Current status of the swine leukocyte antigen complex

Aspects of histocompatibility testing in xenotransplantation

Xenotransplantation, using genetically-modified pigs for clinical organ transplantation, is a solution to the organ shortage. The biggest barrier to clinical implementation is the antigenicity of pig cells. Humans possess preformed antibody to pig cells that initiate antibody-mediated rejection of pig organs in primates. Advances in genetic engineering have led to the development of a pig lacking the three known glycan xenoantigens (triple-knockout [TKO] pigs). A significant number of human sera demonstrate no antibody binding to TKO pig cells. As a result of the TKO pig's low antigen expression, survival of life-supporting pig organs in immunosuppressed nonhuman primates has significantly increased, and hope has been renewed for clinical trials of xenotransplantation. It is important to understand the context in which xenotransplantation's predecessor, allotransplantation, has been successful, and the steps needed for the success of xenotransplantation. Successful allotransplantation has been based on two main immunological approaches - (i) adequate immunosuppressive therapy, and (ii) careful histocompatibility matching. In vivo studies suggest that the available immunosuppressive regimens are adequate to suppress the human anti-pig cellular response. Methods to evaluate and screen patients for the first clinical xenotransplantation trial are the next challenge. The goal of this review is to summarize the history of histocompatibility testing, and the available tools that can be utilized to determine xenograft histocompatibility.

Introduction: The Present Status of Xenotransplantation Research

There is a well-known worldwide shortage of deceased human donor organs for clinical transplantation. The transplantation of organs from genetically engineered pigs may prove an alternative solution. In the past 5 years, there have been sequential advances that have significantly increased pig graft survival in nonhuman primates. This progress has been associated with (1) the availability of increasingly sophisticated genetically engineered pigs; (2) the introduction of novel immunosuppressive agents, particularly those that block the second T-cell signal (costimulation blockade); (3) a better understanding of the inflammatory response to pig xenografts; and (4) increasing experience in the management of nonhuman primates with pig organ or cell grafts. The range of investigations required in experimental studies has increased. The standard immunologic assays are still carried out, but increasingly investigations aimed toward other pathobiologic barriers (e.g., coagulation dysregulation and inflammation) have become more important in determining injury to the graft.Now that prolonged graft survival, extending to months or even years, is increasingly being obtained, the function of the grafts can be more reliably assessed. If the source pigs are bred and housed under biosecure isolation conditions, and weaned early from the sow, most microorganisms can be eradicated from the herd. The potential risk of porcine endogenous retrovirus (PERV) infection remains unknown, but is probably small. Attention is being directed toward the selection of patients for the first clinical trials of xenotransplantation.

Is sensitization to pig antigens detrimental to subsequent allotransplantation?

An important question in xenotransplantation is whether an allotransplant can safely be carried out in a patient who has become sensitized to a pig xenograft. To answer this question, we have searched the literature. We primarily limited our review to the clinically relevant pig-to-non-human primate (NHP) model and found five studies that explored this topic. No NHP that had received a pig graft developed antibodies to alloantigens, and in vitro studies indicated no increased humoral and/or cellular alloreactivity. We carried out a small in vitro study ourselves that confirmed this conclusion. There have been three experiments in which patients undergoing dialysis were exposed to wild-type pig kidneys and three clinical studies related to bridging a patient in hepatic failure to liver allotransplantation. Despite the development of anti-pig antibodies, all subsequent organ (kidney or liver) allografts were successful (except possibly in one case). In addition, pig fetal islets were transplanted into patients with kidney allografts; there was no increase in panel-reactive alloantibodies and the kidney grafts continued to function satisfactorily. In conclusion, the limited data suggest that, after sensitization to pig antigens, there is no evidence of antibody-mediated or accelerated cellular rejection of a subsequent allograft.

