

Immunization of domestic pigs with a DNA vaccine expressing the complete E2 protein of classical swine fever virus (CSFV) conferred total protection against a severe viral challenge. Immunization with three doses of plasmid pcDNA3.1/E2 elicited a consistent and specific, MHC class II restricted T cell response in the three domestic pigs analyzed, in the absence of detectable anti-CSFV antibodies in serum. Upon challenge specific T cell responses were boosted in the three vaccinated pigs, and a rapid rise in the titers of CSFV neutralizing antibodies was noticed in two of them, which correlated with a total protection. In these two pigs, neither disease symptoms were observed nor was virus detected at any time after CSFV infection. Neutralizing antibody titers were lower in the third vaccine, which developed a mild and transient peak of pyrexia. As expected, similar analyses in three control pigs (injected with the empty vector or PBS) did not reveal the induction of specific T cells or viral antibodies and, upon challenge, animals developed severe symptoms of the disease, including high titers of viremia, hyperthermia and virus spread to different organs. Control pigs developed, also, a marked leucopenia, resulting in SWC3+ (myelomonocytic cells) being the major PBMC population, and a drastic decrease CD3+ T cells. This T cell depletion was prevented in animals immunized with pcDNA3.1/E2. The total protection achieved, in the absence of CSFV antibodies before challenge, supports the relevance in the antiviral response observed of specific T cell responses primed by pcDNA3.1/E2 vaccine, which, upon challenge, led to a rapid induction of neutralizing antibodies. The observation that CSFV antibodies could only be detected in protected animals after viral challenge opens the possibility of exploring the potential of the DNA vaccine approach used to develop marker vaccines against CSF.

[Evaluation on the biosafety of classical swine fever DNA vaccine]

The biosafety of DNA vaccine is one of the key questions which should be solved before it is used in the clinical trail. In order to evaluate the biosafety of DNA vaccine, the CSFV DNA vaccine was used in the studying target, two main aspects of the vaccine were explored in the study. Firstly, the possibility of integration of two kinds of DNA vaccine plasmids into pig genome was analyzed by PCR technology after the different vaccines were injected through the intramuscular introduction. The results showed that both plasmids DNA were detected as the form were not integrated into pig genome, it can be detected 30 copies plasmid DNA in 1 microg total genomic DNA as the sensibility of PCR, indicated the safety of the DNA vaccine. Afterward the environmental fecal and soil samples in the experimental pens were picked up. Then the antibiotic resistant bacteria were isolated and its resistant genes were analyzed by PCR and gene sequencing. The results demonstrated that the transfer and spreading of two DNA vaccine plasmids studied into environmental bacteria from receptor pigs were not found. The results showed that the CSFV DNA vaccine is safe to both pigs and the surrounding environment.

Fibrocytes are potent stimulators of anti-virus cytotoxic T cells

Fibrocytes (Fb) are a population of circulating leukocytes reported to be capable of presenting antigen to CD4(+) T lymphocytes. In contrast, no information is available about their capacity to stimulate CD8(+) cytolytic T lymphocyte (CTL) responses. To this end, Fb were isolated from porcine blood to investigate their ability to stimulate CTL responses using a classical swine fever virus model. The isolated Fb (referred to as primary Fb) displayed the phenotype previously reported for mouse and human Fb, particularly in terms of the surface proteins necessary for antigen presentation, major histocompatibility complex (MHC) classes I and II, and CD80/86. These primary Fb endocytosed and degraded antigen efficiently. In absence of exogenous stimuli, endocytosis and MHC II expression were lost when the Fb were passaged and cultured. Treatment of such secondary Fb with interferon-gamma (IFN-gamma) restored the MHC II expression. The primary and secondary Fb were capable of stimulating antigen-specific CD4(+) T lymphocytes relating to previous reports. In addition, an efficient stimulation of virus-specific CD8(+)CTL was measured in terms of CD8(+) T cell proliferation, IFN-gamma production, and cytotoxic activity. This was noted even at low Fb/T lymphocyte ratios, at which dendritic cells were less efficient. Although IFN-gamma pretreatment of Fb was not necessary for this function, it could enhance the Fb activity. These results demonstrate that Fb are efficient, accessory cells for the presentation of viral antigen to specific CD8(+) CTL.

