To Transmissible Gastroenteritis Virus Research Articles

Porcine respiratory coronavirus genome sequences; comparisons and relationships to transmissible gastroenteritis viruses

Porcine respiratory coronavirus (PRCV) was initially detected in Europe, and later in the United States of America (US), in the 1980s. In this study we obtained and compared PRCV sequences from Europe and the US, and investigated how these are related to transmissible gastroenteritis virus (TGEV) sequences.The whole genome sequences of Danish (1/90-DK), Italian (PRCV15087/12 III NPTV Parma), and Belgian PRCV (91V44) strains are presented. These sequences were aligned with nine other PRCV sequences from Europe and the US, and 43 TGEV sequences. Following alignment of the PRCV sequences, it was apparent that multiple amino acid variations in the structural proteins were distinct between the European and US strains. The alignments were used to build phylogenetic trees to infer the evolutionary relationships between the strains. In these trees, the European PRCV strains clustered as a separate group, whereas the US strains of PRCV all clustered with TGEVs.

North American Porcine Reproductive and Respiratory Syndrome Viruses Inhibit Type I Interferon Production by Plasmacytoid Dendritic Cells

Although enveloped viruses typically trigger the prodigious secretion of alpha interferon (IFN-α) by plasmacytoid dendritic cells (pDC), porcine pDC remain quiescent when exposed to porcine reproductive and respiratory syndrome virus (PRRSV). This inactivity is likely due to virus-mediated interference since the typical IFN-α response by either purified or nonsorted porcine pDC to transmissible gastroenteritis virus (TGEV) or the Toll-like receptor 9 agonist, oligodeoxynucleotide (ODN) D19, was markedly reduced in the presence of PRRSV. Suppression occurred independently of virus viability and acidification of pDC early endosomes but correlated with diminished levels of IFN-α mRNA. This change was attributed to an abrogation of transcription resulting from a decrease in the otherwise enhanced amounts of the requisite interferon regulatory factor 7 (IRF-7), whose gene expression in turn was limited as a consequence of a lessened availability of nuclear-localized signal transducer and activator of transcription 1 (STAT1). While PRRSV also inhibited tumor necrosis factor alpha (TNF-α) synthesis by pDC responding to either agent, only the interleukin-2 (IL-2) and IL-6 production instigated by ODN D19 exposure was blocked. Likewise, PRRSV did not impact a specific TGEV-associated enhancement of IL-8 expression. Moreover, an augmented phosphorylation of NF-κB seen in activated pDC was not only unaffected by PRRSV but actually occurred in its presence. Thus, as supported by a demonstrated resilience of pDC to PRRSV infection, this pathogen may interact with a cell surface protein(s) to selectively impede the completion of cascades involved in cytokine production by stimulated pDC.

Binding characterization of determinants in porcine aminopeptidase N, the cellular receptor for transmissible gastroenteritis virus

Four truncated porcine aminopeptidase N (pAPN, a cellular receptor for porcine coronaviruses) proteins were expressed in prokaryotic cells. The recognizing of a specific serum against pAPN to these proteins was investigated by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. The binding ability of the proteins to transmissible gastroenteritis virus (TGEV), a porcine coronavirus, was analyzed by ELISA. The inhibitory effect of these proteins to cell infection by TGEV was analyzed using plaque assays. Our data indicate that three truncated pAPNs positively reacted with the specific antiserum and the major binding regions of pAPN were limited in regions 36aa–223aa, 349aa–591aa and 592–963aa. The proteins showed discrepant binding activity to either pAPN antibody or TGE virions. Moreover, the truncated proteins blocked the infection of cells by TGEV to different extent. The results suggest that the major antibody-binding domains of pAPN may associate with the receptor-binding determinants. The role of APN is discussed in the context of virus receptor usage.

