Pathobiology at the Ontario Veterinary College--the first 100 years

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Characterization of the early region 4 of porcine adenovirus type 3

The nucleotide sequence of a 3028 bp DNA segment, located between map co-ordinates 100 and 92 in the genome of porcine adenovirus type 3 (PAV-3), was determined. The segment includes the entire early region 4 (E-4) and the right inverted terminal repeat sequences. There were two TATA boxes and one canonical polyadenylation signal on the 1 strand. Homology searches of the GenBank data base for the predicted amino acid sequences revealed that, of the eight open reading frames (ORFs) on the 1 strand, and four ORFs on the r strand, only ORF 8 on the 1 strand showed homology with the 34 kDa E-4 protein of human adenovirus types 2, 12 and 34. Northern blot analysis showed that transcription from the E-4 region of PAV-3 began 4 h after infection, peaked at 8 h and declined after 10 h, before DNA replication began 16 h after infection. The E-4 region of PAV-3 was further characterized by 5' and 3' end mapping of the transcription unit.

Edward Watson and the eradication of dourine in Canada

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Porcine adenoviruses types 1, 2 and 3 have short and simple early E-3 regions

The nucleotide sequence of the E-3 region genes, the hexon associated protein pVIII genes, and part of the fiber genes coding for the N-terminal tail regions, of porcine adenovirus (PAV) types 1 and 2 were determined. The sizes of the E-3 regions were found to be 1162 and 1222 bp, respectively. The five open reading frames (ORF) encoded within the sequenced regions of PAV types 1 and 2 shared a high degree of homology with the published sequences of the corresponding ORFs of PAV-3. The E-3 regions of PAV types 1, 2 and 3 were further characterized by Northern blot analysis and 5' and 3' end mapping of the transcripts by S1 nuclease analysis. The results of these experiments indicated that the E-3 regions in these three viruses are shorter and simpler in organization than the E-3 regions of human adenoviruses. A potential promoter for the E-3 regions of these PAVs was identified.

Partial transcriptional mapping of the fowlpox virus genome and analysis of the EcoRI L fragment

Several fowlpox virus (FPV) DNA fragments were selected by differential hybridization using cDNA of transcripts that were strongly transcribed early and/or later after infection of QT-35 cells. The EcoRI L fragment contained three strongly transcribed FPV genes: L1L, a late 1452 bp partial (amino end) ORF; L2R, an early/late 522 bp ORF; and L3R, a late 948 bp ORF. The protein products of L1L, L2R and L3R shared homology with the products of vaccinia virus (VV) genes H4L (RAP94), H5R (Ag35) and H6R (topoisomerase), respectively, suggesting a conservation of gene structure and order between VV and FPV. The 5' upstream non-coding sequences of L1L and L3R were A + T rich and the sequence 5' TAAATG 3' overlapped the predicted translation start codon. Primer extension analysis of the L2R transcript mapped the transcriptional start sites of early and late mRNAs 14 nt downstream of a VV early promoter-like critical region sequence, AAAATTGAA-AAAAAAA. A VV-like TAAAT late transcriptional element was present 20 nt upstream of the L2R ATG translational start codon. A plasmid with the putative early L2R promoter cloned upstream of the Newcastle disease virus haemagglutinin-neuraminidase (HN) cDNA as a reporter gene was at least 6-fold more effective in generating HN MRNa than plasmids containing the P7.5 or P11 VV promoters in transient expression assays in FPV-infected CEF cells treated with cytosine arabinoside. The L2R promoter was also able to express an amount of HN mRNA equal to that expressed by the VV promoters late in infection.

Comparison of the inverted terminal repetition sequences from five porcine adenovirus serotypes

The nucleotide sequences of the region of inverted terminal repetition from representative strains of all five porcine adenovirus (PAV) serotypes were determined and analyzed. The first 17 nucleotides of this region were identical in PAV-1 to 3 and PAV-5, and 10 bp of identical sequence was found in all the PAVs. The closest relationships were among PAV-1 to 3, which shared more common sequences than the other serotypes. PAV-4 had the longest inverted terminal repeat reported for any adenovirus. The proximal 54-bp AT-rich region was partially conserved and the distal GC-rich region was less well conserved among all five serotypes.

Antiviral action of interferon-alpha against porcine transmissible gastroenteritis virus

Swine testis (ST) cell cultures were treated with various doses of recombinant human interferon-alpha 2a (IFN), and assayed for 2',5' oligoadenylate synthetase (2-5 A synthetase) activity. Treatment with 100 or 1000 units/ml of IFN resulted in increased 2-5 A synthetase activity, but there was no significant response to 1 unit/ml of IFN. Titres of porcine transmissible gastroenteritis virus (TGEV) were reduced between 6 and 15 hours post-infection in ST cells treated with 1000 or 2500 units/ml of IFN. Polyacrylamide gel electrophoresis of lysates of TGEV-infected ST cells, and of lysates immunoprecipitated with anti-TGEV antibodies, revealed that the synthesis of the N and S proteins of TGEV was reduced in cells treated with 100 or 1000 units/ml of IFN. Viral RNA production, as determined with a probe which hybridized to the S gene of TGEV, was found to be reduced in ST cells treated with 1000 units/ml of IFN, but not in cells treated with 100 units/ml. It was concluded that, in IFN-treated ST cells, TGEV protein production may be decreased in the absence of reduced viral RNA production, and that 2-5 A synthetase may not be a significant factor in the antiviral activity of IFN against TGEV.

Restriction endonuclease analysis and physical mapping of the genome of porcine adenovirus type 5

The HNF61 and HNF70 isolates of porcine adenovirus type 5 (PAV-5) were cultivated in PK-15 cells, and viral DNA was extracted from the infected cells by a modified Hirt procedure. The DNAs were digested by each of 9 restriction endonucleases, and fragments representing the entire genomes were cloned. Based on the sizes of the restriction enzyme fragments, the genome of each isolate was estimated to be 33.2 kb. Physical maps for the 9 restriction endonucleases were constructed. The physical maps of the two isolates were identical for 5 of the restriction endonucleases, but 4 enzymes revealed differences in restriction sites occurring mainly between map units 78 and 83, which may include the E3 region of the genome. There were no similarities between the physical maps of PAV-5 and those described for the other 4 serotypes of PAV.