Immunoprotective properties of transgenic plants expressing E2 glycoprotein from CSFV and cysteine protease from Fasciola hepatica

Immune responses were elicited in laboratory animals after oral vaccination by transgenic plants (lettuce and alfalfa) expressing the E2 glycoprotein of Classical Swine Fever Virus (CSFV) or cysteine protease from Fasciola hepatica. ELISA analyses demonstrated that the oral route is effective in inducing a specific antibody response against these antigens in mice.

[Sensitivity of methods of titration of the vaccine strain of porcine fever virus]

Methods of titration of the CS vaccine strain of classical swine fever virus were compared in vitro and vivo. The titration in the TL and PK-15 cell culture without cytopathic effect is based on the detection of virus antigen by labeled antibodies. The infection intensity in the cell culture virtually correlated with the antigenic and immunogenic activity of dry vaccine used for swine.

Long-term monitoring of classical swine fever in wild boar (Sus scrofa sp.) using serological data

In the European Community, epizootics of classical swine fever (CSF) in the wild boar (Sus scrofa) are compulsorily monitored because transmission may occur between wild boars and domestic pigs, causing heavy economic losses to the pork industry. The estimation of incidence in populations of wild boars is generally based on viroprevalence. However, viral isolation becomes rare when the incidence is low because the virus cannot be detected for more than a few weeks following infection. On the contrary, seroprevalence is detectable at low incidence levels, because antibodies can be detected for the lifetime of the infected animal. We thus attempted to analyse the long-term evolution of CSF incidence using serological data. The data came from France, where CSF had been monitored from 1992 to 2002, and where the virus has not been detected since 1997. We assumed that the overall seroprevalence would estimate the proportion of immune wild boars, that seroprevalence in juveniles would approximate incidence and that seroprevalence in different age classes would show the evolution of incidence in a given cohort. Spatial and temporal trends of incidence and seroprevalence were explored using logistic modelling and the spatial trend was analysed using polynomial regression. In 1992, incidence peaked in the northern area. After 1993, incidence decreased but remained the highest in the northern area. After 2000, no seropositive juvenile was observed, suggesting the extinction of the epizootic. Our results support the reliability of serological monitoring since it allowed a longer detection of viral transmission and provided more information on the spatio-temporal evolution of incidence than did viral isolation. We advocate that the highest persistence of infection in northeastern France is not independent from infection persistence in Reinland-Pfalz (Germany). Such persistence may be due to favourable local conditions and/or the social organisation of wild boars.

[Identification and comparison of neutralizing epitopes of glycoprotein E(rns) of classical swine fever virus]

Structural and envelope glycoprotein E(rns) (gp48) of classical swine fever virus (CSFV) is the second antigenic protein being responsible for eliciting neutralizing antibodies and conferring protective immunity. Infection of cells with CSFV is mediated by the interaction of glycoprotein E(rns) and E2 with the cell surface receptors. The glycoprotein E(rns) has been shown to contain RNase activity, which plays a role in the viral life cycle and is also involved in virus neutralization. Neutralizing epitopes of glycoprotein E(rns) had been mapped by screening a 12-mer random peptide phage display library using the neutralizing monoclonal antibodies (MAbs) 1B5, b4-22 and 24/16, raised against CSFV strain alfort T bingen and reacted with glycoprotein E(rns). Three major epitope (mimotope) motifs, WxNxxP, DKNR (Q) G and A (T) CxYxKN (around amino acid position aa351-aa356 or aa348-aa350, aa384-aa386 and aa322-aa323, aa380-aa386 of glycoprotein E(rns) of CSFV) were identified respectively and characterized immunologically by the MAbs, 1b5, b4-22 and 24/16. MAbs b4-22 and 24/16 shared a part of binding motif sequence KN, and recognized the similar antigenic domain on the glycoprotein E(rns) but showed a distinct pattern of flank sequence and reactivities with the mimotopes by Western blot and inhibition of immunofluorescent antibody analysis.

