From Snoot to Tail: A Brief Review of Influenza Virus Infection and Immunity in Pigs.

Pigs play an important role in influenza A virus (IAV) epidemiology because they support replication of human, avian, and swine origin viruses and act as an IAV reservoir for pigs and other species, including humans. Moreover, novel IAVs with human pandemic potential may be generated in pigs. To minimize the threat of IAVs to human and swine health, it is crucial to understand host defense mechanisms that restrict viral replication and pathology in pigs. In this article, we review IAV strains circulating in the North American swine population, as well as porcine innate and acquired immune responses to IAV, including recent advances achieved through immunological tools developed specifically for swine. Furthermore, we highlight unique aspects of the porcine pulmonary immune system, which warrant consideration when developing vaccines and therapeutics to limit IAV in swine or when using pigs to model human IAV infections.

Assessment of DNA methylation in porcine immune cells reveals novel regulatory elements associated with cell-specific gene expression and immune capacity traits.

BACKGROUND: Genetics studies in the porcine immune system have enhanced selection practices for disease resistance phenotypes and increased the efficacy of porcine models in biomedical research; however limited functional annotation of the porcine immunome has hindered progress on both fronts. Among epigenetic mechanisms that regulate gene expression, DNA methylation is the most ubiquitous modification made to the DNA molecule and influences transcription factor binding as well as gene and phenotype expression. Human and mouse DNA methylation studies have improved mapping of regulatory elements in these species, but comparable studies in the pig have been limited in scope. RESULTS: We performed whole-genome bisulfite sequencing to assess DNA methylation patterns in nine pig immune cell populations: CD21+ and CD21- B cells, four T cell fractions (CD4+, CD8+, CD8+CD4+, and SWC6γδ+), natural killer and myeloid cells, and neutrophils. We identified 54,391 cell differentially methylated regions (cDMRs), and clustering by cDMR methylation rate grouped samples by cell lineage. 32,737 cDMRs were classified as cell lowly methylated regions (cLMRs) in at least one cell type, and cLMRs were broadly enriched in genes and regions of intermediate CpG density. We observed strong correlations between differential methylation and expression across immune cell populations, with cell-specific low methylation disproportionately impacting genes exhibiting enriched gene expression in the same cell type. Motif analysis of cLMRs revealed cell type-specific enrichment of transcription factor binding motifs, indicating that cell-specific methylation patterns may influence accessibility by trans-acting factors. Lastly, cDMRs were enriched for immune capacity GWAS SNPs, and many such overlaps occurred within genes known to influence immune cell development and function (CD8B, NDRG1). CONCLUSION: Our DNA methylation data improve functional annotation of the porcine genome through characterization of epigenomic regulatory patterns that contribute to immune cell identity and function, and increase the potential for identifying mechanistic links between genotype and phenotype.

Evaluation of the recombinant proteins RlpB and VacJ as a vaccine for protection against Glaesserella parasuis in pigs.

BACKGROUND: Glaesserella parasuis, the causative agent of Glӓsser's disease, is widespread in swine globally resulting in significant economic losses to the swine industry. Prevention of Glӓsser's disease in pigs has been plagued with an inability to design broadly protective vaccines, as many bacterin based platforms generate serovar or strain specific immunity. Subunit vaccines are of interest to provide protective immunity to multiple strains of G. parasuis. Selected proteins for subunit vaccination should be widespread, highly conserved, and surface exposed. RESULTS: Two candidate proteins for subunit vaccination (RlpB and VacJ) against G. parasuis were identified using random mutagenesis and an in vitro organ culture system. Pigs were vaccinated with recombinant RlpB and VacJ, outer membrane proteins with important contributions to cellular function and viability. Though high antibody titers to the recombinant proteins and increased interferon-γ producing cells were found in subunit vaccinated animals, the pigs were not protected from developing systemic disease. CONCLUSIONS: It appears there may be insufficient RlpB and VacJ exposed on the bacterial surface for antibody to bind, preventing high RlpB and VacJ specific antibody titers from protecting animals from G. parasuis. Additionally, this work confirms the importance of utilizing the natural host species when assessing the efficacy of vaccine candidates.

Acute systemic inflammatory response to lipopolysaccharide stimulation in pigs divergently selected for residual feed intake.

