Phenotypic characterization of porcine IFN-gamma-producing lymphocytes by flow cytometry

Characterization of T-cell subsets in response to foot-and-mouth disease bivalent inactivated vaccine in Chinese Holstein cows

IMPORTANCE

Vaccination plays a crucial role in the prevention and control of FMD; however, outbreaks persist occurring worldwide. Assessing the immune response to FMD vaccines is essential for effective prevention of FMD. In this study, a seven-color flow cytometry protocol was developed to systematically evaluate the T-cell response of Chinese Holstein cows vaccinated with FMD bivalent inactivated vaccine. Our findings showed that while most T-cell subsets (%) decreased post-vaccination, a significant increase was observed in CD4+CD8+ DP T cells, which was consistent with the levels of specific foot-and-mouth disease virus (FMDV) antibodies. These findings suggested that CD4+CD8+ DP T cells could serve as a potential biomarker for the evaluation of cellular and humoral responses to FMDV vaccination. Additionally, we should be aware of the potential decline in cellular immunity among cattle during FMD vaccination, as this may increase the risk of other pathogen-related issues.

CD9 expression in porcine blood CD4+ T cells delineates two subsets with phenotypic characteristics of central and effector memory cells

In this report, we describe the characterization of a new monoclonal antibody, named 4H5CR4, against porcine CD9. Its use in combination with antibodies to CD4, CD8α, and 2E3 allows to distinguish at least five main CD4⁺ T cell subsets. Analysis on these subsets of CD45RA, CD27, CD29, CD95, CCR7, and SLA-DR markers depicts a progressive model of CD4⁺ T cell development. CD4⁺ 2E3⁺ CD8α^- CD9^- cells are the least differentiated population of naïve cells, whereas the CD4⁺ 2E3^- CD8α⁺CD9⁺ and CD4⁺ 2E3^- CD8α⁺ CD9^- cells display phenotypic features of central and effector memory T helper cells, respectively. The latter subsets were able to produce IFN-γ after polyclonal activation with PMA/Ionomycin; however, in vitro virus-specific IFN-γ production of PBMCs collected at 38-44 days after pseudorabies virus vaccination was dominated by cells with a CD9⁺ phenotype. Therefore, CD9 appears to be a useful marker to investigate CD4⁺ T cell heterogeneity in swine.

Japanese Encephalitis Virus Persistence in Porcine Tonsils Is Associated With a Weak Induction of the Innate Immune Response, an Absence of IFNγ mRNA Expression, and a Decreased Frequency of CD4+CD8+ Double-Positive T Cells

In humans, Japanese encephalitis virus (JEV) causes a devastating neurotropic disease with high mortality, whereas in pigs, the virus only causes mild symptoms. Besides tropism to the central nervous system, JEV seems to harbor a particular tropism for the tonsils in pigs. This secondary lymphoid organ appears to act as a reservoir for the virus, and we show that it is found up to 21 days post infection at high viral titers. The immune response in the tonsils was studied over time upon intradermal inoculation of pigs. Entry of the virus in the tonsils was accompanied by a significant increase in anti-viral OAS1 and IFNβ mRNA expression. This limited antiviral response was, however, not sufficient to stop JEV replication, and importantly, no IFNγ or innate inflammatory cytokine mRNA expression could be observed. Strikingly, the persistence of JEV in tonsils was also associated with a significant decreased frequency of CD4⁺CD8⁺ double-positive T lymphocytes. Furthermore, it is important to note that JEV persistence in tonsils occurred despite a strong induction of the adaptive immune response. JEV-specific antibodies were found after 6 days post infection in serum, and cell-mediated immune responses upon NS3 restimulation of PBMCs from experimentally infected pigs showed that CD4⁺CD8⁺ double-positive T cells were found to display the most prominent proliferation and IFNγ production among lymphocyte subtypes. Taken together, these results suggest that an inadequate induction of the innate immune response and the absence of an IFNγ antiviral response contribute to the persistence of JEV in the tonsils and is associated with a decrease in the frequency of CD4⁺CD8⁺ double-positive T cells.