Specificity Characterization of SLA Class I Molecules Binding to Swine-Origin Viral Cytotoxic T Lymphocyte Epitope Peptides in Vitro

Swine leukocyte antigen (SLA) class I molecules play a crucial role in generating specific cellular immune responses against viruses and other intracellular pathogens. They mainly bind and present antigens of intracellular origin to circulating MHC I-restricted cytotoxic T lymphocytes (CTLs). Binding of an appropriate epitope to an SLA class I molecule is the single most selective event in antigen presentation and the first step in the killing of infected cells by CD8+ CTLs. Moreover, the antigen epitopes are strictly restricted to specific SLA molecules. In this study, we constructed SLA class I complexes in vitro comprising viral epitope peptides, the extracellular region of the SLA-1 molecules, and β2-microglobulin (β2m) using splicing overlap extension polymerase chain reaction (SOE-PCR). The protein complexes were induced and expressed in an Escherichia coli prokaryotic expression system and subsequently purified and refolded. Specific binding of seven SLA-1 proteins to one classical swine fever virus (CSFV) and four porcine reproductive and respiratory syndrome virus (PRRSV) epitope peptides was detected by enzyme-linked immunosorbent assay (ELISA)-based method. The SLA-1^∗13:01, SLA-1^∗11:10, and SLA-1^∗11:01:02 proteins were able to bind specifically to different CTL epitopes of CSFV and PRRSV and the MHC restrictions of the five epitopes were identified. The fixed combination of Asn¹⁵¹Val¹⁵² residues was identified as the potentially key amino acid residues influencing the binding of viral several CTL epitope peptides to SLA-1^∗13:01 and SLA-1^∗04:01:01 proteins. The more flexible pocket E in the SLA-1^∗13:01 protein might have fewer steric limitations and therefore be able to accommodate more residues of viral CTL epitope peptides, and may thus play a critical biochemical role in determining the peptide-binding motif of SLA-1^∗13:01. Characterization of the binding specificity of peptides to SLA class I molecules provides an important basis for epitope studies of infectious diseases in swine, and for the rational development of novel porcine vaccines, as well as for detailed studies of CTL responses in pigs used as animal models.

Peripheral nerve regeneration using autologous porcine skin-derived mesenchymal stem cells

Porcine skin-derived mesenchymal stem cells (pSMSCs) were evaluated on their biological MSC characterizations and differentiation into mesenchymal lineages, along with in vitro and in vivo neural inductions. Isolated pSMSCs showed plate-adherent growth, expression of various MSC-marker proteins and transcriptional factors, and differentiation potential into mesenchymal lineages. Neuron-like cell morphology and various neural markers were highly detected at 6 h and 24 h after in vitro neural induction of pSMSCs, but their neuron-like characteristics disappeared as induction time extended to 48 and 72 h. To evaluate the in vivo peripheral nerve regeneration potential of pSMSCs, a total of 5 × 10(6) autologous pSMSCs labelled with tracking dye, supplemented with fibrin glue scaffold and collagen tubulization, were transplanted into the peripheral nerve defected miniature pigs. At 2 and 4 weeks after cell transplantation, well-preserved transplanted cells and remarkable in vivo nerve regeneration, including histologically complete nerve bundles, were observed in the regenerated nerve tissues. Moreover, S-100 protein and p75 nerve growth factor receptor were more highly detected in regenerated nerve fibres compared to non-cell grafted control fibres. These results suggest that autologous pSMSCs transplanted with fibrin glue scaffold can induce prominent nerve regeneration in porcine peripheral nerve defect sites.

Myelogenous leukemia in adult inbred MHC-defined miniature swine: a model for human myeloid leukemias

This manuscript reports on five cases of spontaneous myelogenous leukemia, similar to human disease, occurring within highly inbred, histocompatible sublines of Massachusetts General Hospital (MGH) MHC-defined miniature swine. In cases where a neoplasm was suspected based on clinical observations, samples were obtained for complete blood count, peripheral blood smear, and flow cytometric analysis. Animals confirmed to have neoplasms were euthanized and underwent necropsy. Histological samples were obtained from abnormal tissues and suspect lesions. The phenotype of the malignancies was assessed by flow cytometric analysis of processed peripheral blood mononuclear cells and affected tissues. Five cases of spontaneous myeloid leukemia were identified in adult animals older than 30 months of age. All animals presented with symptoms of weight loss, lethargy, and marked leukocytosis. At autopsy, all animals had systemic disease involvement and presented with severe hepatosplenomegaly. Three of the five myelogenous leukemias have successfully been expanded in vitro. The clustered incidence of disease in this closed herd suggests that genetic factors may be contributing to disease development. Myelogenous leukemia cell lines established from inbred sublines of MGH MHC-defined miniature swine have the potential to be utilized as a model to evaluate therapies of human leukemia.

