The Null/gamma delta TCR+ T cell family in the pig

γδ T cells in artiodactyls: Focus on swine

Vaccination is the most effective medical strategy for disease prevention but there is a need to improve livestock vaccine efficacy. Understanding the structure of the immune system of swine, which are considered a γδ T cell "high" species, and thus, particularly how to engage their γδ T cells for immune responses, may allow for development of vaccine optimization strategies. The propensity of γδ T cells to home to specific tissues, secrete pro-inflammatory and regulatory cytokines, exhibit memory or recall responses and even function as antigen-presenting cells for αβ T cells supports the concept that they have enormous potential for priming by next generation vaccine constructs to contribute to protective immunity. γδ T cells exhibit several innate-like antigen recognition properties including the ability to recognize antigen in the absence of presentation via major histocompatibility complex (MHC) molecules enabling γδ T cells to recognize an array of peptides but also non-peptide antigens in a T cell receptor-dependent manner. γδ T cell subpopulations in ruminants and swine can be distinguished based on differential expression of the hybrid co-receptor and pattern recognition receptors (PRR) known as workshop cluster 1 (WC1). Expression of various PRR and other innate-like immune receptors diversifies the antigen recognition potential of γδ T cells. Finally, γδ T cells in livestock are potent producers of critical master regulator cytokines such as interferon (IFN)-γ and interleukin (IL)-17, whose production orchestrates downstream cytokine and chemokine production by other cells, thereby shaping the immune response as a whole. Our knowledge of the biology, receptor expression and response to infectious diseases by swine γδ T cells is reviewed here.

Subpopulations of swine γδ T cells defined by TCRγ and WC1 gene expression

γδ T cells constitute a major portion of lymphocytes in the blood of both ruminants and swine. Subpopulations of swine γδ T cells have been distinguished by CD2 and CD8α expression. However, it was not clear if they have distinct expression profiles of their T-cell receptor (TCR) or WC1 genes. Identifying receptor expression will contribute to understanding the functional differences between these subpopulations and their contributions to immune protection. Here, we annotated three genomic assemblies of the swine TCRγ gene locus finding four gene cassettes containing C, J and V genes, although some haplotypes carried a null TRGC gene (TRGC4). Genes in the TRGC1 cassette were homologs of bovine TRGC5 cassette while the others were not homologous to bovine genes. Here we evaluated three principal populations of γδ T cells (CD2⁺/SWC5^-, CD2^-/SWC5⁺, and CD2^-/SWC5^-). Both CD2^- subpopulations transcribed WC1 co-receptor genes, albeit with different patterns of gene expression but CD2⁺ cells did not. All subpopulations transcribed TCR genes from all four cassettes, although there were differences in expression levels. Finally, the CD2⁺ and CD2^- γδ T-cell populations differed in their representation in various organs and tissues, presumably at least partially reflective of different ligand specificities for their receptors.

Porcine reproductive and respiratory syndrome virus induces pronounced immune modulatory responses at mucosal tissues in the parental vaccine strain VR2332 infected pigs

Porcine reproductive and respiratory syndrome (PRRS) is a chronic viral disease of pigs caused by PRRS virus (PRRSV). The PRRSV VR2332 is the prototype North American parental strain commonly used in the preparation of vaccines. Goal of this study was to understand missing information on VR2332 induced immune modulation at the lungs and lymphoid tissues, the sites of PRRSV replication. Pigs were infected intranasally and samples collected at post-infection day (PID) 15, 30, and 60. Microscopically, lungs had moderate interstitial pneumonia, and the virus was detected in all the tested tissues. Peak antibody response and the cytokine IFN-γ secretion were detected at PID 30, with increased TGF-β until PID 60. Population of CD8(+), CD4(+), and CD4(+)CD8(+)T cells, Natural killer (NK) cells, and γδ T cells in the lungs and lymphoid tissues were significantly modulated favoring PRRSV persistence. The NK cell-mediated cytotoxicity was significantly reduced in infected pigs. In addition, increased population of immunosuppressive T-regulatory cells (Tregs) and associated cytokines were also observed in VR2332 strain infected pigs.

Fenugreek seed affects intestinal microbiota and immunological variables in piglets after weaning

Fenugreek seed has been shown to affect the intestinal microbiota and immunological responses in animals. A feeding trial with male castrated piglets was performed over 28 d without or with the addition of 1·5 g fenugreek seeds/kg complete diet in ten and eleven piglets, weaned at 21 d. In the intestinal tract, pH, lactate and SCFA were measured as major bacterial metabolites. Immune cell phenotypes, phagocytic activity and lymphocyte proliferation after stimulation with pokeweed mitogen, concanavalin A and phytohaemagglutinin M were measured by flow cytometry. Health status and performance of the piglets were not affected by fenugreek. The pH in the caecum and colon were reduced compared with the control (P< 0·05). Higher concentrations of l-lactic acid were recorded in the small-intestinal digesta (average concentrations from the duodenum, jejunum and ileum; P< 0·05), while the concentrations of SCFA remained unchanged except an increase in n-butyric acid in colon contents (P< 0·05). The piglets fed the fenugreek diet had higher Lactobacillus and clostridium cluster I concentrations and lower Escherichia, Hafnia and Shigella concentrations in the small intestine. The addition of fenugreek increased the relative concentration of the γδ T-cell population (TCR1+CD8α-) in the blood with a simultaneous reduction of antigen-presenting cells (MHCII+CD5-) (P< 0·05). Proliferation rate and phagocytosis activity of monocytes were not affected by the additive. In conclusion, fenugreek seeds might be interesting as a feed ingredient for young piglets due to their effects on the intestinal microbiota and immunological variables. The impact on performance and animal health has to be further evaluated.

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.

