Modified live vaccine strains of porcine reproductive and respiratory syndrome virus cause immune system dysregulation similar to wild strains

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) emerged about 30 years ago and continues to cause major economic losses in the pork industry. The lack of effective modified live vaccines (MLV) allows the pandemic to continue.

Background and objective

We have previously shown that wild strains of PRRSV affect the nascent T cell repertoire in the thymus, deplete T cell clones recognizing viral epitopes essential for neutralization, while triggering a chronic, robust, but ineffective antibody response. Therefore, we hypothesized that the current MLV are inappropriate because they cause similar damage and fail to prevent viral-induced dysregulation of adaptive immunity.

Methods

We tested three MLV strains to demonstrate that all have a comparable negative effect on thymocytes in vitro. Further in vivo studies compared the development of T cells in the thymus, peripheral lymphocytes, and antibody production in young piglets. These three MLV strains were used in a mixture to determine whether at least some of them behave similarly to the wild virus type 1 or type 2.

Results

Both the wild and MLV strains cause the same immune dysregulations. These include depletion of T-cell precursors, alteration of the TCR repertoire, necrobiosis at corticomedullary junctions, low body weight gain, decreased thymic cellularity, lack of virus-neutralizing antibodies, and production of non-neutralizing anti-PRRSV antibodies of different isotypes.

Discussion and conclusion

The results may explain why the use of current MLV in young animals may be ineffective and why their use may be potentially dangerous. Therefore, alternative vaccines, such as subunit or mRNA vaccines or improved MLV, are needed to control the PRRSV pandemic.

The order of immunoglobulin light chain κ and λ usage in primary and secondary lymphoid tissues of germ-free and conventional piglets

In pigs (Sus scrofa), the initial immunoglobulin rearrangement of the κ light chain is replaced by λ before the heavy chains rearrange, and the light chains may rearrange even later. This study investigates whether these developmental differences are reflected in the usage of IGK and IGL genes. We found large differences between peripheral B cells and those developing in the bone marrow, and between B cells in germ-free piglets and conventional pigs. During early B cell development in the bone marrow, more 3' V and 5' J gene segments for both light chains are used. However, in the peripheral naive repertoire, more 5' IGLV and 3' IGLJ genes are used. A similar shift toward the use of more 5' IGKV and 3' IGKJ genes is observed later after antigen exposure in conventional pigs. The expression profile showed that most λ⁺ B cells are generated earlier, while κ⁺ B cells develop from late precursors that already contain the λ rearrangement. The initial λ rearrangement is retained in both λ⁺ and κ⁺ B lymphocytes, and multiple λ transcripts can be found in individual cells. The overall pool of the IGLV repertoire is therefore much larger and more diversified than for IGKV. The κ repertoire is further restricted to the preferential use of only two major IGKV genes, reflecting the limitation for only two consecutive rearrangements. Tracing of silenced λ transcripts in κ⁺ B cells further confirmed the unconventional mechanism of differential rearrangements in pigs. Our results underline the diversity of the immune system among mammals.

Comparative Aspects of Immunoglobulin Gene Rearrangement Arrays in Different Species

Studies in humans and mice indicate the critical role of the surrogate light chain in the selection of the productive immunoglobulin repertoire during B cell development. However, subsequent studies using mutant mice have also demonstrated that alternative pathways are allowed. Our recent investigation has shown that some species, such as pig, physiologically use preferential rearrangement of authentic light chains, and become independent of surrogate light chains. Here we summarize the findings from swine and compare them with results in other species. In both groups, allelic and isotypic exclusions remain intact, so the different processes do not alter the paradigm of B-cell monospecificity. Both groups also retained some other essential processes, such as segregated and sequential rearrangement of heavy and light chain loci, preferential rearrangement of light chain kappa before lambda, and functional κ-deleting element recombination. On the other hand, the respective order of heavy and light chains rearrangement may vary, and rearrangement of the light chain kappa and lambda on different chromosomes may occur independently. Studies have also confirmed that the surrogate light chain is not required for the selection of the productive repertoire of heavy chains and can be substituted by authentic light chains. These findings are important for understanding evolutional approaches, redundancy and efficiency of B-cell generation, dependencies on other regulatory factors, and strategies for constructing therapeutic antibodies in unrelated species. The results may also be important for explaining interspecies differences in the proportional use of light chains and for the understanding of divergences in rearrangement processes. Therefore, the division into two groups may not be definitive and there may be more groups of intermediate species.

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.

The occupied electronic structure of ultrathin boron doped diamond

Using angle-resolved photoelectron spectroscopy, we compare the electronic band structure of an ultrathin (1.8 nm) δ-layer of boron-doped diamond with a bulk-like boron doped diamond film (3 μm). Surprisingly, the measurements indicate that except for a small change in the effective mass, there is no significant difference between the electronic structure of these samples, irrespective of their physical dimensionality, except for a small modification of the effective mass. While this suggests that, at the current time, it is not possible to fabricate boron-doped diamond structures with quantum properties, it also means that nanoscale boron doped diamond structures can be fabricated which retain the classical electronic properties of bulk-doped diamond, without a need to consider the influence of quantum confinement.