Interferon induction in swine lymphocyte antigen-defined miniature pigs

Interferon was induced in two groups of swine lymphocyte antigen (SLA)-defined miniature pigs with polyinosinic: polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose. The group 1 pigs were low antibody-response phenotypes (SLAa/a, SLAa/c, SLAc/c), and the group 2 pigs were high antibody-response phenotypes (SLAd/d, SLAd/g, SLAg/g). Six hours after induction the antiviral tires were not influenced by the SLA group, but higher titres were observed in females. Higher antiviral titres were found in group 2 pigs before treatment and 24 hours after treatment, and higher titres were found in female pigs. The antiviral titres before and after treatment were also influenced by the sire. Group 2 pigs had a lower total leucocyte counts before treatment, and there was a significant reduction in leucocyte numbers in both groups six hours after induction, due mainly to a large reduction in lymphocyte counts.

Sequence analysis of putative pVIII, E3 and fibre regions of porcine adenovirus type 3

Sequence analysis of a region of the genome of porcine adenovirus type 3 from map unit 79.5 to map unit 92 was performed. Homology studies revealed genes coding for the hexon-associated protein pVIII on the left and for the fibre protein on the right of the sequenced region. By analogy with the genomic organization of other adenoviruses, the 1179 bp sequence between the pVIII and fibre open reading frames, extending from map unit 81.3 to map unit 84.7, was identified as the equivalent of the E3 region of human adenoviruses. The deduced amino acid sequence of one of the three open reading frames of the putative E3 region showed homology with the 13.3K E3 protein of canine adenovirus type 2. The primary structure of the putative fibre protein was similar to that described for human adenovirus types 2 and 5, with a 14 pseudorepeat motif in the shaft region of the fibre. A 742 bp tandem repeat starting in the middle of the fibre gene and extending beyond the termination codon of this gene was observed.

Molecular cloning and physical mapping of porcine adenovirus types 1 and 2

The 25R strain of porcine adenovirus type 1 (PAV-1) and the A47 strain of PAV-2 were propagated in ST cells, and DNA was extracted from the infected cells by a modified Hirt method. The DNA of each virus was digested by each of nine restriction endonucleases, and restriction enzyme fragments representing the entire genome were cloned. The genomic size of each virus was approximately 33 kb. Physical maps for the nine restriction endonucleases were constructed from the results of double digestion and Southern blot hybridization experiments, and oriented with respect to the PAV-3 genome. PAV-1 and PAV-2 were found to be related genetically to PAV-3, and there was a closer relationship between PAV-1 and PAV-3 than between PAV-1 and PAV-2 or between PAV-2 and PAV-3.

Passive protection of piglets by recombinant baculovirus induced transmissible gastroenteritis virus specific antibodies

Sera of pigs immunized with parts of the transmissible gastroenteritis virus (TGEV) spike (S) protein expressed by recombinant baculoviruses were tested, together with a TGEV hyperimmune antiserum, for their abilities to protect three-day-old piglets against TGEV infection. The piglets were infected with virulent TGEV and the sera were given orally 3 h before infection, together with the virus, and every 6 h postinfection during the 30 h of the experiment. Virus shedding was monitored by TGEV isolation from rectal swab samples. The sera containing antibodies induced by the complete S protein or the amino terminal half of the S protein showed protective properties, indicated by delayed onset of clinical signs and virus shedding, similar to the TGEV hyperimmune serum. Those immune sera containing antibodies induced by shorter recombinant proteins were not protective.

Cellular receptors for transmissible gastroenteritis virus on porcine enterocytes

The activity of aminopeptidase-N (APN), reported to be a major receptor for porcine transmissible gastroenteritis virus (TGEV), in enterocyte fractions harvested from the jejunal villi and crypts of newborn and weaned piglets, did not correspond with the levels of saturable virus binding previously demonstrated for the same fractions. Plasma membranes prepared from enterocytes harvested from the jejunal villi of a newborn piglet were used in the preparation of a monoclonal antibody (MAb) which blocked the binding of TGEV, but not that of the porcine respiratory coronavirus (PRCV), to ST cells. This MAb immunoprecipitated a 200 kDa non-glycosylated protein from lysates of ST cells, which was not precipitated by an anti-APN MAb. The 200 kDa protein was shown by immunostaining and fluorescence activated cell scanning to be present on ST cells and on villous enterocytes from newborn piglets, but not on MDBK cells or enterocytes from weaned piglets. APN was demonstrated by the same techniques to be present on villous enterocytes from both newborn and weaned piglets, as well as on ST cells. It was concluded that the 200 kDa protein may be a second receptor for TGEV, contributing to the high susceptibility of newborn piglets to the virus.

Evidence for a putative second receptor for porcine transmissible gastroenteritis virus on the villous enterocytes of newborn pigs

Aminopeptidase-N (APN) has been identified [B. Delmas, J. Gelfi, R. L'Haridon, L. K. Vogel, H. Sjostrom, O. Noren, and H. Laude, Nature (London) 357:417-420, 1992] as a major receptor for porcine transmissible gastroenteritis virus (TGEV). Binding of TGEV to villous enterocytes from the jejuna of newborn pigs is saturable and at a higher level than that of binding of virus to newborn cryptal enterocytes or to enterocytes from older piglets (H. M. Weingartl and J. B. Derbyshire, Vet. Microbiol. 35:23-32, 1993). The distribution of APN in enterocytes in the jejuna of neonatal and 3 week-old-piglets, as determined by the measurement of enzymatic activity and by labeling of the cells with an anti-APN monoclonal antibody, did not correspond with the reported distribution of saturable binding sites on enterocytes. Monoclonal antibodies, which were prepared against plasma membranes derived from enterocytes harvested from the upper villi of newborn pigs, blocked the replication of TGEV, but not the porcine respiratory coronavirus, in ST cells and immunoprecipitated a 200-kDa protein in ST cell lysates. This protein was demonstrated by immunohistochemistry and by fluorescence-activated cell scanning to be present on the villous enterocytes of newborn pigs but to be lacking on the cryptal enterocytes of newborn pigs and on the villous and cryptal enterocytes of 3-week-old piglets. Since this distribution of the protein corresponds to the previously demonstrated distribution of saturable binding sites, we conclude that the 200-kDa protein may be an additional receptor for TGEV which is restricted to the villous enterocytes of newborn pigs and which contributes to the age sensitivity of these animals to the virus.

