Mucosal immunity: an overview and studies of enteric and respiratory coronavirus infections in a swine model of enteric disease

Establishment of enzyme-linked immunosorbent assays based on recombinant S1 and its truncated proteins for detection of PEDV IgA antibody

Porcine epidemic diarrhea virus (PEDV) can infect pigs of all ages, especially piglets. PEDV has spread across Asia since the 1980s. The highly virulent variant PEDV broke out on a large scale and caused huge economic losses to the pig industry in late 2010 in China. Rapid detection methods with high specificity and sensitivity are urgently needed for the diagnosis and control of the disease. In this study, we divided the PEDV S1 gene into three segments and constructed the recombinant plasmids pFastBac1-S1T1 (aa 21–279), pFastBac1-S1T2 (aa 280–539) and pFastBac1-S1T3 (aa 540–788), which carry the different antigenic regions of the S1 gene. Truncated S1 proteins PEDV-S1T1/S1T2/S1T3 were obtained by a Bac-to-Bac expression system, with protein sizes of 36 kDa, 38 kDa and 38 kDa, respectively. Recombinant proteins presented high reactivity with the monoclonal antibody against PEDV and positive pig serum. Based on full-length S1 protein and these truncated proteins, we established indirect ELISA methods for the detection of PEDV IgA antibody. A total of 213 clinical serum samples were tested by the above indirect ELISA methods, and IFA was used as the gold standard. ROC curves revealed a significant correlation between S1-ELISA and S1T2-ELISA with a 0.9134 correlation coefficient and favourable sensitivity and specificity of S1-ELISA (93.24%, 95.68%) and S1T2-ELISA (89.33%, 94.16%). Our results also indicated that serum with higher neutralizing activity (SNT ≥ 40) had a higher IgA antibody level based on S1-ELISA, S1T1-ELISA and S1T2-ELISA. In conclusion, both S1-ELISA and S1T2-ELISA can be used as candidate systems for detecting anti-PEDV IgA antibody titers in serum, which can reflect the level of neutralizing activity in pigs after natural infection or vaccination. The above research results provide a basis for the prevention and control of PEDV and can be used in the detection of host anti-infective immunity and evaluation of vaccine immune effects.

Systemic Homologous Neutralizing Antibodies Are Inadequate for the Evaluation of Vaccine Protective Efficacy against Coinfection by High Virulent PEDV and PRRSV

G2 porcine epidemic diarrhea virus (G2 PEDV) and highly pathogenic porcine reproductive and respiratory syndrome virus 2 (HP-PRRSV2) are two of the most prevalent swine pathogens in China's swine herds, and their coinfection occurs commonly. Several PED and PRRS vaccines have been utilized in China for decades, and systemic homologous neutralizing antibodies (shnAbs) in serum are frequently used to evaluate the protective efficacy of PED and PRRS vaccines. To develop a vaccine candidate against G2 PEDV and HP-PRRSV2 coinfection, in this study, we generated a chimeric virus (rJSTZ1712-12-S) expressing S protein of G2 PEDV using an avirulent HP-PRRSV2 rJSTZ1712-12 infectious clone as the viral vector. The rJSTZ1712-12-S strain has similar replication efficacies as the parental rJSTZ1712-12 virus. In addition, animal inoculation indicated that rJSTZ1712-12-S is not pathogenic to piglets and can induce shnAbs against both G2 PEDV and HP-PRRSV2 isolates after prime-boost immunization. However, passive transfer study in neonatal piglets deprived of sow colostrum showed that rJSTZ1712-12-S-induced shnAbs may only decrease PEDV and PRRSV viremia but cannot confer sufficient protection against dual challenge of high virulent G2 PEDV XJ1904-34 strain and HP-PRRSV2 XJ17-5 isolate. Overall, this study provides the first evidence that shnAbs confer insufficient protection against PEDV and PRRSV coinfection and are inadequate for the evaluation of protective efficacy of PED and PRRS bivalent vaccine (especially for the PED vaccine). IMPORTANCE Porcine epidemic diarrhea virus (PEDV) and porcine reproductive and respiratory syndrome virus (PRRSV) coinfection occurs commonly and can synergistically reduce feed intake and pig growth. Vaccination is an effective strategy utilized for PED and PRRS control, and systemic homologous neutralizing antibodies (shnAbs) in serum are commonly used for protective efficacy evaluation of PED and PRRS vaccines. Currently, no commercial vaccine is available against PEDV and PRRSV coinfection. This study generated a chimeric vaccine candidate against the coinfection of prevalent PEDV and PRRSV in China. The chimeric strain can induce satisfied shnAbs against both PEDV and PRRSV after prime-boost inoculation in pigs. But the shnAbs cannot confer sufficient protection against PEDV and PRRSV coinfection in neonatal piglets. To the best of our knowledge, these findings provide the first evidence that shnAbs confer insufficient protection against PEDV and PRRSV coinfection and are inadequate for evaluating PED and PRRS bivalent vaccine protective efficacy.

Swine as biomedical animal model for T-cell research-Success and potential for transmittable and non-transmittable human diseases

Swine is biologically one of the most relevant large animal models for biomedical research. With its use as food animal that can be exploited as a free cell and tissue source for research and its high susceptibility to human diseases, swine additionally represent an excellent option for both the 3R principle and One Health research. One of the previously most limiting factors of the pig model was its arguably limited immunological toolbox. Yet, in the last decade, this toolbox has vastly improved including the ability to study porcine T-cells. This review summarizes the swine model for biomedical research with focus on T cells. It first contrasts the swine model to the more commonly used mouse and non-human primate model before describing the current capabilities to characterize and extend our knowledge on porcine T cells. Thereafter, it not only reflects on previous biomedical T-cell research but also extends into areas in which more in-depth T-cell analyses could strongly benefit biomedical research. While the former should inform on the successes of biomedical T-cell research in swine, the latter shall inspire swine T-cell researchers to find collaborations with researchers working in other areas - such as nutrition, allergy, cancer, transplantation, infectious diseases, or vaccine development.

A novel spike subunit 1-based enzyme-linked immunosorbent assay reveals widespread porcine torovirus infection in eastern China

Toroviruses (ToVs), closely related but genetically distinct from coronaviruses, are known to infect horses, cows, pigs, goats and humans, mainly causing enteritic disorders. However, due to the lack of an adaptive culture system, porcine ToV (PToV) has received less attention. In this study, we developed a novel serological detection method based on the PToV envelope spike subunit 1 (S1) protein for the first time, and compared it to an existing indirect enzyme-linked immunosorbent assay (ELISA) based on the nucleocapsid protein. By using the S1-based ELISA, we carried out the first seroepidemiological survey of PToV in China, assaying both specific IgG and IgA responses in 1,037 serum samples collected from diarrheic pigs in eastern China. There was a relatively high incidence of seropositivity in pigs of different ages, especially one-week-old piglets and sows (78% and 43%), the former probably reflecting maternal antibodies. Furthermore, 3/20 (15%) of faecal samples collected from one PToV-seropositive swine herd in Zhejiang province tested positive by RT-PCR. The complete PToV genome was sequenced from one of these samples, and its phylogenetic relationship with other full-length PToV sequences available in GenBank was determined. Our data provide the first serological evidence for PToV infection in pigs from China, which will help elucidate the potential pathogenicity of PToV in pigs.

