Porcine IgG: structure, genetics, and evolution

Structural profile and diversity of immunoglobulin genes in the Arctic Fox

Immunoglobulins are important components of humoral immunity and play a crucial role in protecting the body from external antigens. The Arctic fox is an important member of furbearer farming, but due to the lack of research on the immune system of the Arctic fox, animal welfare regarding Arctic fox farming has still not received enough attention. In this study, we used the Arctic fox as a research subject, described the gene locus structure of the Arctic fox immunoglobulin germline by genome comparison, and analysed the mechanism of expression diversity of the antibody pool of the Arctic fox by rapid amplification of cDNA 5' ends and high-throughput sequencing. The results showed that the Arctic fox IgH, Igκ and Igλ loci were located on chromosome 6, chromosome 5 and chromosome 14, respectively. The number of variable (V) genes identified were 18, 11 and 10, and the number of joining (J) were 3, 4 and 13 and six diversity (D) genes in the heavy chain, respectively. Among them, the D genes, J genes and constant region genes of the heavy chain were arranged in the middle of the two variable heavy gene clusters; Arctic fox had a strong preference for the use of V genes, D genes and J genes, which resulted in a low level of V(D)J recombination diversity; linkage diversity analyses showed that random deletion of the V and J genes and insertion of the N and P nucleotides of the immunoglobulins of the Arctic foxes had a large impact on the linkage diversity of the IgH, whereas the light chain The linkage diversity was mainly contributed by the random deletion of V and J genes, and the insertion of N and P nucleotides had a smaller effect; somatic hypermutation (SHM) analysis showed that the mutation types of SHM of the heavy and light chains of the Arctic fox had a strong bias towards G>A and A>G, and the bias exhibited by the three chains was basically the same. By analysing the structure and expression diversity analysis of the Arctic fox gene loci, this study could provide a theoretical basis for antibody design and vaccine development in the Arctic fox, and provide new insights to further improve the animal welfare level of Arctic fox farming.

Considerations on the stability of IgG antibody in clinical specimens

The 1890s marked a significant milestone with the introduction of antibody-based agglutination and precipitation assays, revolutionizing the detection of bacterial pathogens in both animals and humans. This era also witnessed pivotal contributions to our understanding of humoral immunity, as researchers elucidated the structure and functions of antibody molecules, laying the groundwork for diagnostic applications. Among antibody isotypes, IgG is of paramount importance in diagnostic investigations given its definitive indication of infection or vaccination, coupled with its widespread presence and detectability across various specimen types, such as serum, colostrum, milk, oral fluids, urine, feces, and tissue exudate. Despite their resilience, immunoglobulins are susceptible to structural alterations induced by physicochemical and enzymatic processes, which can compromise the reliability of their detection. Here we review comprehensively the historical milestones, underlying mechanisms, and influencing factors (e.g., temperature, pH, storage) that shape the structural integrity and stability of IgG antibodies in aqueous solutions and various clinical specimens.

Single-Cell Antigen Receptor Sequencing in Pigs with Influenza

Understanding the pulmonary adaptive immune system of pigs is important as respiratory pathogens present a major challenge for swine producers and pigs are increasingly used to model human pulmonary diseases. Single-cell RNA sequencing (scRNAseq) has accelerated the characterization of cellular phenotypes in the pig respiratory tract under both healthy and diseased conditions. However, combining scRNAseq with recovery of paired T cell receptor (TCR) α and β chains as well as B cell receptor (BCR) heavy and light chains to interrogate their repertoires has not to our knowledge been demonstrated for pigs. Here, we developed primers to enrich porcine TCR α and β chains along with BCR κ and λ light chains and IgM, IgA, and IgG heavy chains that are compatible with the 10x Genomics VDJ sequencing protocol. Using these pig-specific assays, we sequenced the T and B cell receptors of cryopreserved lung cells from CD1D-expressing and -deficient pigs after one or two infections with influenza A virus (IAV) to examine whether natural killer T (NKT) cells alter pulmonary TCR and BCR repertoire selection. We also performed paired single-cell RNA and receptor sequencing of FACS-sorted T cells longitudinally sampled from the lungs of IAV-vaccinated and -infected pigs to track clonal expansion in response to IAV exposure. All pigs presented highly diverse repertoires. Pigs re-exposed to influenza antigens from either vaccination or infection exhibited higher numbers of expanded CD4 and CD8 T cell clonotypes with activated phenotypes, suggesting potential IAV reactive T cell populations. Our results demonstrate the utility of high throughput single-cell TCR and BCR sequencing in pigs.

Evaluation of vaccine efficacy with 2B/T epitope conjugated porcine IgG-Fc recombinants against foot-and-mouth disease virus

The inactivated vaccine is effective in controlling foot-and-mouth disease (FMD), but it has drawbacks such as the need for a biosafety level 3 laboratory facility to handle live foot-and-mouth disease virus (FMDV), high production costs, and biological safety risks. In response to these challenges, we developed a new recombinant protein vaccine (2BT-pIgG-Fc) containing porcine IgG-Fc to enhance protein stability in the body. This vaccine incorporates two-repeat B-cell and one-single T-cell epitope derived from O/Jincheon/SKR/2014. Our study confirmed that 2BT-pIgG-Fc and a commercial FMDV vaccine induced FMDV-specific antibodies in guinea pigs at 28 days post-vaccination. The percentage inhibition (PI) value of 2BT-pIgG-Fc was 90.43%, and the commercial FMDV vaccine was 81.75%. The PI value of 2BT-pIgG-Fc was 8.68% higher than that of commercial FMDV vaccine. In pigs, the primary target animals for FMDV, all five individuals produced FMDV-specific antibodies 42 days after vaccination with 2BT-pIgG-Fc. Furthermore, serum from 2BT-pIgG-Fc-vaccinated pigs exhibited neutralizing ability against FMDV infection. Intriguingly, the 2BT-pIgG-Fc recombinant demonstrated FMDV-specific antibody production rates and neutralization efficiency similar to commercial inactivated vaccines. This study illustrates the potential to enhance vaccine efficacy by strategically combining well-known antigenic domains in the development of recombinant protein-based vaccines.