Role of natural interferon‐producing cells and T lymphocytes in porcine monocyte‐derived dendritic cell maturation

Maturation of dendritic cells (DC) is a key immunological process regulating immune responses to pathogens and vaccines, as well as tolerance and autoimmune processes. Consequently, the regulation of DC maturation should reflect these multifaceted immunological processes. In the present study, we have defined the role of particular cytokines, Toll-like receptor (TLR) ligands and T lymphocytes in the porcine monocyte-derived DC (MoDC). Interferon-α (IFN-α) alone was a poor inducer of MoDC maturation, but in association with tumour necrosis factor-α (TNF-α), or TLR ligands such as lipopolysaccharide and polyinosinic-polycytidylic acid I:C, an up-regulation of major histocompatibility complex II and CD80/86 expression was noted, along with reduced endocytic activity. In contrast, TNF-α alone or in combination with the TLR ligands was a poor inducer of DC maturation, but co-operated with T-lymphocytes in the presence of antigen to induce DC maturation. Natural interferon producing cells (NIPC, or plasmacytoid DCs) represent a danger-recognition system of the immune defences, and can respond to viruses not otherwise recognized as posing a danger. Indeed, MoDC did not respond to transmissible gastroenteritis virus (TGEV), whereas NIPC produced high levels of IFN-α and TNF-α after TGEV stimulation. Moreover, supernatants from the stimulated NIPC induced maturation in MoDCs. These matured MoDCs displayed an enhanced ability to present antigen to and thus stimulate T cells. Taken together, the present work demonstrates that maturation of MoDC not only results from TLR signalling, but can require co-operation with various cell types – principally NIPC and activated T cells – which would reflect the particular immunological situation.

Application of reverse transcription polymerase chain reaction to detect porcine epidemic diarrhea virus in Vero cell culture.

Porcine epidemic diarrhea (PED) is a contagious diarrheal disease of swine. The disease is very similar to transmissible gastroenteritis (TGE), with high mortality in swine of all ages and high morbidity in neonates. 3,5 PED virus (PEDV), a coronavirus, was identified in 1978 as the etiologic agent of the disease. 4 PEDV is unable to grow in porcine cell cultures permissive to TGE virus. A method to propagate PEDV in Vero cells was described in 10 years after the first report of PED. 1 However, the high cost and prolonged time required to isolate and propagate PEDV in Vero cells have propelled the search for other diagnostic tests. Virus isolation has important implications in the diagnosis, epidemiology, and control of disease. The development of new techniques for the rapid identification of PEDV adaptation in Vero cells would greatly enhance PEDV detection. The objective of the present study was to describe the application of the reverse transcription polymerase chain reaction (RTPCR) technique to detect PEDV in Vero cell culture. Cell growth medium consisted of minimal essential medium (MEM) buffered with 20 mM HEPES and 0.2% (w/v) bicarbonate, supplemented with 5% (v/v) fetal bovine serum and antibiotics (10,000 IU/ml and penicillin, 10 mg/ml dihydrostreptomycin, 5 mg/ml neomycin, 10,000 IU/ml polymyxin). Virus infection medium consisted of MEM with 30 mM HEPES, a 1% (v/v) 0.3 M NaOH, 0.3% (w/v) tryptose phosphate broth, b 10 mg/ml trypsin (1:250), and antibiotics. Forty-one piglets from 35 farms were used to isolate PEDV. The presence of PEDV in the intestinal tissue of each of the pigs was confirmed by direct immunofluorescence antibody test using an anti-PEDV‐fluorescein isothiocyanate conjugate. c The mucosa and the content of the small intestine were collected and pooled, diluted 1:5 in phosphate-buffered saline (0.01 M, pH 7.2), ground by homogenization, and centrifuged for 20 minutes at 9,000 3 g. Before inoculation, the cell growth medium of monolayered Vero cells grown in 25-cm 2 flasks was removed, and the monolayers were washed twice with cell growth medium. The cells were inoculated with 1 ml of the homogenate per flask. After adsorption in the dark for 2 hours at room temperature, virus infection medium was added (5 ml/flask) without removing the virus inoculum. Because trypsin is thermolabile, 80% of virus infection medium was changed daily. Inoculated cell cultures were checked microscopically for cytopathic effects (CPE) daily. If the cell layer did not show CPE after 4 days of incubation, cells and supernatant fluids were frozen and thawed 3 times to release intracellular virus