Systemic and intestinal porcine epidemic diarrhea virus-specific antibody response and distribution of antibody-secreting cells in experimentally infected conventional pigs

Porcine epidemic diarrhea (PED) is a coronavirus disease characterized by the rapid spread of severe diarrhea among pigs. PED virus (PEDV) infects and replicates mainly in the epithelial cells of the duodenum, jejunum, ileum and colon. Serum or mucosal IgA antibody levels have been used to predict both vaccine efficacy and the level of protective immunity to enteric infectious diseases in individuals or herds. Details of the B-cell immune response upon PEDV infection, such as the systemic and mucosal PEDV IgA antibody response, the distribution of IgA antibody-secreting cells (ASCs), and their role in virus clearance are not yet clear. In this experimental infection study, we observed similar fluctuations in PEDV IgA antibody levels in serum and intestinal contents of the upper and lower jejunum and ileum, but not fecal samples, over the 4-week experimental course. ASCs that actively secrete PEDV IgA antibody without in vitro stimulation were distributed mainly in the upper jejunum, whereas memory B cells that showed enhanced PEDV IgA antibody production upon in vitro stimulation were observed in mesenteric lymph nodes and the ileum. Our findings will contribute to the development of effective vaccines and diagnostic methods for PEDV.

Applying Immune Instincts and Maternal Intelligence from Comparative Microbiology to COVID-19

New data specific to COVID-19 are emerging quickly on key issues of immunity and prevention, but past research in coronavirology and for other human pathogens (e.g., Mycoplasma pneumoniae) has been available and of great relevance. Considerable study of endemic human coronaviruses has shown that neutralizing antibody correlates with protection, but effective clinical protection is variable for subsequent virus exposure. Animal coronavirus research has emphasized the importance of local mucosal protection (especially IgA) and systemic responses. Animal model and human post-infection studies for SARS-CoV and MERS-CoV are largely corroborative. Whether for passive therapeutic strategies or vaccination, these findings provide a template for COVID-19. Many approaches to vaccination have emerged, and there may be more than one vaccine that will be applied, but individualized obstacles and concerns for administration, efficacy, and safety are inevitable. Regardless of safeguards or promises that may be understood from laboratory or vertebrate experiments, observations from large-scale human trials will ultimately prove to shape the medical future. Focus on common mucosal immunity can be underrated, and equally or more, focus on lactogenic immunity may be underestimated. In understanding both passive immunity and protection, the body is already primed to educate us with decisions of what constitutes protection and harm. This review provides key insights that drive hypotheses into how the instinct of immunity and the intelligence of the maternal component of the common mucosal immune system has already guided us and may continue to do so effectively into a bright and safe future.

Development of an indirect ELISA for detecting porcine deltacoronavirus IgA antibodies

Porcine deltacoronavirus (PDCoV) is a novel coronavirus that can cause vomiting and watery diarrhea in pigs and death in piglets. Since PDCoV was first detected in 2009 in Hong Kong, the prevalence of PDCoV has increased in recent years, resulting in serious economic losses to the swine industry. The coronavirus spike (S) protein is an antigen that has been demonstrated to contain epitopes that induce neutralizing antibodies. The presence of serum and milk IgA antibodies against pathogens that replicate primarily on mucosal surfaces is important for mucosal immunity. Here, an indirect anti-PDCoV IgA antibody enzyme-linked immunosorbent assay (PDCoV S1 IgA ELISA) using the purified S1 portion of S protein as the coating antigen was developed to detect PDCoV IgA antibodies in serum and sow’s milk. A receiver operating characteristic (ROC) curve analysis showed high specificity and sensitivity of the PDCoV-S1-IgA-ELISA based on samples confirmed by IFA. Anti-PDCoV IgA antibodies in 152 serum samples and 65 milk samples collected from six farms that had experienced diarrhea outbreaks within previous last two years were detected by this assay, and 62.5% of the serum samples and 100% of the milk samples were positive for PDCoV. The indirect ELISA method established in this study will provide a convenient tool for measurement of serum and milk IgA levels against PDCoV in pig herds, rapid detection of PDCoV infection in pigs, and evaluation of the immunogenicity of vaccines.

Circular RNA CircEZH2 Suppresses Transmissible Gastroenteritis Coronavirus-induced Opening of Mitochondrial Permeability Transition Pore via Targeting MiR-22 in IPEC-J2

Transmissible gastroenteritis (TGE) is a contagious and infectious disease that is characterized by severe vomiting and diarrhea of swine , especially piglet, and caused by transmissible gastroenteritis coronavirus (TGEV) . TGEV infection provokes mitochondrial damage of porcine intestinal epthelial cell (IPEC), which is responsible for inflammation and cell death. In our previous study, we have demonstrated that circular RNA circEZH2 was down-regulated during TGEV infection and promoted the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) via targeting miR-22 in porcine intestinal epithelial cell line (IPEC-J2). Activation of NF-κB is an important factor for mitochondrial damage. Mitochondrial permeability transition pore (mPTP) opening is a key reason for mitochondrial damage. So, we speculate that circEZH2 may regulate TGEV-induced mPTP opening via NF-kB pathway. In the present study, we found that mPTP opening of IPEC-J2 was occured during TGEV infection and suppressed by circEZH2 via attaching miR-22. Hexokinase 2 (HK2) and interleukin 6 (IL-6) were identified as the targets of miR-22. Silencing HK2 enhanced TGEV-induced mPTP opening, while no effect on NF-κB pathway. Silencing IL-6 promoted TGEV-induced mPTP opening and inhibited NF-κB pathway. Inhibitor of NF-κB increased TGEV-induced mPTP opening. The data revealed that TGEV-induced mPTP opening was regulated via two pathways: circEZH2/miR-22/HK2 axis and circEZH2/miR-22/IL-6/NF-κB axis.

Display of Porcine Epidemic Diarrhea Virus Spike Protein on Baculovirus to Improve Immunogenicity and Protective Efficacy

A new variant of the porcine epidemic diarrhea virus (PEDV) is an emerging swine disease, killing considerable numbers of neonatal piglets in North America and Asia in recent years. To generate immunogens mimicking the complex spike (S) protein folding with proper posttranslational modification to mount a robust immune response against the highly virulent PEDV, two baculoviruses displaying the full-length S protein (S-Bac) and the S1 protein (S1-Bac) of the virulent Taiwan genotype 2b (G2b) PEDV Pintung 52 (PEDV-PT) strain were constructed. Intramuscular immunizations of mice and piglets with the S-Bac and S1-Bac demonstrated significantly higher levels of systemic anti-PEDV S-specific IgG, as compared with control group. Our results also showed that piglets in the S-Bac group elicited superior PEDV-specific neutralizing antibodies than those of the S1-Bac and control groups. The highly virulent PEDV-PT strain challenge experiment showed that piglets immunized with S-Bac and S1-Bac showed milder clinical symptoms with significantly less fecal viral shedding as compared with non-immunized control piglets. More importantly, piglets immunized with the S-Bac exhibited no to mild clinical signs, with a delayed, minimal viral shedding. Our results demonstrated that the S-Bac could serve as a safe, easy to manipulate, and effective vaccine candidate against the PEDV infection.

Transmissible gastroenteritis virus infection induces NF-κB activation through RLR-mediated signaling

Transmissible gastroenteritis virus (TGEV) is a porcine enteric coronavirus which causes lethal severe watery diarrhea in piglets. The pathogenesis of TGEV is strongly associated with inflammation. In this study, we found that TGEV infection activates transcription factors NF-κB, IRF3 and AP-1 in a time- and dose-dependent manner in porcine kidney cells. Treatment with the NF-κB-specific inhibitor BAY11-7082 significantly decreased TGEV-induced proinflammatory cytokine production, but did not affect virus replication. Phosphorylation of NF-κB subunit p65 and proinflammatory cytokine production were greatly decreased after knockdown of retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) or its adaptors MAVS and STING, while only slight reduction was observed in cells following silencing of Toll-like receptor adaptors, MyD88 and TRIF. Furthermore, TGEV infection significantly upregulated mRNA expression of RIG-I and MDA5. Taken together, our results indicate that the RLR signaling pathway is involved in TGEV-induced inflammatory responses.