BACKGROUND: It is unclear whether improving feed efficiency by selection for low residual feed intake (RFI) compromises pigs' immunocompetence. Here, we aimed at investigating whether pig lines divergently selected for RFI had different inflammatory responses to lipopolysaccharide (LPS) exposure, regarding to clinical presentations and transcriptomic changes in peripheral blood cells. RESULTS: LPS injection induced acute systemic inflammation in both the low-RFI and high-RFI line (n = 8 per line). At 4 h post injection (hpi), the low-RFI line had a significantly lower (p = 0.0075) mean rectal temperature compared to the high-RFI line. However, no significant differences in complete blood count or levels of several plasma cytokines were detected between the two lines. Profiling blood transcriptomes at 0, 2, 6, and 24 hpi by RNA-sequencing revealed that LPS induced dramatic transcriptional changes, with 6296 genes differentially expressed at at least one time point post injection relative to baseline in at least one line (n = 4 per line) (|log2(fold change)| ≥ log2(1.2); q < 0.05). Furthermore, applying the same cutoffs, we detected 334 genes differentially expressed between the two lines at at least one time point, including 33 genes differentially expressed between the two lines at baseline. But no significant line-by-time interaction effects were detected. Genes involved in protein translation, defense response, immune response, and signaling were enriched in different co-expression clusters of genes responsive to LPS stimulation. The two lines were largely similar in their peripheral blood transcriptomic responses to LPS stimulation at the pathway level, although the low-RFI line had a slightly lower level of inflammatory response than the high-RFI line from 2 to 6 hpi and a slightly higher level of inflammatory response than the high-RFI line at 24 hpi. CONCLUSIONS: The pig lines divergently selected for RFI had a largely similar response to LPS stimulation. However, the low-RFI line had a relatively lower-level, but longer-lasting, inflammatory response compared to the high-RFI line. Our results suggest selection for feed efficient pigs does not significantly compromise a pig's acute systemic inflammatory response to LPS, although slight differences in intensity and duration may occur.

Chlortetracycline Enhances Tonsil Colonization and Fecal Shedding of Multidrug-Resistant Salmonella enterica Serovar Typhimurium DT104 without Major Alterations to the Porcine Tonsillar and Intestinal Microbiota.

Salmonella spp. are estimated to cause 1.2 million cases of human foodborne illness each year in the United States, and pigs can often be asymptomatically colonized with Salmonella spp. (>50% of farms). Recent reports state that 18.3% of Salmonella enterica serovar Typhimurium isolates are resistant to ≥3 antimicrobial classes, and multidrug-resistant (MDR) strains are associated with an increased hospitalization rate and other complications. Chlortetracycline is commonly used in swine production to prevent/treat various diseases; therefore, chlortetracycline treatment of pigs unknowingly colonized with MDR Salmonella may have collateral effects on Salmonella spp. (and other gut bacteria). In this study, we determined the effect of in-feed chlortetracycline (400 g/ton) on shedding and colonization of pigs challenged with the MDR S Typhimurium strain DT104 (n = 11/group). We also assessed the impact on the fecal microbiota over the 12-day experimental period and on the ileum, cecum, and tonsil microbiota at 7 days postinoculation (dpi). In MDR S Typhimurium-inoculated pigs, chlortetracycline administration significantly increased fecal shedding at 2 dpi (+1.4 log10 CFU/g; P < 0.001) and enhanced tonsil colonization (+3.1 log10 CFU/g; P < 0.001). There were few major alterations detected in the gut or tonsillar microbiota of pigs treated with MDR S Typhimurium and/or chlortetracycline. The tonsillar transcriptome was largely unaffected despite increased colonization by MDR S Typhimurium following inoculation of the chlortetracycline-treated pigs. These results highlight the idea that chlortetracycline administration can enhance shedding and colonization of MDR S Typhimurium in pigs, which could increase the risk of environmental dissemination of MDR Salmonella strains.IMPORTANCESalmonella spp. are an important cause of foodborne illness in North America, and pork products are associated with sporadic cases and outbreaks of human salmonellosis. Isolates of Salmonella may be resistant to multiple antibiotics, and infections with multidrug-resistant (MDR) Salmonella spp. are more difficult to treat, leading to increased hospitalization rates. Swine operations commonly use antimicrobials, such as chlortetracycline, to prevent/treat infections, which may have collateral effects on pig microbial populations. Recently, we demonstrated that chlortetracycline induces the expression of genes associated with pathogenesis and invasion in MDR Salmonella enterica serovar Typhimurium in vitro In our current study, we show increased tonsillar colonization and fecal shedding of the MDR S Typhimurium strain DT104 from pigs administered chlortetracycline. Therefore, pigs unknowingly colonized with multidrug-resistant Salmonella spp. and receiving chlortetracycline for an unrelated infection may be at a greater risk for disseminating MDR Salmonella spp. to other pigs and to humans through environmental or pork product contamination.