Active and passive immune responses to transmissible gastroenteritis virus (TGEV) in swine inoculated with recombinant baculovirus-expressed TGEV spike glycoprotein vaccines

Abstract Objective Baculovirus-expressed transmissible gastroenteritis virus (TGEV) spike (S) glycoprotein vaccines were inoculated parenterally in swine to determine whether such vaccines could induce serum and whey virus-neutralizing (VN) antibodies and protective lactogenic immunity for TGEV-challenge-exposed pigs. Animals and Procedures 3 recombinant baculoviruses that expressed full or partial length TGEV Miller strain S glycoproteins were inoculated SC in 17 conventionally raised 11-day-old TGEV-seronegative pigs to determine whether the recombinant S glycoproteins would elicit serum VN antibodies. Eleven TGEV-seronegative pregnant sows were inoculated SC or intramammarily with subunit vaccines (R2-2 or R3-5) or control proteins. Pigs born to 9 of the 11 sows were challenge exposed at 4 to 5 days of age with the virulent Miller strain, and passive immunity was assessed. Serum and whey antibody responses to TGEV were analyzed by VN and ELISA testing. Results Recombinant S glycoproteins (R2-2 or R3-5) containing the 4 major antigenic sites induced similar VN antibody titers to TGEV in serum and colostrum, but low (some sows) or no VN antibody titer was detected in milk. Subcutaneous inoculation of sows with R2-2 or R3-5 elicited IgG, but not IgA antibodies to TGEV in colostrum. Morbidity was 100%, and mortality ranged from 20 to 80% in TGEV challenge-exposed pigs nursing sows inoculated SC or intramammarily with TGEV S glycoprotein vaccines. Conclusions and Clinical Relevance Parenterally administered TGEV S glycoprotein vaccines elicit VN antibodies to TGEV in serum and colostrum that do not fully provide active or passive immunity in swine. (Am J Vet Res 1997;58:242–250)

Contribution of passive immunity to porcine respiratory coronavirus to protection against transmissible gastroenteritis virus challenge exposure in suckling pigs

Abstract Objective To determine the ability of porcine respiratory coronavirus (PRCV) infections to induce passive immunity in suckling pigs to transmissible gastroenteritis virus (TGEV) challenge exposure. Design and Animals 4 TGEV seronegative sows and their litters (group A) served as controls, whereas 2 other groups (B and C) of sows (also TGEV seronegative) were oronasally inoculated with live PRCV during 1 or 2 subsequent pregnancies, respectively. Procedure Effectiveness of passive immunity provided to pigs via colostrum and milk was assessed after TGEV challenge exposure, and TGEV antibody responses in colostrum and milk were analyzed. Results Mortality in the 3 groups of young pigs correlated with severity of clinical signs of TGEV infection and was highest in control litters (86% in group-A pigs) and lowest in litters of sows inoculated with PRCV in 2 subsequent pregnancies (14% in group-C pigs). Virus-neutralization and IgA and IgG TGEV antibody titers of milk collected from sows at challenge exposure had significant positive correlation with litter survival. Significantly higher numbers of TGEV-specific IgA and IgG antibody-secreting cells were found in group-A pigs than in group-C pigs, suggesting that high titer of maternal antibodies (induced in group-C sows multiply exposed to PRCV) may interfere with active antibody responses. Conclusions and Clinical Relevance Results suggest that, in PRCV-infected pig herds, multiple exposures of pregnant sows are associated with higher IgA and IgG antibody titers to TGEV in milk, and these titers contribute to protection against TGEV infection. (Am J Vet Res 1996; 57:664–671)

Use of nonradioactive cDNA probes to differentiate porcine respiratory coronavirus and transmissible gastroenteritis virus isolates.