A TLR7/8 agonist increases efficacy of anti-fentanyl vaccines in rodent and porcine models

Opioid use disorders (OUD) and overdose are public health threats worldwide. Widespread access to highly potent illicit synthetic opioids such as fentanyl is driving the recent rise in fatal overdoses. Vaccines containing fentanyl-based haptens conjugated to immunogenic carrier proteins offer a long-lasting, safe, and cost-effective strategy to protect individuals from overdose upon accidental or deliberate exposure to fentanyl and its analogs. Prophylactic or therapeutic active immunization with an anti-fentanyl vaccine induces the production of fentanyl-specific antibodies that bind the drug in the blood and prevent its distribution to the brain, which reduces its reinforcing effects and attenuates respiratory depression and bradycardia. To increase the efficacy of a lead anti-fentanyl vaccine, this study tested whether the incorporation of synthetic toll-like receptor (TLR) 4 and TLR7/8 agonists as vaccine adjuvants would increase vaccine efficacy against fentanyl challenge, overdose, and self-administration in either rats or Hanford miniature pigs. Formulation of the vaccine with a nucleolipid TLR7/8 agonist enhanced its immunogenicity and efficacy in preventing fentanyl-induced respiratory depression, analgesia, bradycardia, and self-administration in either rats or mini-pigs. These studies support the use of TLR7/8 adjuvants in vaccine formulations to improve their clinical efficacy against OUD and potentially other substance use disorders (SUD).

Assessing developability early in the discovery process for novel biologics

Beyond potency, a good developability profile is a key attribute of a biological drug. Selecting and screening for such attributes early in the drug development process can save resources and avoid costly late-stage failures. Here, we review some of the most important developability properties that can be assessed early on for biologics. These include the influence of the source of the biologic, its biophysical and pharmacokinetic properties, and how well it can be expressed recombinantly. We furthermore present in silico, in vitro, and in vivo methods and techniques that can be exploited at different stages of the discovery process to identify molecules with liabilities and thereby facilitate the selection of the most optimal drug leads. Finally, we reflect on the most relevant developability parameters for injectable versus orally delivered biologics and provide an outlook toward what general trends are expected to rise in the development of biologics.

The major role of junctional diversity in the horse antibody repertoire

The antibody repertoire (Rep-seq) sequencing revolutionized the diversity of antigen B cell receptor studies, allowing deep and quantitative analysis to decipher the role of adaptive immunity in health and disease. Particularly, horse (Equus caballus) polyclonal antibodies have been produced and used since the century XIX to treat and prophylaxis diphtheria, tuberculosis, tetanus, pneumonia, and, more recently, COVID-19. However, our knowledge about the horse B cell receptors repertories is minimal. We present a deep horse antibody heavy chain repertoire (IGH) characterization of non-infected horses using NGS (Next generation sequencing). This study obtained a mean of 248,169 unique IgM clones and 66,141 unique IgG clones from four domestic adult horses. Rarefaction analysis showed sequence coverage was between 52 % and 82 % in IgM and IgG isotypes. We observed that besides horses antibody can use all functional IGHV genes, around 80 % of their antibodies use only three IGHV gene segments, and around 55 % use only one IGHJ gene segment. This limited VJ diversity seems to be compensated by the junctional diversity of these antibodies. We observed that the junctional diversity in horse antibodies is widespread, present in more than 90 % of horse antibodies. Besides this, the length of this region seems to be higher in horse antibodies than in other species. N1 and N2 nucleotides addition range from 0 to 111 nucleotides. In addition, around 45 % of the antibody clones have more than ten nucleotides in both the N1 and N2 junction regions. This diversity mechanism may be one of the most important in providing variability to the equine antibody repertoire. This study provides new insights regarding horse antibody composition, diversity generation, and particularities compared to other species, such as the frequency and length of N nucleotide addition. This study also points out the urgent need to better characterize TdT in horses and other species to better understand antibody repertoire characteristics.

Orally-active bivalent VHH construct prevents proliferation of F4+ enterotoxigenic Escherichia coli in weaned piglets

A major challenge in industrial pig production is the prevalence of post-weaning diarrhea (PWD) in piglets, often caused by enterotoxigenic Escherichia coli (ETEC). The increased use of antibiotics and zinc oxide to treat PWD has raised global concerns regarding antimicrobial resistance development and environmental pollution. Still, alternative treatments targeting ETEC and counteracting PWD are largely lacking. Here, we report the design of a pH, temperature, and protease-stable bivalent V_HH-based protein BL1.2 that cross-links a F4⁺ ETEC model strain by selectively binding to its fimbriae. This protein inhibits F4⁺ ETEC adhesion to porcine epithelial cells ex vivo and decreases F4⁺ ETEC proliferation when administrated as a feed additive to weaned F4⁺ ETEC challenged piglets. These findings highlight the potential of a highly specific bivalent V_HH-based feed additive in effectively delimiting pathogenic F4⁺ ETEC bacteria proliferation in piglets and may represent a sustainable solution for managing PWD while circumventing antimicrobial resistance development.

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A binding protein was designed as a bivalent V_HH construct with a (GGGGS)₃ linker

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The protein can cross-link F4⁺ enterotoxigenic Escherichia coli (ETEC) in vitro

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The protein can prevent adhesion of F4⁺ ETEC to porcine epithelial cells ex vivo

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The protein can prevent proliferation of F4⁺ ETEC in piglets

Fc-Mediated Functions of Porcine IgG Subclasses

The pig is an important agricultural species and powerful biomedical model. We have established the pig, a large natural host animal for influenza with many physiological similarities to humans, as a robust model for testing the therapeutic potential of monoclonal antibodies. Antibodies provide protection through neutralization and recruitment of innate effector functions through the Fc domain. However very little is known about the Fc-mediated functions of porcine IgG subclasses. We have generated 8 subclasses of two porcine monoclonal anti influenza hemagglutinin antibodies. We characterized their ability to activate complement, trigger cytotoxicity and phagocytosis by immune cells and assayed their binding to monocytes, macrophages, and natural killer cells. We show that IgG1, IgG2a, IgG2b, IgG2c and IgG4 bind well to targeted cell types and mediate complement mediated cellular cytotoxicity (CDCC), antibody dependent cellular cytotoxicity (ADCC) and antibody mediated cell phagocytosis (ADCP). IgG5b and IgG5c exhibited weak binding and variable and poor functional activity. Immune complexes of porcine IgG3 did not show any Fc-mediated functions except for binding to monocytes and macrophages and weak binding to NK cells. Interestingly, functionally similar porcine IgG subclasses clustered together in the genome. These novel findings will enhance the utility of the pig model for investigation of therapeutic antibodies.