Use of flow cytometry to develop and characterize a set of monoclonal antibodies specific for rabbit leukocyte differentiation molecules

Flow cytometry was used to identify and characterize monoclonal antibodies (mAbs) that react with rabbit leukocyte differentiation molecules (LDM). Screening sets of mAbs, developed against LDM in other species, for reactivity with rabbit LDM yielded 11 mAbs that recognize conserved epitopes on rabbit LDM orthologues and multiple mAbs that recognize epitopes expressed on the major histocompatibility class I or class II molecules. Screening of mAbs submitted to the Animal Homologues Section of the Eighth Human Leukocyte Differentiation Workshop yielded 7 additional mAbs. Screening of mAbs generated from mice immunized with leukocytes from rabbit thymus or spleen or concanavalin A activated peripheral blood and/or spleen lymphocytes has yielded 42 mAbs that recognize species restricted epitopes expressed on one or more lineages of leukocytes. Screening of the anti-rabbit mAbs against leukocytes from other species yielded one additional mAb. The studies show that screening of existing sets of mAbs for reactivity with rabbit LDM will not be productive and that a direct approach will be needed to develop mAbs for research in rabbits. The flow cytometric approach we developed to screen for mAbs of interest offers a way for individual laboratories to identify and characterize mAbs to LDM in rabbits and other species. A web-based program we developed provides a source of information that will facilitate analysis. It contains a searchable data base on known CD molecules and a data base on mAbs, known to react with LDM in one or more species of artiodactyla, equidae, carnivora, and or lagomorpha.

Genomic dissection of mucosal immunobiology in the porcine small intestine

The enteric immune system of swine protects against infectious and noninfectious environmental insults and discriminates ingested nutrients, food, and commensal microflora from pathogenic agents. The molecular and cellular elements of the immune system have been selected over evolutionary time in response to the specific environment of pigs. Thus, models of immune function based on mouse and human need to be applied cautiously in the pig. To better understand how the mucosal immune system of the small intestine accomplishes the conflicting functions of food tolerance and immunity to enteric infection, we used a genomic approach to profile gene expression in the Peyer's patch. More than 40% of mRNA enriched by differential subtraction for Peyer's patch-specific expressed sequences represented genes of unknown function or had no match in GenBank. Microarray analysis and radiation hybrid mapping validated their porcine origin and provided additional insights into putative functions. The abundance of expressed genes of unknown function indicates that a substantial fraction of the immunological and physiological processes of the Peyer's patch remains to be discovered. It further suggests that swine have evolved specialized biochemical and immunological processes in the small intestine. Further elucidation of these processes are expected to provide novel insights into swine enteric mucosal immune function.

Porcine γδ T cells: Possible roles on the innate and adaptive immune responses following virus infection

gammadelta T cells recognise different types of antigen in alternative ways to alphabeta T cells, and thus appear to play a complementary role in the immune response. However, unlike alphabeta T cells, the role or function of gammadelta T cells is still unclear. As pigs possess a high proportion of circulating gammadelta T cells, they are suitable large animal model to study gammadelta T cell functions. This as yet has not been fully exploited, leaving porcine gammadelta T cell biology and its role in immunity in its infancy. Foot-and-mouth disease (FMD) high potency "emergency" vaccines are able to induce early protection from challenge and it has been suggested that, in part, there is some involvement of innate immune responses. The antigen component of the vaccine is able to stimulate purified naive pig gammadelta T cells and induce the mRNA of various cytokines and chemokines. This observation suggests that gammadelta T cells probably contribute to the early phase of the immune responses to FMD vaccination, and perhaps infection. A subset of these circulating gammadelta T cells display a phenotype similar to professional antigen presenting cells and are able to take up and present soluble antigen to CD4(+) T cells in a direct cell-cell interaction via MHC class II. This direct interaction between gammadelta T cells and CD4(+) T cells is likely to have a significant influence on the out come of the adaptive immune response.

Peripheral T lymphocyte changes in neonatal piglets: Relationship with growth hormone (GH), prolactin (PRL) and cortisol changes

Taking into account the role played by the neuroendocrine network in affecting the early development of the immune response, the present study aims to assess neonatal immunity in piglets by testing peripheral lymphocyte age-related changes in relationship to plasma levels of some relevant immunoregulatory hormones, such as growth hormone (GH), prolactin (PRL) and cortisol. For this purpose, we studied the peripheral lymphocyte age-related changes in relationship to plasma levels of GH, PRL and cortisol in conventional piglets from birth (day 0) to 41 days of age. A significant decrease was observed in the total number of lymphocytes at day 0, with a subsequent constant increment up to 41 days of age. Concomitantly, the number of T cell subsets (mainly CD8(+) cells and double positive CD4(+)CD8(+)) was low at birth, with strong increments between the 19th and 41st days of life. The CD4(+) T cell number subset was less diminished at birth than that of CD8(+), albeit with significant increments in the post-weaning period. Of interest, gammadelta T cells, which are more involved in innate immune efficiency, displayed the same trend as CD8(+) T cells from birth to the 41st day of life. From day 0 up to the 19th day, significant inverse correlations were found between T cell subsets and GH or PRL or cortisol, albeit with more significant inverse correlations with cortisol. The high levels of GH and PRL in the pre-weaning period may be due to the fact that they have to counteract the cortisol-mediated negative effect on lymphocyte production and development. These findings suggest that stress condition occurs at birth with decreases in the immune parameters, in the same way as in human newborns, with a subsequent gradual normalisation and immune development, as shown by decreased cortisol, GH and PRL normalisation and concomitant increments in T cell subsets.

Differential requirements for proliferation of CD4+ and γδ+ T cells to spirochetal antigens

Alphabeta+ and gammadelta+ T cells have different mechanisms of epitope recognition and are stimulated by antigens of different chemical nature. An immunization model with antigens from the spirochete Brachyspira hyodysenteriae was used to examine the requirements for proliferation of circulating porcine CD4+ and gammadelta+ T cells in mixed lymphocyte cultures. CD4+ T cells only responded to stimulation with B. hyodysenteriae antigens, whereas gammadelta+ T cells proliferated when cultures were stimulated with either spirochetal antigens or interleukin-2 (IL-2). T cells that had proliferated expressed high levels of IL-2-receptor-alpha (IL-2Ralpha). Furthermore, neutralization of IL-2 at the beginning of the culture period was more efficient in blocking gammadelta+ than CD4+ T cell proliferation. Immunization induced interferon-gamma (IFN-gamma) production by CD4+ T cells, whereas only a small fraction of the antigen-stimulated gammadelta+ T cells produced this cytokine. Our results indicate that, under the same environmental conditions, CD4+ T cell functions are more tightly regulated when compared to gammadelta+ T cells. We conclude that these differences are due, in part, to the enhanced gammadelta+ T cell responsiveness to IL-2.