Porcine respiratory coronavirus (PRCV), a member of the family Coronaviridae, is antigenically related to transmissible gastroenteritis virus (TGEV) of swine. PRCV, now thought to be a mutant of TGEV, was first isolated in 1984 from pigs in Belgium that were seropositive for TGEV but did not have a history of clinical transmissible gastroenteritis (TGE). Since the initial isolation of PRCV, it has been found that infections of swine in Europe with PRCV are widespread. PRCV has also been isolated in swine in the United States, 7,11,20,24 but its prevalence in herds within the United States is not known. There are several similarities between PRCV and TGEV. Both viruses have 3 major structural proteins: the surface spike (S) glycoprotein, the integral membrane glycoprotein, and an internal nucleoprotein. Nucleotide sequences of PRCV isolates thus far studied show that they are closely related to TGEV but that there are some striking differences. PRCV isolates have a characteristic deletion in the 5' end of the S gene when compared to TGEV, and PRCV has a different tissue tropism than TGEV. TGEV replicates in both the respiratory and intestinal tissues and causes gastroenteritis, 14 whereas PRCV replicates to high titers in lung tissue of swine and with little or no replication in the intestinal tissues and no evidence of gastroenteritis and villous atrophy. PRCV is antigenically related to TGEV in that polyclonal sera which neutralize TGEV also neutralize PRCV. Thus, conventional serologic methods are not useful in determining if a swine herd with anti-TGEV antibodies has been infected with PRCV or TGEV. Anti-TGEV neutralizing monoclonal antibodies (MAbs) directed against the S glycoprotein readily neutralize PRCV; however, there are some nonneutralizing anti-TGEV MAbs directed against the S glycoprotein that can be used to distinguish between PRCV and TGEV isolates in a competitive binding assay. Of the European PRCV isolates that have had their nucleotide sequences published, all have a 672-nucleotide deletion in the 5' end of the S gene. The US PRCV isolates Ind/89 and ISU-1 have a 681-nucleotide deletion present in the 5' end of the S gene. Recently the PRCV isolates AR310 and LEPP have been shown to have a smaller S gene deletion of 621 nucleotides present. Additionally, the PRCV isolate IA1894 has recently been shown to have a 678-nucleotide deletion in the 5' end of its S gene. Hence, a cDNA probe that encompasses the region of the TGEV S gene that is characteristically deleted from PRCV isolates can be used

Immunity to transmissible gastroenteritis virus and porcine respiratory coronavirus infections in swine

Despite the pioneering efforts to identify correlates of passive immunity to transmissible gastroenteritis virus (TGEV), effective vaccines for the control of TGE in suckling pigs have remained elusive. The initial concept of an enteromammary immunologic axis in monogastrics originated from studies of lactogenic immunity to TGEV in swine. These studies revealed that infection of pregnant swine with virulent TGEV stimulated high titers of SIgA antibodies in milk which correlated with protection of suckling pigs against TGE; parenteral or oral inoculation with live attenuated or killed TGEV vaccines induced mainly IgG antibodies in milk which generally provided poor protection to suckling pigs. The recent appearance of PRCV infections in swine and continuing studies of TGEV infections, present a unique model for further studies of mucosal immunity. Research using these viruses has increased our understanding of the various components of the common mucosal immune system and their interactions. Although the most important consideration in designing an effective vaccine for TGEV is the stimulation of GALT through intestinal virus replication, studies addressing the contribution of BALT to immunity to TGEV and PRCV may provide insights for alternative vaccine approaches. The mechanism by which exposure to PRCV elicits a variable degree of immunity to TGEV challenge is unknown. Virus replication in the gut or respiratory tract is a major factor affecting the magnitude of the immune response at the respective site and may be necessary for the recruitment of specific immune cells from other mucosal inductive sites, i.e., GALT to BALT and BALT to GALT migration. Further studies on the induction and immune regulation of specific responses to TGEV and PRCV that affect the distribution patterns of IgM-, IgG- and IgA-antibody-secreting cells (ASC) and T lymphocytes should provide valuable insights for optimizing vaccine regimens to elicit the highest mucosal immune responses and optimal protection against TGEV challenge.