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Transmissible gastroenteritis virus (TGEV) infection activates NF-κB.

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Inhibition of NF-κB activation does not affect TGEV replication.

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RLR signaling pathway is involved in TGEV-induced inflammatory responses.

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TGEV infection significantly upregulates mRNA expression of RIG-I and MDA5.

A phase trial of the oral Lactobacillus casei vaccine polarizes Th2 cell immunity against transmissible gastroenteritis coronavirus infection

Transmissible gastroenteritis coronavirus (TGEV) is a member of the genus Coronavirus, family Coronaviridae, order Nidovirales. TGEV is an enteropathogenic coronavirus that causes highly fatal acute diarrhoea in newborn pigs. An oral Lactobacillus casei (L. casei) vaccine against anti-transmissible gastroenteritis virus developed in our laboratory was used to study mucosal immune responses. In this L. casei vaccine, repetitive peptides expressed by L. casei (specifically the MDP and tuftsin fusion protein (MT)) were repeated 20 times and the D antigenic site of the TGEV spike (S) protein was repeated 6 times. Immunization with recombinant Lactobacillus is crucial for investigations of the effect of immunization, such as the first immunization time and dose. The first immunization is more important than the last immunization in the series. The recombinant Lactobacillus elicited specific systemic and mucosal immune responses. Recombinant L. casei had a strong potentiating effect on the cellular immunity induced by the oral L. casei vaccine. However, during TGEV infection, the systemic and local immune responses switched from Th1 to Th2-based immune responses. The systemic humoral immune response was stronger than the cellular immune response after TGEV infection. We found that the recombinant Lactobacillus stimulated IL-17 expression in both the systemic and mucosal immune responses against TGEV infection. Furthermore, the Lactobacillus vaccine stimulated an anti-TGEV infection Th17 pathway. The histopathological examination showed tremendous potential for recombinant Lactobacillus to enable rapid and effective treatment for TGEV with an intestinal tropism in piglets. The TGEV immune protection was primarily dependent on mucosal immunity.

Human microbiota-associated swine: current progress and future opportunities

Gnotobiotic (GN) rodent models have provided insight into the contributions of the gut microbiota to host health and preventing disease. However, rodent models are limited by several important physiological and metabolic differences from humans, and many rodent models do not dependably replicate the clinical manifestations of human diseases. Due to the high degree of similarity in anatomy, physiology, immunology and brain growth, the domestic pig (Sus scrofa) is considered a clinically relevant model to study factors influencing human gastrointestinal, immune, and brain development. Gnotobiotic piglet models have been developed and shown to recapitulate key aspects of GN rodent models. Human microbiota-associated (HMA) piglets have been established using inocula from infants, children, and adults. The gut microbiota of recipient HMA piglets was more similar to that of the human donor than that of conventionally reared piglets harboring a pig microbiota. Moreover, Bifidobacterium and Bacteroides, two predominant bacterial groups of infant gut, were successfully established in the HMA piglets. Thus, the HMA pig model has the potential to be a valuable model for investigating how the gut microbiota composition changes in response to environmental factors, such as age, diet, vaccination, antibiotic use and infection. The HMA also represents a robust model for screening the efficacy of pre- and probiotic interventions. Lastly, HMA piglets can be an ideal model with which to elucidate microbe-host interactions in human health and disease due to the similarities to humans in anatomy, physiology, developmental maturity at birth, and the pathophysiology of many human diseases.

Detection of immunoglobulin (Ig) A antibodies against porcine epidemic diarrhea virus (PEDV) in fecal and serum samples

Many assays for detection of antibodies against porcine epidemic diarrhea virus (PEDV) are based on detection of neutralizing antibodies or immunoglobulin (Ig) G in serum samples. However, due to the particular features of the mucosal immune system, presence of serum antibodies against enteric pathogens, such as PEDV, not always correlates with protection. In contrast, anti-PEDV IgA antibodies correlate with protection against subsequent challenges. An indirect PEDV IgA ELISA was previously developed to monitor IgA levels in colostrum and milk samples. In the present paper we describe an adaptation of the protocol for detection of IgA antibodies in serum and fecal samples.•

The adapted protocol will aid in future assessment of protective levels of humoral response against PEDV infection by measuring IgA levels in serum and fecal samples.

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Fecal samples are non-invasive and easy to collect at any time by animal caretakers and therefore offering advantages over the serum sample collection procedure.

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A strong positive correlation between the anti-PEDV levels in fecal and serum samples was identified; however, detection of IgA antibodies was often more successful in serum than in paired fecal samples due to overall lower sample-to-positive (S/P) ratios for the latter sample type.

Evidence for a common mucosal immune system in the pig

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There is evidence that the common mucosal immune system exists in pigs.

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Vaccination at an easily accessible mucosal site may assist in providing protection at other mucosal sites.

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Local and distal mucosal sites should be sampled after vaccinations to define the optimal dose and formulation which promotes the common mucosal immune system in pigs.

The majority of lymphocytes activated at mucosal sites receive instructions to home back to the local mucosa, but a portion also seed distal mucosa sites. By seeding distal sites with antigen-specific effector or memory lymphocytes, the foundation is laid for the animal's mucosal immune system to respond with a secondary response should to this antigen be encountered at this site in the future. The common mucosal immune system has been studied quite extensively in rodent models but less so in large animal models such as the pig. Reasons for this paucity of reported induction of the common mucosal immune system in this species may be that distal mucosal sites were examined but no induction was observed and therefore it was not reported. However, we suspect that the majority of investigators simply did not sample distal mucosal sites and therefore there is little evidence of immune response induction in the literature. It is our hope that more pig immunologists and infectious disease experts who perform mucosal immunizations or inoculations on pigs will sample distal mucosal sites and report their findings, whether results are positive or negative. In this review, we highlight papers that show that immunization/inoculation using one route triggers mucosal immune system induction locally, systemically, and within at least one distal mucosal site. Only by understanding whether immunizations at one site triggers immunity throughout the common mucosal immune system can we rationally develop vaccines for the pig, and through these works we can gather evidence about the mucosal immune system that may be extrapolated to other livestock species or humans.

Antigenic structures stably expressed by recombinant TGEV-derived vectors

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

Advances in swine immunology help move vaccine technology forward

In veterinary animal species, vaccines are the primary tool for disease prevention, a key tool for treatment of infection, and essential for helping maintain animal welfare and productivity. Traditional vaccine development by trial-and-error has achieved many successes. However, effective vaccines that provide solid cross-protective immunity with excellent safety are still needed for many diseases. The path to development of vaccines against difficult pathogens requires recognition of uniquely evolved immunological interactions of individual animal hosts and their specific pathogens. Here, general principles that currently guide veterinary immunology and vaccinology research are reviewed, with an emphasis on examples from swine. Advances in genomics and proteomics now provide the community with powerful tools for elucidation of regulatory and effector mechanisms of protective immunity that provide new opportunities for successful translation of immunological discoveries into safe and effective vaccines.