Proportions and phenotypic expression of peripheral blood leucocytes in pigs vaccinated with an attenuated C strain and a subunit E2 vaccine against classical swine fever

The influence of an attenuated classical swine fever virus C strain vaccine and a subunit E2 vaccine against classical swine fever on the peripheral blood leucocyte proportion and phenotypic expression in 12-week-old pigs was studied. The C strain was amplified in minipig kidney cell culture and final product contained 10(4 +/- 0.15) TCID50/ml, while the subunit vaccine contained 32 microg per dose of gp E2. Haematological findings showed that the vaccines did not cause leucopenia or lymphocytopenia and the number of neutrophils and eosinophils during the observation period was within physiological range. The results of the proportion of CD4a+, CD5a+, CD8a+, wCD21+, CD45RA+, CD45RC+ , non-T non-B, SWC3a+ and CD11b+ cells were gained by single-colour flow cytometry. At the end of the trial a significantly increase of percentage of CD4+, CD5a+, CD8+, wCD21+ cells has been found in pigs that received the subunit vaccine and the percentage of CD4+, CD5a+, CD8+, CD45RA+ and CD45RC+ cells was higher in pigs that received the attenuated vaccine. Twenty-eight days after vaccination the percentage of CD4+, CD45RA+ and CD45RC+ was significantly higher in pigs vaccinated with the C strain than in pigs vaccinated with the subunit vaccine. In contrary, the percentage of the wCD21- cells was higher in pigs that received the subunit vaccine. Statistically higher values of SWC3a+ and lower values of CD11b+ cells was observed in pigs that received the attenuated vaccine than in pigs vaccinated with the subunit vaccine. Taken altogether, our results showed that the subunit vaccine produced a better stimulation of B cells and CD11b+ monocytes/macrophages /granulocytes/NK cells, whereas the attenuated vaccine induced a higher response of Th cells, naive/memory cells and macrophages/neutrophils. Thus, both vaccines were able to influence the porcine immune system, by activating different subsets of the immune effector/accessory cells.

The inflammatory cell infiltrates in porcine cysticercosis: immunohistochemical analysis during various stages of infection

Taenia solium metacestodes cause cysticercosis in both humans and pigs. In the former host species, the central nervous system involvement (neurocysticercosis (NCC)) may range from asymptomatic to life-threatening, but little is known about the corresponding variation in tissue response due to the difficulty in obtaining parasite-infected brain biopsies. The use of pigs as animal models for cysticercosis is ideal because the histological description of the animal's response around the parasites resembles the one recorded in human specimens. In this study the histological features of the immune response in swine were complemented by immunohistochemical analysis to determine the phenotype of the inflammatory cells. The presence of mononuclear cells and eosinophils, and the co-localization of MHC-II with B lymphocytes and monocytes/macrophages within the granulomas surrounding the parasites, were features that closely resembled the descriptions made in prior studies with human specimens. In addition, there were novel findings such as the upregulation of the adhesin CD44 in cells resembling monocytes/macrophages, eosinophils and in astrocytes from the central nervous system. The upregulation of CD44 may be important for the recruitment of inflammatory cells to the site of the lesion. Finally, the presence of null-gamma delta-T cells since stage I of the immune response was similar to the early detection of these cells in mouse models for cysticercosis.

Experimental Schistosomiasis japonica in the pig: immunohistology of the hepatic egg granuloma

Use of the pig as an animal model in schistosomiasis research is increasing, but knowledge of the porcine immune response to schistosome infection is still very limited. We investigated the immunohistology of different maturation stages of the Schistosoma japonicum egg granuloma in pigs. Liver sections from pigs experimentally infected with S.japonicum for 9, 12 or 21 weeks were examined by immunohistochemistry using a three-step streptavidin-biotin-complex/immunoperoxidase method or a two-step alkaline phosphatase-mediated system. All granulomas showed marked expression of major histocompatibility complex (MHC) class II in epithelioid macrophages and were dominated by T lymphocytes, comprising both CD4+ and CD8+ phenotypes, with consistently higher proportions noted for CD8+ cells. B lymphocytes, as identified by expression of CD21, were confined to lymphoid nodular structures primarily associated with mature granulomas. Early and mature granulomas contained numerous immunoglobulin (Ig)G+ plasma cells. Significant differences in immunohistology related to duration of infection were not observed. The results indicate that all stages of the hepatic S.japonicum egg granuloma in the pig manifests MHC class II-dependent CD4+ T cell activity concomitant with infiltration of CD8+ T cells. B cell activity preceding the effector cell stage appears to occur in granuloma-associated lymphoid nodules, whereas antibody, mainly IgG, is produced within the granuloma.

Functional and phenotypic characterization of distinct porcine dendritic cells derived from peripheral blood monocytes

Dendritic cells (DCs) are bone marrow-derived antigen-presenting cells that have an exquisite capacity to interact with T cells and modulate their responses. Little is known about porcine DCs despite the fact that they represent an important target in strategies that are aimed at modulating resistance to infection in pigs and may be of major importance in transplantation biology. We generated immature monocyte-derived porcine dendritic cells (MoDCs) directly from adherent peripheral blood cells treated with porcine granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The cells were observed via electron microscopy and their phenotype was characterized using monoclonal antibodies. The functionality of the porcine MoDCs was demonstrated showing that the cells were capable of different specialized functions relevant to antigen capture and were potent stimulators in a primary allo-mixed leucocyte reaction. Treatment of the MoDCs with porcine cell line-derived necrotic factors resulted in the phenotypic and functional maturation of MoDCs. We confirmed also that monocyte-derived DCs were differentially regulated by cytokines, showing that transforming growth factor-beta1 (TGF-beta1) is able to redirect monocytic precursors into the differentiation pathway of Langerhans' cells presenting typical Birbeck granules. Interestingly, and in contrast to the human and murine model, we showed that the monocyte-derived porcine Langerhans'-type cells (MoLCs) were much more potent activators of allogeneic T cells than MoDCs obtained without TGF-beta1.