A sero-epizootiological study of porcine respiratory coronavirus in Belgian swine.

A porcine respiratory coronavirus (PRCV), antigenically closely related to transmissible gastroenteritis virus (TGEV), appeared in the European swine population in 1984. The present serological study was performed to obtain insight into the epizootiology of PRCV and of TGEV. PRCV-induced neutralizing antibodies were found in 90.6 per cent of the 160 sera collected from sows at slaughter, demonstrating the enzootic appearance of PRCV in the Belgian swine population. A serological study of fattening swine on 33 farms revealed that 11 farms situated in an area with a high farm density (all farms within 4 km2) and 11 on 22 closed breeding-fattening farms situated in areas with a low farm density (only one to four farms per 12 km2) were infected with PRCV throughout the year, whereas the other 11 closed breeding-fattening farms were temporarily free of PRCV. PRCV disappeared from the farms mainly in spring and summer. All the 11 farms became reinfected in autumn or winter, indicating that PRCV is regularly reintroduced in farms in the colder seasons. There was no correlation between the herd size and the temporary disappearance of PRCV from farms. It was observed on some farms that PRCV could infect pigs shortly after weaning in the presence of declining maternal antibodies, indicating that PRCV can persist on a farm by regularly infecting newly weaned pigs. TGEV-specific antibodies were found in 7.6 per cent of the 160 sera from the slaughterhouse sows. TGEV-specific antibodies were also detected in sera from fattening swine of 5 of the above mentioned 33 farms. TGEV-outbreaks were not observed on these farms.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of a Monoclonal Antibody Capture ELISA (MACELISA) to Indirect ELISA and Virus Neutralization Test for the Serodiagnosis of Transmissible Gastroenteritis Virus

An enzyme-linked immunosorbent assay (ELISA) in which the antigen is captured to the plate by monoclonal antibodies (MACELISA) was developed for the detection of antibodies to transmissible gastroenteritis virus (TGEV). The viral antigen was semipurified from TGEV-infected cells by simple ultracentrifugation. MACELISA results with 258 field sera were compared with those of a standard indirect ELISA and with the virus neutralization test (VNT). Sensitivity, specificity, and kappa values of MACELISA indicated a strong correlation with VNT results, whereas an indirect ELISA was less sensitive and much less specific than VNT. The serologic response of 4 pigs orally inoculated and intraperitoneally boostered with TGEV was compared using the 3 tests. Its sensitivity, specificity, and ability to use unpurified antigen make the MACELISA the advisable first step in TGEV serodiagnosis.

Infection of pigs with transmissible gastroenteritis virus from contaminated carcases

Sixteen 6-month-old pigs were exposed to transmissible gastroenteritis (TGE) virus by placing them in close contact with piglets infected at 1 week of age. Fourteen of the older pigs were slaughtered between 1 and 5 d after exposure to infection and their carcases dressed in simulated abattoir conditions. Samples of muscle, bone marrow and carcase lymph nodes were stored at -25 degrees C for at least 30 d and then homogenised and fed to groups of 1-week-old and 3-week-old pigs. Four of 12 one-week-old pigs died and TGE virus was isolated from intestinal contents of one of these. All pigs of both age groups developed neutralising antibody to TGE virus over the ensuing 4 w. The results indicate that carcases from pigs infected with TGE virus can represent a source of infection for susceptible pigs given access to them.

Antigenic homology among coronaviruses related to transmissible gastroenteritis virus

The antigenic homology of 26 coronavirus isolates, of which 22 were antigenically related to transmissible gastroenteritis virus (TGEV), was determined with 42 monoclonal antibodies. Type, group, and interspecies specific epitopes were defined. Two group specific MAbs distinguished the enteric TGEV isolates from the respiratory variants. An antigenic subsite involved in neutralization was conserved in porcine, feline, and canine coronavirus. The classification of the human coronavirus 229E in a taxonomic cluster distinct from TGEV group is suggested.