Abdominal Functional Electrical Stimulation to Augment Respiratory Function in Spinal Cord Injury

Background: Functional electrical stimulation (FES) is the application of electrical pulses to a nerve to achieve a functional muscle contraction. Surface electrical stimulation of the nerves that innervate the abdominal muscles, termed abdominal FES, can cause the abdominal muscles to contract, even when paralysed after spinal cord injury. As the abdominal muscles are the major expiratory muscles, and commonly partially or completely paralysed in tetraplegia, abdominal FES offers a promising method of improving respiratory function for this patient group. Objective: The aim of the article is to provide readers with a better understanding of how abdominal FES can be used to improve the health of the spinal cord-injured population. Methods: A narrative review of the abdominal FES literature was performed. Results: Abdominal FES can achieve an immediate effective cough in patients with tetraplegia, while the repeated application over 6 weeks of abdominal FES can improve unassisted respiratory function. Ventilator duration and tracheostomy cannulation time can also be reduced with repeated abdominal FES. Conclusion: Abdominal FES is a noninvasive method to achieve functional improvements in cough and respiratory function in acute and chronically injured people with tetraplegia. Potential practical outcomes of this include reduced ventilation duration, assisted tracheostomy decannulation, and a reduction in respiratory complications. All of these outcomes can contribute to reduced morbidity and mortality, improved quality of life, and significant potential cost savings for local health care providers.

T cells in swine completely rearrange immunoglobulin heavy chain genes

Porcine thymus contains three independent populations of cells that have rearranged immunoglobulin heavy chain VDJ_H genes. The first population can be found exclusively in medulla and it consists of existing mature B cells and plasma cells. The second consists of developing B cells characterized by the presence of selected VDJ_H rearrangement, similar to B cell lymphogenesis in the bone marrow. The third population is entirely unaffected by selection mechanism for productive VDJ_H rearrangement and represents T lineage cells that rearrange immunoglobulin genes. Transcription of unselected VDJ_H repertoire is not allowed in T cells. Sequence analysis of unselected VDJ_H repertoire from T cells also revealed important consequences for B cell lymphogenesis and selection of B cell repertoire. As far as we know, this is the first evidence that some species completely rearrange VDJ_H genes in T cells. Our results also support the finding that B cells actively develop in the thymus.

Perturbation of Thymocyte Development Underlies the PRRS Pandemic: A Testable Hypothesis

Porcine reproductive and respiratory syndrome virus (PRRSV) causes immune dysregulation during the Critical Window of Immunological Development. We hypothesize that thymocyte development is altered by infected thymic antigen presenting cells (TAPCs) in the fetal/neonatal thymus that interact with double-positive thymocytes causing an acute deficiency of T cells that produces “holes” in the T cell repertoire allowing for poor recognition of PRRSV and other neonatal pathogens. The deficiency may be the result of random elimination of PRRSV-specific T cells or the generation of T cells that accept PRRSV epitopes as self-antigens. Loss of helper T cells for virus neutralizing (VN) epitopes can result in the failure of selection for B cells in lymph node germinal centers capable of producing high affinity VN antibodies. Generation of cytotoxic and regulatory T cells may also be impaired. Similar to infections with LDV, LCMV, MCMV, HIV-1 and trypanosomes, the host responds to the deficiency of pathogen-specific T cells and perhaps regulatory T cells, by “last ditch” polyclonal B cell activation. In colostrum-deprived PRRSV-infected isolator piglets, this results in hypergammaglobulinemia, which we believe to be a “red herring” that detracts attention from the thymic atrophy story, but leads to our second independent hypothesis. Since hypergammaglobulinemia has not been reported in PRRSV-infected conventionally-reared piglets, we hypothesize that this is due to the down-regulatory effect of passive maternal IgG and cytokines in porcine colostrum, especially TGFβ which stimulates development of regulatory T cells (Tregs).

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.

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.

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.

The comparative profile of lymphoid cells and the T and B cell spectratype of germ-free piglets infected with viruses SIV, PRRSV or PCV2

Lymphocyte subsets isolated from germ-free piglets experimentally infected with swine influenza virus (SIV), porcine reproductive and respiratory syndrome virus (PRRSV) or porcine circovirus type 2 (PCV2) were studied and the profile of these subsets among these three infections was monitored. Germ-free piglets were used since their response could be directly correlated to the viral infection. Because SIV infections are resolved even by colostrum-deprived neonates whereas PRRSV and PCV2 infections are not, SIV was used as a benchmark for an effectively resolved viral infection. PRRSV caused a large increase in the proportion of lymphocytes at the site of infection and rapid differentiation of B cells leading to a high level of Ig-producing cells but a severe reduction in CD2^—CD21⁺ primed B cells. Unlike SIV and PCV2, PRRSV also caused an increase in terminally differentiated subset of CD2⁺CD8α⁺ γδ cells and polyclonal expansion of major Vβ families suggesting that non-specific helper T cells drive swift B cell activation. Distinct from infections with SIV and PRRSV, PCV2 infection led to the: (a) prevalence of MHC-II⁺ T cytotoxic cells, (b) restriction of the T helper compartment in the respiratory tract, (c) generation of a high proportion of FoxP3⁺ T cells in the blood and (d) selective expansion of IgA and IgE suggesting this virus elicits a mucosal immune response. Our findings suggest that PRRSV and PCV2 may negatively modulate the host immune system by different mechanisms which may explain their persistence.