Characterization of human killer cell reactivity against porcine target cells: differential modulation by cytokines

The cytotoxic cell response to porcine cells by human lymphocytes, and the modulation of cytolytic cellular activity by human cytokines were investigated. Human peripheral blood mononuclear cells (PBMC) and purified lymphocyte subsets were co-cultured with fresh irradiated porcine stimulator cells and examined for the development of lytic activity and for their proliferative response. Porcine target cells included a new cell line, MS-PBMC-J2 (designated J2; SLA-DR+MHC class I+CD2+CD3 CD8+CDI6+CD45+), aortic and microvascular endothelial cells. Initial results showed that natural killer (NK) cells were fivefold more efficient in killing porcine target cells compared with T cells. IL-12 augmented the killing of porcine target cells by human NK cells beyond that induced by stimulation with cells alone. In contrast, IL-2 and IL-15 often induced substantial human NK cell mediated killing of porcine target cells, including endothelial cells in the case of IL-2 where such targets were examined, even in the absence of stimulator cells. Finally, neither IL-18 nor IL-8 had any effect beyond background on NK cell mediated killing of porcine target cells. These findings show that cytokines that would be produced in a xenograft setting clearly modulate the ability of human cytolytic cells to kill porcine targets. In addition, fresh unstimulated human NK cells lysed J2 and porcine aortic endothelial cells, but not porcine microvascular endothelial cells, suggesting the possibility of rapid attack of xenografts by NK cells, and differential susceptibility of endothelial cells from different vascular structures to this attack.

Antigen-specific proliferation of porcine CD8alphaalpha cells to an extracellular bacterial pathogen

A vaccine inducing protective immunity to a spirochaete-induced colitis of pigs predominantly stimulates expansion of CD8+ cells in vivo and in antigen-stimulated lymphocyte cultures. CD8+ cells, however, are rarely considered necessary for protection against extracellular bacterial pathogens. In the present study, pigs recovering from colitis resulting from experimental infection with Brachyspira (Serpulina) hyodysenteriae had increased percentages of peripheral blood CD4- CD8+ (alphaalpha-expressing) cells compared with non-infected pigs. CD8alphaalpha+ cells proliferated in antigen-stimulated cultures of peripheral blood mononuclear cells from B. hyodysenteriae-vaccinated pigs. Proliferating CD8alphaalpha+ cells consisted of CD4-, CD4+ and gammadelta T-cell receptor-positive cells. CD4- CD8alphabeta+ cells from vaccinated or infected pigs did not proliferate upon in vitro antigen stimulation. Of the CD8alphaalpha cells that had proliferated, flow cytometric analysis indicated that the majority of the CD4+ CD8+ cells were large (i.e. lymphoblasts) whereas the CD4- CD8+ cells were predominantly small. Addition of monoclonal antibodies (mAb) specific for either porcine major histocompatibility complex (MHC) class I or class II antigens diminished B. hyodysenteriae-specific proliferative responses whereas addition of mAb to porcine MHC II, but not porcine MHC I, reduced the CD8alphaalpha response. In vitro depletion of CD4+ cells by flow cytometric cell sorting diminished, but did not completely abrogate, the proliferative response of cells from vaccinated pigs to B. hyodysenteriae antigen stimulation. These results suggest that CD8alphaalpha cells are involved in recovery and possibly protection from a spirochaete-induced colitis of pigs; yet, this response appears to be partially dependent upon CD4+ cells.

Flow cytometric analysis of an immunodeficiency disorder affecting juvenile llamas

The present study was undertaken to characterize the immune system of llamas and alpacas and establish the basis for an immunodeficiency disorder affecting juvenile llamas. Flow cytometric (FC) analysis of the immune system with a panel of monoclonal antibodies (mAbs) revealed the immune system of llamas and alpacas is similar in leukocyte subset composition to that in ruminants. Peripheral blood mononuclear cells in adults are comprised of surface immunoglobulin (sIg(+)) B-cells (31%+/-8 S.D.), alphabeta T-cells (27%+/-12 S.D.), WC1(+) gammadelta T-cells (16%+/-11 S.D.), and 5-16% monocytes. In contrast to cattle, goats, and sheep, however, the frequency of WC1(+) gammadelta T-cells is not high in juveniles but similar to the frequency in adults. Also, sIg(+) B-cells are present in high concentration in juveniles (43%+/-11 S.D. ). Expression of major histocompatibility class II molecules on resting T-cells was low or absent. Comparative analysis of peripheral blood lymphocyte composition in normal juvenile llamas and llamas presenting with the signs of the juvenile llama immunodeficiency syndrome (JLIDS) revealed the concentration of B-cells is extremely low (1-5%) in affected animals. The findings suggest JLIDS is attributable to an autosomal recessive genetic defect in the development of B-cells.

Cellular immune responses of pigs induced by vaccination with either a whole cell sonicate or pepsin-digested Brachyspira (Serpulina) hyodysenteriae bacterin

Brachyspira (Serpulina) hyodysenteriae infection of pigs (swine dysentery) causes a mucohemorrhagic diarrhea resulting in significant economic losses for producers. A commercial vaccine consisting of a proteinase-digested bacterin has shown efficacy in the reduction of disease due to B. hyodysenteriae. Vaccines consisting of whole cell bacterins, however, generally fail to protect pigs from disease. In the present study, cellular immune responses induced by a proteinase-digested bacterin were compared to responses induced by a whole cell sonicate antigen preparation. In addition, usage of either squalene or Freund's incomplete adjuvants in combination with each antigen preparation was also compared. Both antigen preparations induced significant cellular immune responses as measured by in vitro (IFN-gamma production and T cell proliferation) and in vivo methods (DTH responses). No significant differences were detected in proliferative, interferon-gamma (IFN-gamma), or delayed type hypersensitivity (DTH) responses by pigs receiving either adjuvant or antigen preparation. T cells (CD3(+)) but not B cells from vaccinated animals proliferated in response to in vitro stimulation with B. hyodysenteriae antigen. CD8(+) (single positive and CD4/CD8 double positive) and gammadelta(+) T cells were particularly responsive. In addition, high percentages of both CD8 single positive and CD4/CD8 double positive cells were detected in antigen-stimulated cultures. These findings demonstrate the unique sensitivity of porcine CD8(+) T cells to priming for recall response by vaccination with a proteinase-digested B. hyodysenteriae bacterin.