Local and Systemic T Cell Immunity in Fighting Pig Viral and Bacterial Infections

T cells are an essential component of the adaptive immune system. Over the last 15 years, a constantly growing toolbox with which to study T cell biology in pigs has allowed detailed investigations on these cells in various viral and bacterial infections. This review provides an overview on porcine CD4, CD8, and γδ T cells and the current knowledge on the differentiation of these cells following antigen encounter. Where available, the responses of these cells to viral infections like porcine reproductive and respiratory syndrome virus, classical swine fever virus, swine influenza A virus, and African swine fever virus are outlined. In addition, knowledge on the porcine T cell response to bacterial infections like Actinobacillus pleuropneumoniae and Salmonella Typhimurium is reviewed. For CD4 T cells, the response to the outlined infections is reflected toward the Th1/Th2/Th17/Tfh/Treg paradigm for functional differentiation. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Swine T-Cells and Specific Antibodies Evoked by Peptide Dendrimers Displaying Different FMDV T-Cell Epitopes

Dendrimeric peptide constructs based on a lysine core that comprises both B- and T-cell epitopes of foot-and-mouth disease virus (FMDV) have proven a successful strategy for the development of FMD vaccines. Specifically, B₂T dendrimers displaying two copies of the major type O FMDV antigenic B-cell epitope located on the virus capsid [VP1 (140–158)], covalently linked to a heterotypic T-cell epitope from either non-structural protein 3A [3A (21–35)] or 3D [3D (56–70)], named B₂T-3A and B₂T-3D, respectively, elicit high levels of neutralizing antibodies (nAbs) and IFN-γ-producing cells in pigs. To assess whether the inclusion and orientation of T-3A and T-3D T-cell epitopes in a single molecule could modulate immunogenicity, dendrimers with T epitopes juxtaposed in both possible orientations, i.e., constructs B₂TT-3A3D and B₂TT-3D3A, were made and tested in pigs. Both dendrimers elicited high nAbs titers that broadly neutralized type O FMDVs, although B₂TT-3D3A did not respond to boosting, and induced lower IgGs titers, in particular IgG2, than B₂TT-3A3D. Pigs immunized with B_2, a control dendrimer displaying two B-cell epitope copies and no T-cell epitope, gave no nABs, confirming T-3A and T-3D as T helper epitopes. The T-3D peptide was found to be an immunodominant, as it produced more IFN-γ expressing cells than T-3A in the in vitro recall assay. Besides, in pigs immunized with the different dendrimeric peptides, CD4⁺ T-cells were the major subset contributing to IFN-γ expression upon in vitro recall, and depletion of CD4⁺ cells from PBMCs abolished the production of this cytokine. Most CD4⁺IFN-γ⁺ cells showed a memory (CD4⁺2E3⁻) and a multifunctional phenotype, as they expressed both IFN-γ and TNF-α, suggesting that the peptides induced a potent Th1 pro-inflammatory response. Furthermore, not only the presence, but also the orientation of T-cell epitopes influenced the T-cell response, as B₂TT-3D3A and B₂ groups had fewer cells expressing both cytokines. These results help understand how B₂T-type dendrimers triggers T-cell populations, highlighting their potential as next-generation FMD vaccines.