The enigma of the lower gut-associated lymphoid tissue (GALT)

Artiodactyls possess GALT that appears in fetal life and is located at the extreme end of the ileum. These IPP contain mostly B cells and involute early in postnatal life. Rabbits have a similarly located lymphoid organ, called the sacculus rotundus. Studies in sheep and rabbits have led to the concept that the lower hindgut GALT represents primary lymphoid tissue for B cells and is necessary for normal B cell development, analogous to the bursa of Fabricius. This review traces the history of the observations and theories that have led to the existing concept concerning the role of lower GALT. We then review recent data from piglets with resected IPP that challenges the concept that the IPP is primary B cell lymphoid tissue and that artiodactyls and rabbits are members of the GALT group in the same context as gallinaceous birds. Eliminating the IPP as the primary lymphoid tissue for B cells leads to the hypothesis that the IPP acts as first-responder mucosal lymphoid tissue.

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.

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.

Cathodoluminescence of natural, plastically deformed pink diamonds

The 49 type I natural pink diamonds examined exhibit color restricted to lamellae or bands oriented along {111} that are created by plastic deformation. Pink diamonds fall into two groups: (1) diamonds from Argyle in Australia and Santa Elena in Venezuela are heavily strained throughout and exhibit pink bands alternating with colorless areas, and (2) diamonds from other localities have strain localized near the discrete pink lamellae. Growth zones are highlighted by a blue cathodoluminescence (CL) and crosscut by the pink lamellae that emit yellowish-green CL that originates from the H3 center. This center probably forms by the recombination of nitrogen-related centers (A-aggregates) and vacancies mobilized by natural annealing in the Earth's mantle. Twinning is the most likely mechanism through which plastic deformation is accommodated for the two groups of diamonds. The plastic deformation creates new centers visible through spectroscopic methods, including the one responsible for the pink color, which remains unidentified. The differences in the plastic deformation features, and resulting CL properties, for the two groups might correlate to the particular geologic conditions under which the diamonds formed; those from Argyle and Santa Elena are deposits located within Proterozoic cratons, whereas most diamonds originate from Archean cratons.

Antibody repertoire development in fetal and neonatal piglets. XV. Porcine circovirus type 2 infection differentially affects serum IgG levels and antibodies to ORF2 in piglets free from other environmental factors

Porcine circovirus type 2 (PCV2) is an important pathogen in the porcine respiratory disease complex (PRDC) and its persistence may be due to dysregulation of systemic immunity. We examined this contention using isolator piglets. We present data on Ig levels in serum and bronchio-alveolar lavage (BAL), on antibody response to PCV2 and to TNP conjugates used as model antigens in 48 PCV2-infected isolator piglets. We compared these to data from TNP-immunized isolator piglets colonized with a probiotic flora, those infected with swine influenza (S-FLU) and those infected with porcine respiratory and reproductive syndrome virus (PRRSV). We found that PCV2 infection does not cause generalized hypergammaglobulinemia that characterizes PRRSV infections, but causes an unexplained increase in serum IgA. All animals had serum IgG to the ORF2 gene product of PCR2, but neither IgA nor IgG anti-ORF2 responses in BAL. PCV2 infection is a poor adjuvant since only natural anti-TNP antibodies were found. Unexpectedly, immunization appeared to result in lower Ig levels and lower anti-ORF2 responses. There was extreme variation in serum Ig levels in response to infection that could in part be traced to genetic and gender differences. These data suggest that non-replicating vaccines are unlikely to result in a significant primary antibody response but may prime the system for a secondary antibody and cytotoxic response following actual infection. In any case, developers may have to contend with significant genetic differences in the response of piglets to PCV2.

Antibody repertoire development in fetal and neonatal piglets. XXII. λ Rearrangement precedes κ rearrangement during B-cell lymphogenesis in swine

VDJ and VJ rearrangements, expression of RAG-1, Tdt and VpreB, and the presence of signal joint circles (SJC) were used to identify sites of B-cell lymphogenesis. VDJ, VλJλ but not VκJκ rearrangements or SJC were recovered from yolk sac (YS) at 20 days of gestation (DG) along with strong expression of VpreB and RAG-1 but weak Tdt expression. VλJλ rearrangements but not VκJκ rearrangements were recovered from fetal liver at 30-50 DG. SJC were pronounced in bone marrow at 95 DG where VκJκ rearrangements were first recovered. The VλJλ rearrangements recovered at 20-50 DG used some of the same Vλ and Jλ segments seen in older fetuses and adult animals. Hence the textbook paradigm for the order of light-chain rearrangement does not apply to swine. Consistent with weak Tdt expression in early sites of lymphogenesis, N-region additions in VDJ rearrangements were more frequent at 95 DG. Junctional diversity in VλJλ rearrangement was limited at all stages of development. There was little evidence for B-cell lymphogenesis in the ileal Peyer's patches. The widespread recovery of VpreB transcripts in whole, non-lymphoid tissue was unexpected as was its recovery from bone marrow and peripheral blood monocytes. Based on recovery of SJC, B-cell lymphogenesis continues for at least 5 weeks postpartum.

