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.

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.

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.

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.

Generation of antibody- and B cell-deficient pigs by targeted disruption of the J-region gene segment of the heavy chain locus

A poly(A)-trap gene targeting strategy was used to disrupt the single functional heavy chain (HC) joining region (J_H) of swine in primary fibroblasts. Genetically modified piglets were then generated via somatic cell nuclear transfer (SCNT) and bred to yield litters comprising J_H wild-type littermate (+/+), J_H heterozygous knockout (±) and J_H homozygous knockout (−/−) piglets in the expected Mendelian ratio of 1:2:1. There are only two other targeted loci previously published in swine, and this is the first successful poly(A)-trap strategy ever published in a livestock species. In either blood or secondary lymphoid tissues, flow cytometry, RT-PCR and ELISA detected no circulating IgM⁺ B cells, and no transcription or secretion of immunoglobulin (Ig) isotypes, respectively in J_H −/− pigs. Histochemical and immunohistochemical (IHC) studies failed to detect lymph node (LN) follicles or CD79α⁺ B cells, respectively in J_H −/− pigs. T cell receptor (TCR)_β transcription and T cells were detected in J_H −/− pigs. When reared conventionally, J_H −/− pigs succumbed to bacterial infections after weaning. These antibody (Ab)- and B cell-deficient pigs have significant value as models for both veterinary and human research to discriminate cellular and humoral protective immunity to infectious agents. Thus, these pigs may aid in vaccine development for infectious agents such as the pandemic porcine reproductive and respiratory syndrome virus (PRRSV) and H1N1 swine flu. These pigs are also a first significant step towards generating a pig that expresses fully human, antigen-specific polyclonal Ab to target numerous incurable infectious diseases with high unmet clinical need.

Targeted disruption of the porcine immunoglobulin kappa light chain locus

Inactivation of the endogenous pig immunoglobulin (Ig) loci, and replacement with their human counterparts, would produce animals that could alleviate both the supply and specificity issues of therapeutic human polyclonal antibodies (PAbs). Platform genetics are being developed in pigs that have all endogenous Ig loci inactivated and replaced by human counterparts, in order to address this unmet clinical need. This report describes the deletion of the porcine kappa (κ) light chain constant (Cκ) region in pig primary fetal fibroblasts (PPFFs) using gene targeting technology, and the generation of live animals from these cells via somatic cell nuclear transfer (SCNT) cloning. There are only two other targeted loci previously published in swine, and this is the first report of a targeted disruption of an Ig light chain locus in a livestock species. Pigs with one targeted Cκ allele (heterozygous knockout or ±) were bred together to generate Cκ homozygous knockout (-/-) animals. Peripheral blood mononuclear cells (PBMCs) and mesenteric lymph nodes (MLNs) from Cκ -/- pigs were devoid of κ-containing Igs. Furthermore, there was an increase in lambda (λ) light chain expression when compared to that of wild-type littermates (Cκ +/+). Targeted inactivation of the Ig heavy chain locus has also been achieved and work is underway to inactivate the pig lambda light chain locus.

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.

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.

Antibody Repertoire Development in Fetal and Neonatal Piglets. XVII. IgG Subclass Transcription Revisited with Emphasis on New IgG3

Fetal piglets offer an in vivo model for determining whether Ag-independent IgG subclass transcription proceeds in a manner that differs from subclass transcription in pigs exposed to environmental Ags and TLR ligands. Our data from approximately 12,000 Cgamma clones from > 60 piglets provide the first report on the relative usage of all known porcine Cgamma genes in fetal and young pigs. Studies revealed that among the six Cgamma genes, allelic variants of IgG1 comprised 50-80% of the repertoire, and IgG2 alleles comprised < 10% in nearly all tissues. However, relative transcription of allelic variants of IgG1 randomly deviate from the 1:1 ratio expected in heterozygotes. Most surprising was the finding that IgG3 accounted for half of all Cgamma transcripts in the ileal Peyer's patches (IPPs) and mesenteric lymph nodes but on average only approximately 5% of the clones from the thymus, tonsil, spleen, peripheral blood, and bone marrow of newborns. Lymphoid tissues from late term fetuses revealed a similar expression pattern. Except for IgG3 in the IPPs and mesenteric lymph nodes, no stochastic pattern of Cgamma expression during development was seen in animals from mid-gestation through 5 mo. The age and tissue dependence of IgG3 transcription paralleled the developmental persistence of the IPP, and its near disappearance corresponds to the diversification of the preimmune VDJ repertoire in young piglets. We hypothesize that long-hinged porcine IgG3 may be important in preadaptive responses to T cell-independent Ags similar to those described for its murine namesake.