Maternal Autogenous Inactivated Virus Vaccination Boosts Immunity to PRRSV in Piglets

Maternal-derived immunity is a critical component for the survival and success of offspring in pigs to protect from circulating pathogens such as Type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-2). The purpose of this study is to investigate the transfer of anti-PRRSV immunity to piglets from gilts that received modified-live virus (MLV) alone (treatment (TRT) 0), or in combination with one of two autogenous inactivated vaccines (AIVs, TRT 1+2). Piglets from these gilts were challenged with the autogenous PRRSV-2 strain at two weeks of age and their adaptive immune response (IR) was evaluated until 4 weeks post inoculation (wpi). The systemic humoral and cellular IR was analyzed in the pre-farrow gilts, and in piglets, pre-inoculation, and at 2 and 4 wpi. Both AIVs partially protected the piglets with reduced lung pathology and increased weight gain; TRT 1 also lowered piglet viremia, best explained by the AIV-induced production of neutralizing antibodies in gilts and their transfer to the piglets. In piglets, pre-inoculation, the main systemic IFN-γ producers were CD21α⁺ B cells. From 0 to 4 wpi, the role of these B cells declined and CD4 T cells became the primary systemic IFN-γ producers. In the lungs, CD8 T cells were the primary and CD4 T cells were the secondary IFN-γ producers, including a novel subset of porcine CD8α⁻CCR7⁻ CD4 T cells, potentially terminally differentiated CD4 T_EMRA cells. In summary, this study demonstrates that maternal AIV vaccination can improve protection of pre-weaning piglets against PRRSV-2; it shows the importance of transferring neutralizing antibodies to piglets, and it introduces two novel immune cell subsets in pigs—IFN-γ producing CD21α⁺ B cells and CD8α⁻CCR7⁻ CD4 T cells.

Phenotypic Characterization of Porcine IFNγ-Producing Lymphocytes in Porcine Reproductive and Respiratory Syndrome Virus Vaccinated and Challenged Pigs

Porcine reproductive and respiratory syndrome (PRRS) continues to be one of the most important swine diseases worldwide. Interferon-γ (IFNγ)-mediated type I cell-mediated immune response plays an important role in protection from, and clearance of, PRRS virus (PRRSV). Several lymphocyte subsets including T-helper, CTLs, Th/memory cells, and γδ T lymphocytes were previously reported to produce IFNγ during PRRSV infection. However, the proportion and phenotypic characterization of these IFNγ-secreting lymphocytes have not been explored. In this study, IFNγ producted by different lymphocyte subsets was assessed by multi-color flow cytometry after vaccination with PRRSV modified live vaccine (PRRSV-MLV) and challenge with homogeneous or heterogeneous PRRSV. The results showed that T-helper cells were the major IFNγ-secreting cell population after PRRSV-MLV vaccination and PRRSV challenge. Additionally, the proportion of IFNγ producing Th/memory cells and γδ T cells increased after PRRSV challenge. This difference was accounted for an enhanced ability to produce IFNγ in Th/memory cells and an enlarged quantity of γδ T cells. The results presented here could contribute to our understanding of the roles of IFNγ in protective immunity against PRRSV infection and may be useful for assessment of cell-mediated immunity in vaccine tests.

Peripheral canine CD4(+)CD8(+) double-positive T cells - unique amongst others

T lymphocytes co-expressing CD4 and CD8 ("double-positive T cells") are commonly associated with a thymic developmental stage of T cells. Their first description in humans and pigs as extrathymic T cells with a memory phenotype almost 30 years ago came as a surprise. Meanwhile peripheral double-positive T cells have been described in a growing number of different species. In this review we highlight novel data from our very recent studies on canine peripheral double-positive T cells which point to unique features of double-positive T cells in the dog. In contrast to porcine CD4(+)CD8(+) T cells forming a homogenous cellular population based on their expression of CD4 and CD8α, canine CD4(+)CD8(+) T cells can be divided into three different cellular subsets with distinct expression levels of CD4 and CD8α. Double-positive T cells expressing CD8β are present in humans and dogs but absent in swine. Moreover, canine CD4(+)CD8(+) T cells can not only develop from CD4(+) single-positive T cells but also from CD8(+) single-positive T cells. Together, this places canine CD4(+)CD8(+) T cells closer to their human than porcine counterparts since human double-positive T cells also appear to be heterogeneous in their CD4 and CD8α expression and have both CD4(+) and CD8(+) T cells as progenitor cells. However, CD4(+) single-positive T cells are the more potent progenitors for canine double-positive T cells, whereas CD8(+) single-positive T cells are more potent progenitors for human double-positive T cells. Canine double-positive T cells have an activated phenotype and may have as yet unrecognized roles in vivo in immunity to infection or in inflammatory diseases such as chronic infection, autoimmunity, allergy, or cancer.