Alphacoronavirus protein 7 modulates host innate immune response

Innate immune response is the first line of antiviral defense resulting, in most cases, in pathogen clearance with minimal clinical consequences. Viruses have developed diverse strategies to subvert host defense mechanisms and increase their survival. In the transmissible gastroenteritis virus (TGEV) as a model, we previously reported that accessory gene 7 counteracts the host antiviral response by associating with the catalytic subunit of protein phosphatase 1 (PP1c). In the present work, the effect of the absence of gene 7 on the host cell, during infection, was further analyzed by transcriptomic analysis. The pattern of gene expression of cells infected with a recombinant mutant TGEV, lacking gene 7 expression (rTGEV-Δ7), was compared to that of cells infected with the parental virus (rTGEV-wt). Genes involved in the immune response, the interferon response, and inflammation were upregulated during TGEV infection in the absence of gene 7. An exacerbated innate immune response during infection with rTGEV-Δ7 virus was observed both in vitro and in vivo. An increase in macrophage recruitment and activation in lung tissues infected with rTGEV-Δ7 virus was observed compared to cells infected with the parental virus. In summary, the absence of protein 7 both in vitro and in vivo led to increased proinflammatory responses and acute tissue damage after infection. In a porcine animal model, which is immunologically similar to humans, we present a novel example of how viral proteins counteract host antiviral pathways to determine the infection outcome and pathogenesis.

Detection of four human coronaviruses in respiratory infections in children: a one-year study in Colorado

Lower respiratory tract infections are the leading cause of death in children worldwide. Studies on the epidemiology and clinical associations of the four human non‐SARS human coronaviruses (HCoVs) using sensitive polymerase chain reaction (PCR) assays are needed to evaluate the clinical significance of HCoV infections worldwide. Pediatric respiratory specimens (1,683) submitted to a diagnostic virology laboratory over a 1‐year period (December 2004–November 2005) that were negative for seven respiratory viruses by conventional methods were tested for RNA of four HCoVs using sensitive RT‐PCR assays. Coronavirus RNAs were detected in 84 (5.0%) specimens: HCoV‐NL63 in 37 specimens, HCoV‐OC43 in 34, HCoV‐229E in 11, and HCoV‐HKU1 in 2. The majority of HCoV infections occurred during winter months, and over 62% were in previously healthy children. Twenty‐six (41%) coronavirus positive patients had evidence of a lower respiratory tract infection (LRTI), 17 (26%) presented with vomiting and/or diarrhea, and 5 (8%) presented with meningoencephalitis or seizures. Respiratory specimens from one immunocompromised patient were persistently positive for HCoV‐229E RNA for 3 months. HCoV‐NL63‐positive patients were nearly twice as likely to be hospitalized (P = 0.02) and to have a LRTI (P = 0.04) than HCoV‐OC43‐positive patients. HCoVs are associated with a small, but significant number (at least 2.4% of total samples submitted), of both upper and lower respiratory tract illnesses in children in Colorado. Our data raise the possibility that HCoV may play a role in gastrointestinal and CNS disease. Additional studies are needed to investigate the potential roles of HCoVs in these diseases. J. Med. Virol. 81:1597–1604, 2009. © 2009 Wiley‐Liss, Inc.

Intragastric administration of attenuated Salmonella typhimurium harbouring transmissible gastroenteritis virus (TGEV) DNA vaccine induced specific antibody production

Attenuated Salmonella typhimurium was selected as a transgenic vehicle for the development of live mucosal vaccines against transmissible gastroenteritis virus (TGEV). A 2.2kb DNA fragment, encoding for N-terminal domain glycoprotein S of TGEV, was amplified by RT-PCR and cloned into eukaryotic expression vector pVAX1. The recombinant plasmid pVAX-S was transformed by electroporation into attenuated S. typhimurium SL7207, the expression and translation of the pVAX-S delivered by recombinant S. typhimurium SL7207 (pVAX-S) was detected in vitro and in vivo respectively. BALB/c mice were inoculated orally with SL7207 (pVAX-S) at different dosages, the bacterium was safe to mice at dosage of 2x10(9)CFU and eventually eliminated from the spleen and liver at week 4 post-immunization. Mice immunized with different dosages of SL7207 (pVAX-S) elicited specific anti-TGEV local mucosal and humoral responses as measured by indirect ELISA assay. Moreover, the immunogenicity of the DNA vaccine was highly dependent on the dosage of the attenuated bacteria used for oral administration, 10(9)CFU dosage group showed higher antibody response than 10(8)CFU and 10(7)CFU dosages groups during week 4-8 post-immunization. The results indicated that attenuated S. typhimurium could be used as a delivery vector for oral immunization of TGEV DNA vaccine.

Studies on Mucosal Immunity Induced by Transmissible Gastroenteritis Virus Nucleocapsid Protein Recombinant Lactobacillus casei in Mice and Sow

Mucosal immunity plays an important role in protecting pigs against transmissible gastroenteritis virus (TGEV) infection. To elicit mucosal immune response against TGEV, we developed a surface antigen display system using the poly-[.gamma]-glutamate synthetase A (pgsA) protein of Bacillus subtilis as an anchoring matrix to express recombinant fusion proteins of pgsA and nucleocapsid protein of TGEV in Lactobacillus casei. Surface location of fusion protein was verified by ELISA and indirect immunofluorescence test. Oral and intranasal inoculations of pregnant sow and mice with recombinant L. casei resulted in high levels of serum immunoglobulin G (IgG) and secretory immunoglobulin A (sIgA) against recombinant N protein as demonstrated by ELISA. More importantly, the level of specific sIgA in colostrum significantly increased compared with that of IgG. The serum IgG levels of the piglets increased after suckling colostrum produced by sows was previously inoculated with recombinant L. casei. These results indicate that immunization with recombinant L. casei expressing TGEV N protein on its surface elicited high levels of specific sIgA and circulating IgG against TGEV N protein.

Surface-displayed porcine epidemic diarrhea viral (PEDV) antigens on lactic acid bacteria

In this report, for surface display of viral antigen on lactobacilli, we have developed a surface antigen display system using the poly-gamma-glutamate synthetase A protein (pgsA) of Bacillus subtilis as an anchoring matrix. Recombinant fusion proteins comprised of pgsA and neucleocapsid protein of PEDV were stably expressed in Lactobacillus casei. Surface location of fusion protein was verified by ELISA, immunofluoresence microscopy. Oral and intranasal inoculations of recombinant L. casei into pregnant sow and mice resulted in high levels of serum immunoglobuline G (IgG) and mucosal IgA, as demonstrated by rnELISA(recombinant N protein ELISA) using recombinant N protein. Absorbance of IgG in pregnant sow sera highly increased duration of the experiment. More importantly, the level of IgA in colostrum were increased significantly higher than that of IgG. The IgG levels of the piglets were increased after suckling colostrum secreted from sows previously inoculated recombinant L. casei. These results indicate that mucosal immunization with recombinant L. casei expressing PEDV N protein (neucleoprotein of PEDV) on its surface elicited high levels of mucosal IgA and circulation IgG immune responses against the antigen N of PEDV.

High-cell-passage canine coronavirus vaccine providing sterilising immunity

Objectives: To evaluate the ability of a high‐cell‐passage canine coronavirus vaccine to immunise dogs against challenge with a field isolate of the virus.

Methods: Three dogs that had previously tested seronegative and virus‐negative for canine coronavirus were inoculated twice, at 21‐day intervals, with the vaccine and kept under observation. Two seronegative and virus‐negative dogs served as unvaccinated controls. For safety tests, two additional dogs were inoculated oronasally with 10 times the vaccinal dose and no reactions were observed. Faecal samples were collected daily from the vaccinated dogs after the first and second inoculations. Both vaccinated and control dogs were challenged two weeks after the second vaccination with a field canine coronavirus strain. Blood samples were collected for serological tests before vaccination and at weekly intervals after vaccinations and challenge.

Results: Virus was not detected in faecal samples after the first or second vaccinations by virus isolation assays and PCR. Significantly, the vaccinated dogs did not have clinical signs after challenge and no virus shedding was observed. The two unvaccinated control dogs had moderate enteritis, and virus was detected in cell cultures starting from three days postchallenge (dog 1) and two days postchallenge (dog 2), and by PCR for 23 median days.