Experimental evaluation of protection and immunogenicity of Streptococcus suis bacterin-based vaccines formulated with different commercial adjuvants in weaned piglets

Streptococcus suis is an important swine pathogen responsible for economic losses to the swine industry worldwide. There is no effective commercial vaccine against S. suis. The use of autogenous (“bacterin”) vaccines to control S. suis outbreaks is a frequent preventive measure in the field, although scientific data on immunogenicity and reduction in mortality and morbidity are scarce. The goal of our study is to experimentally evaluate the immunogenicity and protective efficacy against homologous challenge in weaned piglets of a S. suis serotype 2 bacterin-based vaccine formulated with six different commercial adjuvants (Alhydrogel®, Emulsigen®-D, Quil-A®, Montanide™ ISA 206 VG, Montanide™ ISA 61 VG, and Montanide™ ISA 201 VG). The vaccine formulated with Montanide™ ISA 61 VG induced a significant increase in anti-S. suis antibodies, including both IgG1 and IgG2 subclasses, protected against mortality and significantly reduced morbidity and severity of clinical signs. Vaccines formulated with Montanide ISA 206 VG or Montanide ISA 201 VG also induced a significant increase in anti-S. suis antibodies and showed partial protection and reduction of clinical signs severity. Vaccines formulated with Alhydrogel®, Emulsigen®-D, or Quil-A® induced a low and IgG1-shifted antibody response and failed to protect vaccinated piglets against a homologous challenge. In conclusion, the type of adjuvant used in the vaccine formulation significantly influenced the immune response and efficacy of the vaccine against a homologous challenge.

Survival patterns of Streptococcus suis serotypes 1 and 14 in porcine blood indicate cross-reactive bactericidal antibodies in naturally infected pigs

Streptococcus suis serotype (cps) 1 and cps14 have been detected in association with severe diseases such as meningitis and polyarthritis in pigs. Though these two cps are very similar, only cps14 is an important zoonotic agent in Asia and only cps1 is described to be associated with diseases in suckling piglets rather than weaning piglets. The main objective of this study was to assess restriction of survival of cps14 and cps1 in porcine blood by IgG and IgM putatively cross-reacting with these two cps. Furthermore, we differentiate recent European cps1/14 strains by agglutination, cpsK sequencing, MLST and virulence-associated gene profiling. Our data confirmed cps1 of clonal complex 1 as an important pathotype causing polyarthritis in suckling piglets in Europe. The experimental design included also bactericidal assays with blood samples drawn at different ages of piglets naturally infected with different S. suis cps types including cps1 but not cps14. We report survival of a cps1 and a cps14 strain (both of sequence type 1) in blood of suckling piglets with high levels of maternal IgG binding to the bacterial surface. In contrast, killing of cps1 and cps14 was recorded in older piglets due to an increase of IgM as demonstrated by specific cleavage of IgM. Heterologous absorption of antibodies with cps1 or cps14 is sufficient to significantly increase the survival of the other cps. In conclusion, IgM elicited by natural S. suis infection is crucial for killing of S. suis cps1 and cps14 in older weaning piglets and has most likely the potential to cross-react between cps1 and cps14.

Liquid chromatography-tandem mass spectrometry glycoproteomic study of porcine IgG and detection of subtypes

RATIONALE

While high-throughput proteomic methods have been widely applied to monoclonal antibodies and human immunoglobulin gamma (IgG) samples, less information is available on porcine IgG. As pigs are considered one of the most suitable species for xenotransplantation, it is important to characterize IgG amino acid sequences and glycosylation profiles, which is the focus of this study.

METHODS

Three different purified porcine IgG samples, including wild-type and knockout species, were digested with trypsin and enriched for glycopeptides. Digestion mixtures were spiked with a mixture of six standard peptides. Analysis was performed using electrospray ionization liquid chromatography-tandem mass spectrometry (MS/MS) in standard MS/MS data-dependent acquisition mode on a hybrid triple quadrupole time-of-flight mass spectrometer.

RESULTS

To facilitate the classification of subtypes detected experimentally, UniprotKB database entries were organized using comparative alignment scores. Sequences were grouped based on 11 different subtypes as translated from GenBank entries. Proteomic searches were accomplished automatically using specialized software, whereas glycoprotein searches were performed manually by monitoring the extracted chromatograms of diagnostic MS/MS glycan fragments and studying their corresponding mass spectra; 40-50 non-glycosylated peptides and 4-5 glycosylated peptides were detected in each sample, with several glycoforms per sequence.

CONCLUSIONS

Proteomic analysis of porcine IgG is complicated by factors such as the presence of several subtypes, redundant heavy chain (HC) sequences in protein databases, and the lack of consistent cross-referencing between databases. Aligning and comparing HC sequences were necessary to eliminate redundancy. This study highlights the complexity of pig IgG and shows the importance of MS in proteomics and glycoproteomics.

Göttingen Minipigs as a Model to Evaluate Longevity, Functionality, and Memory of Immune Response Induced by Pertussis Vaccines

Evaluation of the short-term and long-term immunological responses in a preclinical model that simulates the targeted age population with a relevant vaccination schedule is essential for human vaccine development. A Göttingen minipig model was assessed, using pertussis vaccines, to demonstrate that vaccine antigen-specific humoral and cellular responses, including IgG titers, functional antibodies, Th polarization and memory B cells can be assessed in a longitudinal study. A vaccination schedule of priming with a whole cell (DTwP) or an acellular (DTaP) pertussis vaccine was applied in neonatal and infant minipigs followed by boosting with a Tdap acellular vaccine. Single cell RNAsequencing was used to explore the long-term maintenance of immune memory cells and their functionality for the first time in this animal model. DTaP but not DTwP vaccination induced pertussis toxin (PT) neutralizing antibodies. The cellular immune response was also characterized by a distinct Th polarization, with a Th-2-biased response for DTaP and a Th-1/Th-17-biased response for DTwP. No difference in the maintenance of pertussis-specific memory B cells was observed in DTaP- or DTwP-primed animals 6 months post Tdap boost. However, an increase in pertussis-specific T cells was still observed in DTaP primed minipigs, together with up-regulation of genes involved in antigen presentation and interferon pathways. Overall, the minipig model reproduced the humoral and cellular immune responses induced in humans by DTwP vs. DTaP priming, followed by Tdap boosting. Our data suggest that the Göttingen minipig is an attractive preclinical model to predict the long-term immunogenicity of human vaccines against Bordetella pertussis and potentially also vaccines against other pathogens.