Adjuvant effects of therapeutic glycolipids administered to a cohort of NKT cell-diverse pigs

CD1d-restricted natural killer T (NKT) cells are a unique lymphocyte population that makes important contributions to host defense against numerous microbial pathogens. The powerful immunomodulatory effects of these cells can be exploited in mice by cognate antigens for multiple therapeutic purposes, including for protection from infectious diseases and as adjuvants to improve vaccines against microbial organisms. These applications have potential to treat and prevent infectious diseases in livestock species that express NKT cells, including pigs. In this study, immune tissues from commercial swine of mixed genetic background were compared for NKT cell frequency, cytokine secretion and subset ratios. Pigs were also injected with the model antigen hen-egg lysozyme (HEL) in conjunction with one of three glycosphingolipids, alpha-galactosylceramide (αGC), OCH and C-glycoside that selectively activate NKT cells, to assess the adjuvant potential of each. There was significant variation between individual pigs for all NKT cell parameters measured. The NKT cell agonists elicited HEL-specific immune responses of different quality, but only αGC increased the systemic concentration of NKT cells. Peripheral blood NKT cell frequency measured prior to treatment was a poor predictor of how individual animals responded to NKT cell therapy. However, our results show that although NKT cells vary considerably between pigs, there exists considerable potential to harness these cells to protect swine from infectious diseases.

Primate models in organ transplantation

Large animal models have long served as the proving grounds for advances in transplantation, bridging the gap between inbred mouse experimentation and human clinical trials. Although a variety of species have been and continue to be used, the emergence of highly targeted biologic- and antibody-based therapies has required models to have a high degree of homology with humans. Thus, the nonhuman primate has become the model of choice in many settings. This article will provide an overview of nonhuman primate models of transplantation. Issues of primate genetics and care will be introduced, and a brief overview of technical aspects for various transplant models will be discussed. Finally, several prominent immunosuppressive and tolerance strategies used in primates will be reviewed.

Analysis of chemokine receptor CCR7 expression on porcine blood T lymphocytes using a CCL19-Fc fusion protein

The chemokine receptor CCR7 has been a useful marker for the characterization of human and mouse T cell subsets. We have produced the porcine CCR7 ligand CCL19 fused to the human IgG1 Fc fragment, and used it to analyse CCR7 expression in swine. CCL19-Fc bound to and induced the migration of cells expressing porcine CCR7 but not of untransfected cells, corroborating its specificity. On blood lymphocytes, CCL19-Fc labelled the majority of CD4(+) T cells expressing the 2E3 marker, associated with a naïve phenotype, whereas the 2E3(-) cells were mostly negative. Among CD8(+) T cells CCL19-Fc labelled two subsets: one, CD8β(hi) CD11a(lo) CD45RA(+), perforin(-/lo) , which produced low amounts of IFN-γ after stimulation, which might correspond to naïve cells; and a second small population of CD8β(lo) cells which expressed high levels of CD11a, and were mostly CD45RA(-), a phenotype which resembles that of human central memory T cells.