Porcine signal regulatory protein alpha binds to human CD47 to inhibit phagocytosis: Implications for human hematopoietic stem cell transplantation into severe combined immunodeficient pigs.

BACKGROUND: Severe combined immunodeficient (SCID) pigs are an emerging animal model being developed for biomedical and regenerative medicine research. SCID pigs can successfully engraft human-induced pluripotent stem cells and cancer cell lines. The development of a humanized SCID pig through xenotransplantation of human hematopoietic stem cells (HSCs) would be a further demonstration of the value of such a large animal SCID model. Xenotransplantation success with HSCs into non-obese diabetic (NOD)-derived SCID mice is dependent on the ability of NOD mouse signal regulatory protein alpha (SIRPA) to bind human CD47, inducing higher phagocytic tolerance than other mouse strains. Therefore, we investigated whether porcine SIRPA binds human CD47 in the context of developing a humanized SCID pig. METHODS: Peripheral blood mononuclear cells (PBMCs) were collected from SCID and non-SCID pigs. Flow cytometry was used to assess whether porcine monocytes could bind to human CD47. Porcine monocytes were isolated from PBMCs and were subjected to phagocytosis assays with pig, human, and mouse red blood cell (RBC) targets. Blocking phagocytosis assays were performed by incubating human RBCs with anti-human CD47 blocking antibody B6H12, non-blocking antibody 2D3, and nonspecific IgG1 antibody and exposing to human or porcine monocytes. RESULTS: We found that porcine SIRPA binds to human CD47 in vitro by flow cytometric assays. Additionally, phagocytosis assays were performed, and we found that porcine monocytes phagocytose human and porcine RBCs at significantly lower levels than mouse RBCs. When human RBCs were preincubated with CD47 antibodies B6H12 or 2D3, phagocytosis was induced only after B6H12 incubation, indicating the lower phagocytic activity of porcine monocytes with human cells requires interaction between porcine SIRPA and human CD47. CONCLUSIONS: We have shown the first evidence that porcine monocytes can bind to human CD47 and are phagocytically tolerant to human cells, suggesting that porcine SCID models have the potential to support engraftment of human HSCs.

Use of Proteins Identified through a Functional Genomic Screen To Develop a Protein Subunit Vaccine That Provides Significant Protection against Virulent Streptococcus suis in Pigs.

Streptococcus suis is a bacterium that is commonly carried in the respiratory tract and that is also one of the most important invasive pathogens of swine, commonly causing meningitis, arthritis, and septicemia. Due to the existence of many serotypes and a wide range of immune evasion capabilities, efficacious vaccines are not readily available. The selection of S. suis protein candidates for inclusion in a vaccine was accomplished by identifying fitness genes through a functional genomics screen and selecting conserved predicted surface-associated proteins. Five candidate proteins were selected for evaluation in a vaccine trial and administered both intranasally and intramuscularly with one of two different adjuvant formulations. Clinical protection was evaluated by subsequent intranasal challenge with virulent S. suis While subunit vaccination with the S. suis proteins induced IgG antibodies to each individual protein and a cellular immune response to the pool of proteins and provided substantial protection from challenge with virulent S. suis, the immune response elicited and the degree of protection were dependent on the parenteral adjuvant given. Subunit vaccination induced IgG reactive against different S. suis serotypes, indicating a potential for cross protection.

Escherichia coli O157:H7 virulence factors differentially impact cattle and bison macrophage killing capacity.