Vaccination of chickens with a recombinant fowlpox virus containing the hemagglutinin-neuraminidase gene of Newcastle disease virus under the control of the fowlpox virus thymidine kinase promoter

When chickens were vaccinated with a recombinant fowlpox virus (FPV) containing the Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) cDNA under the control of the thymidine kinase (TK) promoter and inserted into the FPV TK gene, the FPV antibody response to the recombinant virus was similar to the response to vaccination with standard FPV, and the recombinant virus protected chickens against challenge with virulent FPV. While the presence of the NDV HN cDNA was demonstrated in the recombinant virus, which was stable on serial passage, expression of HN was not detected by hemagglutination, Western blot analysis or immunoprecipitation of infected cell lysate. Chickens vaccinated with the recombinant virus failed to mount an NDV hemagglutination-inhibition antibody response, and they did not resist challenge with velogenic NDV. It was concluded that the TK promoter was too weak to drive the HN gene, but that the insertion into the FPV TK gene did not reduce the immunogenicity of the virus.

Development and evaluation of a non-isotopically labeled DNA probe for the diagnosis of infectious laryngotracheitis

A digoxigenin-labeled cloned infectious laryngotracheitis virus (ILTV) DNA fragment was evaluated as a nonradioactive alternative probe in the diagnosis of infectious laryngotracheitis. The dot-blot hybridization protocol was optimized and was capable of detecting 40 pg of purified ILTV DNA and as few as 50 ILTV-infected chicken embryo liver cells. The utility of this approach for diagnostic use was evaluated through four ILTV inoculation trials using a mild field isolate, a virulent challenge strain, a tissue-culture-origin vaccine, and an egg-origin vaccine. Birds were examined for clinical signs of ILT, and conjunctival and pharyngeal swabs from inoculated and sentinel birds were tested for ILTV by the digoxigenin-labeled probe and by virus isolation. In general, higher numbers of ILTV-positive samples were detected by both assays from conjunctival swabs. For the non-vaccine strains, detection by dot-blot hybridization was equivalent to that for virus isolation. However, for the two vaccine strains, there was some lack of correlation between the dot-blot results and the virus-isolation results. The kappa values between virus-isolation results and dot-blot results for the tissue-culture-origin vaccine, egg-origin vaccine, Ont 1598 field isolate, and virulent strain were 0.00, 0.16, 0.39, and 0.24, respectively, for pharyngeal samples and 0.19, 0.29, 0.58, and 0.48, respectively, for conjunctival samples.

Studies of fowlpox virus recombination in the generation of recombinant vaccines

A p7.5/beta-galactosidase (7.5 lacZ) gene construct, cloned adjacent to the fowlpox virus (FPV) thymidine kinase (tk) gene was used as a marker to identify the products of recombination as 'blue' FPV plaques. The rFPVs were detected as early as 4 h after the introduction of plasmid DNAs and by 72 h post-infection (p.i.) for one transfer vector comprised 0.48% of the viral population. The proportion of rFPV increased linearly from 0.073% to 0.62% as the cumulative length of homologous sequences in the transfer vector increased from 0.73 to 4.5 kb. Two approaches using a second reporter gene, the Newcastle disease virus haemagglutinin-neuraminidase (NDV HN) gene were tested to differentiate between single and double cross-over events. In one, the HN gene was cloned into the FPV tk gene and the 7.5 lacZ cloned outside of the homologous region. Progeny of a single cross-over with FPV DNA generated an unstable plaque containing the HN gene and subsequent intramolecular recombination resulted in excision of the 7.5 lacZ and the generation of a stable 'white' plaque. For virus grown in CEF cells (tk+) in the presence of 5-bromo-deoxyuridine, only those viruses which contained a tk gene disrupted by the HN gene formed plaques. This approach allowed us to easily identify rFPV containing the HN gene but lacking 7.5 lacZ or other bacterial sequences. In a second approach, a double cross-over between rFPV DNA containing a stably expressed beta-galactosidase gene cloned into the tk gene (blue plaque) and plasmid DNA containing the HN gene flanked by tk sequences would allow transplacement of the 7.5 lacZ gene with the HN gene, and generating a white plaque. We were unable to generate recombinant viruses with the HN gene and which generated a white plaque, indicating that double cross-over events do not occur at a sufficiently high frequency in FPV.

Immunogenicity of the S protein of transmissible gastroenteritis virus expressed in baculovirus

Seven fragments of the spike (S) gene cDNA of transmissible gastroenteritis virus (TGEV), as well as the full length cDNA, were cloned and expressed in baculovirus vectors. Piglets were immunized with cells infected with the recombinant viruses. Each of the recombinants induced TGEV-specific antibodies detected in a fixed cell enzyme immunoassay. The amino terminal half of the S protein, containing all four major antigenic sites (A, B, C and D), and encoded by a 2.2 kb fragment of the S gene, induced virus neutralizing (VN) antibody titers comparable with those induced by the complete S protein. Recombinant proteins lacking the A antigenic site, or with a deletion including the putative receptor binding sites and the D antigenic site, were not capable of inducing levels of VN antibodies similar to those induced by the whole S protein.

Antiviral activity of interferon against transmissible gastroenteritis virus in cell culture and ligated intestinal segments in neonatal pigs

Segments of jejunum in 5 to 6 days old piglets were surgically ligated, inoculated with transmissible gastroenteritis virus (TGEV) and 18 hours later the segments were fixed for histology or suspensions were prepared for plaque assay in swine testis (ST) cell cultures to determine the yield of virus. When the virulent Purdue strain of TGEV was used, villous atrophy was seen and TGEV antigen was demonstrated immunohistochemically in the villous enterocytes. The Miller M6 strain of virus produced less extensive lesions in the segments, but since it was titratable by plaque assay it was used in the subsequent yield reduction assays to determine the antiviral activity of interferon. When intestinal segments were inoculated simultaneously with either 3200 units of natural porcine interferon-alpha or up to 1000,000 units of recombinant human interferon-alpha 2 a, and TGEV, there no reductions in virus yield, although the same cytokines exerted an antiviral effect in ST cells treated in a similar way. However, virus yields were significantly reduced in intestinal segments in piglets treated parenterally with the synthetic interferon inducer polyinosinic: polycytidylic acid 6 hours before challenge of the segments with TGEV. There was also a trend for the antiviral effects of interferon induction before challenge to be augmented by the inclusion of interferon with the virus inoculum. It was concluded that interferon would be ineffective as a therapeutic for TGEV, although it might be useful prophylactically.