Identification of IgF, a hinge-region-containing Ig class, and IgD in Xenopus tropicalis

Only three Ig isotypes, IgM, IgX, and IgY, were previously known in amphibians. Here, we describe a heavy-chain isotype in Xenopus tropicalis, IgF (encoded by C(phi)), with only two constant region domains. IgF is similar to amphibian IgY in sequence, but the gene contains a hinge exon, making it the earliest example, in evolution, of an Ig isotype with a separately encoded genetic hinge. We also characterized a gene for the heavy chain of IgD, located immediately 3' of C(mu), that shares features with the C(delta) gene in fish and mammals. The latter gene contains eight constant-region-encoding exons and, unlike the chimeric splicing of muC(H)1 onto the IgD heavy chain in teleost fish, it is expressed as a unique IgD heavy chain. The IgH locus of X. tropicalis shows a 5' V(H)-D(H)-J(H)-C(mu)-C(delta)-C(chi)-C(upsilon)-C(phi) 3' organization, suggesting that the mammalian and amphibian Ig heavy-chain loci share a common ancestor.

Development of the neonatal B and T cell repertoire in swine: implications for comparative and veterinary immunology

Birth in all higher vertebrates is at the center of the critical window of development in which newborns transition from dependence on innate immunity to dependence on their own adaptive immunity, with passive maternal immunity bridging this transition. Therefore we have studied immunological development through fetal and early neonatal life. In swine, B cells appear earlier in fetal development than T cells. B cell development begins in the yolk sac at the 20th day of gestation (DG20), progresses to fetal liver at DG30 and after DG45 continues in bone marrow. The first wave of developing T cells is gammadelta cells expressing a monomorphic Vdelta rearrangement. Thereafter, alphabeta T cells predominate and at birth, at least 19 TRBV subgroups are expressed, 17 of which appear highly homologous with those in humans. In contrast to the T cell repertoire and unlike humans and mice, the porcine pre-immune VH (IGHV-D-J) repertoire is highly restricted, depending primarily on CDR3 for diversity. The V-KAPPA (IGKV-J) repertoire and apparently also the V-LAMBDA (IGLV-J) repertoire, are also restricted. Diversification of the pre-immune B cell repertoire of swine and the ability to respond to both T-dependent and T-independent antigen depends on colonization of the gut after birth in which colonizing bacteria stimulate with Toll-like receptor ligands, especially bacterial DNA. This may explain the link between repertoire diversification and the anatomical location of primary lymphoid tissue like the ileal Peyers patches. Improper development of adaptive immunity can be caused by infectious agents like the porcine reproductive and respiratory syndrome virus that causes immune dysregulation resulting in immunological injury and autoimmunity.