Nanobody Nb6 fused with porcine IgG Fc as the delivering tag to inhibit porcine reproductive and respiratory syndrome virus replication in porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious virus that has led to enormous economic loss worldwide because of ineffective prevention and treatment. In view of their minimized size, high target specificity and affinity, nanobodies have been extensively investigated as diagnostic tools and treatments of many diseases. Previously, a PRRSV Nsp9-specific nanobody (Nb6) was identified as a PRRSV replication inhibitor. When it was fused with cell-penetrating peptide (CPP) TAT, Nb6-TAT could enter the cells for PRRSV suppression. However, delivery of molecules by CPP lack cell specificity and have a short duration of action. PRRSV has a tropism for monocyte/macrophage lineage, which expresses high levels of Fcγ receptors. Herein, we designed a nanobody containing porcine IgG Fc (Fcγ) to inhibit PRRSV replication in PRRSV permissive cells. Fcγ fused Nb6 chimeric antibody (Nb6-pFc) was assembled into a dimer with interchain disulfide bonds and expressed in a Pichia pastoris system. The results show that Nb6-pFc exhibits a well-binding ability to recombinant Nsp9 or PRRSV-encoded Nsp9 and that FcγR-mediated endocytosis of Nb6-pFc into porcine alveolar macrophages (PAM) was in a dose-dependent manner. Nb6-pFc can inhibit PRRSV infection efficiently not only by binding with Nsp9 but also by upregulating proinflammatory cytokine production in PAM. Together, this study proposes the design of a porcine IgG Fc-fused nanobody that can enter PRRSV susceptible PAM via FcγR-mediated endocytosis and inhibit PRRSV replication. This research reveals that nanobody-Fcγ chimeric antibodies might be effective for the control and prevention of monocyte/macrophage lineage susceptible pathogeneses.

Revisiting the Pig IGHC Gene Locus in Different Breeds Uncovers Nine Distinct IGHG Genes

IgG subclass diversification is common in placental mammals. It has been well documented in humans and mice that different IgG subclasses, with diversified functions, synergistically regulate humoral immunity. However, our knowledge on the genomic and functional diversification of IgG subclasses in the pig, a mammalian species with high agricultural and biomedical importance, is incomplete. Using bacterial artificial chromosome sequencing and newly assembled genomes generated by the PacBio sequencing approach, we characterized and mapped the IgH C region gene locus in three indigenous Chinese breeds (Erhualian, Xiang, and Luchuan) and compared them to that of Duroc. Our data revealed that IGHG genes in Chinese pigs differ from the Duroc, whereas the IGHM, IGHD, IGHA, and IGHE genes were all single copy and highly conserved in the pig breeds examined. Most striking were differences in numbers of IGHG genes: there are seven genes in Erhualian pigs, six in the Duroc, but only five in Xiang pigs. Phylogenetic analysis suggested that all reported porcine IGHG genes could be classified into nine subclasses: IGHG1, IGHG2a, IGHG2b, IGHG2c, IGHG3, IGHG4, IGHG5a, IGHG5b, and IGHG5c. Using sequence information, we developed a mouse mAb specific for IgG3. This study offers a starting point to investigate the structure-function relationship of IgG subclasses in pigs.

Generation and characterization of genetically stable heterohybridomas producing foot-and-mouth disease virus-specific porcine monoclonal antibodies

This report covers the methodology for generation of stable heterohybridoma clones producing Foot-and-mouth disease virus (FMDV) reactive porcine monoclonal antibodies (mAbs). Swine received five inoculations of an inactivated O1 Manisa FMDV vaccine prior to the harvest of splenocytes. Due to the lack of a species-specific hybridoma fusion partner, the Sp2/0 murine myeloma cell line was utilized for the formation of porcine-murine heterohybridoma clones. Twenty-nine FMDV-reactive parental clones were generated. Following sub-cloning and monitoring of reactivity over 20 serial passages, eleven subclones derived from unique parental origins were characterized and are reported herein. This methodology demonstrated the production of porcine mAbs by fusion of porcine splenocytes from immunized pigs with murine myeloma cells to generate heterohybridomas. The porcine immune response may differ from the murine immune response in relation to recognized epitopes. Therefore, application of this methodology may provide valuable resources for swine immunology and enhance the understanding of the mechanisms for antibody based protection from diseases in swine.

Efficient mucosal vaccination of a novel classical swine fever virus E2-Fc fusion protein mediated by neonatal Fc receptor

Classical swine fever (CSF) remains one of the most important highly contagious and fatal viral disease of swine with high morbidity and mortality. CSF is caused by classical swine fever virus (CSFV), a small, enveloped RNA virus of the genus Pestivirus. The aim of this study was to construct the a novel CSFV Fc-fusion recombinant protein and evaluate the efficacy as a vaccine against CSFV. Here, we obtained a novel subunit vaccine expressing CSFV E2 recombinant fusion protein in CHO-S cells. Functional analysis revealed that CSFV Fc-fusion recombinant protein (CSFV-E2-Fc) could bind to FcγRI on antigen-presenting cells (APCs) and significantly increase IgA levels in serum and feces, inducing stronger mucosal immune response in swine. Additionally, CSFV-E2-Fc immunization enhanced CSFV-specific T cell immune response with a Th1-like pattern of cytokine secretion, remarkably stimulated the Th1-biased cellular immune response and humoral immune response. Further, the protective effects of CSFV-E2-Fc subunit vaccines were confirmed. The data suggest that CSFV E2-Fc recombinant fusion protein may be a promising candidate subunit vaccine to elicit immune response and protect against CSFV.

Targeting of HA to chemokine receptors induces strong and cross-reactive T cell responses after DNA vaccination in pigs

Efficient influenza vaccination of pigs can reduce disease burdens for the swine industry, but also represents an important measure for reducing the risk from novel viral reassortments that pose pandemic threats to the human population. Here, we have vaccinated pigs with a DNA vaccine encoding influenza virus hemagglutinin (HA) linked to the chemokine MIP1α that bind chemokine receptors 1, 3, and 5 expressed on antigen presenting cells (APC). Such MIP1α targeting of HA to APC enhanced induction of HA reactive antibodies, particularly IgG2. In addition, the MIP1α- HA vaccine induced strong T cell responses that could cross-react with different influenza subtypes. Thus, the strategy of targeting HA to chemokine receptors could be important for inducing broad protection against antigenically diverse influenza strains in pigs.

Binding affinities of human IgG1 and chimerized pig and rabbit derivatives to human, pig and rabbit Fc gamma receptor IIIA

While pigs and rabbits are used as models for human immune diseases, FcγR binding is poorly characterized in both test species. To evaluate antibody binding to FcγRIIIA, a receptor involved in antibody-dependent cellular cytotoxicity, chimerized antibodies were generated by grafting the variable regions of a human IgG1 onto scaffolds from both species. The affinities of the parent and chimeric antibodies to the FcγRIIIA proteins from all three species were determined. While the human IgG1 and rabbit IgG had similar affinities for each FcγRIIIA with notable differences across species, pig IgG1 only bound pig FcγRIIIA with appreciable affinity. Also, the functional pig and rabbit proteins described here can be used in future experiments, such as pharmacology and mechanism of action studies.

The Binding of Human IgG to Minipig FcγRs - Implications for Preclinical Assessment of Therapeutic Antibodies

Purpose

The Göttingen minipig is a relevant non-rodent species for regulatory toxicological studies. Yet, its use with therapeutic antibodies has been limited by the unknown binding properties of human immunoglobulins (huIgG) to porcine Fc gamma receptors (poFcγR) influencing safety and efficacy readouts. Therefore, knowing IgG-FcγR interactions in the animal model is a prerequisite for the use of minipigs in preclinical safety and efficacy studies with therapeutic antibodies.