Clinical Significance: This study showed the efficacy of a high‐cell‐passage canine coronavirus vaccine in preventing infection of dogs by virulent virus and, specifically, its ability to induce sterilising immunity.

Effective inhibition of porcine transmissible gastroenteritis virus replication in ST cells by shRNAs targeting RNA-dependent RNA polymerase gene

Transmissible gastroenteritis virus (TGEV) is identified as one of the most important pathogenic agents during swine enteric infection, leading to high mortality in neonatal pigs and severe annual economic loss in swine-producing areas. Up to date, various vaccines developed against TGEV still need to be improved. To exploit the possibility of using RNA interference (RNAi) as a strategy against TGEV infection, two shRNA-expressing plasmids (pEGFP-U6/P1 and pEGFP-U6/P2) targeting the RNA-dependent RNA polymerase (RdRp) gene of TGEV were constructed and transfected into swine testicular (ST) cells. The cytopathic effect (CPE) and MTS assays demonstrated that both shRNAs were capable of protecting cells against TGEV invasion with very high specificity and efficiency. A real-time quantitative RT-PCR further confirmed that the amounts of viral RNAs in cell cultures pre-transfected with the two plasmids were reduced by 95.2% and up to 100%, respectively. Our results suggest that RNAi might be a promising new strategy against TGEV infection.

Comparison of a fimbrial versus an autotransporter display system for viral epitopes on an attenuated Salmonella vaccine vector

Attenuated Salmonella have been used as vectors to deliver foreign antigens as live vaccines. We have previously developed an efficient surface-display system by genetically engineering 987P fimbriae to present transmissible gastroenteritis virus (TGEV) C and A epitopes for the induction of anti-TGEV antibodies with a Salmonella vaccine vector. Here, this system was compared with an autotransporter protein surface display system. The TGEV C and A epitopes were fused to the passenger domain of the MisL autotransporter of Salmonella. Expression of both the MisL- and 987P subunit FasA-fusions to the TGEV epitopes were under the control of in vivo-induced promoters. Expression of the TGEV epitopes from the Salmonella typhimurium CS4552 (crp cya asd pgtE) vaccine strain was greater when the epitopes were fused to MisL than when they were fused to the 987P FasA subunit. However, when BALB/c mice were orally immunized with the Salmonella vector expressing the TGEV epitopes from either one of the fusion constructs or both together, the highest level of anti-TGEV antibody was obtained with the 987P-TGEV immunogen-displaying vector. This result suggested that better immune responses towards specific epitopes could be obtained by using a polymeric display system such as fimbriae.

Preliminary evaluation of the use of the sefA fimbrial gene to elicit immune response against Salmonella enterica serotype Enteritidis in chickens

In the last 2 decades, the prevalence of Salmonella enterica serotype Enteritidis (Salmonella Enteritidis) has dramatically increased worldwide, becoming the leading cause of food-borne illnesses and an important public health issue. Many studies have suggested the role of the SEF14 fimbrial protein in the adhesion of Salmonella Enteritidis to the host. In the present study, the sefA gene, which encodes the main subunit of the SEF14 fimbrial protein, was cloned into a temperature-sensitive expression vector and transformed into a nonpathogenic, avirulent strain of Escherichia coli. The recombinant strain was used as a vaccine to elicit specific immune response against the SefA protein of Salmonella Enteritidis in 1-day-old chickens. The recombinant strain was reisolated from the intestines of treated birds for up to 21 days posttreatment, demonstrating its ability to colonize the intestinal tracts of 1-day-old chickens. In addition, immunoglobulin A (IgA) against the SefA protein was detected in intestinal secretions from treated birds at 7 days posttreatment and in bile samples from 14 to 21 days posttreatment by enzyme-linked immunosorbent assay. Nontreated birds did not show any evidence of intestinal colonization by the recombinant strain or anti-SefA IgA response in their bile or intestinal secretions. Preliminary evaluation of the recombinant strain showed a potential use of this strain to elicit protection against Salmonella Enteritidis infection in chickens. Further experiments are needed to study the ability of the recombinant strain to protect birds against Salmonella Enteritidis colonization.

Fecal immunoglobulin A antibodies in dogs infected or vaccinated with canine coronavirus

Fecal secretory immunoglobulin A (IgA) antibodies in dogs infected or vaccinated with canine coronavirus (CCV) were evaluated by an enzyme-linked immunosorbent assay. The study was carried out with 32 fecal samples collected just before inoculation and at 28 days postinoculation. Five groups were studied: naturally infected dogs, experimentally infected dogs, dogs inoculated with a modified live (ML) CCV vaccine by the intramuscular route, dogs inoculated with an ML CCV vaccine by the oronasal route, and dogs given an inactivated CCV vaccine. Both the naturally and the experimentally infected dogs developed high levels of fecal IgAs. Interestingly, dogs inoculated with the ML CCV vaccine by the oronasal route developed levels of fecal IgA that were higher than those observed in the dogs inoculated with the same CCV vaccine by the intramuscular route or those observed in dogs inoculated with the inactivated vaccine. A relationship between the level of fecal IgAs to CCV and the degree of protection against CCV infection was observed.

Safety and efficacy of a modified-live canine coronavirus vaccine in dogs

The safety and the efficacy of a modified-live (ML) canine coronavirus (CCoV) vaccine strain 257/98-3c was evaluated in 14 dogs seronegative and virus negative for CCoV. For the safety test, four dogs were inoculated, two by intramuscular and two by oronasal route, with 10 times the vaccinal dose. During the observation period (28 days) all dogs did not display any local or systemic reaction. For the efficacy test, eight dogs were vaccinated by intramuscular (four dogs-group A) or by oronasal route (four dogs-group B). Two dogs were maintained as non-vaccinated controls. In the dogs of group A, vaccinal virus was not detected in faecal samples by virus isolation (VI) and by PCR assay, while in the dogs of group B, the virus was revealed for six median days only by PCR. Twenty-eight days later, the vaccinated and control dogs were challenged with a field CCoV strain. After the challenge, the vaccinated dogs did not display clinical signs and the dogs of group A shed virus for 5.5 median days, evaluated by VI, and for 10 median days evaluated by PCR. Virus shedding was not observed, both by VI and PCR assay, in the dogs of group B. The two control dogs displayed moderate clinical signs and the virus was detected by VI for 14.5 median days starting from day 3 post-challenge (dpc 3) and by PCR assay for 23 median days starting from dpc 1.