Resolution of an immunodiagnostic dilemma: heavy chain chimeric antibodies for species in which plasmocytomas are unknown

The immunoglobulin (Ig) genes of many vertebrates have been characterized but IgG subclasses, IgD and IgE proteins are only available for three species in which plasmacytomas occur. This creates a major problem in the production and specificity verification of diagnostic anti-Ig reagents for the vast majority of mammals. We describe a novel solution using the swine system with its eleven different variants of IgG. It involves the in vitro synthesis of chimeric porcine-camelid heavy chain antibodies (HCAbs) that do not require light chains and therefore only a single transfection vector. The expressed chimeric HCAbs are comprised of the camelid VHH domain encoding specificity for lysozyme and the hinge, CH2 and CH3 domains of the various porcine IgGs. These HCAb retain their antigenic integrity and their ability to recognize lysozyme. The engineered specificity assures that these HCAb can be immobilized in native configuration when used for testing the specificity of anti-swine IgG antibodies. Comparative data to illustrate the importance of this point are provided. These are now available for use in hybridoma selection and as reference standards for evaluating the specificity of currently available anti-swine IgG antibodies.

The porcine antibody repertoire: variations on the textbook theme

The genes encoding the heavy and light chains of swine antibodies are organized in the same manner as in other eutherian mammals. There are ∼30 VH genes, two functional DH genes and one functional JH gene, 14-60 Vκ genes, 5 Jκ segments, 12-13 functional Vλ genes, and two functional Jλ genes. The heavy chain constant regions encode the same repertoire of isotypes common to other eutherian mammals. The piglet models offers advantage over rodent models since the fetal repertoire develops without maternal influences and the precocial nature of their multiple offspring allows the experimenter to control the influences of environmental and maternal factors on repertoire development postnatally. B cell lymphogenesis in swine begins in the fetal yolk sac at 20 days of gestation (DG), moves to the fetal liver at 30 DG and eventually to the bone marrow which dominates until birth (114 DG) and to at least 5 weeks postpartum. There is no evidence that the ileal Peyers patches are a site of B cell lymphogenesis or are required for B cell maintenance. Unlike rodents and humans, light chain rearrangement begins first in the lambda locus; kappa rearrangements are not seen until late gestation. Dissimilar to lab rodents and more in the direction of the rabbit, swine utilize a small number of VH genes to form >90% of their pre-immune repertoire. Diversification in response to environmental antigen does not alter this pattern and is achieved by somatic hypermutation (SHM) of the same small number of VH genes. The situation for light chains is less well studied, but certain Vκ and Jκ and Vλ and Jλ are dominant in transcripts and in contrast to rearranged heavy chains, there is little junctional diversity, less SHM, and mutations are not concentrated in CDR regions. The transcribed and secreted pre-immune antibodies of the fetus include mainly IgM, IgA, and IgG3; this last isotype may provide a type of first responder mucosal immunity. Development of functional adaptive immunity is dependent on bacterial MAMPs or MAMPs provided by viral infections, indicating the importance of innate immunity for development of adaptive immunity. The structural analysis of Ig genes of this species indicate that especially the VH and Cγ gene are the result of tandem gene duplication in the context of genomic gene conversion. Since only a few of these duplicated VH genes substantially contribute to the antibody repertoire, polygeny may be a vestige from a time before somatic processes became prominently evolved to generate the antibody repertoire. In swine we believe such duplications within the genome have very limited functional significance and their occurrence is therefore overrated.

Antibody repertoire development in fetal and neonatal piglets XXI. Usage of most VH genes remains constant during fetal and postnatal development

Usage of variable region gene segments during development of the antibody repertoire in mammals is unresolved in part because of the complexity of the locus in mice and humans and the difficulty of distinguishing intrinsic from extrinsic influences in these species. We present the first vertical studies on VH usage that spans the fetal and neonatal period using the piglet model. We tracked VH usage in DNA rearrangements and in VDJ transcripts throughout 75 days of gestation (DG) in outbred fetuses, thereafter in outbred germfree and colonized isolator piglets, isolator piglets infected with swine influenza and in conventionally reared nematode-infected adults. Seven VH genes account for >90% of the pre-immune repertoire which is the same among tissues and in both transcripts and DNA rearrangements. Statistical modeling supports the view that proportional usage of the major genes remains constant during fetal life and that postnatal usage ranking is similar to that during fetal life. Changes in usage ranking are developmental not antigen dependent. In this species exposure to environmental antigens results in diversification of the repertoire by somatic hypermutation of the same small number of VH genes that comprise the pre-immune repertoire, not by using other VH gene available in the germline. Therefore in swine a small number of VH genes shape the antibody repertoire throughout life questioning the need for extensive VH polygeny.