Molecular genetics of the swine major histocompatibility complex, the SLA complex

The swine major histocompatibility complex (MHC) or swine leukocyte antigen (SLA) complex is one of the most gene-dense regions in the swine genome. It consists of three major gene clusters, the SLA class I, class III and class II regions, that span approximately 1.1, 0.7 and 0.5Mb, respectively, making the swine MHC the smallest among mammalian MHC so far examined and the only one known to span the centromere. This review summarizes recent updates to the Immuno Polymorphism Database-MHC (IPD-MHC) website (http://www.ebi.ac.uk/ipd/mhc/sla/) which serves as the repository for maintaining a list of all SLA recognized genes and their allelic sequences. It reviews the expression of SLA proteins on cell subsets and their role in antigen presentation and regulating immune responses. It concludes by discussing the role of SLA genes in swine models of transplantation, xenotransplantation, cancer and allergy and in swine production traits and responses to infectious disease and vaccines.

Membrane markers of the immune cells in swine: an update

Besides their breeding value, swine are increasingly used as biomedical models. As reported in three international swine clusters of differentiation (CD) workshops and in the animal homologue section of the last workshop for the determination of human leukocyte differentiation antigens (HLDA 8), characterisation of leukocyte surface antigens by monoclonal antibodies and other molecular studies have determined the cell lineages and blood leukocyte subsets implicated in the immune response, including cell adhesion molecules involved in cell trafficking. This review focusses on the current state of knowledge of porcine leukocyte differentiation and major histocompatibility complex (SLA) molecules. Examples of porcine particularities such as the double-positive T lymphocytes with the phenotype CD(4+)CD8(low) and CD(4-)CD8(low) alphabeta T cell subsets and the persistence of SLA class II after T-lymphocyte activation are illustrated, as well as the shared characteristics of the Artiodactyla group, such as the high proportion of gammadelta TcR (T cell receptor) T cells in blood and other lymphoid tissues. Furthermore, discrepancies between swine and humans, such as CD16 expression on dendritic cells and CD11b (wCD11R1) tissue distribution are outlined. The rapidly growing information should facilitate manipulation of the swine immune system towards improving disease control, and open new avenues for biomedical research using the pig as a model.

The effects of floor heating on body temperature, water consumption, stress response and immune competence around parturition in loose-housed sows

The aim of the present study was to study whether floor heating from 12h after onset of nest building until 48 h after birth of the first piglet had any effect on measures related to body temperature, water consumption, stress response and immune competence in loose-housed sows (n=23). In conclusion, the present results indicate that floor heating for a limited period around parturition did not compromise physiological and immunological parameters, water intake and body temperature in loose-housed sows. The water intake peaked the day before parturition and the body temperature peaked on the day of parturition. A cortisol peak at parturition, a transient rise in the number of leucocytes and neutrophils and a transient reduction in the number of lymphocytes, erythrocytes and in the PCV value were observed. Around and after parturition some non-specific immunological variables seemed to be stimulated while others seemed to be compromised.

Characterization of swine leukocyte antigen polymorphism by sequence-based and PCR-SSP methods in Meishan pigs

Resource herds of swine leukocyte antigen (SLA)-characterized pigs are an important tool for the study of immune responses, disease resistance, and production traits. They are also valuable large animal models for biomedical research, such as transplantation. The Meishan breed of pig is an economically significant breed that is available at several research institutions in the United States. We have characterized the SLA polymorphism of the breeding stock in the herd maintained at the University of Illinois and developed a simple assay to SLA type individuals within that herd. We have used a reverse transcription-polymerase chain reaction (RT-PCR)-based SLA typing method to clone and DNA sequence 19 SLA alleles at three SLA class Ia (SLA-1, SLA-2, and SLA-3) and two SLA class II (SLA-DRB1 and SLA-DQB1) loci. Based on this sequence information, a rapid SLA typing assay was developed to discriminate each allele using PCR with sequence-specific primers (PCR-SSP). Using this method, we were able to characterize the entire Meishan breeding stock and identify four SLA haplotypes present in the herd. The combination of SLA typing by cloning and DNA sequencing with PCR-SSP is therefore a valuable tool for the characterization of SLA alleles and haplotypes in resource herds of pigs.