Induction of mucosal immune responses and protection against enteric viruses: rotavirus infection of gnotobiotic pigs as a model

Enteric viruses are a major cause of diarrhea in animals and humans. Among them, rotaviruses are one of the most important causes of diarrhea in young animals and human infants. A lack of understanding of mechanisms to induce intestinal immunity and the correlates of protective immunity in neonates has impaired development of safe and effective vaccines against enteric viruses. Studies of candidate vaccines using an adult mouse model of subclinical enteric viral infections often do not predict vaccine efficacy against disease evaluated in neonatal large animals. A series of studies have been conducted using a neonatal gnotobiotic pig model of rotavirus infection and diarrhea to identify correlates of protective immunity and to evaluate traditional and novel vaccine approaches for the induction of mucosal immune responses and protection to enteric viruses. Gnotobiotic pigs recovered from infection with virulent Wa human rotavirus (HRV) (mimic natural infection) had high numbers of intestinal IgA rotavirus-specific primary antibody-secreting cells (ASCs) and memory B-cells (to recall antigen) measured by ELISPOT assay, which correlated with complete protection against rotavirus challenge. Most short-term IgA memory B-cells were resident in the ileum, the major site of rotavirus replication. Spleen, not the bone marrow, was the major resident site for longer-term IgG memory B-cells. Candidate rotavirus vaccines evaluated in pigs for their ability to induce intestinal or systemic ASC and protection against rotavirus infection and diarrhea included attenuated live virus, inactivated virus, and baculovirus-expressed double-layered rotavirus-like particles (2/6-VLPs). In combination with those candidate vaccines, various adjuvants, delivery systems, and immunization routes were tested, including incomplete Freund's adjuvant for i.m. immunization, and a mutant Escherichia coli heat labile enterotoxin R192G (mLT) for i.n. immunization. It was shown that orally administered replicating vaccines were most effective for priming for intestinal IgA ASC and memory B-cell responses, but i.n. administered non-replicating 2/6-VLPs plus mLT were effective as booster vaccines. We conclude that protective immunity depends on the magnitude, location, viral protein-specificity, and isotype of the antibody responses induced by vaccination. Therefore highly effective enteric viral vaccines should: (i) induce sufficient levels of intestinal IgA antibodies; (ii) include viral antigens that induce neutralizing antibodies; and (iii) require the use of effective mucosal adjuvants or antigen delivery systems for non-replicating oral or i.n. vaccines.

Development and compartmentalization of the porcine TCR delta repertoire at mucosal and extraintestinal sites: the pig as a model for analyzing the effects of age and microbial factors

gammadelta T cells are an important component of the mucosal immune system. Previously, we have shown that the TCR delta repertoire in human intestine is polyclonal at birth and becomes increasingly restricted with age. In this study, we expand those studies to the pig which allows more extensive experiments including several organs. Tissues from different mucosal sites like the stomach, duodenum, ileum, Peyer's patches, jejunum, and colon, and also extraintestinal sites like the lung, spleen, thymus and mesenteric lymph nodes, were obtained from conventionally reared pigs aged 2 wk to 5.5 years. In addition, tissues were also obtained from 10-wk-old specified pathogen- and germ-free pigs. TCRDV1-DV5 transcripts were amplified by RT-PCR after which complementarity-determining region 3 spectratyping was performed. Individual bands were excised from the gels and directly sequenced. The intestinal TCR delta repertoire showed increasing restriction with age and was highly oligoclonal in the adult 2- to 5.5-year-old pigs. In old pigs, we observed a striking compartmentalization. Different TCR delta repertoires were present between the lungs and the intestinal mucosa but also within different parts of the gastrointestinal tract. However, occasionally we observed identical TCR delta transcripts in the intestine and the lungs and shared clones could be detected also along the entire gastrointestinal tract. Thus, subsets of gammadelta T cells are likely to transport immunological information between different compartments of the immune system. Furthermore, these data support the hypothesis that in each mucosal site, different Ags are responsible for selecting and maintaining the gammadelta TCR over time.

Mucosal and systemic isotype-specific antibody responses and protection in conventional pigs exposed to virulent or attenuated porcine epidemic diarrhoea virus

Eleven-day-old conventionally reared piglets were inoculated orally with two different doses of the cell-culture adapted strain CV-777 of the porcine epidemic diarrhoea virus (PEDV) or the virulent isolate of the same strain and challenged with the same virulent PEDV 3 weeks later. Pigs inoculated with the two doses of the attenuated virus did not show any typical sign of the disease, and virus shedding was not frequent. In contrast, 31% of pigs exposed to the virulent PEDV developed diarrhoea and virus shedding was demonstrated in 100%. At different postinoculation day (PID) and postchallenge day (PCD) virus-specific antibody-secreting cells (ASC) in gut associated lymphoid tissues (duodenum and ileum lamina propria and mesenteric lymph nodes) and systemic locations (blood and spleen) were assessed by enzyme-linked immunospot (ELISPOT). Only a small response was detected in the groups inoculated with attenuated PEDV, whereas in the group previously exposed to the virulent virus on PID 21 a large number of IgG and IgA ASC was detected. Isotype-specific antibody responses in serum were investigated by ELISA. IgG responses were detected in all groups, although the highest response corresponded to the group inoculated with virulent virus and only this group showed an IgA response. The pigs exposed to virulent PEDV were completely protected against the challenge with a higher dose of the same virulent virus on PID 21 and none of them shed the virus. The pigs inoculated with the attenuated strain were partially protected against the challenge, and 25% of the low dose- and 50% of the high dose-exposed pigs did not shed virus after challenge. All the pigs from a control group, not previously exposed to the virus, excreted the virus in faeces. A strong positive correlation was established between protection and the ASC responses detected in gut associated lymphoid tissues and blood at the challenge day and also between protection and serum isotype-specific antibody titers on that day. In addition, the IgA and IgG ASC responses detected in the blood on PID 21 also correlated with the responses found in the gut associated lymphoid tissues. The ASC and serum antibody responses after the challenge corresponded to a secondary immune response in the groups inoculated with attenuated virus, whereas a primary response was evident in the control group. No increase was seen in any of the parameters studied in the pigs inoculated with virulent PEDV.

Isotype-specific antibody-secreting cells in systemic and mucosal associated lymphoid tissues and antibody responses in serum of conventional pigs inoculated with PEDV

An enzyme-linked immunospot (ELISPOT) has been developed to detect porcine epidemic diarrhea virus (PEDV)-specific antibody secreting cells (ASC) in gut associated lymphoid tissues (duodenum and ileum lamina propria and mesenteric lymph nodes) and systemic locations (spleen and blood) of conventional pigs so as to characterise the mucosal and systemic antibody response generated by the infection with PEDV. A total number of 28 eleven-day-old conventional pigs were orally inoculated with the field isolate of the PEDV strain CV-777. Diarrhea was observed in 32% of the pigs and virus shedding was demonstrated in 100% between postinoculation day (PID) 1 and 8. Serum IgG and IgA antibodies to PEDV were detected by isotype ELISA from PID 12 and 15, respectively, reaching maximum values at PID 32 (IgG) and 21 (IgA). PEDV specific IgM ASC occurred in all the tissues between PID 4 and 7, with the strongest response in the intestinal lamina propria. IgA and IgG ASC responses were evident in the intestinal lymphoid tissues from PID 21, the highest number of specific ASC corresponded to the duodenum lamina propria. In the systemic lymphoid tissues the number of IgG and IgA ASC detected were lower than in the mucosal tissues, however, in the blood, presence of IgA ASC was constantly detected from PID 14 until the end of the experiment. Memory antibody response to the PEDV was also studied by secondary in vitro stimulation of the mononuclear cells (MNC) isolated from mesenteric lymph nodes, spleen and blood. The memory B cell response was prominent at PID 21 and 25 and consisted in IgG and IgA ASC. To our knowledge, this is the first report to research into the presence and distribution of specific ASC in different locations of the systemic and the gut associated lymphoid tissues after a PEDV infection as well as the presence of memory B cells.