Lactogenic Immunity to Transmissible Gastroenteritis (TGE) of swine induced by the attenuated nouzilly strain of TGE virus: Passive protection of piglets and detection of serum and milk antibody classes by ELISA

Piglets of eight sows vaccinated by different routes with the attenuated TGE mutant coronavirus, Nouzilly (N) strain, and piglets from two field seropositive sows were challenged with a virulent TGE strain. On the day of challenge and 10 days after challenge, milk and serum samples from sows were analysed for their level of neutralizing antibodies, total immunoglobulin classes and TGE antibody classes by an ELISA. No direct relationship was seen between the level of protection of the litters and the titres of the different antibody classes on the day of challenge. However, an inverse correlation was seen 10 days after challenge between protection and the level of TGE antibodies.

Isolation of peplomer glycoprotein E2 of transmissible gastroenteritis virus and application in enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) based on peplomer glycoprotein E2 was developed for the detection of antibodies to transmissible gastroenteritis virus (TGEV). Purified preparations of E2 were isolated by solubilization of the viral membrane with nonion detergent Nonidet P-40, followed by sucrose density gradient sedimentation. ELISA optical density values with E2 antigen significantly exceeded the indices when other TGEV protein or intact virion antigen was used. It was shown that a virus protein concentration in the E2 preparation of 500 ng per well is sufficient to sensitize the solid phase of microplates. A comparison of the ELISA and the virus neutralization test for the detection of TGEV antibodies was conducted. A significant correlation between the ELISA and the virus neutralization test was shown (r = 0.97). This serological test may be successfully used for various immunologic investigations.

Identification of a 17000 molecular weight antigenic polypeptide in transmissible gastroenteritis virus-infected cells.

Pulse labelling of cells with [35S]methionine at different times after infection followed by SDS-PAGE was used to resolve and to identify polypeptides designated as specific to transmissible gastroenteritis virus (TGEV)-infected swine testicular (ST) cell cultures. The major TGEV structural proteins, with apparent molecular weights of 200,000 (200K), 47K and 30K were detected in radiolabelled cell extracts by 6 h postinfection. Additionally, a 17K major polypeptide was present in infected cells but not in mock-infected control cultures. Labelling with [3H]glucosamine revealed only the 200K and 30K proteins to be glycosylated. TGEV-primed porcine lymphocytes, secondarily stimulated in vitro with sucrose gradient-purified virus, produced antibody only to the two glycoproteins (gp) indicating that the 17K polypeptide is not a surface feature of the virion. Two pigs were infected oronasally with the virulent Miller strain of TGEV and their sera were analysed by immunoprecipitation. At 25 days postinfection convalescent sera responded strongly to gp30 and gp200 and there was a weak initial response to the 17K polypeptide. Serum immunoglobulins at 60 days postinfection reacted strongly to the 17K protein while the antibody response to gp30 was significantly reduced and that to gp200 was slightly reduced.

Antigenic relationship of the feline infectious peritonitis virus to coronaviruses of other species.

SummaryUtilizing the direct and indirect fluorescent antibody procedure, the antigenic relationship of the feline infectious peritonitis virus (FIPV) to 7 other human and animal coronaviruses was studied. FIPV was found to be closely related to transmissible gastroenteritis virus (TGEV) of swine. Transmissible gastroenteritis virus and FIPV were in turn antigenically related to human coronavirus 229E (HCV-229E) and canine coronavirus (CCV). An interesting finding in the study was that the 8 coronaviruses selected for this study fell into one of two antigenically distinct groups. Viruses in each group were antigenically related to each other to varying degrees, but were antigenically unrelated to coronaviruses of the second group. The first antigenically related group was comprised of mouse hepatitis virus, type 3 (MHV-3), hemeagglutinating encephalomyelitis virus 67N (HEV-67N) of swine, calf diarrhea coronavirus (CDCV), and human coronavirus OC43 (HCV-OC43). The second antigenically related group was comprised of FIPV, TGEV, HCV-229E and CCV.