Analysis of cellular immune response in pigs recovered from porcine respiratory and reproductive syndrome infection

The cellular immune response to a European isolate of porcine reproductive and respiratory syndrome (PRRS) virus in animals recovered from the experimental infection has been studied in vitro. Peripheral blood mononuclear cells (PBMC) from these pigs proliferated specifically when they were stimulated with PRRS virus. This response was not detectable until 4 weeks after inoculation and remained for more than 3 months. Addition of blocking monoclonal antibodies to the cultures showed that this proliferation was mainly dependent on CD4(+) cells with the participation of SLA-class II molecules. T-cell cultures established by stimulating responding cells with PRRS virus and maintained in culture for up to 3 weeks showed an increase of CD8(+) CD4(+) and CD4(-) CD8(+) subsets within activated cells, gated according to their light scatter parameters, whereas CD4(+) CD8(-) cells declined along the time in culture. Within the activated cells, those expressing the TcR gammadelta receptor also increased, being most of them also positive for the CD8 marker. By RT-PCR, T-cells responding to the virus showed a Th1 type cytokine production pattern. During the culture period the cytotoxic activity against K-562 cells increased from 15 to 35% of specific lysis. This cellular immune response may play a relevant role in the clearance of PRRS virus and the recovery of the infection.

Active immunity and T-cell populations in pigs intraperitoneally inoculated with baculovirus-expressed transmissible gastroenteritis virus structural proteins

The intraperitoneal inoculation of pigs with baculovirus-expressed transmissible gastroenteritis virus (TGEV) structural proteins (S, N, M) in conjunction with thermolabile Escherichia coli mutant toxin (LT-R192G) in incomplete Freund's adjuvant (IFA) was tested in an attempt to elicit active immunity to TGEV in gut-associated lymphoid tissues (GALT). Four groups of 63 (1-5-week-old) suckling, TGEV-seronegative pigs were used to assess the efficacy of the recombinant protein vaccine (group 3) in comparison with sham (group 1), commercial vaccine (group 2), and virulent TGEV Miller-strain-inoculated pigs (group 4). The TGEV-specific mucosal and systemic immune responses were measured after in vivo and in vitro stimulation with TGEV-antigens. The major T-cell subset distribution was analyzed in vivo and in vitro after stimulation of mononuclear cells with TGEV (from mesenteric lymph nodes of group 3 inoculated with TGEV-recombinant proteins). Induction of active immunity was assessed by challenge of pigs with virulent TGEV at 27 days of age. Baculovirus-expressed TGEV proteins coadministered with LT-R192G in IFA induced mesenteric lymph node immune responses associated with IgA-antibodies to TGEV and partial protection against TGEV-challenge. The high titers of serum IgG- and virus-neutralizing-antibodies to TGEV in group 3 pigs most likely reflected the dose of TGEV S-protein administered. At the day of TGEV-challenge, the in vitro stimulation of mononuclear cells from the mesenteric lymph nodes of group 3 pigs with inactivated TGEV resulted in an increase in double positive (CD4+CD8+), natural killer (CD2+CD4-CD8+dim) and cytotoxic (CD2+CD4-CD8+bright) T-cell phenotypes, accompanied by increased expression of interleukin-2 receptor and a decrease of the null (CD2-CD4-CD8-/SW6+) cell phenotype.

Quantification of B, T and null lymphocyte subpopulations in the blood and lymphoid organs of the pig

Research on the pig's immune system is not only of general biological interest; the pig is also becoming more important as a large animal model in human biomedical research, e.g. as a donor for xeno-transplantation. With the increasing panel of monoclonal antibodies against porcine lymphocyte markers it is possible to gain more insight into the distribution and phenotype of lymphocyte subpopulations in the pig. In this study we investigated B cells (surface IgG: sIgG, sIgM and sIgA) and T cells (CD2, CD4, CD8, 8/1, MAC320) in the peripheral blood (pBL), thymus, spleen, tonsil, mesenteric and inguinal lymph nodes (mLN, iLN), jejunal and ileal Peyer's patches (jejPP, ilPP) in Göttingen minipigs. A flow cytometric technique was employed which enabled three color indirect immunofluorescence. B cell stained for surface IgG and surface IgA were found only in small percentages. Surface IgM positive cells were distributed at higher rates, with up to 24.9% in the iLN. Up to 64.2% of CD4+ and up to 73.1% of CD8+ cells were observed in the thymus. Most of the CD4+ cells were CD4/CD8 double positive cells. These cells were mostly triple positive in combination with CD2. A larger fraction of CD2- were CD8- which are taken to be NK cells. MAC320, a marker for a subtype of gamma/delta T cells, was predominantly found on cells in the pBL. The standardized flow cytometric technique produced comparable data on the distribution of major lymphocyte subpopulations in the blood and different lymphoid organs of the pig. The results provide a basis for future studies using the pig as animal model.

Characterization of porcine T lymphocytes and their immune response against viral antigens

T lymphocytes play a central role in the antigen-specific immune response against various pathogens. To detect and to characterize porcine T lymphocytes, monoclonal antibodies (mAb) against leukocyte differentiation antigens had been raised and classified for their specificity. Analyses of porcine T lymphocytes with specific mAb against CD4 and CD8 differentiation antigens revealed differences in the composition of the porcine T-lymphocyte population compared to other species. In addition to the known subpopulations, CD4+CD8- T helper cells and CD4-CD8+ cytolytic T lymphocytes, extra-thymic CD4+CD8+ T lymphocytes and a substantial proportion of CD2-CD4-CD8- T cell receptor (TcR)-gamma delta+ T cells could be detected in swine. Functional analyses of porcine T-lymphocyte subpopulations revealed the existence of two T-helper cell fractions with the phenotype CD4+CD8- and CD4+CD8+. Both were reactive in primary immune responses in vitro, whereas only cells derived from the CD4+CD8+ T-helper-cell subpopulation were able to respond to recall antigen in a secondary immune response. With regard to T lymphocytes with cytolytic activities, two subsets within the CD4-CD8+ T-cell subpopulation could be defined by the expression of CD6 differentiation antigens: CD6- cells which showed spontaneous cytolytic activity and CD6+ MHC I-restricted cytolytic T lymphocytes including virus-specific cytolytic T lymphocytes. These results enable now a detailed view into the porcine T-cell population and the reactivity of specific T cells involved in the porcine immune response against pathogens. Furthermore this knowledge offers the possibility to investigate specific interactions of porcine T lymphocytes with virus-specific epitopes during vaccination and viral infections.