Comparative effects of vaccination against porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) in a PCV2-PRRSV challenge model

The objective of the present study was to determine the effects of porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) vaccinations in an experimental PCV2-PRRSV challenge model, based on virological (viremia), immunological (neutralizing antibodies [NAs], gamma interferon-secreting cells [IFN-γ-SCs], and CD4(+) CD8(+) double-positive cells), and pathological (lesions and antigens in lymph nodes and lungs) evaluations. A total of 72 pigs were randomly divided into 9 groups (8 pigs per group): 5 vaccinated and challenged groups, 3 nonvaccinated and challenged groups, and a negative-control group. Vaccination against PCV2 induced immunological responses (NAs and PCV2-specific IFN-γ-SCs) and reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PCV2 did not affect the PRRSV immunological responses (NAs and PRRSV-specific IFN-γ-SCs), PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. Vaccination against PRRSV did not induce immunological responses (PRRSV-specific IFN-γ-SCs) or reduce PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. In addition, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. In summary, vaccination against PCV2 reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. Therefore, the PCV2 vaccine decreased the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs. In contrast, the PRRSV vaccine alone did not decrease the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs.

Interleukin-10 antisense oligodeoxynucleotide suppresses IL-10 expression and effects on proinflammatory cytokine responses to porcine reproductive and respiratory syndrome virus

Upregulation of interleukin-10 (IL-10) expression has been suggested to be the mechanism by which the porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the innate and adaptive immune response in infected pigs. In this study we evaluated the potential of phosphorothioate-modified IL-10 antisense oligodeoxynucleotide specific to the translation initiation region of porcine IL-10 mRNA (IL-10AS) in enhancing proinflammatory cytokine responses to PRRSV. Naïve peripheral blood mononuclear cells from eight PRRSV-seronegative pigs were transfected with IL-10AS in vitro prior to PRRSV inoculation and phorbol 12-myristate 13-acetate plus ionomycin or concanavalin A stimulation. The effects of IL-10AS on mRNA expression of IL-10, interferon-gamma (IFN-gamma), IFN-alpha, tumor necrosis factor-alpha (TNF-alpha), IL-2, and IL-4 were tested by real-time PCR. The percentages of IFN-gamma-producing T-cell subsets were determined by flow cytometry. Compared to the controls, the levels of IL-10 and IL-2 mRNA were significantly reduced, while those of IFN-gamma mRNA were increased, and TNF-alpha, IFN-alpha, and IL-4 mRNA were unchanged. An increase in the percentage of the IFN-gamma+ population was also observed in lymphocytes and CD8beta+ T cells. Our results suggest that IL-10AS has the potential to enhance proinflammatory cytokine responses to PRRSV infection.

A new model of induced experimental systemic lupus erythematosus (SLE) in pigs and its amelioration by treatment with a tolerogenic peptide

INTRODUCTION

Systemic lupus erythematosus (SLE) is characterized by a variety of autoantibodies and systemic clinical manifestations. A tolerogenic peptide, hCDR1, ameliorated lupus manifestations in mice models. The objectives of this study were to induce experimental SLE in pigs and to determine the ability of hCDR1 to immunomodulate the disease manifestations.

RESULTS AND DISCUSSION

We report here the successful induction, by a monoclonal anti-DNA antibody, of an SLE-like disease in pigs, manifested by autoantibody production and glomerular immune complex deposits. Treatment of pigs with hCDR1 ameliorated the lupus-related manifestations. Furthermore, the treatment downregulated the gene expression of the pathogenic cytokines, interleukin (IL)-1beta, tumor necrosis factor alpha, interferon gamma, and IL-10, and upregulated the expression of the immunosuppressive cytokine transforming growth factor beta, the antiapoptotic molecule Bcl-xL, and the suppressive master gene, Foxp3, hence restoring the expression of the latter to normal levels. Thus, hCDR1 is capable of ameliorating lupus in large animals and is a potential candidate for the treatment of SLE patients.