Antibody responses of pigs to defined Erns fragments after infection with classical swine fever virus

Antibody responses of pigs to defined Erns fragments, after classical swine fever virus (CSFV) infection, were studied by using an enzyme-linked immunosorbent assay (ELISA). Selection of various E(rns) fragments was based on an immunodominant Erns region encompassing three overlapping antigenic regions, amino acids 65 to 145 (Erns(aa)65-145) (AR1), 84 to 160 (Erns(aa)84-160) (AR2), and 109 to 220 (Erns(aa)109-220) (AR3), identified earlier by our group (M. Lin, E. Trottier, J. Pasick, and M. Sabara, J. Biochem., in press). Defined Erns fragments, including AR1, AR2, AR3, Erns(aa)65-160 (AR12), Erns(aa)84-220 (AR23), Erns(aa)65-220 (AR123), Erns(aa)109-145 (the consensus region defined by the three overlapping regions), and Erns(aa)109-160 (a fragment 15 amino acids larger than the consensus region), were expressed in Escherichia coli, purified by nickel chelate affinity chromatography, and used to measure antibody responses in 20 sera serially collected from pigs experimentally infected with CSFV. Based on the optimum cutoffs determined by receiver operating characteristic analysis after testing 238 negative field sera from Canadian sources, all the Erns fragments were capable of distinguishing positive from negative antibody responses with sensitivities ranging between 75 and 90% and specificities ranging between 83.2 and 100%. Detection of antibody responses to refolded Erns(aa)109-145 and Erns(aa)109-160 by ELISA (this study) but not by Western blots (Lin et al., in press) indicated that the epitopes within the consensus region are conformational. When cutoff values were raised to give a specificity of 100%, four Erns fragments (AR2, AR23, Erns(aa)109-145, and Erns(aa)109-160) offered much higher sensitivities (75 to 90%) than those obtained with other fragments (20 to 65%). Erns(aa)109-145 and Erns(aa)109-160 were capable of detecting antibody responses in infected pigs as early as 7 days postinfection. Demonstration of antibody responses to either one of the four fragments can thus be an alternative to use of the full-length protein in ELISA for serological diagnosis of CSFV infection. An advantage of such a test would be its utilization for serological survey in a classical swine fever-free country (e.g., Canada) in biocontainment level 2 laboratories.

Quality management in reference tests for the diagnosis of classical swine fever

Inter-laboratory comparison tests for the diagnosis of classical swine fever (CSF) have been established by the national swine fever laboratories of European Union (EU) Member States. They provide a method of measuring both the quality of the results of diagnostic tests performed by laboratories and the competence with which they were performed. The objective is that all laboratories obtain the same result when investigating the same sample. This study evaluates the results of serological and virological reference tests for CSF (neutralisation test and virus isolation) performed over a period of three years. The sensitivity of the serological diagnosis for the detection of CSF antibodies was very good and revealed a tolerance limit of the scored antibody titres of one dilution step. Results on the same sample in two consecutive years were similar. The variation of the scored antibody titres was larger when testing sera with a low CSF antibody titre. The interpretation of the antibody titres as 'CSF positive or negative' was only slightly altered by these variations. The backtitration of a neutralisation test (used as a control measure) is a more mathematical value which does not correlate directly with the biological system. Commercial CSF antibody enzyme-linked immunosorbent assays still display a lower sensitivity on individual samples compared to the reference neutralisation test. Classical swine fever virus isolation was well established in all participating laboratories and caused very few problems. Specificity of CSF diagnosis by investigating CSF antibody and CSF virus negative sera was not problematic either. In general, the reference tests for CSF diagnosis are well established in the EU. They are based on living systems, e.g. cells and virus, and consequently they have a different tolerance limit than pure mathematical values. What is important is that the interpretation of the test result is identical in all laboratories.

Inclusion bodies from recombinant bacteria as a novel system for delivery of vaccine antigen by the oral route

A fragment of non-glycosylated E2 antigen of classical swine fever virus (CSFV), lacking the trans-membrane anchor (TM-) of the native glycoprotein, was produced in recombinant Escherichia coli strain BL21(DE3) in the form of inclusion bodies. These inclusion bodies isolated from the bacteria cells were administrated orally to mice twice at either 10 or 50 microg per dose. Each mouse fed with inclusion bodies carrying the E2 antigen responded with plasma antibodies and/or fecal IgA at least once during the entire investigation. Our study showed the capacity of inclusion bodies to induce both systemic and mucosal responses as well as to evoke relatively-long mucosal memory when fed to mice at low-number vaccination schedule and without any adjuvant. We propose the use of inclusion bodies for oral vaccination as an alternative to artificial systems for delivery of recombinant antigens by the oral route. Very few steps are needed to obtain an antigen ready for use as a vaccine. The procedure is easy and inexpensive and can be used for development of vaccine against classical swine fever.