Methods

Here, we describe the cloning and expression of poFcγRs and their interactions with free and complexed human therapeutic IgG1 by surface plasmon resonance and flow cytometry.

Results

We show here that poFcγRIa, poFcγRIIa, and poFcγRIIb bind huIgG1 antibodies with comparable affinities as corresponding huFcγRs. Importantly, poFcγRs bind huIgG immune complexes with high avidity, thus probably allowing human-like effector functions. However, poFcγRIIIa binds poIgG1a but not to huIgG1.

Conclusions

The lack of binding of poFcγRIIIa to huIgG1 might cause underestimation of FcγRIIIa-mediated efficacy or toxicity as mediated by porcine natural killer cells. Therefore, the suitability of minipigs in preclinical studies with human therapeutic antibodies has to be assessed case by case. Our results facilitate the use of Göttingen minipigs for assessment of human therapeutic antibodies in preclinical studies.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2574-y) contains supplementary material, which is available to authorized users.

Identification of a new European rabbit IgA with a serine-rich hinge region

In mammals, the most striking IgA system belongs to Lagomorpha. Indeed, 14 IgA subclasses have been identified in European rabbits, 11 of which are expressed. In contrast, most other mammals have only one IgA, or in the case of hominoids, two IgA subclasses. Characteristic features of the mammalian IgA subclasses are the length and amino acid sequence of their hinge regions, which are often rich in Pro, Ser and Thr residues and may also carry Cys residues. Here, we describe a new IgA that was expressed in New Zealand White domestic rabbits of IGHVa1 allotype. This IgA has an extended hinge region containing an intriguing stretch of nine consecutive Ser residues and no Pro or Thr residues, a motif exclusive to this new rabbit IgA. Considering the amino acid properties, this hinge motif may present some advantage over the common IgA hinge by affording novel functional capabilities. We also sequenced for the first time the IgA14 CH2 and CH3 domains and showed that IgA14 and IgA3 are expressed.

The antibody loci of the domestic goat (Capra hircus)

The domestic goat (Capra hircus) is an important ruminant species both as a source of antibody-based reagents for research and biomedical applications and as an economically important animal for agriculture, particularly for developing nations that maintain most of the global goat population. Characterization of the loci encoding the goat immune repertoire would be highly beneficial for both vaccine and immune reagent development. However, in goat and other species whose reference genomes were generated using short-read sequencing technologies, the immune loci are poorly assembled as a result of their repetitive nature. Our recent construction of a long-read goat genome assembly (ARS1) has facilitated characterization of all three antibody loci with high confidence and comparative analysis to cattle. We observed broad similarity of goat and cattle antibody-encoding loci but with notable differences that likely influence formation of the functional antibody repertoire. The goat heavy-chain locus is restricted to only four functional and nearly identical IGHV genes, in contrast to the ten observed in cattle. Repertoire analysis indicates that light-chain usage is more balanced in goats, with greater representation of kappa light chains (~ 20-30%) compared to that in cattle (~ 5%). The present study represents the first characterization of the goat antibody loci and will help inform future investigations of their antibody responses to disease and vaccination.

Antibody Repertoire Development in Swine

We describe the domestication of the species, explore its value to agriculture and bioscience, and compare its immunoglobulin (Ig) genes to those of other vertebrates. For encyclopedic information, we cite earlier reviews and chapters. We provide current gene maps for the heavy and light chain loci and describe their polygeny and polymorphy. B-cell and antibody repertoire development is a major focus, and we present findings that challenge several mouse-centric paradigms. We focus special attention on the role of ileal Peyer's patches, the largest secondary lymphoid tissues in newborn piglets and a feature of all artiodactyls. We believe swine fetal development and early class switch evolved to provide natural secretory IgA antibodies able to prevent translocation of bacteria from the gut while the bacterial PAMPs drive development of adaptive immunity. We discuss the value of using the isolator piglet model to address these issues.

Transcriptomic Signatures of Tacaribe Virus-Infected Jamaican Fruit Bats

As reservoir hosts of viruses associated with human disease, little is known about the interactions between bats and viruses. Using Jamaican fruit bats infected with Tacaribe virus (TCRV) as a model, we characterized the gene expression responses to infection in different tissues and identified pathways involved with the response to infection. This report is the most detailed gene discovery work in the species to date and the first to describe immune gene expression responses in bats during a pathogenic viral infection.

Tacaribe virus (TCRV) is a mammalian arenavirus that was first isolated from artibeus bats in the 1950s. Subsequent experimental infection of Jamaican fruit bats (Artibeus jamaicensis) caused a disease similar to that of naturally infected bats. Although substantial attention has focused on bats as reservoir hosts of viruses that cause human disease, little is known about the interactions between bats and their pathogens. We performed a transcriptome-wide study to illuminate the response of Jamaican fruit bats experimentally infected with TCRV. Differential gene expression analysis of multiple tissues revealed global and organ-specific responses associated with innate antiviral responses, including interferon alpha/beta and Toll-like receptor signaling, activation of complement cascades, and cytokine signaling, among others. Genes encoding proteins involved in adaptive immune responses, such as gamma interferon signaling and costimulation of T cells by the CD28 family, were also altered in response to TCRV infection. Immunoglobulin gene expression was also elevated in the spleens of infected bats, including IgG, IgA, and IgE isotypes. These results indicate an active innate and adaptive immune response to TCRV infection occurred but did not prevent fatal disease. This de novo assembly provides a high-throughput data set of the Jamaican fruit bat and its host response to TCRV infection, which remains a valuable tool to understand the molecular signatures involved in antiviral responses in bats.

IMPORTANCE As reservoir hosts of viruses associated with human disease, little is known about the interactions between bats and viruses. Using Jamaican fruit bats infected with Tacaribe virus (TCRV) as a model, we characterized the gene expression responses to infection in different tissues and identified pathways involved with the response to infection. This report is the most detailed gene discovery work in the species to date and the first to describe immune gene expression responses in bats during a pathogenic viral infection.