Nomenclature for factors of the SLA class-I system, 2004

A systematic nomenclature for the genes and alleles of the swine major histocompatibility complex (MHC) is essential to the development and communication of research in swine immunology. The Swine Leucocyte Antigen (SLA) Nomenclature Committee of the International Society for Animal Genetics has reviewed all of the DNA sequence information for MHC class-I genes, available in GenBank/EMBL/DDBJ databases, and the associated published reports in order to develop such a systematic nomenclature. This report summarizes the proposed nomenclature, which parallels the World Health Organization's nomenclature for factors of the human MHC. The classical class-I SLA genes are designated as SLA-1, SLA-2 and SLA-3; the non-classical as SLA-6, SLA-7 and SLA-8. Nomenclature assignments for all SLA class-I GenBank sequences are now noted. The Committee will add new SLA class-I allele designations, as they are discovered, and will maintain a publicly available list of all recognized genes and alleles by using the International ImMunoGeneTics Project and its Immuno Polymorphism Database/MHC (IPD/MHC) sequence database for MHC sequences in veterinary species.

Immune response characteristics following emergency vaccination of pigs against foot-and-mouth disease

Pigs were vaccinated with the emergency inactivated foot-and-mouth disease virus (FMDV) vaccine--water-in-oil-in-water emulsion with Montanide ISA206--known to protect after 3-5 days. Peripheral blood leukocyte (PBL) sub-populations did not differ between vaccinates and controls post-vaccination. There was neither lymphopenia nor inflammatory reaction. FMDV-specific antibody and T lymphocyte activity developed in the vaccinates. Virus-induced Th1-like cytokine protein and mRNA (IFNgamma and IL-2) were identified, particularly IFNgamma. Th2-like cytokine protein and mRNA (IL-4 and IL-6) were also induced in an FMDV-specific manner. IL-10 was induced by both virus and mock antigen. The current emergency FMDV vaccine induces a diverse immune defence network--innate, and both Th1-like and Th2-like responses--without adverse reactions such as lymphopenia or inflammatory responses.

Persistent chimerism despite antidonor MHC in vitro responses in miniature swine following allogeneic hematopoietic cell transplantation

BACKGROUND

T-cell chimerism predominates in miniature swine receiving hematopoietic-cell transplantation without myelosuppressive conditioning. Several chimeric recipients have become hyporesponsive to donor-major histocompatibility complex (MHC) in vitro and accepted donor-matched renal transplants without immunosuppression. However, some retained antidonor in vitro responses and subsequently rejected donor renal allografts despite the persistence of peripheral blood chimerism. In this study, we characterize the donor cells in both "tolerant" and "nontolerant" chimeric miniature swine.

METHODS

Peripheral blood chimerism was determined by flow cytometry. In vitro antidonor responsiveness was determined by mixed lymphocyte reaction (MLR) and cell-mediated lymphocytotoxicity (CML). Donor cells were separated from chimeras by immunomagnetic bead separation and used as stimulators or targets in CML assays. Phenotypic analysis of donor cells in chimeras was performed using flow cytometry.

RESULTS

Peripheral blood chimerism stabilized beyond 100 days and was made up almost entirely of T cells. PBMC from nontolerant chimeras could be stimulated in vitro to kill donor cells isolated from the mixed chimera itself. In contrast, PBMC from tolerant chimeras hyporesponsive to donor-type cells could not be stimulated in vitro to kill their own sorted donor cells.

CONCLUSIONS

The in vivo persistence of donor T cells in mixed chimeric animals with in vitro antidonor responsiveness is not caused by an inability of these cells to be killed but rather by the poor stimulating capacity of these donor T cells. The nature of donor T cells that persist in the face of in vitro antidonor responses, has important implications for the induction of transplant tolerance by way of the generation of mixed chimerism.