Ileal Peyer's patches are not necessary for systemic B cell development and maintenance and do not contribute significantly to the overall B cell pool in swine

Based on studies of sheep, ileal Peyer's patches (IPP) have been regarded as a type of primary lymphoid tissue similar to the bursa of Fabricius in chicken. Because bursectomy results in B cell deficiency, we wondered whether resection of the IPP of piglets would have a similar effect. Comparison of IPP-resected, surgical shams and untreated germ-free piglets, all of which were later colonized with a defined commensal flora, demonstrated that resection of the IPP did not alter the level and phenotype of B and T cells in lymphoid tissues and the blood 10 wk after surgery. Additionally, colonization of IPP caused a shift from the fetal type of lymphocyte distribution to the adult type that is characterized by prevalence of B cells, with many of them representing IgA(+) switched B cells or displaying a more mature CD2(-)CD21(+) and CD2(-)CD21(-) phenotype. Moreover, colonization leads to appearance of effector CD4(+)CD8(+) αβ T helper and CD2(+)CD8(-) γδ T cells. Comparison of germ-free with colonized pigs and experiments utilizing surgical transposition of jejunal Peyer's patch into terminal ileum or construction of isolated ileal loops indicated that lymphocyte development in IPP is dependent on colonization. Although our studies confirmed higher mitotic and apoptotic rates in IPP, they failed to identify any cell populations that resemble developing B lineage cells in the bone marrow. These results indicate that porcine IPP are not required for systemic B cell generation or maintenance, but they are secondary lymphoid tissue that appears important in immune responses to colonizing bacteria.

Recent advances using FcRn overexpression in transgenic animals to overcome impediments of standard antibody technologies to improve the generation of specific antibodies

This review illustrates the salutary effects of neonatal Fc receptor (FcRn) overexpression in significantly improving humoral immune responses in the generation of antibodies for immunotherapy and diagnostics. These include: (1) improved IgG protection; (2) augmented antigen-specific humoral immune response with larger numbers of antigen specific B cells, thus offering a wider spectrum of clones; (3) generation of antibodies against weakly immunogenic antigens; (4) significant improvements in the number and substantial developments in the diversity of hybridomas. FcRn transgenesis thus confers a number of practical benefits, including faster antibody production, higher antibody yields and improved generation of hybridomas for monoclonal antibody production. Notably, these efficiencies in polyclonal antibody production were also demonstrated in FcRn transgenic rabbits. Overall, FcRn transgenic animals yield more antibodies and provide a route to the generation of antibodies against antigens of low immunogenicity that are difficult to obtain using currently available methods.

Note: Laser ablation technique for electrically contacting a buried implant layer in single crystal diamond

The creation of thin, buried, and electrically conducting layers within an otherwise insulating diamond by annealed ion implantation damage is well known. Establishing facile electrical contact to the shallow buried layer has been an unmet challenge. We demonstrate a new method, based on laser micro-machining (laser ablation), to make reliable electrical contact to a buried implant layer in diamond. Comparison is made to focused ion beam milling.

Intestinal resection and anastomosis in neonatal gnotobiotic piglets

We describe a surgical method for ileal resection and anastomosis in newborn germfree piglets that was undertaken to establish a model that can be used for immunologic research and other applications. A preliminary experiment indicated that neonatal piglets with resection of approximately 60 cm of their ileum (removal of approximately 90% of the continuous ileal Peyer patches; group A) and those in which the ileum was transected (group B) could be maintained germfree for 35 d, colonized with defined gut flora, and maintained in a clean room until 70 d of age. In the final study, 12 piglets (4 each for groups A and B and 4 untreated controls), were monitored for postoperative feeding behavior, malaise, evidence for contamination with pathogenic bacteria, and weight gain. All surgical animals were free from incidental contamination from pathogens and environmental organisms with atypical colony types for 35 d. Two piglets in group B died postoperatively (1 during the preliminary experiment and 1 during the final study). Control (group C) piglets gained significantly more weight than did those in group A. These studies demonstrated that surgical resection of the ileal Peyer patches under germfree conditions can be accomplished successfully without compromising piglet health or introducing pathogens and with only a modest reduction in weight gain.

The little brown bat, M. lucifugus, displays a highly diverse V H, D H and J H repertoire but little evidence of somatic hypermutation

Myotis lucifugus populations in Northeastern US are being decimated by a fungal disease. Since almost nothing is known about the immune system of bats, we are characterizing the immunoglobulin genes of bats. We show that M. lucifugus has a diverse V(H) gene repertoire comprised of five of the seven human V(H) gene families and an estimated 236V(H)3 genes. 95% of these germline VH3 genes differ in FR3. A comparison of 67 expressed V(H)3 genes with 75 germline V(H)3 genes revealed a mutation frequency similar to fetal piglets never exposed to environmental antigens. Analysis of CDR3 regions identified at least 13 putative J(H) segments and a large D(H) repertoire. The low mutation frequency, highly diverse V(H), D(H), and J(H) germline repertoire suggests that this species may rely more on combinatorial and junctional diversity than on somatic hypermutation raising questions about the ability of M. lucifugus to respond rapidly to emerging pathogens.