Molecular Cloning and Characterization of a Novel CD1 Gene from the Pig

Much effort is underway to define the immunological functions of the CD1 multigene family, which encodes a separate lineage of Ag presentation molecules capable of presenting lipid and glycolipid Ags. To identify porcine CD1 homologues, a cosmid library was constructed and screened with a degenerate CD1 α3 domain probe. One porcine CD1 gene (pCD1.1) was isolated and fully characterized. The pCD1.1 gene is organized similarly to MHC class I and other CD1 genes and contains an open reading frame of 1020 bp encoding 339 amino acids. Expression of pCD1.1 mRNA was observed in CD3− thymocytes, B lymphocytes, and tissue macrophages and dendritic cells. The pCD1.1 cDNA was transfected into Chinese hamster ovary cells, and subsequent FACS analysis demonstrated that mAb 76-7-4, previously suggested to be a pig CD1 mAb, recognizes cell surface pCD1.1. Structurally, the pCD1.1 α1 and α2 domains are relatively dissimilar to those of other CD1 molecules, whereas the α3 domain is conserved. Overall, pCD1.1 bears the highest similarity with human CD1a, and the ectodomain sequences characteristically encode a hydrophobic Ag-binding pocket. Distinct from other CD1 molecules, pCD1.1 contains a putative serine phosphorylation motif similar to that found in human, pig, and mouse MHC class Ia molecules and to that found in rodent, but not human, MHC class-I related (MR1) cytoplasmic tail sequences. Thus, pCD1.1 encodes a molecule with a conventional CD1 ectodomain and an MHC class I-like cytoplasmic tail. The unique features of pCD1.1 provoke intriguing questions about the immunologic functions of CD1 and the evolution of Ag presentation gene families.

Ex vivo assessment of immunosuppression in undiluted whole blood from pigs dosed with tacrolimus (FK506)

To assess the duration of immunosuppression in FK506-dosed pigs, an undiluted whole blood assay was established to measure reactivities of T cells in their physiological milieu. PMA and ionomycin were shown to induce IL-2 production in swine blood. The IC50 of FK506 in inhibiting IL-2 production in whole blood and isolated PBMC stimulated with PMA and ionomycin measured 1.2 and 0.04 nM, respectively. These data underscore the influence of red blood cells and plasma proteins on drug potency. IL-2 levels were determined in blood drawn immediately before and 1, 24, 48, and 72 h after iv dosing. For pigs dosed with 0.05 mg/kg, 50% recovery of IL-2 production was observed at 16 h and 100% at 35 h after dosing. For pigs dosed with 0.15 mg/kg, 50% recovery was observed at 38 h and 100% at 72 h. Blood concentrations of FK506 at 50 and 100% recovery of IL-2 production measured 10.8 and 2.2 nM for pigs dosed with 0.05 mg/kg and 6.1 and 1.1 nM for pigs dosed with 0.15 mg/kg, respectively. These concentrations are severalfold higher than predicted from the IC50 of FK506 for inhibiting IL-2 production in the whole blood assay. These data suggest that the true potency of FK506 in blood after dosing is influenced by additional factors, which could include plasma protein binding, the presence of active or interfering metabolites, serum interfering factors, and sequestration of drug in blood cells. Our results demonstrate the utility of an undiluted whole blood assay for assessing the duration of immunosuppression in drug-dosed animals and emphasize the importance of assessing drug potency in the whole blood environment ex vivo.

Comparison of the unique characteristics of the immune system in different species of mammals

The current interpretation of how cytokines regulate immune responses is based largely on studies conducted in humans and rodents. As summarized here, comparative studies have revealed significant differences in the composition of the immune system in other species. The difference noted emphasize that it will not be possible to fully understand the role of cytokines in immune regulation without comparative studies that include analysis of cytokine function in additional species.

Activation of bovine lymphocyte subpopulations by staphylococcal enterotoxin C

Staphylococcus aureus is a major mastitis-causing pathogen in cattle. The chronic nature of bovine staphylococcal mastitis suggests that some products or components of S. aureus may interfere with the development of protective immunity. One class of molecules that could be involved are superantigens (SAgs). Although a significant number of mastitis isolates produce SAgs, the effect of these molecules on the bovine immune system is unresolved. To determine if immunosuppression caused by SAgs could play a role in pathogenesis, we monitored bovine lymphocytes exposed to staphylococcal enterotoxin C1 (SEC1). Activation of bovine lymphocytes by either SEC1 or concanavalin A (ConA) was influenced by the gammadelta/alphabeta T-cell ratio in the culture. Compared to ConA-induced stimulation, cultures stimulated with SEC1 generated small numbers of CD4+ alphabeta T cells expressing high levels of interleukin-2 receptor alpha chain (IL-2R alpha) and major histocompatibility complex class II (MHCII), suggesting that SAg exposure does not lead to full activation of these cells. This state of partial activation was most pronounced in cultures with a high gammadelta/alphabeta ratio. In contrast, significant numbers of CD8+ alphabeta T cells expressed high levels of IL-2R alpha and MHCII, regardless of the gammadelta/alphabeta ratio and the stimulant used. CD8+ blasts in cultures stimulated with SEC1 also expressed another activation marker, ACT3, previously detected predominantly on thymocytes and CD4+ T cells. Although gammadelta CD2- and CD2+ T cells expressed MHCII and IL-2R alpha following stimulation with SEC1, only a few cells increased to blast size, suggesting that they were only partially activated. The results suggest ways in which SAgs might facilitate immunosuppression that promotes the persistence of bacteria in cattle and contributes to chronic intramammary infection.

Summary of the first round analyses of the Second International Swine CD Workshop

The reactivity of 176 monoclonal antibodies (mAb) submitted to the Second International Swine CD Workshop, together with 19 internal standards, was analyzed by flow cytometry on 16 different cell types as a means of establishing the proper cell subset for later detailed clustering analyses. The exact CD subset reactivity of the 19 internal standard mAb had been characterized in the First International Swine CD Workshop. The flow cytometric analyses resulted in 40 data sets which were then subjected to statistical clustering using the Leukocyte Typing Database IV (LTDB4) software. As result of this work, 22 clusters were defined. After review of these results, panels of mAb from the defined first round clusters were assigned to cell subsets. The respective mAb in those first round clusters were then distributed to subset group researchers for further examination during the second round of the workshop.