Efficacy of E2-sub-unit marker and C-strain vaccines in reducing horizontal transmission of classical swine fever virus in weaner pigs

At present, two types of vaccines against classical swine fever (CSF) virus are commercially available: E2 sub-unit marker vaccines and the conventional attenuated live C-strain vaccines. To evaluate the reduction of the horizontal virus transmission, three comparable experiments were carried out in which groups of weaner pigs (vaccinated with a marker vaccine or a C-strain vaccine) were challenged with CSF virus at 0, 7, and 14 days post-vaccination (dpv). Virus transmission was prevented totally when the challenge occurred at 14 dpv with an E2-marker vaccine (0/12 contact pigs positive in virus isolation (VI); R = 0 (0; 1.5)). At 7 dpv, transmission was reduced slightly (5/12 contact pigs positive in VI; R = 1.0 (0.3; 3.0)), whereas at 0dpv, vaccination had no effect on transmission (10/12 contact pigs positive in VI; R = 2.9 (1.5; 10.8)). In the C-strain-vaccinated pigs, no virus transmission was detected even when the challenge was performed at the same day as the vaccination (0/12 contact pigs positive in VI; R = 0 (0; 1.5)).

Development of maternal antibodies after oral vaccination of young female wild boar against classical swine fever

An experimental study was performed to investigate the development of maternal antibodies after oral immunisation of young female wild boar against classical swine fever (CSF) using C-strain vaccine. Our results demonstrated that maternal antibodies do not persist in the offspring for more than 3 months. Based on the neutralising serum antibody titres, we assume that piglets of wild sows vaccinated orally twice or immunised once a long time before conception have protective antibodies for approximately 2 months. Furthermore, it seems that the level and the duration of maternal antibodies in the offspring are depend on the age of the female animals at the moment of vaccination as demonstrated in our experiment. The recent vaccination procedure consists of three double vaccinations in spring, summer and autumn. Especially vaccinations in summer and autumn could be crucial for transfer of high maternal antibody titres to the offspring.

Regulating effects of porcine interleukin-6 gene and CpG motifs on immune responses to porcine trivalent vaccines in mice

In order to develop novel immunoadjuvants to boost immune response of conventional vaccines, experiments were conducted to investigate the regulating effects of porcine interleukin-6 gene and CpG motifs as the molecular adjuvants on immune responses of mice that were co-inoculated with trivalent vaccines against Swine fever, the Pasteurellosis and Erysipelas suis. Synthetic oligodeoxynuleotides containing CpG motifs were ligated into pUC18, forming recombinant pUC18-CpG plasmid. Eukaryotic plasmid expressing porcine interleukin-6 (VPIL-6) were also constructed as molecular adjuvants in an attempt to enhance levels of immune responses of mice co-administered with the trivalent vaccines in this paper. The cellular and humoral immune responses of mice were systematically analysed, and the experimental results were observed that the number of white blood cells, monocytes, granuloytes and lymphocytes significantly increased, respectively, in the mice immunized with VPIL-6, compared with those of the control; the IgG content and titre of specific antibodies to the trivalent vaccine mounted remarkably in the sera from the VPIL-6 vaccinated mice; the proliferation of lymphocytes and induced IL-2 activities were significantly increased in the vaccinated groups. The above-mentioned immune responses of mice co-inoculated with pUC18-CpG plasmid were significantly stronger than those of co-inoculated with pUC18 plasmid, suggesting that the immunostimulatory effect of oligodeoxynuleotides CpG is closely connected with the number of CpG motifs. These results suggest that the porcine IL-6 gene and CpG motifs could be employed as effective immunoadjuvants to elevate immunity to conventional vaccines.

Classical Swine Fever Virus Strain 'C'. How Long is it Detectable After Oral Vaccination?