Antibody repertoire development in swine

Swine belong to the Order Artiodactyla and like mice and humans, express IgM, IgD, IgG, IgE and IgA antibodies but a larger number of IgG subclasses. Like rabbits and chickens, expressed V(H) genes belong to the ancestral V(H)3 family and only 5 comprise >80% of the pre-immune repertoire. Since they use primarily two D(H) segments and have a single J(H) like chickens, junctional diversity plays a relatively greater role in repertoire formation than in humans and mice. Proportional light chain usage surprisingly resembles that in humans and is therefore distinctly different from the predominant kappa chain usage (>90%) of lab rodents and predominant lambda chain usage in other ungulates (>90%). The pre-immune V(kappa) repertoire also appears restricted since >95% of V(kappa)J(kappa) rearrangements use only a few members of the IGKV2 family and only J(kappa)2. Two V(lambda) families (IGLV3 and IGLV8) are used in forming the pre-immune repertoire. Antibodies that do not utilize light chains as in camelids, or the lengthy CDR3 regions seen in cattle that use V(H)4 family genes, have not been reported in swine. B cell lymphogenesis first occurs in the yolk sac but early VDJ rearrangements differ from mice and humans in that nearly 100% are in-frame and N-region additions are already present. Swine possess ileal Peyers patches like sheep which may be important for antigen-independent B cell repertoire diversification. The presence of pro B-like cells in interlobular areas of thymus and mature B cells in the thymic medulla that have switched to especially IgA in early gestation, is so far unique among mammals. The offspring of swine are believed to receive no passive immunity in utero and are precosial. Thus, they are a useful model for studies on fetal-neonatal immunological development. The model has already shown that: (a) colonization of the gut is required for responsiveness to TD and TI-2 antigens, (b) responsiveness due to colonization depends on bacterial PAMPs and (c) some viral pathogens can interfere with the establishment of immune homeostasis in neonates. Studies on swine reinforce concerns that caution be used when paradigms arising from studies in one mammal are extrapolated to other mammals, even when similarities are predicted by taxonomy and phylogeny. Swine exemplify a situation in which evolutionary diversification of the immune system is not characteristic of an entire order or even of other related systems in the same species.

The pre-immune variable kappa repertoire of swine is selectively generated from certain subfamilies of Vkappa2 and one Jkappa gene

Combinatorial diversity is highly restricted during formation of the pre-immune heavy chain repertoire of swine, raising the question of whether the same is true for the pre-immune light chain repertoire. Before addressing this question, we first used competitive PCR to show that kappa and lambda light chains in swine are equally expressed in mature B cells similar to the situation in humans but alike that in other studied Ungulates. This justified efforts to examine the repertoire of both light chain types. These studies also revealed that lambda is preferentially expressed at sites of B cells lymphogenesis, perhaps because of the use of a surrogate light chain containing lambda5. Data are presented here on >100 VkappaJkappa-containing transcripts and approximately 180 genomic Vkappa genes to show that >90% of the pre-immune repertoire is generated from three subfamilies of IGKV2 genes and one of five Jkappa segments. The kappa locus contains >or=50 IGKV2 genes belonging to at least five subfamilies and an undetermined but perhaps equal number of IGKV1 genes. The porcine IGKV1 and IGKV2 genes share 87% sequence similarity with their human counterparts and Jkappa1 through Jkappa5 share sequence and organizational homology with those in sheep, horse, human and mouse. Swine have a single Ckappa gene. These findings contrast with those from rodents and primates but are reminiscent of those on the pre-immune heavy chain repertoire of swine in that it is generated using a relatively restricted number of gene segments. These restricted pre-immune repertoires may reflect the minimal exposure of the fetus to maternal factors and environmental antigens. The significance for swine immunology of characterizing the pre-immune repertoire is discussed.

Comparison of the expressed porcine Vbeta and Jbeta repertoire of thymocytes and peripheral T cells

Transcripts of more than 300 unique T-cell receptor-beta (TCR-beta) V-D-J rearrangements recovered from porcine thymocytes and peripheral T cells were compared. We identified 19 groups (families) of porcine Vbeta genes in seven supergroups and provisionally named 17 groups based on their sequence similarity with recognized human Vbeta gene families. TRBV4S, 5S, 7S and 12S accounted for >80% of all Vbeta usage, and usage of these groups by thymocytes and peripheral T cells was highly correlated. No TRBV group was uniquely expressed in significant numbers in thymocytes, although small numbers of TRBV groups 2S, 9S and 15S were only recovered from T cells. Usage of Jbeta segments from the 5' D-J-C duplicon in thymocytes and peripheral T cells directly correlated with their 5' position in the locus, and Jbeta1.1, 1.2 and 1.3 accounted for >or= 35% of all Jbeta usage in both cell types. This contrasts with the usage of Jbeta2 segments in that Jbeta2.4, 2.5 and 2.7 accounted for approximately 30% of Jbeta usage by T cells and thymocytes. Jbeta2.7 was threefold more frequent among T cells than thymocytes. The Vbeta/Jbeta combination was not random. Jbeta1.1 and 1.2 were used in 29% of rearrangements with high frequency among the major Vbeta groups. Combinations of TRBV4 and V12 with Jbeta2.7 were only found in T cells and accounted for half of all Jbeta2.7 usage. These studies show that unlike porcine heavy chain V(H) genes, the occurrence and relative usage of porcine TCR-Vbeta groups resembles that of humans. Thus, highly related gene systems can individually diverge within a species.