Age-dependent changes of proinflammatory cytokine production by porcine peripheral blood phagocytes

The aim of the present study was to determine postnatal ontogeny of proinflammatory cytokines IL-1beta, IL-8 and TNF-alpha production by in vitro stimulated porcine blood leukocytes. Four age categories of pigs were chosen. Cytokine production was determined using intracellular flow cytometry. It was found that IL-8 and TNF-alpha production by blood monocytes significantly increased during the postnatal period while production of IL-1beta remained unchanged. In blood neutrophils, the IL-8 production increased only during the postnatal period, while the levels of TNF-alpha and IL-1beta were undetectable during the whole postnatal period. Generally, the most intensive changes in cytokine production occurred before weaning. The production of low levels of cytokines by monocytes and neutrophils from young pigs was not caused by a delayed cytokine response because the cytokine production after 8-h stimulation was lower than that after 4-h stimulation in all age categories. The ontogenetical changes showed the same trends when two different stimulators (LPS, heat-inactivated E. coli) were used, suggesting that the ontogenetical changes are not caused by a simple defect in one signalling pathway, but it is probably a more complex process. No differences in cytokine production between the whole blood and the isolated cells supplemented with newborn or adult serum were found. Thus the ability of newborn monocytes and neutrophils to produce proinflammatory cytokines was not decreased due to the influence of composition of the microenvironment, where the cells were present. In conclusion, the ability of porcine blood leukocytes to produce cytokines develops during postnatal life.

Enhanced mucosal immunoglobulin A response and solid protection against foot-and-mouth disease virus challenge induced by a novel dendrimeric peptide

The successful use of a dendrimeric peptide to protect pigs against challenge with foot-and-mouth disease virus (FMDV), which causes the most devastating animal disease worldwide, is described. Animals were immunized intramuscularly with a peptide containing one copy of a FMDV T-cell epitope and branching out into four copies of a B-cell epitope. The four immunized pigs did not develop significant clinical signs upon FMDV challenge, neither systemic nor mucosal FMDV replication, nor was its transmission to contact control pigs observed. The dendrimeric construction specifically induced high titers of FMDV-neutralizing antibodies and activated FMDV-specific T cells. Interestingly, a potent anti-FMDV immunoglobulin A response (local and systemic) was observed, despite the parenteral administration of the peptide. On the other hand, peptide-immunized animals showed no antibodies specific of FMDV infection, which qualifies the peptide as a potential marker vaccine. Overall, the dendrimeric peptide used elicited an immune response comparable to that found for control FMDV-infected pigs that correlated with a solid protection against FMDV challenge. Dendrimeric designs of this type may hold substantial promise for peptide subunit vaccine development.

Intracellular cytokine detection by flow cytometry in pigs: Fixation, permeabilization and cell surface staining

Intracellular flow cytometry is a method of cytokine detection that allows simultaneous detection of intracellular cytokines and cell surface markers. This important method is not extensively used in pigs, in particular due to the inaccessibility of proper methodological protocols modifying comprehensive human protocols. The aim of this study was to find the best procedure for fixation and permeabilization of porcine blood leukocytes and simultaneous cell surface staining. Permeabilization with commercial kits gave better results in most of the chosen parameters compared with combinations of different concentrations of paraformaldehyde and saponin. Among the commercial kits tested, the best results were obtained with the IntraStain kit. Cell surface markers were detected on cells stimulated for cytokine production by antibodies anti-CD14 (clone MIL-2), anti-SWC3, anti-CD4 and anti-CD8 except anti-CD14 (clone Tük4). While anti-CD8 (clone MIL-12) must be used for staining of unfixed cells, the other antibodies recognize fixed and/or permeabilized cells. Moreover, anti-SWC3 and anti-CD14 (clone MIL-2) antibodies can stain cells during the permeabilization step. These modifications of the cell surface staining protocol allow the researcher to speed up the procedure of intracellular cytokine staining or to combine cell surface staining and intracellular cytokine staining. The present study can serve as a particular protocol of intracellular cytokine detection and as a suggestion for optimization of the fixation, permeabilization and cell surface staining procedure in any laboratory.