Protective immunity and antibody-secreting cell responses elicited by combined oral attenuated Wa human rotavirus and intranasal Wa 2/6-VLPs with mutant Escherichia coli heat-labile toxin in gnotobiotic pigs

Two combined rotavirus vaccination regimens were evaluated in a gnotobiotic pig model of rotavirus infection and disease and were compared to previously tested rotavirus vaccination regimens. The first (AttHRV/VLP2x) involved oral inoculation with one dose of attenuated (Att) Wa human rotavirus (HRV), followed by two intranasal (i.n.) doses of a rotavirus-like particle (2/6-VLPs) vaccine derived from Wa (VP6) and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were coadministered with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT) adjuvant. For the second regimen (VLP2x/AttHRV), two i.n. doses of 2/6-VLPs+mLT were given, followed by one oral dose of attenuated Wa HRV. To compare the protective efficacy and immune responses induced by the combined vaccine regimens with individual rotavirus vaccine regimens, we included in the experiments the following vaccine groups: one oral dose of attenuated Wa HRV (AttHRV1x and Mock2x/AttHRV, respectively), three oral doses of attenuated Wa HRV (AttHRV3x), three i.n. doses of 2/6-VLPs plus mLT (VLP3x), three i.n. doses of purified double-layered inactivated Wa HRV plus mLT (InactHRV3x), mLT alone, and mock-inoculated pigs. The isotype, magnitude, and tissue distribution of antibody-secreting cells (ASCs) in the intestinal and systemic lymphoid tissues were evaluated using an enzyme-linked immunospot assay. The AttHRV/VLP2x regimen stimulated the highest mean numbers of intestinal immunoglobulin A (IgA) ASCs prechallenge among all vaccine groups. This regimen induced partial protection against virus shedding (58%) and diarrhea (44%) upon challenge of pigs with virulent Wa HRV. The reverse VLP2x/AttHRV regimen was less efficacious than the AttHRV/VLP2x regimen in inducing IgA ASC responses and protection against diarrhea (25% protection rate) but was more efficacious than VLP3x or InactHRV3x (no protection). In conclusion, the AttHRV/VLP2x vaccination regimen stimulated the strongest B-cell responses in the intestinal mucosal immune system at challenge and conferred a moderately high protection rate against rotavirus disease, indicating that priming of the mucosal inductive site at the portal of natural infection with a replicating vaccine, followed by boosting with a nonreplicating vaccine at a second mucosal inductive site, may be a highly effective approach to stimulate the mucosal immune system and induce protective immunity against various mucosal pathogens.

Semen from boars infected with porcine reproductive and respiratory syndrome virus (PRRSV) contains antibodies against structural as well as nonstructural viral proteins

The seminal excretion of antibodies against porcine reproductive and respiratory syndrome virus (PRRSV) was examined in a group of five boars experimentally infected by the nasopharyngeal route. By using phage-displayed peptide epitopes from the PRRSV replicase and envelope glycoproteins as ELISA antigen, we were able to separately and specifically assay antibody responses against structural and nonstructural viral proteins. Antibodies against structural as well as nonstructural viral proteins were consistently found in the semen of all boars, beginning from 1-4 weeks postinfection. This is the first report documenting the presence of anti-PRRSV antibodies in boar semen. Seminal antiviral IgA was also detected, and we observed a correlation between seminal IgA responses against nonstructural viral proteins, and the duration of PRRSV RNA excretion in semen. The implications of these findings for the diagnostics and pathogenesis of venereal PRRSV infection are discussed.

Immunity to Rhodococcus equi: antigen-specific recall responses in the lungs of adult horses

Rhodococcal pneumonia is an important disease of young horses that is not seen in immunocompetent adults. Since all foals are normally exposed to Rhodococcus equi in their environment, we hypothesized that most develop protective immune responses. Furthermore, these antigen-specific responses were hypothesized to operate throughout adult life to prevent rhodococcal pneumonia. A better understanding of the mechanisms of immune clearance in adult horses would help define the requirements for an effective vaccine in foals. Adult horses were challenged with virulent R. equi by intrabronchial inoculation into the right lung, and pulmonary immune responses were followed for 2 weeks by bronchoalveolar lavage. Local responses in the inoculated right lung were compared to the uninfected left lung and peripheral blood. Challenged horses rapidly cleared R. equi infection without significant clinical signs. Clearance of bacteria was associated with increased mononuclear cells in bronchoalveolar lavage fluid (primarily lymphocytes) and inversion of the normal macrophage:lymphocyte ratio. There was no significant increase in neutrophils at 7 days post-challenge. Flow cytometric analysis of bronchoalveolar lavage fluid demonstrated that clearance correlated with significant increases in pulmonary T-lymphocytes, both CD4+ and CD8+. Prior to challenge, most adult horses demonstrated low proliferative responses when pulmonary lymphocytes were stimulated with soluble R. equi ex vivo. However, clearance was associated with marked increases in lymphoproliferative responses to soluble R. equi antigen and recombinant VapA, a virulence associated protein of R. equi and candidate immunogen. These results are compatible with previous work in mice which showed that both CD4+ and CD8+ T-cells play a role in immune clearance of R. equi. Recognition of VapA in association with clearance lends further support to its testing as an immunogen. Importantly, the cellular responses to R. equi challenge were relatively compartmentalized. Responses were more marked and the sensitivity to antigen dose was increased at the site of challenge. The blood, including peripheral blood mononuclear cells, was an insensitive indicator of local pulmonary responses.

Enhanced immune responses to viral epitopes by combining macrophage-inducible expression with multimeric display on a Salmonella vector

In this study, the immunogenicity of chimeric 987P fimbriae on a Salmonella vaccine strain was improved by optimizing fimbrial expression. The constitutive tetA promoter and the in vivo activated nirB and pagC promoters were evaluated for their use to express two epitopes of the transmissible gastroenteritis virus (TGEV) spike protein carried by fimbriae which were displayed on a Salmonella vaccine strain. Constructs with the pagC promoter were shown to drive increased expression of chimeric 987P fimbriae in macrophages as well as in Mg(2+)-poor media, mimicking a major environmental signal found in Salmonella-containing endocytic vacuoles of macrophages. Mice immunized orally with a Salmonella vaccine strain which expressed chimeric fimbriae from the pagC promoter elicited significantly higher mucosal and systemic immune responses to both the 987P fimbriae and the TGEV epitopes than mice immunized with the same strain hosting a tetA or nirB promoter-driven expression plasmid. Moreover, only the Salmonella vaccine strains harboring a plasmid with the pagC promoter, with or without an additional tetA promoter in tandem, elicited neutralizing antibodies to TGEV. This indicated that the pagC promoter can be used successfully to improve epitope-display by chimeric fimbriae on Salmonella vaccine strains for the induction of a desired immune response.

Mucosal and systemic immune responses to chimeric fimbriae expressed by Salmonella enterica serovar typhimurium vaccine strains

Recombinant live oral vaccines expressing pathogen-derived antigens offer a unique set of attractive properties. Among these are the simplicity of administration, the capacity to induce mucosal and systemic immunity, and the advantage of permitting genetic manipulation for optimal antigen presentation. In this study, the benefit of having a heterologous antigen expressed on the surface of a live vector rather than intracellularly was evaluated. Accordingly, the immune response of mice immunized with a Salmonella enterica serovar Typhimurium vaccine strain expressing the Escherichia coli 987P fimbrial antigen on its surface (Fas(+)) was compared with the expression in the periplasmic compartment (Fas(-)). Orally immunized BALB/c mice showed that 987P fimbriated Salmonella serovar Typhimurium CS3263 (aroA asd) with pCS151 (fas(+) asd(+)) elicited a significantly higher level of 987P-specific systemic immunoglobulin G (IgG) and mucosal IgA than serovar Typhimurium CS3263 with pCS152 (fasD mutant, asd(+)) expressing 987P periplasmic antigen. Further studies were aimed at determining whether the 987P fimbriae expressed by serovar Typhimurium chi4550 (cya crp asd) could be used as carriers of foreign epitopes. For this, the vaccine strain was genetically engineered to express chimeric fimbriae carrying the transmissible gastroenteritis virus (TGEV) C (379-388) and A (521-531) epitopes of the spike protein inserted into the 987P major fimbrial subunit FasA. BALB/c mice administered orally serovar Typhimurium chi4550 expressing the chimeric fimbriae from the tet promoter in pCS154 (fas(+) asd(+)) produced systemic antibodies against both fimbria and the TGEV C epitope but not against the TGEV A epitope. To improve the immunogenicity of the chimeric fimbriae, the in vivo inducible nirB promoter was inserted into pCS154, upstream of the fas genes, to create pCS155. In comparison with the previously used vaccine, BALB/c mice immunized orally with serovar Typhimurium chi4550/pCS155 demonstrated significantly higher levels of serum IgG and mucosal IgA against 987P fimbria. Moreover, mucosal IgA against the TGEV C epitope was only detected with serovar Typhimurium chi4550/pCS155. The induced antibodies also recognized the epitopes in the context of the full-length TGEV spike protein. Hence, immune responses to heterologous chimeric fimbriae on Salmonella vaccine vectors can be optimized by using promoters known to be activated in vivo.