The two suborders of chiropterans have the canonical heavy-chain immunoglobulin (Ig) gene repertoire of eutherian mammals

Bats comprise 20% of all mammals, yet little is known about their immune system and virtually nothing about their immunoglobulin genes. We show that four different bat species transcribe genes encoding IgM, IgE, IgA and IgG subclasses, the latter which have diversified after speciation; the canonical pattern for eutherian mammals. IgD transcripts were only recovered from insectivorous bats and were comprised of CH1, CH3 and two hinge exons; the second hinge exon was fused to CH3. IgA in all species resembles human IgA2 with the putative cysteine forming the bridge to the light chain found at position 77. Sequence comparisons yielded no evidence for a diphyletic origin of the suborders. Bats show no close similarity to another mammalian order; the strongest association was with carnivores. Data reveal that CH diversity and VDJ and CDR3 organization are similar to other eutherian mammals, although the expressed VH3 family repertoire was unusually diverse.

Movement of the human upper airway during inspiration with and without inspiratory resistive loading

The electromyographic (EMG) activity of human upper airway muscles, particularly the genioglossus, has been widely measured, but the relationship between EMG activity and physical movement of the airway muscles remains unclear. We aimed to measure the motion of the soft tissues surrounding the airway during normal and loaded inspiration on the basis of the hypothesis that this motion would be affected by the addition of resistance to breathing during inspiration. Tagged MR imaging of seven healthy subjects was performed in a 3-T scanner. Tagged 8.6-mm-spaced grids were used, and complementary spatial modulation of magnetization images were acquired beginning ∼200 ms before inspiratory airflow. Deformation of tag line intersections was measured. The genioglossus moved anteriorly during normal and loaded inspiration, with less movement during loaded inspiration. The motion of tissues at the anterior border of the upper airway was nonuniform, with larger motions inferiorly. At the level of the soft palate, the lateral dimension of the airway decreased significantly during loaded inspiration (-0.15 ± 0.09 and -0.48 ± 0.09 mm during unloaded and loaded inspiration, respectively, P < 0.05). When resistance to inspiratory flow was added, genioglossus motion and lateral dimensions of the airway at the level of the soft palate decreased. Our results suggest that genioglossus motion begins early to dilate the airway prior to airflow and that inspiratory loading reduces the anterior motion of the genioglossus and increases the collapse of the lateral airway walls at the level of the soft palate.

DNA polymerases nu and theta are required for efficient immunoglobulin V gene diversification in chicken

The chicken DT40 B lymphocyte line diversifies its immunoglobulin (Ig) V genes through translesion DNA synthesis-dependent point mutations (Ig hypermutation) and homologous recombination (HR)-dependent Ig gene conversion. The error-prone biochemical characteristic of the A family DNA polymerases Polnu and Pol led us to explore the role of these polymerases in Ig gene diversification in DT40 cells. Disruption of both polymerases causes a significant decrease in Ig gene conversion events, although POLN(-/-)/POLQ(-/-) cells exhibit no prominent defect in HR-mediated DNA repair, as indicated by no increase in sensitivity to camptothecin. Poleta has also been previously implicated in Ig gene conversion. We show that a POLH(-/-)/POLN(-/-)/POLQ(-/-) triple mutant displays no Ig gene conversion and reduced Ig hypermutation. Together, these data define a role for Polnu and Pol in recombination and suggest that the DNA synthesis associated with Ig gene conversion is accounted for by three specialized DNA polymerases.

Probing the corticospinal link between the motor cortex and motoneurones: some neglected aspects of human motor cortical function

This review considers the operation of the corticospinal system in primates. There is a relatively widespread cortical area containing corticospinal outputs to a single muscle and thus a motoneurone pool receives corticospinal input from a wide region of the cortex. In addition, corticospinal cells themselves have divergent intraspinal branches which innervate more than one motoneuronal pool but the synergistic couplings involving the many hand muscles are likely to be more diverse than can be accommodated simply by fixed patterns of corticospinal divergence. Many studies using transcranial magnetic stimulation of the human motor cortex have highlighted the capacity of the cortex to modify its apparent excitability in response to altered afferent inputs, training and various pathologies. Studies using cortical stimulation at 'very low' intensities which elicit only short-latency suppression of the discharge of motor units have revealed that the rapidly conducting corticospinal axons (stimulated at higher intensities) drive motoneurones in normal voluntary contractions. There are also major non-linearities generated at a spinal level in the relation between corticospinal output and the output from the motoneurone pool. For example, recent studies have revealed that the efficacy of the human corticospinal connection with motoneurones undergoes activity-dependent changes which influence the size of voluntary contractions. Hence, corticospinal drives must be sculpted continuously to compensate for the changing functional efficacy of the descending systems which activate the motoneurones. This highlights the need for proprioceptive monitoring of movements to ensure their accurate execution.

Reflection anisotropy spectroscopy of the oxidized diamond (001) surface

We report reflection anisotropy spectroscopy (RAS) measurements of the oxidized (001) surface of a type IIb natural diamond. These measurements were made possible due to recent developments in diamond surface preparation. We compare RAS results from the hydrogenated, clean and oxidized C(001) surface and demonstrate that RAS is sensitive to the structural transition of the surface from the 2 × 1 reconstruction of the clean surface to the 1 × 1 reconstruction of the oxidized surface.