The Florida manatee (Trichechus manatus latirostris) immunoglobulin heavy chain suggests the importance of clan III variable segments in repertoire diversity

Manatees are a vulnerable, charismatic sentinel species from the evolutionarily divergent Afrotheria. Manatee health and resistance to infectious disease is of great concern to conservation groups, but little is known about their immune system. To develop manatee-specific tools for monitoring health, we first must have a general knowledge of how the immunoglobulin heavy (IgH) chain locus is organized and transcriptionally expressed. Using the genomic scaffolds of the Florida manatee (Trichechus manatus latirostris), we characterized the potential IgH segmental diversity and constant region isotypic diversity and performed the first Afrotherian repertoire analysis. The Florida manatee has low V(D)J combinatorial diversity (3744 potential combinations) and few constant region isotypes. They also lack clan III V segments, which may have caused reduced VH segment numbers. However, we found productive somatic hypermutation concentrated in the complementarity determining regions. In conclusion, manatees have limited IGHV clan and combinatorial diversity. This suggests that clan III V segments are essential for maintaining IgH locus diversity.

Surface displaying of swine IgG1 Fc enhances baculovirus-vectored vaccine efficacy by facilitating viral complement escape and mammalian cell transduction

Baculovirus-mediated gene transfer has been developed as a vaccine design strategy against a number of diseases without apparent viral replication. However, it has been hampered by complement-dependent inactivation, thus hindering the in vivo application of baculovirus. A variety of approaches have been exploited to bypass the complement system in the serum. In this study, we constructed and screened a series of baculovirus vectors displaying complement interfering factors, of which a baculovirus vector displaying swine IgG1 Fc (pFc) showed the highest complement antagonism (75.6%). Flow cytometry analysis of transduced cells demonstrated that the baculovirus display of pFc had a significant increase in transduction efficiency and transgene expression of reporter genes. On this basis, a VSV-G-pseudotyped with swine IgG1 Fc surface displayed baculovirus vector was developed to express the classical swine fever virus (CSFV) E2 gene. The translational enhancers Syn21 and P10UTR were incorporated to improve the antigen expression. The E2 gene was efficiently expressed in both insect and mammalian cells. Pigs immunized with this recombinant baculovirus developed high levels of E2-specific antibody, CSFV-specific neutralizing antibody and IFN-γ-secreting cellular immune responses. These results demonstrate that the strategy of surface-displaying swine IgG1 Fc has a great potential to improve the efficiency of baculovirus-vectored vaccine for CSFV and other swine pathogens.

Antibody repertoire development in fetal and neonatal piglets. XXIV. Hypothesis: The ileal Peyer patches (IPP) are the major source of primary, undiversified IgA antibodies in newborn piglets

The ileal Peyers patches (IPP) of newborn germfree (GF) piglets were isolated into blind loops and the piglets colonized with a defined probiotic microflora. After 5 weeks, IgA levels in the intestinal lavage (IL) of loop piglets remained at GF levels and IgM comprised ∼70% while in controls, IgA levels were elevated 5-fold and comprised ∼70% of total Igs. Loop piglets also had reduced serum IgA levels suggesting the source of serum IgA had been interrupted. The isotype profile for loop contents was intermediate between that in the IL of GF and probiotic controls. Surprisingly, colonization alone did not result in repertoire diversification in the IPP. Rather, colonization promoted pronounced proliferation of fully switched IgA(+)IgM(-) B cells in the IPP that supply early, non-diversified "natural" SIgA antibodies to the gut lumen and a primary IgA response in serum.

Novel IgG-Degrading Enzymes of the IgdE Protease Family Link Substrate Specificity to Host Tropism of Streptococcus Species

Recently we have discovered an IgG degrading enzyme of the endemic pig pathogen S. suis designated IgdE that is highly specific for porcine IgG. This protease is the founding member of a novel cysteine protease family assigned C113 in the MEROPS peptidase database. Bioinformatical analyses revealed putative members of the IgdE protease family in eight other Streptococcus species. The genes of the putative IgdE family proteases of S. agalactiae, S. porcinus, S. pseudoporcinus and S. equi subsp. zooepidemicus were cloned for production of recombinant protein into expression vectors. Recombinant proteins of all four IgdE family proteases were proteolytically active against IgG of the respective Streptococcus species hosts, but not against IgG from other tested species or other classes of immunoglobulins, thereby linking the substrate specificity to the known host tropism. The novel IgdE family proteases of S. agalactiae, S. pseudoporcinus and S. equi showed IgG subtype specificity, i.e. IgdE from S. agalactiae and S. pseudoporcinus cleaved human IgG1, while IgdE from S. equi was subtype specific for equine IgG7. Porcine IgG subtype specificities of the IgdE family proteases of S. porcinus and S. pseudoporcinus remain to be determined. Cleavage of porcine IgG by IgdE of S. pseudoporcinus is suggested to be an evolutionary remaining activity reflecting ancestry of the human pathogen to the porcine pathogen S. porcinus. The IgG subtype specificity of bacterial proteases indicates the special importance of these IgG subtypes in counteracting infection or colonization and opportunistic streptococci neutralize such antibodies through expression of IgdE family proteases as putative immune evasion factors. We suggest that IgdE family proteases might be valid vaccine targets against streptococci of both human and veterinary medical concerns and could also be of therapeutic as well as biotechnological use.

Progress in the use of swine in developmental immunology of B and T lymphocytes

The adaptive immune system of higher vertebrates is believed to have evolved to counter the ability of pathogens to avoid expulsion because their high rate of germline mutations. Vertebrates developed this adaptive immune response through the evolution of lymphocytes capable of somatic generation of a diverse repertoire of their antigenic receptors without the need to increase the frequency of germline mutation. The focus of our research and this article is on the ontogenetic development of the lymphocytes, and the repertoires they generate in swine. Several features are discussed including (a) the "closed" porcine placenta means that de novo fetal development can be studied for 114 days without passive influence from the mother, (b) newborn piglets are precocial permitting them to be reared without their mothers in germ-free isolators, (c) swine are members of the γδ-high group of mammals and thus provides a greater opportunity to characterize the role of γδ T cells and (d) because swine have a simplified variable heavy and light chain genome they offer a convenient system to study antibody repertoire development.

Identification and Characterization of IgdE, a Novel IgG-degrading Protease of Streptococcus suis with Unique Specificity for Porcine IgG

Streptococcus suisis a major endemic pathogen of pigs causing meningitis, arthritis, and other diseases. ZoonoticS. suisinfections are emerging in humans causing similar pathologies as well as severe conditions such as toxic shock-like syndrome. Recently, we discovered an IdeS family protease ofS. suisthat exclusively cleaves porcine IgM and represents the first virulence factor described, linkingS. suisto pigs as their natural host. Here we report the identification and characterization of a novel, unrelated protease ofS. suisthat exclusively targets porcine IgG. This enzyme, designated IgdE forimmunoglobulinG-degradingenzyme ofS. suis, is a cysteine protease distinct from previous characterized streptococcal immunoglobulin degrading proteases of the IdeS family and mediates efficient cleavage of the hinge region of porcine IgG with a high degree of specificity. The findings that allS. suisstrains investigated possess the IgG proteolytic activity and that piglet serum samples contain specific antibodies against IgdE strongly indicate that the protease is expressedin vivoduring infection and represents a novel and putative important bacterial virulence/colonization determinant, and a thus potential therapeutic target.