Restriction endonuclease analysis of a porcine isolate of bovine herpesvirus type 1

Deoxyribonucleic acid (DNA) was extracted from bovine herpesvirus type 1 (BHV-1) isolated from a stillborn porcine fetus, from the Cooper reference strain of BHV-1, and from an Ontario bovine respiratory isolate. Each DNA was digested with the restriction endonucleases HindIII, EcoRI, HpaI and BamHI. Except for very minor differences in the patterns produced after digestion with EcoRI and HindIII, the DNA of the porcine isolate reacted in a similar manner to the bovine viruses, and it was concluded that the porcine virus is genetically similar to bovine isolates of BHV-1.

Potential viral vectors for the stimulation of mucosal antibody responses against enteric viral antigens in pigs

Four viruses were compared for their ability to induce an intestinal antibody response in piglets. Antibodies were not detected in response to oral vaccination with either fowlpox virus or a baculovirus (BV). Simultaneous oral dosing and parenteral inoculation with high concentrations of BV in an oil emulsion adjuvant induced high levels of circulating virus neutralising (VN) antibodies, and also low levels of intestinal antibodies when booster doses of virus were given. In response to oral vaccination with swinepox virus (SPV), low levels of circulating and intestinal VN antibodies, and higher titres of antibodies reactive in an enzyme immunoassay, including intestinal antibodies of the IgA class, were detected. Oral vaccination with porcine adenovirus type 3 (PAV-3) stimulated both circulating and intestinal VN antibodies, and IgA antibodies were demonstrated in the intestinal contents. It was concluded that SPV and PAV-3 might be suitable vectors for the expression of genes encoding the protective antigens of porcine enteric viruses.

Binding of porcine transmissible gastroenteritis virus by enterocytes from newborn and weaned piglets

Enterocytes were harvested by chelation in a series of seven fractions from the tips of the villi to the crypts of the jejunum of newborn or weaned piglets. Binding of the low cell culture passaged Miller-6 strain of transmissible gastroenteritis virus (TGEV) to villous enterocytes from newborn piglets was at a high level, similar to that observed to cultured swine testis (ST) cells. Binding of the virus to cryptal enterocytes from newborn piglets or to villous or cryptal enterocytes from weaned piglets was significantly lower. In a competitive virus binding assay with radiolabelled virus, the binding of TGEV to ST cells was found to be saturable, while binding to MDBK cells, in which the virus fails to replicate, was at a lower level and was non-saturable. In the same assay, virus binding to the villous enterocytes from the jejunum of a newborn piglet was saturable, while binding to cryptal enterocytes from a newborn piglet, and to villous and cryptal enterocytes from a weaned piglet, was non-saturable. It was concluded that the high susceptibility of newborn piglets to TGEV infection, and the tropism of the virus for villous enterocytes, may relate to the presence of specific, saturable binding sites on the plasma membrane of villous enterocytes.

Restriction endonuclease analysis and molecular cloning of porcine adenovirus type 3

The 6618 strain of porcine adenovirus type 3 was cultivated in swine testis cells, and viral DNA was extracted from the infected cells by a modified Hirt procedure. The DNA was digested by each of 13 restriction endonucleases, and the number of cleavage sites which were identified varied from 1 to 17. The size of the porcine adenovirus type 3 genome, estimated from the sizes of the restriction enzyme fragments, was approximately 35 kb. Fragments representing the entire genome were cloned. Physical maps were constructed based on the results of restriction endonuclease analyses and hybridization and oriented with respect to the genome of bovine adenovirus type 3.

Transmissible gastroenteritis virus antibody production in vitro by porcine peripheral blood leukocytes

The purpose of this study was to demonstrate the in vitro production of transmissible gastroenteritis virus (TGEV)-specific antibodies by peripheral blood leukocytes (PBL) harvested from piglets infected with TGEV. Piglets were infected with the virulent Purdue strain of TGEV and at intervals postinfection their PBL were cultivated in the presence of TGEV antigen, control antigen or pokeweed mitogen (PWM). The culture supernatants were tested for TGEV antibodies by a fixed cell enzyme immunoassay. Antibodies were never found in the supernatants of unprimed PBL cultures from control piglets, nor in cultures stimulated with control antigen, and antibodies were produced more frequently in response to stimulation of primed PBL with viral antigen than with PWM. In PBL cultures stimulated with viral antigen, TGEV antibodies of the IgG class were produced more frequently than IgA class antibodies. Optimal antibody responses were produced by PBL harvested two weeks after infection and cultivated at a concentration of 10(7) cells/mL for five days.

Interferon induction in porcine leukocytes with transmissible gastroenteritis virus

Leukocytes were harvested from the peripheral blood, mesenteric lymph node and small intestinal lamina propria from groups of three piglets before, and 1, 2 and 3 weeks after infection with virulent transmissible gastroenteritis virus (TGEV) at 2 weeks of age. The donor piglets developed clinical signs of transmissible gastroenteritis which persisted for up to 3 days, and they developed peak serum titres of TGEV-neutralizing antibodies 2 weeks post-infection. The leukocytes were cultured in the presence of pokeweed mitogen (PWM), various dilutions of purified TGEV, or control media for 3 or 5 days, and the culture supernatants were tested for antiviral activity in MDBK cells challenged with vesicular stomatitis virus. The antiviral activity was characterized as porcine interferon (IFN)-alpha or porcine IFN-tau on the basis of its stability at pH 2.0 and neutralization by anti-human IFN-alpha antibodies. Viability of the leukocytes in culture, determined by trypan blue exclusion, was highest for the peripheral blood leukocytes and lowest for the mesenteric lymph node leukocytes. There were no consistent differences in antiviral activity between cultures incubated for 3 or 5 days. Porcine IFN-alpha was found in the supernatants of the leukocyte cultures stimulated with TGEV antigen, harvested before or after infection of the donor piglets with TGEV. Porcine IFN-tau was demonstrated in the supernatants of the leukocyte cultures stimulated with PWM, more frequently when the leukocytes were harvested post-infection. This was the first demonstration of IFN induction in vitro in leukocytes from porcine gut-associated lymphoid tissue.