To determine the persistence period of C-strain vaccine virus in immunized animals, domestic pigs and wild boars were vaccinated orally and killed on different days post vaccinationem (dpv). Tissue samples were taken at necropsy from both species for detection of C-strain virus. From domestic pigs nasal swabs and faeces were also collected. During the investigation period (2-12 dpv) vaccine virus could never be detected in nasal secretions and in faeces of vaccinated domestic pigs. In contrast, C-strain virus was found in organs until day 8 pv in domestic pigs and until day 9 pv in wild boars. Whereas in domestic pigs virus was detected in tonsils, Ln. mandibularis or in spleen, in wild boar it only was found in tonsils. We conclude that C-strain vaccine virus is not detectable in wild boars longer than 10-12 days after intake of the vaccine baits.

An avirulent chimeric Pestivirus with altered cell tropism protects pigs against lethal infection with classical swine fever virus

A chimeric Pestivirus was constructed using an infectious cDNA clone of bovine viral diarrhea virus (BVDV) [J. Virol. 70 (1996) 8606]. After deletion of the envelope protein E2-encoding region, the respective sequence of classical swine fever virus (CSFV) strain Alfort 187 was inserted in-frame resulting in plasmid pA/CP7_E2alf. After transfection of in vitro-transcribed CP7_E2alf RNA, autonomous replication of chimeric RNA in bovine and porcine cell cultures was observed. Efficient growth of chimeric CP7_E2alf virus, however, could only be demonstrated on porcine cells, and in contrast to the parental BVDV strain CP7, CP7_E2alf only inefficiently infected and propagated in bovine cells. The virulence, immunogenicity, and "marker vaccine" properties of the generated chimeric CP7_E2alf virus were determined in an animal experiment using 27 pigs. After intramuscular inoculation of 1 x 10(7) TCID(50), CP7_E2alf proved to be completely avirulent, and neither viremia nor virus transmission to contact animals was observed; however, CSFV-specific neutralizing antibodies were detected from day 11 after inoculation. In addition, sera from all animals reacted positive in an E2-specific CSFV-antibody ELISA, but were negative for CSFV-E(RNS)-specific antibodies as determined with a CSFV marker ELISA. After challenge infection with highly virulent CSFV strain Eystrup, pigs immunized with CP7_E2alf were fully protected against clinical signs of CSFV infection, viremia, and shedding of challenge virus, and almost all animals scored positive in a CSFV marker ELISA. From our results, we conclude that chimeric CP7_E2alf may not only serve as a tool for a better understanding of Pestivirus attachment, entry, and assembly, but also represents an innocuous and efficacious modified live CSFV "marker vaccine".

Leukocyte subsets and specific antibodies in pigs vaccinated with a classical swine fever subunit (E2) vaccine and the attenuated ORF virus strain D1701

Total white blood cell (WBC) counts and percentages of CD4a+, CD8a+, CD5a+, CD45RA+, CD45RC+, wCD21+ and SWC3a+ cells in the peripheral blood of pigs were analysed in this study. Blood samples were collected before and on days 4, 10, 21 and 28 after vaccination. Group 1 pigs were vaccinated with a subunit E2 vaccine (gp E2 32 microg/dose), and Group 2 received a subunit vaccine combined with an attenuated ORF virus strain D1701 10(6.45) TCID50/dose. Control pigs received a placebo. The total WBC count and percentage of particular cell types were within the normal range in vaccinated and control pigs. Although the mechanism of attenuated ORF virus activity is not clear, changes were observed in CD4a+, CD5a+, CD8a+, CD45RA+ and CD45RC+ cells in pigs that received the combination of a subunit vaccine and ORF virus. However, the percentage of wCD21+ and SWC3a+ did not differ significantly from that recorded in pigs given only the subunit vaccine. At days 4 and 10 the number of pigs positive to E2 antibodies was higher in the group that received the subunit vaccine and ORF virus than in pigs vaccinated with the subunit vaccine only. A higher percentage of memory cells (CD45RC+) as well as Th and Tc lymphocytes in pigs that received the ORF virus and the subunit vaccine could be ascribed to a nonspecific influence of the ORF virus on the development (through cognate interactions between T and B cells) and the duration (presumed according to the finding of the clonal expression of memory cells) of humoral immunity (assessed by a higher number of seropositive pigs in this group). This seems likely since the proportion of these cells was found to be lower in the pigs that received E2 vaccine only.