Antibody repertoire development in fetal and neonatal pigs. VII. Characterization of the preimmune kappa light chain repertoire

Combinatorial diversity is highly restricted in the preimmune porcine H chain repertoire compared with that in humans and mice. This raised the question of whether similar restriction characterized the preimmune L chain repertoire. In this study we present evidence that >90% of all expressed Vkappa genes in the porcine preimmune repertoire belong to three subfamilies of Vkappa genes that share 87% sequence similarity with human IGKV2. This porcine Vkappa family also shares sequence similarity with some, but not all, Vkappa genes from sheep. Hybridization with sperm DNA and sequence analyses of polynucleotides from overlapping bacterial artificial chromosome clones suggest swine possess approximately 60 IGVK2 genes. The latter method also revealed that certain IGKV2 subfamilies are not expressed in the preimmune repertoire. Six members of an IGVK1 family were also expressed as part of the preimmune repertoire, and these shared 87% sequence similarity with human IGVK1. Five Jkappa segments, complete with recombination signal sequences and separated by approximately 300 nt, were identified approximately 3 kb upstream of a single Ckappa. Surprisingly, Jkappa2 accounted for >90% of all framework region 4 sequences in the preimmune repertoire. These findings show that swine use approximately 10 IGVK2 genes from three of six subfamilies and preferentially one Jkappa segment to generate their preimmune kappa repertoire. These studies, like those of porcine Ig constant regions and MHC genes, also indicate unexpected high sequence similarity with their human counterparts despite differences in phylogeny and the mechanism of repertoire diversification.

Characterization of porcine CD19 and anti-CD19 monoclonal antibodies

CD19 is an important pan B cell marker and co-stimulatory protein in humans and mice. Efforts to further characterize B cell ontogeny in swine have been hampered by the lack of monoclonal antibodies (mAb) to valuable surface markers like Vpre-B, CD19, CD34 and CD43. We report here on the complete nucleotide and deduced amino acid sequence of porcine CD19, the cross-reactivity of anti-human CD19 monoclonals and efforts to prepare anti-porcine CD19 mAb to bacterially-expressed products. Porcine CD19 is highly homologous to those in the few other species studied, i.e. human, mouse and guinea pig, but only in certain domains. Among the 14 CD19 exons, homology approaches 90% to human CD19 in exons 6, 9, 11 and 12 and is approximately 80% with other species in this region. The highly homologous C-terminal cytoplasmic region contains nine tyrosines including the YEND/E motif that binds the SH2 domain of Fyn. Two different porcine CD19 isoforms that differ in their 3' UTRs were identified just as in human CD19. Thus, the signaling properties of CD19 may be similar to those in humans. On the other hand, only 60% sequence similarity was seen in exons 1-5 that encode the N-terminal extracellullar region that is involved in ligand binding and is the target of CD19-specific mAb. This probably explains why only 1 of the 17 anti-human CD19 mAb tested recognized swine B cells. Furthermore, when the extracellular domains of CD19 were expressed in E. coli, mAbs to the bacterially-expressed product did not recognize CD19 on porcine B cells suggesting that carbohydrate-dependent conformation may determine antigenicity.

Regulation of pituitary growth and prolactin gene expression by estrogen

We presented evidence that primary cultures of rat pituitary cells respond to estradiol by increased incorporation of precursors into prolactin. The response is specific for estrogenic hormones and is maximal at physiological concentrations of estradiol. The time course and magnitude of the response in cultured cells is in agreement with that observed under in vivo conditions, suggesting that estrogen exerts its effect mainly through a direct action on the pituitary gland. The data presented indicate that estrogen stimulates prolactin synthesis predominantly through increased prolactin mRNA accumulation, and to a lesser extent, through mammotroph cell proliferation. Chronic treatment with DES caused sustained proliferation of pituitary cells leading to prolactin producing pituitary tumors in the Fischer 344 rat, but not in the Holtzman rat. The genetic basis for these differences are currently under investigation.