Comparative pathogenesis of enteric viral infections of swine

At least 11 enteric viruses belonging to 6 distinct families (Adenoviridae, Astroviridae, Caliciviridae, Coronaviridae, Parvoviridae, and Reoviridae) cause diarrhea in swine mainly during the nursing and immediate post-weaning period. Most infect the small intestinal enterocytes, inducing various degrees of villous atrophy and subsequently a malabsorptive, maldigestive diarrhea. In addition rotaviruses possess an enterotoxin (NSP4) which induces a secretory diarrhea in mice. These viruses have distinct predilections for different vertical (villus/crypt) and horizontal (duodenum, jejunum, ileum, colon) replication sites in the intestine and the diarrhea intensity is often related to the extent of viral replication at these sites. In addition concurrent infections with multiple enteric viruses can produce synergistic or additive effects leading to more extensive villous atrophy throughout the intestine and more severe and prolonged diarrhea. Knowledge of enteric viral replication sites and comparative mechanisms of diarrhea induction may lead to new or improved vaccine strategies or therapeutic approaches for the prevention or treatment of these viral diarrheas.

Active immunity and T-cell populations in pigs intraperitoneally inoculated with baculovirus-expressed transmissible gastroenteritis virus structural proteins

The intraperitoneal inoculation of pigs with baculovirus-expressed transmissible gastroenteritis virus (TGEV) structural proteins (S, N, M) in conjunction with thermolabile Escherichia coli mutant toxin (LT-R192G) in incomplete Freund's adjuvant (IFA) was tested in an attempt to elicit active immunity to TGEV in gut-associated lymphoid tissues (GALT). Four groups of 63 (1-5-week-old) suckling, TGEV-seronegative pigs were used to assess the efficacy of the recombinant protein vaccine (group 3) in comparison with sham (group 1), commercial vaccine (group 2), and virulent TGEV Miller-strain-inoculated pigs (group 4). The TGEV-specific mucosal and systemic immune responses were measured after in vivo and in vitro stimulation with TGEV-antigens. The major T-cell subset distribution was analyzed in vivo and in vitro after stimulation of mononuclear cells with TGEV (from mesenteric lymph nodes of group 3 inoculated with TGEV-recombinant proteins). Induction of active immunity was assessed by challenge of pigs with virulent TGEV at 27 days of age. Baculovirus-expressed TGEV proteins coadministered with LT-R192G in IFA induced mesenteric lymph node immune responses associated with IgA-antibodies to TGEV and partial protection against TGEV-challenge. The high titers of serum IgG- and virus-neutralizing-antibodies to TGEV in group 3 pigs most likely reflected the dose of TGEV S-protein administered. At the day of TGEV-challenge, the in vitro stimulation of mononuclear cells from the mesenteric lymph nodes of group 3 pigs with inactivated TGEV resulted in an increase in double positive (CD4+CD8+), natural killer (CD2+CD4-CD8+dim) and cytotoxic (CD2+CD4-CD8+bright) T-cell phenotypes, accompanied by increased expression of interleukin-2 receptor and a decrease of the null (CD2-CD4-CD8-/SW6+) cell phenotype.

Evaluation of the baculovirus-expressed S glycoprotein of transmissible gastroenteritis virus (TGEV) as antigen in a competition ELISA to differentiate porcine respiratory coronavirus from TGEV antibodies in pigs

The spike (S) glycoprotein of the Miller strain of transmissible gastroenteritis virus (TGEV) was recently cloned and expressed in baculovirus. The recombinant S protein was used as the coating antigen in a competition (blocking) enzyme-linked immunosorbent assay (ELISA) in combination with monoclonal antibodies to the S protein epitope A (conserved on TGEV and porcine respiratory coronavirus [PRCV]) or epitope D (present on TGEV only) to differentiate PRCV- from TGEV-induced antibodies. One set (set A) of 125 serum samples were collected at different times after inoculation of caesarean-derived, colostrum-deprived (n = 52) and conventional young pigs (n = 73) with 1 of the 2 porcine coronaviruses or uninoculated negative controls (TGEV/PRCV/negative = 75/30/20). A second set (set B) of 63 serum samples originated from adult sows inoculated with PRCV and the recombinant TGEV S protein or with mock-protein control and then exposed to virulent TGEV after challenge of their litters. Sera from set A were used to assess the accuracy indicators (sensitivity, specificity, accuracy) of the fixed-cell blocking ELISA, which uses swine testicular cells infected with the M6 strain of TGEV as the antigen source (ELISA 1) and the newly developed ELISA based on the recombinant S protein as antigen (ELISA 2). The sera from set B (adults) were tested for comparison. The plaque reduction virus neutralization test was used as a confirmatory test for the presence of antibodies to TGEV/PRCV in the test sera. The accuracy indicators for both ELISAs suggest that differential diagnosis can be of practical use at least 3 weeks after inoculation by testing the dual (acute/convalescent) samples from each individual in conjunction with another confirmatory (virus neutralization) antibody assay to provide valid and complete differentiation information. Moreover, whereas ELISA 1 had 10-20% false positive results to epitope D for PRCV-infected pigs (set A samples), no false-positive results to epitope D occurred using ELISA 2, indicating its greater specificity. The progression of seroresponses to the TGEV S protein epitopes A or D, as measured by the 2 ELISAs, was similar for both sets (A and B) of samples. Differentiation between TGEV and PRCV antibodies (based on seroresponses to epitope D) was consistently measured after the third week of inoculation.

Intranasal immunization with Yersinia enterocolitica O:8 cellular extract protects against local challenge infection

Yersinia enterocolitica is enteropathogenic for humans and rodents. Immune protection from oral and respiratory pathogens may be most effectively elicited following intranasal (i.n.) vaccination. An experimental murine intranasal challenge model was used to evaluate the immunogenicity of a Y. enterocolitica O:8 cellular extract (CE) in mucosa. This antigenic preparation has demonstrated to induce protection by subcutaneous immunization. Mice were immunized intranasally with two doses of CE. Immunized and nonimmunized animals were challenged with 5 x 10(6) colony-forming units (CFU) by nasal infection. Antibodies in serum and bronchoalveolar lavage (b.a.l.) fluid were assessed before and 48 hr after challenge. The CFU were determined by analysis of lung homogenate samples. The CE immunization induced significant b.a.l.-specific IgA and IgG, and serum-specific IgG, IgA and IgM. Histopathological studies 24 and 48 hr postchallenge demonstrated that immunization protected against progressive lesions resulting from Y. enterocolitica invasion of the pulmonary mucosa. The CFU in the lungs showed that CE immunization led to significant clearance as compared to the bacterial level in nonimmunized controls. From the results obtained, it can be concluded that CE can induce local and systemic immunity and protect against nasal infection.