Vaccination against Newcastle disease with a recombinant baculovirus hemagglutinin-neuraminidase subunit vaccine

Vaccination of chickens with an oil-emulsion vaccine containing a recombinant baculovirus that expressed the hemagglutinin-neuraminidase (HN) of Newcastle disease virus (NDV)-induced hemagglutination-inhibition (HI) and virus-neutralizing antibodies against NDV. HI antibody titers obtained in response to vaccination with the live recombinant virus were higher than those obtained when the recombinant was inactivated with beta-propiolactone, and the titers were lower than those obtained in response to the same HN concentrations in live or beta-propiolactone-inactivated NDV strain B1. The serological response to the recombinant baculovirus was differentiated from the response to NDV by an enzyme-linked immunosorbent assay in which purified NDV nucleoprotein was used as antigen. Chickens vaccinated with the live recombinant or with inactivated NDV resisted an oculonasal challenge with the neurotropic velogenic Texas GB strain of NDV, which was lethal in unvaccinated controls. It was concluded that the HN protein of NDV expressed as a subunit by a recombinant baculovirus was protective against Newcastle disease.

Suppression of lymphocyte blastogenesis by porcine interferon-alpha

Peripheral blood lymphocytes (PBL) from five four-day-old and five six-week-old piglets were treated with 10 to 320 units of porcine interferon-alpha, and their blastogenic responses to phytohaemagglutinin or pokeweed mitogen were compared with those of control lymphocytes. There was significant inhibition of the blastogenic response to phytohaemagglutinin by 320 units of interferon-alpha, and of the response to pokeweed mitogen by 320 and 160 units of interferon-alpha. Porcine interferon-beta was cytotoxic to porcine PBL. The blastogenic response to pokeweed mitogen was significantly higher in PBL from the younger piglets.

Antiviral activity against transmissible gastroenteritis virus, and cytotoxicity, of natural porcine interferons alpha and beta

Porcine interferon (POIFN)-alpha prepared in primed peripheral blood leukocyte cultures induced with Newcastle disease virus and POIFN-beta from PK-15 cell cultures induced with polyinosinic:polycytidylic acid were partially purified by precipitation with potassium thiocyanate and anion exchange chromatography. Mean purification factors in terms of units of POIFN per mg of protein, of 37 and 12 were obtained for POIFN-alpha and POIFN-beta respectively. In yield reduction assays in swine testis and pig kidney cell cultures, POIFN-alpha and POIFN-beta had greater antiviral activity against vesicular stomatitis virus than against transmissible gastroenteritis virus (TGEV). The antiviral effects were greater at higher concentrations of interferon (IFN), and when the IFN treatments were continued postinfection. Porcine interferon-beta showed greater antiviral activity against TGEV than POIFN-alpha, but this may have been partly due to cytotoxicity. There were no major differences in the antiviral activities of crude and partially purified IFN preparations. Both types of IFN showed antiviral activity against TGEV in yield reduction assays in porcine intestinal explant and intestinal epithelial cell cultures. Crude POIFN-beta was found to be rapidly cytotoxic, especially in porcine cells, and some fractions of partially purified POIFN-beta were also cytotoxic. The cytotoxicity of POIFN-beta was partially neutralized by antibodies against human IFN-beta, but human IFN-beta was not cytotoxic for porcine or bovine cells.

Synthesis of Newcastle disease virus (NDV)-like envelopes in insect cells infected with a recombinant baculovirus expressing the haemagglutinin-neuraminidase of NDV

Electron microscopical examination of negatively stained extracellular fluids (ECF) from Spodoptera frugiperda cell cultures infected with a recombinant baculovirus expressing the Newcastle disease virus (NDV) haemagglutinin-neuraminidase (HN) revealed NDV-like envelopes which resembled the envelopes of authentic NDV. Immunogold staining with anti-NDV HN monoclonal antibodies demonstrated HN antigen in spikes on the NDV-like envelopes. The ECF from the recombinant-infected cultures also contained baculovirus particles which resembled standard baculovirus particles except that some showed polar protrusions of the envelope. It was concluded that the HN of NDV, in the absence of the matrix protein, might be able to initiate and control the production of viral envelopes which are morphologically identical to those of authentic NDV.

An improved dot-blot method for virus detection in chicken embryo fibroblast cultures

A simplified dot-blot procedure is described for the detection of fowlpox virus (FPV) in infected monolayers of chicken embryo fibroblasts (CEF) cultured in 96-well microtiter plates. The relative resistance of DNA to hot NaOH, which hydrolyzes other macromolecules including RNA and protein, was exploited to solubilize virus infected cells and denature intracellular DNA in a simple, quick manner. Moreover, there was no need to purify virus or isolate viral DNA from cellular DNA prior to dot blotting. After incubation of CEF with FPV, the extracellular fluid from infected cells was collected for storage in 96-well microtiter plates. The remaining cell monolayers in each well were then solubilized with hot NaOH. The solubilized and denatured DNA was transferred to a nylon membrane using a dot-blot vacuum filtration manifold. Hybridization was carried out with a 32P-labeled FPV DNA probe. With this methodology it was possible to detect specific viral DNA sequences following the infection of cell monolayers with as little as 1 infectious unit per well. The ability to detect specific viral DNA sequences in infected cells, without the need to isolate pure viral DNA, made it possible to analyze large numbers of samples in a single experiment. Moreover, sufficient fowlpox virus was present in the extracellular media from each well for further amplification and analysis of selected samples.

Vaccination of 1-day-old chicks with fowlpox virus by the aerosol, drinking water, or cutaneous routes

Administration of 10(4) mean cell-culture infectious dose (CCID50) per ml of a plaque-purified derivative of a commercial fowlpox virus (FPV) vaccine to 1-day-old chicks by aerosol or drinking water gave inconsistent serological responses and little evidence of protective immunity. In contrast, cutaneous vaccination with the same preparation protected against challenge with virulent FPV at 4 weeks of age. Administration of the vaccine at a concentration of 10(6) CCID50 per ml by the drinking-water route was as effective as conventional cutaneous vaccination in terms of the serological response in an enzyme-linked immuno-sorbent assay and in terms of protection against challenge. Drinking-water vaccination at 2 days of age was no more effective than vaccination on day 1, and oral dosing with the vaccine was less effective than incorporation of the vaccine in the drinking water. It was concluded that 1-day-old chicks may be vaccinated against fowlpox by the drinking-water route if the vaccine contains a sufficiently high concentration of virus.