Development of a rapid in vitro protein refolding assay which discriminates between peptide-bound and peptide-free forms of recombinant porcine major histocompatibility class I complex (SLA-I)

The extracellular domains of swine leukocyte antigen class I (SLA-I, major histocompatibility complex protein class I) were cloned and sequenced for two haplotypes (H4 and H7) which do not share any alleles based on serological typing, and which are the most important in Danish farmed pigs. The extracellular domain of SLA-I was connected to porcine beta2 microglobulin by glycine-rich linkers. The engineered single-chain proteins, consisting of fused SLA-I and beta2 microglobulin, were overexpressed as inclusion bodies in Escherichia coli. Also, variants were made of the single-chain proteins, by linking them through glycine-rich linkers to peptides representing T-cell epitopes from classical swine fever virus (CSFV) and foot-and-mouth disease virus (FMDV). An in vitro refold assay was developed, using a monoclonal anti-SLA antibody (PT85A) to gauge refolding. The single best-defined, SLA-I restricted porcine CD8(+) T-cell epitope currently known is a 9-residue peptide from the polyprotein of CSFV (J. Gen. Virol. 76 (1995) 3039). Based on results with the CSFV epitope and two porcine haplotypes (H4 and H7), the in vitro refold assay appeared able to discriminate between peptide-free and peptide-occupied forms of SLA-I. It remains to be seen whether the rapid and technically very simple in vitro refold assay described here will prove generally applicable for the screening of virus-derived peptides for SLA-I binding.

Systematic characterization of porcine ileal Peyer's patch, I. apoptosis-sensitive immature B cells are the predominant cell type

It is now apparent that the Peyer's patches of some species exhibit structural, functional and developmental heterogeneity. In sheep, for example, the ileal Peyer's patch (IPP) is the primary, antigen-independent site for the generation of the primary immunoglobulin repertoire and consequent production of the systemic B-cell pool. The pig has three distinct Peyer's patches, including an IPP, but the functional status of this organ, as primary or secondary lymphoid tissue, is not clear. Here, we have systematically characterized pig IPP follicular lymphocytes and show that about 90% B cells that are positive for surface immunoglobulin G (sIgM+) and express an immature phenotype characterized by expression of myeloid marker sWC3 (74-22-15) and two molecules recognized by IPP B-cell-specific monoclonal antibodies (F10/4, F12/35). Extensive apoptosis in vivo and in vitro was demonstrated by electron microscopy, immunohistology with TdT-mediated dUTP nick end labelling, DNA analysis and fluorescence-activated cell sorter analysis. Thus, when isolated IPP follicular cells were incubated at 37 degrees in vitro, the majority of them became apoptotic. The few that survived, however, had lost their expression of sWC3, F10/4, F12/35, but showed an increased expression of sIgM and major histocompatibility complex class II indicating that such surviving cells were of a more mature phenotype. Although more T cells were observed in porcine IPP follicles than in sheep IPP, CD3+ cells comprised less than 5% of the IPP follicular lymphocytes. Thus, the results clearly indicate that pig IPP is equivalent to sheep IPP.

Systematic characterization of porcine ileal Peyer's patch, II. A role for CD154 on T cells in the positive selection of immature porcine ileal Peyer's patch B cells

We previously demonstrated that the majority (>/= 90%) of porcine ileal Peyer's patch (IPP) follicular cells are immature B cells destined to die by apoptosis, when incubated at 37 degrees. In this paper we approached the mechanisms responsible for positive selection of porcine IPP follicular immature B-cell selection, by screening for various cell types, cytokines and polyclonal and monoclonal antibodies for promoting the survival of IPP B cells. Of these reagents, only CD3 cross-linked purified T cells from mesenteric lymph nodes were able to rescue IPP follicular B cells from apoptosis, although polyclonal anti-IPP lymphocyte antibodies delayed apoptosis. This survival effect could be reproduced simply by incubating IPP follicular B cells with soluble and cell membrane-expressed CD154, an observation consistent with the demonstrated presence of CD40 and CD154 on porcine IPP follicular B cells and activated T cells, respectively. The IPP follicular B cells rescued in this manner expressed a more mature surface marker phenotype. Immunohistology and fluorescence-activated cell sorter analysis demonstrated that subpopulations of IPP follicular T cells (less than 0.5%) express CD154. Thus, perhaps unexpectedly, CD154 on T cells may play a role in the positive selection of immature B cells in the porcine IPP. The origin and control of the activated T cells identified within the porcine IPP remains to be investigated.