Analysis of monoclonal antibodies that recognize gamma delta T/null cells

Thirty two monoclonal antibodies (mAbs) from the first round of analysis in the Second International Swine CD Workshop were placed together with additional mAb derived from the first workshop in the null cell panel for further evaluation. Preparations of peripheral blood leukocytes, concanavalin A stimulated peripheral blood mononuclear cells, and spleen cells were used in flow cytometric analyses. Nineteen mAbs identified molecules that were not expressed on null cells, not lineage specific, or recognized activation molecules. Sixteen mAbs including control mAbs were identified that were specific for null cells. One of the latter mAbs, 041 (PGBL22A), that recognizes a determinant on a constant region of porcine gamma delta TcR established the majority of null cells are gamma delta T cells. Use of this mAb in further comparisons demonstrated the gamma delta T cell population is comprised of two major subpopulations, one negative and one positive for CD2. Two color analyses demonstrated that 11 of the mAbs formed a broad cluster that included control mAbs 188 (MAC320) that defined the CD2 negative SWC6 cluster in the first workshop and mAb 122 (CC101) that might recognize an orthologue of bovine WC1 and nine mAbs that recognize determinants on one or more molecules with overlapping patterns of expression on subsets of CD2- gamma delta T cells. Two groups of mAbs formed the previously identified subset clusters SWC4 and SWC5. Two new mAbs formed a third subcluster. Three mAbs did not form clusters. Three mAbs predicted to recognize TcR in the first workshop (020 [PT14A], 021 [PT79A], and 022 [MUC127A]) and mAb PGBL22A were shown to immunoprecipitate a 37, 40 kDa heterodimer.

Overview of the Second International Workshop to define swine cluster of differentiation (CD) antigens

The aim of the Second International Swine Cluster of Differentiation (CD) Workshop, supported by the Veterinary Immunology Committee (VIC) of the International Union of Immunological Societies (IUIS), was to standardize the assignment of monoclonal antibodies (mAb) reactive with porcine leukocyte differentiation antigens and to define new antibody clusters. At the summary meeting of the workshop in July, 1995, revisions in the existing nomenclature for Swine CD were approved, so that the rules are now in accord with those for human and ruminant CD. Swine CD numbers will now be given to clusters of mAb to swine orthologues of human CD molecules when homology is proven by (1) suitable tissue distribution and lymphoid cell subset expression, (2) appropriate molecular mass of the antigen recognized by the mAbs, and (3) reactivity of mAbs with the cloned swine gene products, or cross-reactivity of the mAb on the human gene products. In some cases, this reactivity would not be fully proven, mainly due to the lack of cloned gene products; for these CD antigens, the respective clusters will be assigned by the prefix 'w' which will lead to 'wCD' antigens. As a result of the Second International Swine CD Workshop the assignment of 16 mAb to existing CD groups (CD2a, CD4a, CD5a, wCD6, wCD8, CD14, CD18a, wCD21, wCD25) was confirmed, and 2 mAb to existing swine workshop clusters (SWC). More importantly, for the work on the porcine immune system, was the definition of 5 new swine CD antigens, namely CD3 (recognized by 6 new mAb and 3 epitopes), CD16 (1 new mAb), wCD29 (2 mAb), CD45RA (3 mAb) and CD45RC (1 new mAb). Finally, the demarcation of two new SWC molecules in swine, SWC8 (2 mAb) and SWC9 (2 mAb) was confirmed.

Early changes in the phenotypic composition of lymphocytes in the bronchoalveolar lavage of pigs after aerogenic immunization with Pasteurella multocida aerosols

The phenotypic composition of bronchoalveolar lymphocytes (BALL) of healthy untreated pigs and of pigs immunized via aerosol with a live Pasteurella multocida mutant was measured cytofluorometrically in comparison to blood lymphocytes (PBL). Cells were analyzed using monoclonal antibodies against porcine IgM, IgA, IgG and SWC3 in single-colour fluorescence and the following antibody combinations for two-colour fluorescence: CD2/SWC1, SWC1/CD25 and CD4/CD8. In nonimmunized pigs, differences between lymphocyte subsets derived from blood and lung were obvious. The numbers of CD2-SWC1+ T-cells, CD25+ activated lymphocytes and IgG+ cells were significantly higher in the bronchoalveolar compartment. Aerosol immunization with P. multocida caused only insignificant changes in the phenotypic composition of PBL whereas the composition of lung-derived lymphocytes changed markedly. The percentage of CD2-SWC1+ lymphocytes and of CD25+ cells coexpressing the SWC1 antigen in BALL increased up to 10 days after aerosol administration, whereas the percentage of all Ig+ cells decreased. These data reflect an early cellular reaction to an aerogenic immunization with a P. multocida aerosol, characterized by an increase in CD2+ T-cells and a T-cell activation.

Differential expression of CD8 epitopes amongst porcine CD8-positive functional lymphocyte subsets

The swine is a useful model for immunobiological studies as it has a highly heterogeneous lymphocyte pool, containing several subsets not easily accessible in humans and rodents. In particular, the CD8-positive (CD8+) cells contain a variety of lymphocyte subsets, such as alpha beta-T cells, gamma delta-T cells, CD4 CD8 double-positive (DP) cells and natural killer (NK) cells. In order to define these subsets further, we have selected four monoclonal antibodies (mAb) with differential reactivity on CD8+ cells. Thus, mAb CD8.1 (PPT20) bound to CD8hi and CD8lo subpopulations in a similar way to the conventional anti-CD8. The mAb CD8.2 (PPT21), though binding to all of the CD8+ cells, reacted preferably with CD8hi. Two other mAb, CD8.3 (PPT22) and CD8.4 (PPT23), were specific for CD8hi alpha beta-T-cell subpopulation. These results, complemented by immunoprecipitation, co-modulation and enzyme-linked immunosorbent assay experiments, suggest that CD8.1 and CD8.2 react putatively with the CD8 alpha-chain and CD8.3 and CD8.4 with the CD8 beta-chain. Tissue distribution studies revealed that CD8+ thymocytes and peripheral CD8hi alpha beta-T cells expressed both putative CD8 alpha- and beta-chains while peripheral CD4+ CD8+ alpha beta-T cells, CD8lo gamma delta-T cells and NK cells expressed only putative CD8 alpha-chain. Functional studies indicated that the CD8hi alpha beta-T and CD8lo gamma delta-T cells were effector cells in the CD3-redirected cytotoxicity.