Enterohemorrhagic Escherichia coli O157:H7 colonizes the gastrointestinal tract of ruminants, including cattle and bison, which are reservoirs of these zoonotic disease-causing bacteria. Healthy animals colonized by E. coli O157:H7 do not experience clinical symptoms of the disease induced by E. coli O157:H7 infections in humans; however, a variety of host immunological factors may play a role in the amount and frequency of fecal shedding of E. coli O157:H7 by ruminant reservoirs. How gastrointestinal colonization by E. coli O157:H7 impacts these host animal immunological factors is unknown. Here, various isogenic mutant strains of a foodborne isolate of E. coli O157:H7 were used to evaluate bacterial killing capacity of macrophages of cattle and bison, the two ruminant species. Cattle macrophages demonstrated an enhanced ability to phagocytose and kill E. coli O157:H7 compared to bison macrophages, and killing ability was impacted by E. coli O157:H7 virulence gene expression. These findings suggest that the macrophage responses to E. coli O157:H7 might play a role in the variations observed in E. coli O157:H7 fecal shedding by ruminants in nature.

The Bordetella Bps Polysaccharide Is Required for Biofilm Formation and Enhances Survival in the Lower Respiratory Tract of Swine.

Bordetella bronchiseptica is pervasive in swine populations and plays multiple roles in respiratory disease. Additionally, B. bronchiseptica is capable of establishing long-term or chronic infections in swine. Bacterial biofilms are increasingly recognized as important contributors to chronic bacterial infections. Recently the polysaccharide locus bpsABCD has been demonstrated to serve a critical role in the development of mature biofilms formed by the sequenced laboratory strain of B. bronchiseptica We hypothesized that swine isolates would also have the ability to form mature biofilms and the bpsABCD locus would serve a key role in this process. A mutant containing an in-frame deletion of the bpsABCD structural genes was constructed in a wild-type swine isolate and found to be negative for poly-N-acetylglucosamine (PNAG)-like material by immunoblot assay. Further, the bpsABCD locus was found to be required for the development and maintenance of the three-dimensional structures under continuous-flow conditions. To investigate the contribution of the bpsABCD locus to the pathogenesis of B. bronchiseptica in swine, the KM22Δbps mutant was compared to the wild-type swine isolate for the ability to colonize and cause disease in pigs. The bpsABCD locus was found to not be required for persistence in the upper respiratory tract of swine. Additionally, the bpsABCD locus did not affect the development of anti-Bordetella humoral immunity, did not contribute to disease severity, and did not mediate protection from complement-mediated killing. However, the bpsABCD locus was found to enhance survival in the lower respiratory tract of swine.

Vaccine-associated enhanced respiratory disease is influenced by haemagglutinin and neuraminidase in whole inactivated influenza virus vaccines.

Multiple subtypes and many antigenic variants of influenza A virus (IAV) co-circulate in swine in the USA, complicating effective use of commercial vaccines to control disease and transmission. Whole inactivated virus (WIV) vaccines may provide partial protection against IAV with substantial antigenic drift, but have been shown to induce vaccine-associated enhanced respiratory disease (VAERD) when challenged with an antigenic variant of the same haemagglutinin (HA) subtype. This study investigated the role the immune response against HA, neuraminidase (NA) and nucleoprotein (NP) may play in VAERD by reverse engineering vaccine and challenge viruses on a common backbone and using them in a series of vaccination/challenge trials. Mismatched HA between vaccine and challenge virus was necessary to induce VAERD. However, vaccines containing a matched NA abrogated the VAERD phenomenon induced by the HA mismatch and this was correlated with NA-inhibiting (NI) antibodies. Divergence between the two circulating swine N2 lineages (92 % identity) resulted in a loss of NI cross-reactivity and also resulted in VAERD with the mismatched HA. The NP lineage selected for use in the WIV vaccine strains did not affect protection or pathology. Thus the combination of HA and NA in the vaccine virus strains played a substantial role in vaccine protection versus immunopathology, suggesting that vaccines that target the HA protein alone could be more prone to VAERD due to the absence of cross-protective NI antibodies.

The Bordetella bronchiseptica type III secretion system is required for persistence and disease severity but not transmission in swine.