Understanding the chemical vapor deposition of diamond: recent progress

In this paper we review and provide an overview to the understanding of the chemical vapor deposition (CVD) of diamond materials with a particular focus on the commonly used microwave plasma-activated chemical vapor deposition (MPCVD). The major topics covered are experimental measurements in situ to diamond CVD reactors, and MPCVD in particular, coupled with models of the gas phase chemical and plasma kinetics to provide insight into the distribution of critical chemical species throughout the reactor, followed by a discussion of the surface chemical process involved in diamond growth.

The piglet as a model for B cell and immune system development

The ability to identify factors responsible for disease in all species depends on the ability to separate those factors which are environmental from those that are intrinsic. This is particularly important for studies on the development of the adaptive immune response of neonates. Studies on laboratory rodents or primates have been ambiguous because neither the effect of environmental nor maternal factors on the newborn can be controlled in mammals that: (i) transmit potential maternal immunoregulatory factors in utero and (ii) are altricial and cannot be reared after birth without their mothers. Employing the newborn piglet model can address each of these concerns. However, it comes at the price of having first to characterize the immune system of swine and its development. This review focuses on the porcine B cell system, especially on the methods used for its characterization in fetal studies and neonatal piglets. Understanding these procedures is important in the interpretation of the data obtained. Studies on neonatal piglets have (a) provided valuable information on the development of the adaptive immune system, (b) lead to important advances in evolutionary biology, (c) aided our understanding of passive immunity and (d) provided opportunities to use swine to address specific issues in veterinary and biomedical research and immunotherapy. This review summarizes the history of the development of the piglet as a model for antibody repertoire development, thus providing a framework to guide future investigators.

Immunoglobulins, antibody repertoire and B cell development

Swine share with most placental mammals the same five antibody isotypes and same two light chain types. Loci encoding lambda, kappa and Ig heavy chains appear to be organized as they are in other mammals. Swine differ from rodents and primates, but are similar to rabbits in using a single VH family (VH3) to encode their variable heavy chain domain, but not the family used by cattle, another artiodactyl. Distinct from other hoofed mammals and rodents, Ckappa:Clambda usage resembles the 1:1 ratio seen in primates. Since IgG subclasses diversified after speciation, same name subclass homologs do not exist among swine and other mammals unless very closely related. Swine possess six putative IgG subclasses that appear to have diversified by gene duplication and exon shuffle while retaining motifs that can bind to FcgammaRs, FcRn, C1q, protein A and protein G. The epithelial chorial placenta of swine and the precosial nature of their offspring have made piglets excellent models for studies on fetal antibody repertoire development and on the postnatal role of gut colonization, maternal colostrum and neonatal infection on the development of adaptive immunity during the "critical window" of immunological development. This chapter traces the study of the humoral immune system of this species through its various eras of discovery and compiles the results in tables and figures that should be a useful reference for educators and investigators.

The ontogeny of the porcine immune system

Cellular and humoral aspects of the immune response develop sequentially in the fetus. During the ontogeny, the pluripotent stem cells emerge and differentiate into all hematopoietic lineages. Basic questions including the identification of the first lympho-hematopoietic sites, the origin of T and B lymphocytes, the development of different subpopulations of alphabeta T, gammadelta T and B lymphocytes as well as development of innate immunity and the acquisition of full immunological capacities are discussed here for swine and compared with other species. The description of related topics such as fertilization, morphogenesis, maternal-fetal-neonatal physiology and early neonatal development are also discussed.

Movement of the tongue during normal breathing in awake healthy humans

Electromyographic (EMG) activity of the airway muscles suggest that genioglossus is the primary upper airway dilator muscle. However, EMG data do not necessarily translate into tissue motion and most imaging modalities are limited to assessment of the surfaces of the upper airway. In this study, we hypothesized that genioglossus moves rhythmically during the respiratory cycle and that the motion within is inhomogeneous. A 'tagged' magnetic resonance imaging technique was used to characterize respiratory-related tissue motions around the human upper airway in quiet breathing. Motion of airway tissues at different segments of the eupnoeic respiratory cycle was imaged in six adult subjects by triggering the scanner at the end of inspiration. Displacements of the 'tags' were analysed using the harmonic phase method (HARP). Respiratory timing was monitored by a band around the upper abdomen. The genioglossus moved during the respiratory cycle. During expiration, the genioglossus moved posteriorly and during inspiration, it moved anteriorly. The degree of motion varied between subjects. The maximal anteroposterior movement of a point tracked on the genioglossus was 1.02 +/- 0.54 mm (mean +/- s.d.). The genioglossus moved over the geniohyoid muscle, with minimal movement in other muscles surrounding the airway at the level of the soft palate. Local deformation of the tongue was analysed using two-dimensional strain maps. Across the respiratory cycle, positive strains within genioglossus reached peaks of 17.5 +/- 9.3% and negative strains reached peaks of -16.3 +/- 9.3% relative to end inspiration. The patterns of strains were consistent with elongation and compression within a constant volume structure. Hence, these data suggest that even during respiration, the tongue behaves as a muscular hydrostat.