Detection of transmissible gastroenteritis virus neutralising antibody in cats.

SummaryHigh titres of neutralising activity to transmissible gastroenteritis virus (TGEV), a porcine coronavirus, were found in sera and peritoneal fluids from cats infected with feline infectious peritonitis (FIP). A small proportion of cats, from a hospital population unaffected by FIP, also had neutralising activity. Procedures to remove non-specific viral inhibitors, including treatment by heat inactivation, trypsin, sulphydryl reagent and kaolin absorption were unsuccessful. The active component was unable to neutralise another porcine coronavirus, haemagglutinating encephalomyelitis virus or the porcine enterovirus, Talfan. Gel filtration of feline sera and peritoneal fluid demonstrated high levels of the neutralising activity in the area corresponding to 7S IgG, which could be removed by absorption with specific anti-IgG serum and these properties are suggested to be consistent with those of antibody. These findings imply that there is a coronavirus in cats which is antigenically related to TGEV and its possible nature is discussed.

Passive immunity in transmissible gastroenteritis of swine: immunoglobulin characteristics of antibodies in milk after inoculating virus by different routes.

Pregnant swine were exposed to transmissible gastroenteritis (TGE) virus by different routes, and their serum, colostrum, and mild were examined for titer and immunoglobulin (Ig) class of antibodies. When 2 to 4 days old, the litters of most of these animals were challenged with virulent TGE virus to determine the effectiveness of passive immunity. After two oral/intranasal exposures to attenuated virus, none of the six pregnant animals became sick. TGE antibodies in milk were primarily or solely of the IgG class, although low levels of IgA antibodies were detected in three animals. Pigs in the five challenged litters received some passive immunity, the mortality being 25%. After intramuscular injection of six pregnant swine with virulent virus, two types of clinical and immunological responses were observed, presumably dependent on whether the gut was infected by an hematogenous spread of the virus. Three became sick, showing typical clinical signs of TGE, and their immunological response was characterized by the occurrence in milk of antibodies of the IgA class. A good degree (0% mortality) of passive immunity occurred upon challenge of the suckling pigs. In contrast, in three pregnant animals that did not sicken, antibody in milk was primarily of the IgG calss, and poor (69% mortality) passive immunity occurred. After intramammary injections of three pregnant swine with virulent virus, no sickness was observed and the immunological response was characterized by the occurrence in colostrum of high titers of TGE antibodies that were primarily or solely of the IgG class; good (0% mortality) passive immunity occured. The occurrence in milk of TGE antibodies of the IgA class was associated with an intestinal infection, whereas antibodies of the IgG class resulted from a parenteral antigenic stimulation. The role of antigenic stimulation of the intestinal tract for providing antibodies in milk of the IgA class is discussed. Passive immunity against intestinal infection with TGE virus was generally more complete in pigs ingesting antibodies of the IgA than of the IgG class.

Antibody responses in serum, colostrum, and milk of swine after infection or vaccination with transmissible gastroenteritis virus.

The antibody response of pregnant swine to transmissible gastroenteritis (TGE) virus was studied, with special reference to the titers and the immunoglobulin (Ig) class of TGE neutralizing antibodies in colostrum and milk. Animals vaccinated twice intramuscularly or intramammarily with live attenuated TGE virus developed high levels of antibodies in serum and colostrum, but the levels in milk declined markedly within a few days post-farrowing. In contrast, animals naturally or experimentally infected with virulent virus generally developed lower levels of antibodies in serum and colostrum but maintained higher levels in milk, as compared to the vaccinated animals. Gel filtration studies indicated that antibodies in milk from vaccinated animals were primarily of the IgG class, whereas those from the naturally or experimentally infected animals were primarily of the IgA class. The ability of sows to transmit a high degree of passive immunity to their suckling progeny was more closely associated with TGE antibodies of the IgA than the IgG class. Present evidence suggests that high levels of TGE antibodies of the IgA class occur in milk as a result of an infection of the intestinal tract. Probable reasons for this are discussed.