Cloning and expression of NDV hemagglutinin-neuraminidase cDNA in a baculovirus expression vector system

The hemagglutinin-neuraminidase (HN) gene of the Hitchner B1 strain of Newcastle disease virus (NDV) was cloned as a cDNA and inserted into a baculovirus expression vector. The recombinant HN (recHN) expressed in Spodoptera frugiperda cells had both hemagglutinating and neuraminidase activities both of which were inhibited by polyclonal anti-NDV sera or a monoclonal antibody (MAb) against HN. Infected insect cells could hemadsorb chicken red blood cells suggesting that the recHN is properly glycosylated and transported to the cell surface. A 67-kDa recHN precursor and a 74-kDa, presumably mature, recHN from infected cells were detected by Western blot analysis and were found to comigrate with similar proteins from NDV-infected chick embryo fibroblast cells. The kinetics of synthesis of recHN was similar to that for polyhedrin and some HN appeared in the extracellular medium. HN was copurified with extracellular virus (ECV) from the extracellular medium and was used to immunize chickens. The anti recHN serum was specific to NDV in both ELISA and Western blot analysis.

The induction and characterization of natural porcine interferons alpha and beta

The purpose of this study was to define optimum conditions for the production of high concentrations of natural porcine interferon (POIFN)-alpha and POIFN-beta, and to characterize the IFNs which were produced. The inducers used were Newcastle disease virus (NDV), polyinosinic:polycytidylic acid (poly IC), poly IC complexed with diethylaminoethyl dextran (poly IC-DEAEdx) and poly IC complexed with poly-L-lysine and carboxymethylcellulose. The highest yields of POIFN-alpha were obtained from porcine peripheral blood leukocyte (PBL) cultures induced with NDV. The concentrations of both cells and virus were critical for high yields of IFN, which were also enhanced by priming. Poly IC was found to be a relatively poor IFN inducer in PBL, in which low yields were obtained only after priming or in response to poly IC-DEAEdx. POIFN-beta was prepared by induction of the PK-15 cell line with poly IC or poly IC-DEAEdx. The highest yields were obtained from cultures induced 24 h after seeding, although when poly IC-DEAEdx or superinduction was used, the age of the cells was less critical. Priming had little effect on the yields of POIFN-beta. PK-15 cells induced with NDV gave relatively low yields of IFN. Both POIFN-alpha and POIFN-beta were classified as type I IFN on the basis of their resistance or susceptibility to pH 2.0, ultracentrifugation, 56 degrees C and trypsin treatment. Disulphide bonds essential for antiviral activity were demonstrated in both types of IFN by reduction with 2-beta-mercaptoethanol, and anionic exchange chromatography after treatment with dithiothreitol indicated a second disulphide bond in POIFN-alpha which was not essential for antiviral activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of interferon induction in newborn piglets on the humoral immune response to oral vaccination with transmissible gastroenteritis virus

Groups of newborn piglets were vaccinated orally with a modified live transmissible gastroenteritis (TGE) virus vaccine at 3 days and 13 days of age, and treated with the synthetic interferon (IFN) inducer polyinosinic:polycytidylic acid (poly ICLC) at 2, 3 or 4 days of age. Control groups consisted of piglets which were vaccinated but not treated with poly ICLC, as well as piglets which were treated with poly ICLC but not vaccinated. Significantly higher mean IFN titres were produced in response to induction at 3 or 4 days of age than at 2 days, and the mean IFN titre of the vaccinated piglets treated with poly ICLC at 3 days of age was significantly higher than in the unvaccinated piglets which were treated at the same time. The mean TGE virus neutralizing antibody titres in the vaccinated piglets which were treated with poly ICLC on the day before vaccination were significantly lower than the mean titres in the untreated vaccinated piglets 10 and 14 days after the first dose of vaccine. The mean titres in the vaccinated piglets which were treated with poly ICLC at 3 or 4 days of age did not differ significantly from those in the untreated vaccinated piglets. The piglets which were treated with poly ICLC on the day after vaccination developed severe diarrhoea which persisted for 5-7 days.

Hyporeactivity to interferon induction in newborn piglets

The aim of this study was to produce sustained activation of natural killer (NK) cells in newborn piglets by interferon (IFN) induction with polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose [poly(ICLC)]. When a second dose of poly(ICLC) was given 24 or 48 h after the first dose, the piglets were found to be hyporeactive, and the levels of induced IFN were insufficient to activate NK cells in vivo or in vitro. A hyporeactive factor was demonstrated in the serum of piglets 24 and 48 h after they were treated with poly(ICLC), which inhibited IFN induction in vitro with poly(ICLC) but not with Newcastle disease virus. The IFN response of hyporeactive piglets was partially restored by the administration of prostaglandin (PG) F2 alpha at the same time as the second dose of poly(ICLC); piglets treated in this way at 3 days of age showed significantly higher lymphocytic NK activity at 5 days and 7 days than the activity in untreated piglets and in those given one or two doses of poly(ICLC) in the absence of PG F2 alpha. It was concluded that piglets develop hyporeactivity to IFN induction, but the IFN and NK cell activation responses to poly(ICLC) can be restored by treatment with PG.

Use of human adenovirus-based vectors for antigen expression in animals

An infectious recombinant human adenovirus type 5 (Ad5) vector, AdG12, which carries the glycoprotein gene of vesicular stomatitis virus (VSV) and expresses that gene in cultured HeLa cells was used to examine the host range of insert expression by human Ad vectors. The VSV glycoprotein was expressed in bovine, canine and murine cells when infected with AdG12 in culture. These cell lines are respectively permissive, non-permissive and semi-permissive for human Ad5 replication. Administration of the AdG12 vector to calves, piglets or dogs by either the subcutaneous or oral route resulted in the production of high titres of neutralizing antibodies to VSV. Mice injected intraperitoneally with the vector produced neutralizing antibodies and were protected against subsequent intravenous challenge with normally lethal doses of VSV. This work demonstrates the utility of human adenoviral vectors for antigen expression in a number of non-human cell lines and for the induction of an immune response to the delivered antigen in a number of species.