Genomics of the major histocompatibility complex: haplotypes, duplication, retroviruses and disease

The genomic region encompassing the Major Histocompatibility Complex (MHC) contains polymorphic frozen blocks which have developed by local imperfect sequential duplication associated with insertion and deletion (indels). In the alpha block surrounding HLA-A, there are ten duplication units or beads on the 62.1 ancestral haplotype. Each bead contains or contained sequences representing Class I, PERB11 (MHC Class I chain related (MIC) and human endogenous retrovirus (HERV) 16. Here we consider explanations for co-occurrence of genomic polymorphism, duplication and HERVs and we ask how these features encode susceptibility to numerous and very diverse diseases. Ancestral haplotypes differ in their copy number and indels in addition to their coding regions. Disease susceptibility could be a function of all of these differences. We propose a model of the evolution of the human MHC. Population-specific integration of retroviral sequences could explain rapid diversification through duplication and differential disease susceptibility. If HERV sequences can be protective, there are exciting prospects for manipulation. In the meanwhile, it will be necessary to understand the function of MHC genes such as PERB11 (MIC) and many others discovered by genomic sequencing.

The major histocompatibility complex in swine

In swine, the major histocompatibility complex (Mhc) or swine leukocyte antigen (SLA) is located on chromosome 7 and divided by the centromere. Thus, the telomeric class I and more centromeric class III regions are located on the p arm and the class II region is located on the q arm. The SLA region spans about 2 Mb, in which more than 70 genes have so far been characterized. Despite its division by the centromere, the spatial relationships between the genes in the class II and class III regions, and between the well-conserved non-class I genes of the class I region, are similar to those found in the human HLA complex. On the other hand, no orthologous relationships have been found between the Mhc class I genes in man and swine. In swine, the 12 SLA class I sequences constitute two distinct clusters. One cluster comprises six classical class I-related sequences, while the other comprises five class I-distantly related sequences including two swine homologous genes of the HLA Mhc class I chain-related gene (MIC) sequence family. The number of functional SLA classical class I genes, as defined by serology, probably varies from one to four, depending on the haplotype. Some of the SLA class I-distantly related sequences are clearly transcribed. As regards the SLA class II genes, some of them clearly code for at least one functional SLA-DR and one SLA-DQ heterodimer product, but none code for any DP product. The amino acid alignment of the variable domains of 33 SLA classical class I chains, and 62 DR beta and 20 DQ beta chains confirmed the exceptionally polymorphic pattern of these polypeptides. Among the class II genes, the genes are either monomorphic, like the DRA gene, or oligomorphic, like the DQA genes. In contrast, the DRB and DQB genes display considerable polymorphism, which seems more marked in DRB than DQB genes.

Expression of porcine major histocompatibility antigens in cardiac tissue

In this study we have used monoclonal antibodies directed against antigens of the major histocompatibility complex (MHC) class I and class II to reveal the detailed cellular distribution of swine lymphocyte alloantigens (SLA) in cardiac tissue. By applying a sensitive immunophosphatase staining reaction we detected the ubiquitous expression of SLA class I and class II on the vascular endothelium. Endothelial cells of capillaries and blood vessels were intensely stained structures in the examined swine hearts. Similar staining patterns were observed in control experiments with anti-von Willebrand factor serum and Dolichus biflorus lectin used as immunohistochemical markers for endothelial cells. The luminal layer of studied pulmonary valves exhibited a strong staining reaction with anti-SLA class I and class II antibodies. In contrast, normal cardiac myocytes failed to express immunodetectable amounts of either of the SLA determinants. Intercalated discs in porcine heart tissue did not react with either anti-SLA class I or class II antibodies. Our data showing the abundant expression of SLA molecules on endothelial cells in normal swine heart may have physiological implications in cell-mediated rejection occurring in xenotransplanted hearts.