Bordetella bronchiseptica is pervasive in swine populations and plays multiple roles in respiratory disease. Most studies addressing virulence factors of B. bronchiseptica utilize isolates derived from hosts other than pigs in conjunction with rodent infection models. Based on previous in vivo mouse studies, we hypothesized that the B. bronchiseptica type III secretion system (T3SS) would be required for maximal disease severity and persistence in the swine lower respiratory tract. To examine the contribution of the T3SS to the pathogenesis of B. bronchiseptica in swine, we compared the abilities of a virulent swine isolate and an isogenic T3SS mutant to colonize, cause disease, and be transmitted from host to host. We found that the T3SS is required for maximal persistence throughout the lower swine respiratory tract and contributed significantly to the development of nasal lesions and pneumonia. However, the T3SS mutant and the wild-type parent are equally capable of transmission among swine by both direct and indirect routes, demonstrating that transmission can occur even with attenuated disease. Our data further suggest that the T3SS skews the adaptive immune response in swine by hindering the development of serum anti-Bordetella antibody levels and inducing an interleukin-10 (IL-10) cell-mediated response, likely contributing to the persistence of B. bronchiseptica in the respiratory tract. Overall, our results demonstrate that the Bordetella T3SS is required for maximal persistence and disease severity in pigs, but not for transmission.

Polymorphisms in the haemagglutinin gene influenced the viral shedding of pandemic 2009 influenza virus in swine.

Interactions between the viral surface glycoprotein haemagglutinin (HA) and the corresponding receptors on host cells is one important aspect of influenza virus infection. Mutations in HA have been described to affect pathogenicity, antigenicity and the transmission of influenza viruses. Here, we detected polymorphisms present in HA genes of two pandemic 2009 H1N1 (H1N1pdm09) isolates, A/California/04/2009 (Ca/09) and A/Mexico/4108/2009 (Mx/09), that resulted in amino acid changes at positions 186 (S to P) and 194 (L to I) of the mature HA1 protein. Although not reported in the published H1N1pdm09 consensus sequence, the P186 genotype was more readily detected in primary infected and contact-naïve pigs when inoculated with a heterogeneous mixed stock of Ca/09. Using reverse genetics, we engineered Ca/09 and Mx/09 genomes by introducing Ca/09 HA with two naturally occurring variants expressing S186/I194 (HA-S/I) and P186/L194 (HA-P/L), respectively. The Ca/09 HA with the combination of P186/L194 with either the Ca/09 or Mx/09 backbone resulted in higher and prolonged viral shedding in naïve pigs. This efficiency appeared to be more likely through an advantage in cell surface attachment rather than replication efficiency. Although these mutations occurred within the receptor-binding pocket and the Sb antigenic site, they did not affect serological cross-reactivity. Relative increases of P186 in publicly available sequences from swine H1N1pdm09 viruses supported the experimental data, indicating this amino acid substitution conferred an advantage in swine.

Efficacy in pigs of inactivated and live attenuated influenza virus vaccines against infection and transmission of an emerging H3N2 similar to the 2011-2012 H3N2v.

Vaccines provide a primary means to limit disease but may not be effective at blocking infection and pathogen transmission. The objective of the present study was to evaluate the efficacy of commercial inactivated swine influenza A virus (IAV) vaccines and experimental live attenuated influenza virus (LAIV) vaccines against infection with H3N2 virus and subsequent indirect transmission to naive pigs. The H3N2 virus evaluated was similar to the H3N2v detected in humans during 2011-2012, which was associated with swine contact at agricultural fairs. One commercial vaccine provided partial protection measured by reduced nasal shedding; however, indirect contacts became infected, indicating that the reduction in nasal shedding did not prevent aerosol transmission. One LAIV vaccine provided complete protection, and none of the indirect-contact pigs became infected. Clinical disease was not observed in any group, including nonvaccinated animals, a consistent observation in pigs infected with contemporary reassortant H3N2 swine viruses. Serum hemagglutination inhibition antibody titers against the challenge virus were not predictive of efficacy; titers following vaccination with a LAIV that provided sterilizing immunity were below the level considered protective, yet titers in a commercial vaccine group that was not protected were above that level. While vaccination with currently approved commercial inactivated products did not fully prevent transmission, certain vaccines may provide a benefit by limitating shedding, transmission, and zoonotic spillover of antigenically similar H3N2 viruses at agriculture fairs when administered appropriately and used in conjunction with additional control measures.

Future of Immune Modulation in Animal Agriculture.