Constitutive and inflammatory lymphocyte trafficking

Here we provide a brief overview of lymphocyte trafficking with particular emphasis on the current state of knowledge in the pig. We discuss how the emphasis of research has changed since early studies in the 1960s and outline the current hypothesis of a multistep cascade for lymphocyte migration through specialized endothelia. During the last several years our research has focused mainly on lymphocyte migration in vivo. The inbred Babraham herd of MHC homozygous Large White pigs has allowed study of entry of either labelled (FITC or 51Cr) or unlabelled CD45 allotype-different donor lymphocytes and their subsets into various lymphoid, non-lymphoid and inflammatory tissues. The findings are considered under three different categories. Firstly, constitutive lymphocyte entry via 'high endothelial venules' (HEV-mediated), secondly, non-HEV-mediated lymphocyte homing and thirdly, lymphocyte entry into several models of inflammation with particular reference to the role of E-selectin. These findings demonstrate and underline the complexity and heterogeneity of lymphocyte homing, both at the whole population and subset level and yet, whilst a major step forward, the current hypotheses are perhaps too simple to explain much of this heterogeneity.

Phenotypic classification of porcine lymphocyte subpopulations in blood and lymphoid tissues

The pig is a useful model for the heterogeneity of the mammalian immune system and has also recently received attention as a possible source of organs for human transplantation. Here we report a detailed analysis of porcine lymphocyte phenotypes. Peripheral blood alpha beta T cells consisted of four subsets (CD4+8-, CD4+8lo, CD4-8lo and CD4-8hi) and gamma delta T cells of three (CD2-4-8-, CD2+4-8lo and CD2+4-8-). There were in addition, a large proportion of non-T-non-B lymphocytes with CD2+3-4-8lo surface immunoglobulin-negative phenotype containing natural killer (NK) activity. A striking observation was the relatively low frequency of alpha beta T cells in the blood of young pigs. Similar phenotypes were also identified in the cells from peripheral lymphoid tissues, though the proportions of the gamma delta T cells and the non-T-non-B lymphocytes in the lymph nodes and tonsil were much lower and the majority of the gamma delta T cells in the lymphoid tissues bore CD2 and or CD8. In thymus, the small thymocytes were predominantly CD3-4+8+ while the mature large thymocytes displayed phenotypes similar to those of peripheral T cells. Thus this work has directly defined porcine alpha beta and gamma delta T cells demonstrated the T-cell nature of the unique CD4+8+ subset of peripheral lymphocytes, revealed the high heterogeneity of the CD8+ cells, and established the phenotype of NK cells. The functional properties of these defined porcine lymphocyte subsets can now be experimentally determined in health and disease.

Preparation of monoclonal anti-porcine CD3 antibodies and preliminary characterization of porcine T lymphocytes

The CD3-T-cell receptor complex is the clonotypic surface structure by which T lymphocytes recognize foreign antigens and are subsequently activated. Because of the low immunogenicity of the CD3 molecules, anti-CD3 monoclonal antibodies (mAb) are difficult to prepare and have not been available in several species. Following isolation of porcine CD3, 14 anti-porcine CD3 mAb were prepared, which define six groups of CD3-epsilon epitopes, coprecipitate two types of TCR and reveal considerable heterogeneity of CD3 expression amongst lymphocyte subpopulations. Thus, both CD3 positive and negative subpopulations of CD2 or CD8 positive cells were found in the blood. The density of CD3 on CD2+ or CD8+ cells was relatively low and heterogeneous, whereas the CD2-, CD8- or MAC320+ T cells expressed CD3 at a higher and more homogeneous level. Finally, in the thymus, staining with anti-CD3 resolved large thymocytes into two subsets: one expressing a high level of CD3 and the other being negative. In contrast, small thymocytes expressed CD3 at a low and more homogeneous level. Immunohistological studies confirmed the presence of clearly detectable CD3 in thymus medulla and the T-cell regions of peripheral lymphoid tissues. Most of the mAb were mitogenic, when presented to peripheral blood mononuclear cells in immobilized form. The anti-CD3 mAb also induced redirected cytotoxicity which was shown to be Fc receptor dependent.

Differentiation between MHC-restricted and non-MHC-restricted porcine cytolytic T lymphocytes

The immune system of swine is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of resting extrathymic T lymphocytes. Beyond phenotypic differences to other species, porcine T lymphocytes, particularly when derived from infected animals, are known to show high non-specific cytolytic in vitro activity. Here we describe the putative porcine CD6 antigen (workshop CD6; wCD6) which enables a phenotypic separation of T lymphocytes responsible for major histocompatibility complex (MHC)-restricted and non-MHC-restricted cytotoxicity. The putative porcine CD6 analogue, wCD6, a protein with a molecular mass of 110,000, shows high specificity for T lymphocytes and is neither expressed on B lymphocytes nor on cells of the myeloid lineage. In the extrathymic T-lymphocyte compartment wCD6 characterizes two T-lymphocyte fractions: wCD6+ T lymphocytes including both CD4+ T-helper cell subpopulations (CD4+CD8- and CD4+CD8+) and within the CD4-CD8+ fraction cells with high CD8 antigen density. In contrast the CD4-CD8- gamma/delta T-cell receptor (TCR) subset and CD4-CD8+ cells with low CD8 antigen density are included in the wCD6- T-lymphocyte fraction. Functional studies with separated wCD6 fractions revealed that the wCD6- cells can be characterized by spontaneous and non-MHC restricted cytolytic activity, whereas the wCD6+ T lymphocytes are responsible for MHC-restricted T-cell functions. Thus, the porcine wCD6 is an important antigen to discriminate between MHC-restricted and non-MHC-restricted cytotoxicity.

Transfer of T-cell-mediated, antigen-specific delayed type hypersensitivity reactions to naive recipient inbred pigs

Using inbred major histocompatibility complex-homozygous SLAb/b pigs, delayed-type hypersensitivity (DTH) reactions against either intradermal tuberculin (PPD) or topical 2,4-dinitro-1-fluorobenzene (DNFB) were transferred specifically by the intravenous injection of approximately 6 x 10(8) blood lymphocytes kg-1 bodyweight from donors sensitised, respectively, either with BCG or with DNFB into three-week-old piglets from an inbred litter. This antigen-specific, passively acquired sensitivity was revealed by three measures of DTH reactivity: first, macroscopic inflammation, which developed at the rate and intensity expected for actively acquired sensitivity to DNFB or PPD in older pigs; secondly, similarly enhanced local specific uptake of intravenously injected 51Cr-labelled normal lymphocytes (more than 35-fold for each); and, thirdly, histological evidence of markedly increased local infiltration of CD45+ lymphocytes and polymorphs, endothelial activation and the expression of adhesion molecules.