Haemophilus parasuis: infection, immunity and enrofloxacin

Haemophilus parasuis is an early colonizer of the porcine upper respiratory tract and is the etiological agent of Glasser’s disease. The factors responsible for H. parasuis colonization and systemic infection are not yet well understood, while prevention and control of Glasser’s disease continues to be challenging. Recent studies on innate immunity to H. parasuis have demonstrated that porcine alveolar macrophages (PAMs) are able to differentially up-regulate several genes related to inflammation and phagocytosis, and several pro-inflammatory cytokines are produced by porcine cells upon exposure to H. parasuis. The susceptibility of H. parasuis strains to phagocytosis by PAMs and the bactericidal effect of complement are influenced by the virulent phenotype of the strains. While non-virulent strains are susceptible to phagocytosis and complement, virulent strains are resistant to both. However, in the presence of specific antibodies against H. parasuis, virulent strains become susceptible to phagocytosis. More information is still needed, though, in order to better understand the host immune responses to H. parasuis. Antimicrobials are commonly used in the swine industry to help treat and control Glasser’s disease. Some of the common antimicrobials have been shown to reduce colonization by H. parasuis, which may have implications for disease dynamics, development of effective immune responses and immunomodulation. Here, we provide the current state of research on innate and adaptive immune responses to H. parasuis and discuss the potential effect of enrofloxacin on the development of a protective immune response against H. parasuis infection.

Streptococcus suis vaccines: candidate antigens and progress

Streptococcus suis is a major swine pathogen and an emerging zoonotic agent of human meningitis and streptococcal toxic shock-like syndrome. S. suis is a well-encapsulated pathogen and multiple serotypes have been described based on the capsular polysaccharide antigenic diversity. In addition, high genotypic, phenotypic and geographic variability exits among strains within the same serotype. Besides, S. suis uses an arsenal of virulence factors to evade the host immune system. Together, these characteristics have challenged the development of efficacious vaccines to fight this important pathogen. In this careful and comprehensive review, clinical field information and experimental data have been compiled and compared for the first time to give a precise overview of the current status of vaccine development against S. suis. The candidate antigens and vaccine formulations under research are examined and the feasibility of reaching the goal of a "universal" cross-protective S. suis vaccine discussed.

Leporid immunoglobulin G shows evidence of strong selective pressure on the hinge and CH3 domains

Immunoglobulin G (IgG) is the predominant serum immunoglobulin and has the longest serum half-life of all the antibody classes. The European rabbit IgG has been of significant importance in immunological research, and is therefore well characterized. However, the IgG of other leporids has been disregarded. To evaluate the evolution of this gene in leporids, we sequenced the complete IGHG for six other genera: Bunolagus, Brachylagus, Lepus, Pentalagus, Romerolagus and Sylvilagus. The newly sequenced leporid IGHG gene has an organization and structure similar to that of the European rabbit IgG. A gradient in leporid IgG constant domain diversity was observed, with the CH1 being the most conserved and the CH3 the most variable domain. Positive selection was found to be acting on all constant domains, but with a greater incidence in the CH3 domain, where a cluster of three positively selected sites was identified. In the hinge region, only three polymorphic positions were observed. The same hinge length was observed for all leporids. Unlike the variation observed for the European rabbit, all 11 Lepus species studied share exactly the same hinge motif, suggesting its maintenance as a result of an advantageous structure or conformation.

Porcine reproductive and respiratory syndrome (PRRS): an immune dysregulatory pandemic

Porcine reproductive and respiratory disease syndrome (PRRS) is a viral pandemic that especially affects neonates within the “critical window” of immunological development. PRRS was recognized in 1987 and within a few years became pandemic causing an estimated yearly $600,000 economic loss in the USA with comparative losses in most other countries. The causative agent is a single-stranded, positive-sense enveloped arterivirus (PRRSV) that infects macrophages and plasmacytoid dendritic cells. Despite the discovery of PRRSV in 1991 and the publication of >2,000 articles, the control of PRRS is problematic. Despite the large volume of literature on this disease, the cellular and molecular mechanisms describing how PRRSV dysregulates the host immune system are poorly understood. We know that PRRSV suppresses innate immunity and causes abnormal B cell proliferation and repertoire development, often lymphopenia and thymic atrophy. The PRRSV genome is highly diverse, rapidly evolving but amenable to the generation of many mutants and chimeric viruses for experimental studies. PRRSV only replicates in swine which adds to the experimental difficulty since no inbred well-defined animal models are available. In this article, we summarize current knowledge and apply it toward developing a series of provocative and testable hypotheses to explain how PRRSV immunomodulates the porcine immune system with the goal of adding new perspectives on this disease.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

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.

Orally fed seeds producing designer IgAs protect weaned piglets against enterotoxigenic Escherichia coli infection

Oral feed-based passive immunization can be a promising strategy to prolong maternal lactogenic immunity against postweaning infections. Enterotoxigenic Escherichia coli (ETEC)-caused postweaning diarrhea in piglets is one such infection that may be prevented by oral passive immunization and might avert recurrent economic losses to the pig farming industry. As a proof of principle, we designed anti-ETEC antibodies by fusing variable domains of llama heavy chain-only antibodies (VHHs) against ETEC to the Fc part of a porcine immunoglobulin (IgG or IgA) and expressed them in Arabidopsis thaliana seeds. In this way, four VHH-IgG and four VHH-IgA antibodies were produced to levels of about 3% and 0.2% of seed weight, respectively. Cotransformation of VHH-IgA with the porcine joining chain and secretory component led to the production of light-chain devoid, assembled multivalent dimeric, and secretory IgA-like antibodies. In vitro analysis of all of the antibody-producing seed extracts showed inhibition of bacterial binding to porcine gut villous enterocytes. However, in the piglet feed-challenge experiment, only the piglets receiving feed containing the VHH-IgA-based antibodies (dose 20 mg/d per pig) were protected. Piglets receiving the VHH-IgA-based antibodies in the feed showed a progressive decline in shedding of bacteria, significantly lower immune responses corroborating reduced exposure to the ETEC pathogen, and a significantly higher weight gain compared with the piglets receiving VHH-IgG producing (dose 80 mg/d per pig) or wild-type seeds. These results stress the importance of the antibody format in oral passive immunization and encourage future expression of these antibodies in crop seeds.