The isolator piglet: a model for studying the development of adaptive immunity

The period from late gestation to weaning in neonatal mammals is a critical window when the adaptive immune system develops and replaces the protection temporarily provided by passive immunity and pre-adaptive antibodies. It is also when oral tolerance to dietary antigen and the distinction between commensal and pathogenic gut bacteria becomes established resulting in immune homeostasis. The reproductive biology of swine provides a unique model for distinguishing the effects of different factors on immune development during this critical period because all extrinsic factors are controlled by the experimenter. This chapter reviews this early stage of development and the usefulness of the piglet model for understanding events during this transitional stage. The review also describes the major features of the porcine immune system and the immune stimulatory and dysregulatory factors that act during this period. The value of the model to medical science in such areas as food allergy, organ transplantation, cystic fibrosis and the production of humanized antibodies for immuno-therapy is discussed.

Genomic organization of the immunoglobulin light chain gene loci in Xenopus tropicalis: evolutionary implications

Based on presently available genome data, we characterized the genomic organization of all three light chain gene (rho, sigma and type III) loci in Xenopus tropicalis. The rho gene locus in X. tropicalis, structurally similar to the kappa gene loci in mammals, was shown to contain a single C rho gene and nine J rho segments. The sigma locus also contains a single C gene, although two distinct C sigma genes have previously been found in Xenopus laevis (most likely due to chromosome polyploidy). Four J sigma gene segments were identified upstream of the C sigma. The type III light chain gene locus, spanning approximately 170 kb DNA, structurally resembles the topology of mammalian lambda gene loci, containing three C genes (C III 1-3). C III 2 and C III 3 are both preceded by single, unique, J genes, whereas C III 1 contains three J gene segments. Furthermore, two additional J gene segments, termed J III x1 and J III x2, were found in the intron separating V III 2 and pV III 1 (a pseudogene). Based on BLAST searches against the X. tropicalis EST database, all the C genes identified in this study were shown to be functional. On the basis of similarity of protein sequences, genomic organization and chromosomal location of the light chain genes among frogs and mammals, our data strongly support the previous suggestions that the rho genes belong to the kappa gene lineage, whereas the type III genes share a common origin with the lambda genes.

Antibody repertoire development in fetal and neonatal piglets: XIX. Undiversified B cells with hydrophobic HCDR3s preferentially proliferate in the porcine reproductive and respiratory syndrome

Porcine respiratory and reproductive syndrome virus (PRRSV) causes an extraordinary increase in the proportion of B cells resulting in lymphoid hyperplasia, hypergammaglobulinemia, and autoimmunity in neonatal piglets. Spectratypic analysis of B cells from neonatal isolator piglets show a non-Gaussian pattern with preferential expansion of clones bearing certain H chain third complementary region (HCDR3) lengths. However, only in PRRSV-infected isolator piglets was nearly the identical spectratype observed for all lymphoid tissues. This result suggests dissemination of the same dominant B cell clones throughout the body. B cell expansion in PRRS was not associated with preferential VH gene usage or repertoire diversification and these cells appeared to bear a naive phenotype. The B cell population observed during infection comprised those with hydrophobic HCDR3s, especially sequences encoded by reading frame 3 of DHA that generates the AMVLV motif. Thus, the hydropathicity profile of B cells after infection was skewed to favor those with hydrophobic binding sites, whereas the normally dominant region of the hydropathicity profile containing neutral HCDR3s was absent. We believe that the hypergammaglobulinemia results from the products of these cells. We speculate that PRRSV infection generates a product that engages the BCR of naive B cells, displaying the AMVLV and similar motifs in HCDR3 and resulting in their T-independent proliferation without repertoire diversification.

Antibody repertoire development in fetal and neonatal piglets. XIII. Hybrid VH genes and the preimmune repertoire revisited

The expressed porcine VH genes belong to the VH3 family (clan), four of which, VHA, VHB, VHC, and VHE, alone comprise approximately 80% of the preimmune repertoire. However, so-called "hybrid" VH genes that use CDR1 of one VH gene and the CDR2 of another are frequently encountered. We studied > 3000 cloned VDJs and found that such hybrids can contribute up to 10% of the preimmune repertoire. Based on the 1) recovery of hybrid VH genes from bacterial artificial chromosome clones, 2) frequency of occurrence of certain hybrids in the preimmune repertoire, and 3) failure to recover equal numbers of reciprocal hybrids, we concluded that some chimeric genes are present in the genome and are not PCR artifacts. Two chimeric germline genes (VHZ and VHY), together with VHF and the four genes mentioned above, constitute the major VH genes and these account for > 95% of the preimmune repertoire. Diversification of the preimmune IgG and IgM repertoires after environmental exposure was mainly due to somatic hypermutation of major VH genes with no evidence of gene conversion. Somatic hypermutation was 3- to 10-fold higher in CDRs than in framework regions, most were R mutations and transversions and transitions equally contributed. Data were used to 1) develop an index to quantify the degree of VH repertoire diversification and 2) establish a library of 29 putative porcine VH genes. One-third of these genes are chimeric genes and their sequences suggest that the porcine VH genome developed by duplication and splicing from a small number of prototypic genes.