Vaccine-induced, pseudorabies virus-specific, extrathymic CD4+CD8+ memory T-helper cells in swine

Pseudorabies virus (PRV; suid herpesvirus 1) infection causes heavy economic losses in the pig industry. Therefore, vaccination with live attenuated viruses is practiced in many countries. This vaccination was demonstrated to induce extrathymic virus-specific memory CD4+CD8+ T lymphocytes. Due to their major histocompatibility complex (MHC) class II-restricted proliferation, it is generally believed that these T lymphocytes function as memory T-helper cells. To directly prove this hypothesis, 15-amino-acid, overlapping peptides of the viral glycoprotein gC were used for screening in proliferation assays with peripheral blood mononuclear cells of vaccinated d/d haplotype inbred pigs. In these experiments, two naturally processed T-cell epitopes (T1 and T2) which are MHC class II restricted were identified. It was shown that extrathymic CD4+CD8+ T cells are the T-lymphocyte subpopulation that responds to epitope T2. In addition, we were able to show that cytokine secretion can be induced in these T cells through recall with inactivated PRV and demonstrated that activated PRV-primed CD4+CD8+ T cells are able to induce PRV-specific immunoglobulin synthesis by PRV-primed, resting B cells. Taken together, these results demonstrate that the glycoprotein gC takes part in the priming of humoral anti-PRV memory responses. The experiments identified the first T-cell epitopes so far known to induce the generation of virus-specific CD4+CD8+ memory T lymphocytes and showed that CD4+CD8+ T cells are memory T-helper cells. Therefore, this study describes the generation of virus-specific CD4+CD8+ T cells, which is observed during vaccination, as a part of the potent humoral anti-PRV memory response induced by the vaccine.

Characterization of five monoclonal antibodies specific for swine class II major histocompatibility antigens and crossreactivity studies with leukocytes of domestic animals

A set of five monoclonal antibodies (mAb) against porcine major histocompatibility complex (MHC), or swine leukocyte antigens (SLA), class II molecules has been characterized. These mAbs appear to recognize monomorphic determinants on SLA-DR (2F4, 1F12 and 2E9/13) and SLA-DQ (BL2H5 and BL4H2) molecules, as assessed by flow cytometry and immunoprecipitation. By Western blot, the 2F4, 1F12, BL2H5 and BL4H2 epitopes were located on the beta-chains of these molecules. mAbs 2F4 and 1F12 crossreact with leucocytes of dog, cattle, horse and human; mAbs 2E9/13, BL2H5 and BL4H2 bind leucocytes of cattle but not those of human, dog and horse. These mAbs effectively blocked the mixed lymphocyte reaction and the proliferative response to viral antigens (African swine fever virus) and to staphylococcal enterotoxin B. Therefore, these mAbs can be useful reagents for studying MHC class II molecules of pig and crossreactive species, and the immunological processes where they are involved.

A detailed physical map of the porcine major histocompatibility complex (MHC) class III region: comparison with human and mouse MHC class III regions

A detailed physical map of the porcine MHC class III region on Chr 7 was constructed with a panel of probes in a series of hybridizations on genomic pulsed field gel electrophoresis (PFGE) Southern blots. A precise organization of the 700-kb segment of DNA between G18 and BAT1 can now be proposed, with more than 30 genes mapped to it. Comparison of this region with homologous regions in human and mouse showed only minor differences. The biggest difference was observed in the CYP21/C4 locus with only one CYP21 gene and one C4 gene found, whereas in human and mouse these genes are duplicated. These results show the class III region is very well conserved between pig, human, and mouse, in contrast with the class I and class II regions, which seem more prone to rearrangements.

Mapping of the SLA complex class III region by pulsed field gel electrophoresis

The fine order of genes in the class III region of the swine major histocompatibility complex (MHC), the SLA complex, was examined by pulsed field gel electrophoresis (PFGE) and Southern blot analysis. Four genes, C2, HSP70, TNF alpha, and CYP21, were analyzed. The CYP21, C2, and HSP70 genes were all located within a 200-kb NotI fragment. The C2, HSP70, and TNF alpha genes cohybridized to a 420-kb SalI fragment. The TNF alpha gene is linked to the class I region by a 390-kb NotI fragment. Combined with a previous study from our lab, the order of genes in the SLA complex is class II-class III [(CYP21/C4)-(Bf/C2/HSP70)-TNF alpha]-class I. The size of the class III region from CYP21 to TNF alpha is estimated to be 500 kb. This size and the order of the genes in the swine class III region are similar to those of human, mouse, goat, and rabbit, which confirms the high conservation of class III gene organization across species.