Antibody responses to Sarcoptes scabiei apolipoprotein in a porcine model: relevance to immunodiagnosis of recent infection

No commercial immunodiagnostic tests for human scabies are currently available, and existing animal tests are not sufficiently sensitive. The recombinant Sarcoptes scabiei apolipoprotein antigen Sar s 14.3 is a promising immunodiagnostic, eliciting high levels of IgE and IgG in infected people. Limited data are available regarding the temporal development of antibodies to Sar s 14.3, an issue of relevance in terms of immunodiagnosis. We utilised a porcine model to prospectively compare specific antibody responses to a primary infestation by ELISA, to Sar s 14.3 and to S. scabiei whole mite antigen extract (WMA). Differences in the antibody profile between antigens were apparent, with Sar s 14.3 responses detected earlier, and declining significantly after peak infestation compared to WMA. Both antigens resulted in >90% diagnostic sensitivity from weeks 8-16 post infestation. These data provide important information on the temporal development of humoral immune responses in scabies and further supports the development of recombinant antigen based immunodiagnostic tests for recent scabies infestations.

Antibody repertoire development in fetal and neonatal piglets. XII. Three IGLV genes comprise 70% of the pre-immune repertoire and there is little junctional diversity

We characterized 239 lambda rearrangements from fetal and germfree (GF) piglets to: (1) determine if transcripts recovered from the earliest sites of B cell lymphogenesis were unique (2) determine what proportion of the genome is used to form the pre-immune repertoire (3) estimate the degree of somatic hypermutation and junctional diversity during ontogeny and (4) test whether piglets maintained germfree in isolators (GF piglets) have a more diversified repertoire than fetal piglets. We show that all expressed lambda genes belong to the IGLV3 and IGLV8 families and only IGLJ2 and IGLJ3 were expressed and used equally throughout fetal and neonatal life. Only genes of the IGLV8 family were used in yolk sac and fetal liver and in these tissues, IGLV8-10 comprised >50%. However, the IGLV8 genes recovered at these early sites of B cell lymphogenesis were recovered at all stages of development. Thus, no unique lambda rearrangement was recovered at the first sites of B cell development. The frequency of somatic hypermutation (SHM) in fetal piglets was ~5.9 per Kb equivalent, mutation were concentrated in CDR regions and did not increase in GF piglets. The average CDR3 length was 30 nt ± 2.7 and did not change in GF piglets. Similar to the heavy chain pre-immune repertoire in this species, three IGLV genes account for ~70% of the repertoire. Unlike the heavy chain repertoire, junctional diversity was very limited.

Nanobodies: natural single-domain antibodies

Sera of camelids contain both conventional heterotetrameric antibodies and unique functional heavy (H)-chain antibodies (HCAbs). The H chain of these homodimeric antibodies consists of one antigen-binding domain, the VHH, and two constant domains. HCAbs fail to incorporate light (L) chains owing to the deletion of the first constant domain and a reshaped surface at the VHH side, which normally associates with L chains in conventional antibodies. The genetic elements composing HCAbs have been identified, but the in vivo generation of these antibodies from their dedicated genes into antigen-specific and affinity-matured bona fide antibodies remains largely underinvestigated. However, the facile identification of antigen-specific VHHs and their beneficial biochemical and economic properties (size, affinity, specificity, stability, production cost) supported by multiple crystal structures have encouraged antibody engineering of these single-domain antibodies for use as a research tool and in biotechnology and medicine.

Antibody repertoire development in fetal and neonatal piglets. XVI. Influenza stimulates adaptive immunity, class switch and diversification of the IgG repertoire encoded by downstream Cγ genes

Infection of germ-free isolator piglets with swine influenza (S-FLU) that generates dsRNA during replication causes elevation of immunoglobulins in serum and bronchoalveolar lavage, a very weak response to trinitrophenyl conjugates but an immune response to S-FLU. The increased immunoglobulin levels result mainly from the polyclonal activation of B cells during the infection, but model antigen exposure may contribute. The 10-fold increase in local and serum IgG accompanies a 10-fold decrease in the transcription of IgG3 in the tracheal-bronchial lymph nodes and in the ileal Peyer's patches. Infection results in class switch recombination to downstream Cγ genes, which diversify their repertoire; both features are diagnostic of adaptive immunity. Meanwhile the repertoires of IgM and IgG3 remain undiversified suggesting that they encode innate, natural antibodies. Whereas IgG3 may play an initial protective role, antibodies encoded by downstream Cγ genes with diversified repertoires are predicted to be most important in long-term protection against S-FLU.

Identification of a novel host-specific IgM protease in Streptococcus suis

Streptococcus suis serotype 2 is a highly invasive, extracellular pathogen in pigs with the capacity to cause severe infections in humans. This study was initiated by the finding that IgM degradation products are released after opsonization of S. suis. The objective of this work was to identify the bacterial factor responsible for IgM degradation. The results of this study showed that a member of the IdeS family, designated Ide(Ssuis) (Immunoglobulin M-degrading enzyme of S. suis), is responsible and sufficient for IgM cleavage. Recombinant Ide(Ssuis) was found to degrade only IgM but neither IgG nor IgA. Interestingly, Western blot analysis revealed that Ide(Ssuis) is host specific, as it exclusively cleaves porcine IgM but not IgM from six other species, including a closely related member of the Suidae family. As demonstrated by flow cytometry and immunofluorescence microscopy, Ide(Ssuis) modulates binding of IgM to the bacterial surface. Ide(Ssuis) is the first prokaryotic IgM-specific protease described, indicating that this enzyme is involved in a so-far-unknown mechanism of host-pathogen interaction at an early stage of the host immune response. Furthermore, cleavage of porcine IgM by Ide(Ssuis) is the first identified phenotype reflecting functional adaptation of S. suis to pigs as the main host.

The evolutionary basis for differences between the immune systems of man, mouse, pig and ruminants

Studying the pathogenesis of an infectious disease like colibacillosis requires an understanding of the responses of target hosts to the organism both as a pathogen and as a commensal. The mucosal immune system constitutes the primary line of defence against luminal micro-organisms. The immunoglobulin-superfamily-based adaptive immune system evolved in the earliest jawed vertebrates, and the adaptive and innate immune system of humans, mice, pigs and ruminants co-evolved in common ancestors for approximately 300 million years. The divergence occurred only 100 mya and, as a consequence, most of the fundamental immunological mechanisms are very similar. However, since pressure on the immune system comes from rapidly evolving pathogens, immune systems must also evolve rapidly to maintain the ability of the host to survive and reproduce. As a consequence, there are a number of areas of detail where mammalian immune systems have diverged markedly from each other, such that results obtained in one species are not always immediately transferable to another. Thus, animal models of specific diseases need to be selected carefully, and the results interpreted with caution. Selection is made simpler where specific host species like cattle and pigs can be both target species and reservoirs for human disease, as in infections with Escherichia coli.