Immune modulation in animal agriculture has been of research interest for several decades, yet only a few immunomodulators have received regulatory approval in the United States and around the world. In this review, we summarize market and regulatory environments impacting commercial development of immunomodulators for use in livestock and poultry. In the United States, very few immunomodulators have received regulatory approval for use in livestock by either the US Department of Agriculture Center for Veterinary Biologics or the Food and Drug Administration (FDA). To date, only one immunomodulator has received FDA approval, and an extensive body of peer-reviewed literature is available regarding the basis for its use and health benefits. We present a more thorough review of the history and impact of this immune restorative. Finally, we discuss the interaction of immunomodulators on health, metabolism, and other factors impacting the future of immune modulation in livestock.

Conserved B cell signaling, activation, and differentiation in porcine jejunal and ileal Peyer's patches despite distinct immune landscapes.

Peyer's patches (PPs) are B cell-rich sites of intestinal immune induction, yet PP-associated B cell signaling, activation, and differentiation are poorly defined. Single-cell and spatial transcriptomics were completed to study B cells from porcine jejunum and ileum containing PPs. Intestinal locations had distinct immune landscapes, including more follicular B cells in ileum and increased MHC-II-encoding gene expression in jejunal B cells. Despite distinct landscapes, conserved B cell dynamics were detected across intestinal locations, including B cell signaling to CD4+ macrophages that are putative phagocytic, cytotoxic, effector cells and deduced routes of B cell activation/differentiation, including resting B cells migrating into follicles to replicate/divide or differentiate into antibody-secreting cells residing in intestinal crypts. A six-biomarker panel recapitulated transcriptomics findings of B cell phenotypes, frequencies, and spatial locations via ex vivo and in situ staining. Findings convey conserved B cell dynamics across intestinal locations containing PPs, despite location-specific immune environments. Results establish a benchmark of B cell dynamics for understanding intestinal immune induction important to promoting gut/overall health.

Phenotypic and genomic comparison of three human outbreak and one cattle-associated Shiga toxin-producing Escherichia coli O157:H7.

Escherichia coli O157:H7-adulterated food products are associated with disease outbreaks in humans. Although cattle feces are a source for E. coli O157:H7 contamination, it is unclear if human-associated outbreak isolates differentially colonize and shed in the feces of cattle from that of non-outbreak isolates. It is also unclear if phenotypes, such as biofilm formation, cell attachment, or toxin production, differentiate environmental E. coli O157:H7 isolates from those associated with human illness. The objective of this study was to compare the genotypes and phenotypes of a diverse set of E. coli O157:H7 isolates, with the intent of identifying differences that could inform cattle colonization and fecal shedding, along with virulence potential in humans. Isolates differed in attachment phenotypes on human Caco-2 cells and bovine-derived recto-anal junction squamous epithelial cells, with curli having a strong impact on attachment to the human-derived cell line. The prototypical E. coli O157 isolate EDL933 had the greatest expression of the adhesin gene iha, yet it had decreased expression of the virulence genes stx2, eae, and ehxA compared the lineage I/II isolates RM6067W and/or FRIK1989. Strong or weak biofilm production was not associated with significant differences in cattle colonization or shedding, suggesting biofilms may not play a major role in cattle colonization. No significant differences in cattle colonization and fecal shedding were detected, despite genomic and in vitro phenotypic differences. The outbreak isolate associated with the greatest incidence of hemolytic uremic syndrome, RM6067W, induced the greatest Vero cell cytotoxicity and had the greatest stx2 gene expression. IMPORTANCE: Foodborne illness has major impacts on global health and imposes financial hardships on food industries. Escherichia coli serotype O157:H7 is associated with foodborne illness. Cattle feces are a source of E. coli O157:H7, and routine surveillance has led to an abundance of E. coli O157:H7 genomic data. The relationship between E. coli O157:H7 genome and phenotype is not clearly discerned for cattle colonization/shedding and improved understanding could lead to additional strategies to limit E. coli O157:H7 in the food chain. The goal of the research was to evaluate genomic and phenotypic attributes of E. coli O157:H7 associated with cattle colonization and shedding, environmental persistence, and human illness. Our results indicate variations in biofilm formation and in vitro cellular adherence was not associated with differences in cattle colonization or shedding. Overall, processes involved in cattle colonization and various phenotypes in relation to genotype are complex and remain not well understood.

Restored PB1-F2 in the 2009 pandemic H1N1 influenza virus has minimal effects in swine.