The interferon sensitivity of selected porcine viruses

The objective of this study was to compare the sensitivity of 11 porcine viruses to the antiviral effects of porcine interferon-alpha in serum from piglets which had been infected 19 h previously with transmissible gastroenteritis virus, and of porcine interferon-beta prepared in PK-15 cells by induction with polyinosinic:polycytidylic acid, in yield reduction assays in pig kidney cells which were treated with interferon before virus challenge, and both before and after virus challenge. The most sensitive virus to both types of interferon was vesicular stomatitis. A porcine isolate of bovine herpesvirus type 1, hemagglutinating encephalomyelitis virus and porcine enterovirus types 1 and 2 were also highly sensitive to interferon-alpha. There was little reduction in the yield of porcine parvovirus or porcine rotavirus, while swinepox, swine influenza and transmissible gastroenteritis viruses were intermediate in their sensitivity to interferon-alpha. In addition to vesicular stomatitis virus, porcine adenovirus type 3, swine influenza, hemagglutinating encephalomyelitis and porcine rotavirus were highly sensitive to interferon-beta, while swinepox, bovine herpesvirus type 1, porcine parvovirus, transmissible gastroenteritis and porcine enteroviruses were less sensitive than the above viruses to interferon-beta, although all showed significant reductions in virus yield.

Activation of natural killer cells in newborn piglets by interferon induction

Natural killer (NK) cell activity in the peripheral blood lymphocytes (PBL) of newborn piglets, normally negligible, was stimulated by in vitro treatment with porcine type I interferon (IFN), and the NK activity of PBL from weaned piglets was augmented by the same treatment. Binding of the PBL to the PK-15 targets used in the single cell cytotoxicity assay for NK activity was not affected by age or by IFN treatment. When newborn piglets were treated with a single intravenous dose at 2 days of age of 0.5 mg/kg of polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly ICLC), a synthetic IFN inducer, their IFN levels peaked at 6 h post-induction, and NK activity in their PBL peaked at 24 h post-induction at the level normally found in weaned piglets. The NK activity then declined until 7 days post-induction, when it increased again in a similar manner to that in untreated control piglets. Target-binding of the PBL was not affected by poly ICLC treatment of the piglets. Newborn piglets treated with poly ICLC and subsequently exposed to infection with transmissible gastroenteritis (TGE) virus showed a delay in onset of clinical signs of TGE compared with untreated control piglets. It was concluded that NK cells in newborn piglets can be activated by treatment of the piglets with poly ICLC, and that the presence of active NK cells is associated with some increase in resistance to challenge with TGE virus.

Interferon induction in piglets with polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose

When newborn piglets were inoculated intravenously with 1.0, 0.5 or 0.25 mg kg-1 of polyinosinic:polycytidylic acid (poly I:C) complexed with poly-L-lysine and carboxymethylcellulose (poly ICLC), the highest serum interferon levels and the lowest white blood cell counts were found in response to a dose of 0.5 mg kg-1. Similar responses were observed in weaned piglets inoculated with 0.25 mg kg-1 of poly ICLC. Poly ICLC was a more effective interferon inducer than poly I:C, particularly in newborn piglets.

The effect of interferon induction in parturient sows and newborn piglets on resistance to transmissible gastroenteritis

High titers of interferon were found in the serum and milk of three sows treated two days after farrowing with polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose, but circulating interferon was not found in the piglets suckled by these sows. When two treated sows and their suckling piglets were exposed to infection with transmissible gastroenteritis virus eight hours after treatment, the sows showed no signs of disease, although they developed circulating interferon in response to the virus infection. The piglets suckled by the treated sows developed signs of transmissible gastroenteritis which were identical to those seen in a control litter of piglets suckled by an untreated sow. Piglets treated at two days of age with the polyinosinic:polycytidylic acid complex showed a delay in onset of clinical signs when exposed to infection with transmissible gastroenteritis virus, compared with untreated control piglets. When two sows were treated with the polyinosinic:polycytidylic acid complex before farrowing, neither circulating interferon nor activated natural killer cells were found in the piglets after birth.

The participation of antibody in spontaneous and antibody-dependent cell-mediated cytotoxicity in the pig

Treatment of porcine lymphocytes with trypsin reduced their spontaneous cell-mediated cytotoxicity (SCMC) activity against target cells persistently infected with transmissible gastroenteritis virus (PK15-TGE cells), but had no effect on antibody-dependent cell-mediated cytotoxicity (ADCC). SCMC activity was partially restored to trypsin-treated lymphocytes by incubation in RPMI-1640 medium or in medium containing F(ab')2 fragments of rabbit anti-porcine immunoglobulin, but not by brief incubation in autologous serum. F(ab')2 fragments of anti-porcine immunoglobulin did not block the SCMC reaction, but ADCC was greatly reduced by this reagent. Thus SCMC and ADCC mediated by porcine lymphocytes against PK15-TGE target cells clearly involved two distinct mechanisms in terms of antibody participation and sensitivity to trypsin.

The inactivation of a bovine enterovirus and a bovine parvovirus in cattle manure by anaerobic digestion, heat treatment, gamma irradiation, ensilage and composting

A bovine enterovirus and a bovine parvovirus seeded into liquid cattle manure were rapidly inactivated by anaerobic digestion under thermophilic conditions (55 degrees C), but the same viruses survived for up to 13 and 8 days respectively under mesophilic conditions (35 degrees C). The enterovirus was inactivated in digested liquid manure heated to 70 degrees C for 30 min, but the parvovirus was not inactivated by this treatment. The enterovirus, seeded into single cell protein (the solids recovered by centrifugation of digested liquid manure), was inactivated by a gamma irradiation dose of 1.0 Mrad, but the parvovirus survived this dose. When single cell protein seeded with bovine enterovirus or bovine parvovirus was ensiled with cracked corn, the enterovirus was inactivated after a period of 30 days, while the parvovirus survived for 30 days in one of two experiments. Neither the enterovirus nor the parvovirus survived composting for 28 days in a thermophilic aerobic environment when seeded into the solid fraction of cattle manure. It was concluded that, of the procedures tested, only anaerobic digestion under thermophilic conditions appeared to be reliable method of viral inactivation to ensure the safety of single cell protein for refeeding to livestock. Composting appeared to be a suitable method for the disinfection of manure for use as a soil conditioner.