Purification and characterization of the estrogen-induced protein (IP) of the rat uterus

One of the earliest responses of the rat uterus to estrogen is increased synthesis of a specific cytosol protein (IP). This synthesis is detectable within 40 min and is dependent on an even earlier actinomycin D-sensitive function. IP has now been purified to homogeneity as determined by SDS polyacrylamide gel electrophoresis (SDS PAGE). The procedure was complicated by a tendency of the more homogeneous and concentrated material to aggregate. Purification consisted of sequential chromatography, in the presence of 0.1% triton X-100, via DEAE-cellulose (2x), hydroxylapatite and agarose-acrylamide. These were followed by preparative PAGE and finally SDS PAGE. Molecular weight determination by Ferguson plot analysis yielded an apparent molecular weight of 45 000. On final SDS PAGE, the material consisted of two major bands: the 45 000 molecular weight IP band and a band with an estimated molecular weight of 80 000. This second band displayed an elevated synthesis in E2-stimulated uteri similar to IP and appeared to consist of some form of aggregated IP. Carbohydrate determination on SDS gels using periodic acid-Schiff (PAS) stain was negative. Co-purification of labeled cytosol proteins from uteri of control and E2-stimulated rats revealed that IP is synthesized to some extent in the unstimulated animal as well as the stimulated.

Hormone regulation of growth: stimulatory and inhibitory influences of estrogens on DNA synthesis

Estrogenic hormones first stimulate and then inhibit DNA synthesis in the uterus of the immature rat. Both the stimulatory and the inhibitory effects depend on the sustained presence of estrogen. Thus, estriol, which is equal in effectiveness to estradiol on early (up to 6 hr) responses, has only a partial stimulatory effect on DNA synthesis. Estradiol initially stimulates DNA synthesis, but the sustained presence of this steroid inhibits further synthesis of this macromolecule and cell division. These observations are discussed in terms of their relationship to current models of estrogen action and to estrogen dependency in some types of cancer.

Stimulatory and inhibitory effects of estrogen on uterine DNA synthesis

The induction of long-term responses in the uterus following estrogen treatment is discussed, with special reference to DNA synthesis. Immature female rats injected daily with estradiol-17beta or estriol (0.01 to 1 mug) or a combination of the two steroids for one, two or three consecutive days were sacrificed at intervals from 12 to 24 h after the last injection of vehicle or steroid. In vitro incorporation of [3H]thymidine into DNA [14C]leucine into protein, and oxidation of [14C)glucose to 14CO2 were determined. Nuclear-bound estradiol was determined by use of exchange assay or following incubation of intact uteri with 1 X 10(-8)M ([3H]estradiol for 1 h at 37 C. Injection of estriol only partially stimulated DNA synthesis by 18 to 24 h post-treatment. However, injection of estriol followed by injection of estradiol 6 h later resulted in increased DNA synthesis, suggesting that estrogen must be present for up to 6 h to induce subsequent DNA synthesis. Maximal DNA and protein synthesis and oxidation of glucose occurred at 24 h after injection of estradiol (0.1 or 1 mug) but was depressed to control levels by 24 h after the last of three daily injections. Daily injections of 0.01 mug of estradiol resulted in a similar pattern of DNA synthesis, although of lesser magnitude than that observed after injection of 0.1 or 1 mug of estradiol. However, if rats receiving daily injections of 0.01 mug estradiol were challenged with a higher dose of estradiol (1 mug), uterine DNA synthesis was markedly increased. The data suggest that prolonged exposure to estrogen causes uterine cells to become metabolically "refractory" to further estrogen stimulation. Sequential injections of estriol (1 mug) or intermittent injections of estradiol (1 mug) were ineffective in causing this uterine "refractoriness". Receptor binding of estrogen, translocation to the nucleus, and retention of receptor in the nucleus were not affected by sequential estrogen treatment. The accumulation of an inhibitory product is suggested as a possible explanation for this phenomenon.