PB1-F2 is an 87- to 90-amino-acid-long protein expressed by certain influenza A viruses. Previous studies have shown that PB1-F2 contributes to virulence in the mouse model; however, its role in natural hosts-pigs, humans, or birds-remains largely unknown. Outbreaks of domestic pigs infected with the 2009 pandemic H1N1 influenza virus (pH1N1) have been detected worldwide. Unlike previous pandemic strains, pH1N1 viruses do not encode a functional PB1-F2 due to the presence of three stop codons resulting in premature truncation after codon 11. However, pH1N1s have the potential to acquire the full-length form of PB1-F2 through mutation or reassortment. In this study, we assessed whether restoring the full-length PB1-F2 open reading frame (ORF) in the pH1N1 background would have an effect on virus replication and virulence in pigs. Restoring the PB1-F2 ORF resulted in upregulation of viral polymerase activity at early time points in vitro and enhanced virus yields in porcine respiratory explants and in the lungs of infected pigs. There was an increase in the severity of pneumonia in pigs infected with isogenic virus expressing PB1-F2 compared to the wild-type (WT) pH1N1. The extent of microscopic pneumonia correlated with increased pulmonary levels of alpha interferon and interleukin-1ß in pigs infected with pH1N1 encoding a functional PB1-F2 but only early in the infection. Together, our results indicate that PB1-F2 in the context of pH1N1 moderately modulates viral replication, lung histopathology, and local cytokine response in pigs.

Live attenuated influenza vaccine provides superior protection from heterologous infection in pigs with maternal antibodies without inducing vaccine-associated enhanced respiratory disease.

Control of swine influenza A virus (IAV) in the United States is hindered because inactivated vaccines do not provide robust cross-protection against the multiple antigenic variants cocirculating in the field. Vaccine efficacy can be limited further for vaccines administered to young pigs that possess maternally derived immunity. We previously demonstrated that a recombinant A/sw/Texas/4199-2/1998 (TX98) (H3N2) virus expressing a truncated NS1 protein is attenuated in swine and has potential for use as an intranasal live attenuated influenza virus (LAIV) vaccine. In the present study, we compared 1 dose of intranasal LAIV with 2 intramuscular doses of TX98 whole inactivated virus (WIV) with adjuvant in weanling pigs with and without TX98-specific maternally derived antibodies (MDA). Pigs were subsequently challenged with wild-type homologous TX98 H3N2 virus or with an antigenic variant, A/sw/Colorado/23619/1999 (CO99) (H3N2). In the absence of MDA, both vaccines protected against homologous TX98 and heterologous CO99 shedding, although the LAIV elicited lower hemagglutination inhibition (HI) antibody titers in serum. The efficacy of both vaccines was reduced by the presence of MDA; however, WIV vaccination of MDA-positive pigs led to dramatically enhanced pneumonia following heterologous challenge, a phenomenon known as vaccine-associated enhanced respiratory disease (VAERD). A single dose of LAIV administered to MDA-positive pigs still provided partial protection from CO99 and may be a safer vaccine for young pigs under field conditions, where dams are routinely vaccinated and diverse IAV strains are in circulation. These results have implications not only for pigs but also for other influenza virus host species.

Porcine granulocyte-colony stimulating factor (G-CSF) delivered via replication-defective adenovirus induces a sustained increase in circulating peripheral blood neutrophils.

The use of immunomodulators is a promising area for biotherapeutic, prophylactic, and metaphylactic use to prevent and combat infectious disease. Cytokines, including granulocyte-colony stimulating factor (G-CSF), have been investigated for potential value as biotherapeutic proteins. G-CSF enhances the production and release of neutrophils from bone marrow and is already licensed for use in humans. A limitation of cytokines as immunomodulators is their short half-life which may limit their usefulness as a one-time injectable in production-animal medicine. Here we report that administration of recombinant G-CSF induced a transient neutrophilia in pigs; however, delivery of porcine G-CSF encoded in a replication-defective adenovirus (Ad5) vector significantly increased the neutrophilia pharmacodynamics effect. Pigs given one injection of the Ad5-G-CSF had a neutrophilia that peaked between days 3-11 post-treatment and neutrophil counts remained elevated for more than 2 weeks. Neutrophils from Ad5-G-CSF treated pigs were fully functional based on their ability to release neutrophil extracellular traps and oxidative metabolism after in vitro stimulation. Since acceptable alternatives to the use of antibiotics in food-animal production need to be explored, we provide evidence for G-CSF as a possible candidate for agents in which neutrophils can provide protection.