Application of a modified indirect fluorescent antibody test to the detection of antibodies to bovine respiratory syncytial virus in Ontario cattle

A modified indirect fluorescent antibody test for the detection of serum antibodies to bovine respiratory syncytial virus was developed. The test made use of Terasaki plastic microtiter plates in which bovine respiratory syncytial virus (Saskatchewan strain) infected Georgia bovine kidney cells were grown and fixed in situ by a modified acetone fixation procedure. Evans blue dye was used as a counterstain to reduce nonspecific fluorescence. In a study of 986 field sera from a geographically broad cross-section of mature Ontario cattle, 95% of the samples were found to be positive at or above a 1:2 dilution. No seronegative regions, counties or herds were identified. When representative samples covering a range of indirect fluorescent antibody titers were further examined by a microtiter virus neutralization assay, a significant agreement was found between the two tests. Up to a fourfold decrease in titer was observed when antigen coated plates were stored at -70 degrees C for four months. The modified indirect fluorescent antibody test for bovine respiratory syncytial virus antibody detection proved to be a rapid, practical procedure for use in the diagnostic laboratory. This study confirms that bovine respiratory syncytial virus is widespread in the Ontario cattle population and that most mature cattle can be assumed to have been exposed to this virus.

Characterisation of the effector cells in antibody-dependent and spontaneous cell-mediated cytotoxicity in swine against target cells infected with transmissible gastroenteritis virus

When porcine peripheral blood leucocytes were fractionated, lymphocytes were the most active effectors in both antibody-dependent cell-mediated cytotoxicity (ADCC) and spontaneous cell-mediated cytotoxicity (SCMC), although both polymorphs and macrophages showed some activity in ADCC. Adsorption of lymphocytes to antibody-sensitised or unsensitized PK-15-transmissible gastroenteritis (TGE) cells caused similar reductions in ADCC and SCMC effector activities. Over 60 per cent of the target-binding lymphocytes were non-specific esterase positive large lymphocytes, which did not form erythrocyte (E)-rosettes, and about 30 per cent were non-specific esterase positive medium sized lymphocytes, which formed low avidity E-rosettes. The remainder were non-specific esterase negative small lymphocytes, some of which formed high avidity E-rosettes. None of the eluted lymphocytes stained for surface immunoglobulin and all formed low avidity erythrocyte-antibody rosettes. Porcine killer and natural killer cells resembled in many respects those described in humans and rodents.

The tissue distribution of spontaneous cell-mediated cytotoxicity effector lymphocytes in swine

Peripheral blood lymphocytes, intraepithelial lymphocytes from the small intestine and lymphocytes from the thymus, spleen, mesenteric lymph nodes and Peyer's patches from 5 young adult pigs were used as effector cells in a spontaneous cell-mediated cytotoxicity chromium release assay against PK-15 cells persistently infected with transmissible gastroenteritis virus as targets. Both peripheral blood and intraepithelial lymphocytes caused marked specific chromium release, while the lymphocytes from the remaining tissues were inactive in spontaneous cell-mediated cytotoxicity.

Interferon induction with polyinosinic:polycytidylic acid in the newborn piglet

Newborn piglets were treated with various doses of polyinosinic:polycytidylic acid intravenously and their serum interferon responses determined by a plaque reduction assay with vesicular stomatitis virus in Madin-Darby bovine kidney cells. A single dose of 5 mg of polyinosinic:polycytidylic acid was found consistently to induce detectable levels of interferon in serum, while the response to lower doses was inconsistent and higher doses produced clinical signs of toxicity. Piglets receiving 5 mg of polyinosinic:polycytidylic acid had maximum serum interferon titers between four and eight hours after treatment, and interferon was no longer detected at 72 hours after treatment. Following treatment with polyinosinic:polycytidylic acid leukopenia was observed, coincident with peak serum interferon titers. Elevated levels of serum glutamic oxaloacetic transaminase and blood urea, indicative of hepatic and renal dysfunction respectively, were also observed following interferon induction with polyinosinic:polycytidylic acid. Piglets treated with polyinosinic:polycytidylic acid also demonstrated antiviral activity in their intestinal mucosal tissues and intestinal washes, but the antiviral activity in the intestinal wash was not characterizable as interferon. A factor in the intestinal washes from newborn piglets was found to antagonize the antiviral effects of interferon by enhancing the plaque forming ability of vesicular stomatitis virus.

The role of interferon in spontaneous cell-mediated cytotoxicity in pigs

Specific release of 51Cr and the production of interferon (IFN) increased in parallel in a spontaneous cell-mediated cytotoxicity (SCMC) assay in which uninfected PK-15 cells or PK-15 cells persistently infected with transmissible gastroenteritis virus (PK-15-TGE cells) were used as targets, and peripheral blood lymphocytes (PBL) from a young adult pig were used as effector cells. Higher levels of both specific 51Cr release and IFN were obtained in the assays containing PK-15-TGE cells. Co-cultivation of PBL from newborn piglets with PK-15-TGE cells yielded similar levels of IFN to those produced by co-cultivation of adult PBL and PK-15-TGE cells, but lower levels of IFN were produced by co-cultivation with uninfected PK-15 cells. Pretreatment of adult PBL with IFN augmented their SCMC effector activity for both PK-15 and PK-15-TGE cells in the 51Cr release assay. Pretreatment of the PK-15-TGE target cells with IFN did not affect their release of 51Cr in the SCMC reaction, while IFN pretreatment of PK-15 targets protected them against SCMC. In a single cell cytotoxicity assay the effects of IFN pretreatment on the effector adult PBL and on the PK-15 and PK-15-TGE target cells were confirmed, and SCMC incompetent PBL from neonatal piglets were rendered cytotoxic by pretreatment with IFN. PBL from newborn piglets bound to either target cell with the same frequency as PBL from SCMC competent adult pigs, and IFN pretreatment of either effector or target cells had no effect on target-binding frequency.