Cell-mediated immune responses differentiate infections with Brucella suis from Yersinia enterocolitica serotype O:9 in pigs

Due to almost identical lipopolysaccharide (LPS) O-antigens, infections with Yersinia enterocolitica serotype O:9 (YeO:9) cause false positive serological reactions (FPSR) in tests for Brucella and thus cause problems in National Brucella surveillance programs. As LPS are strong inducers of antibody responses it was hypothesized that cell-mediated immune responses to non-LPS antigens of the two bacteria can be used to separate immune responses to these two biologically very different infections. Following subclinical experimental infections with Brucella suis biovar 2, high interferon-gamma (IFN-gamma) assay responses with a commercial Brucella melitensis antigen preparation (Brucellergene OCB) preceded the development of antibodies. High IFN-gamma responses in the seven B. suis inoculated pigs with serological evidence of infection were consistent throughout a 20-week post-inoculation observation period. In contrast, IFN-gamma responses in two B. suis inoculated pigs without bacteriological or serological evidence of infection were below a cut-point of 25pg/ml at all samplings. IFN-gamma responses in repeated samplings from 5 uninfected control pigs and 18 pigs experimentally infected with YeO:9 were all negative, except for solitary false positives in 3.7% of the samples from both the experimentally YeO:9 infected pigs and control pigs. Skin tests using the same commercial Brucella antigen confirmed the ability of cell-mediated immune responses to differentiate between the two infections. In addition, a field evaluation of the diagnostic use of cell-mediated immune responses by IFN-gamma assay and skin test to resolve serological suspicions of Brucella was conducted in an YeO:9 infected pig herd. Following a screening of 200 pigs 39 pigs were identified with false positive serological Brucellosis reactions. While 36 of the 39 FPSR pigs were also FPSR in a second test, none of the pigs were test positive in whole blood IFN-gamma assay or Brucellergene OCB skin test. In conclusion, use of IFN-gamma assay and skin test as measurements of cell-mediated immune responses to non-LPS Brucella antigens were specific and sensitive in discriminating subclinical experimental infections with B. suis from both natural and experimental infections with YeO:9.

Factors critical for successful vaccination against classical swine fever in endemic areas

Classical swine fever (CSF) or hog cholera, caused by the classical swine fever virus (CSFV), is one of the most important viral diseases that cause serious economic loss to the swine industry worldwide. During the past 5 years, several techniques for measuring porcine cell-mediated immunity (CMI) were applied, in conjunction with other conventional techniques, to study factors that influence the induction of CSFV-specific immunity. Information, obtained from a series of experiments, demonstrated cell-mediated immune responses in providing protective immunity against CSF infection. Although it has been confirmed that commercially available modified live CSF vaccines are able to induce complete protection in vaccinated pigs, several factors including maternal immunity, the age of primary vaccination, vaccination protocol and complications caused by other pathogens, can greatly affect the effectiveness of CSF vaccines in the field.

Immunostimulatory properties of a novel adjuvant administered with inactivated influenza virus vaccine

The immunopotentiating activity of a new delivery system was investigated comparatively to Alhydrogel adjuvant, as an antiviral inactivated vaccine after one injection. The efficiency of the new formulation (BioMed) was evaluated with an inactivated porcine strain of influenza (A/Sw/IN/1726/88 H1N1) in the pig model. The first assessment criteria was the follow-up of selected immunological parameters such as, antibody levels, lymphoproliferation, double positive CD4+CD8+ T lymphocytes and cytokine production (IL-2, IL-4, IFN-gamma). The second criteria was the estimate of the protection level of animals exposed to a homologous challenge of 50 PID50 one month after a single immunizing or control injection. In the BioMed group of animals, 4 pigs (out of 6) were free of macroscopic lesion, while lesions could be seen in all individuals of other groups and virus was isolated in only one animal, whereas all other animals of other groups had virus in their lungs. This better protection of BioMed animals seems to be correlated mainly with higher levels of antibodies and to a lesser extent with a slightly better CMI response and probably with the production of memory CD4+CD8+ T cells.

The kinetics of cytokine production and CD25 expression by porcine lymphocyte subpopulations following exposure to classical swine fever virus (CSFV)

Surface expression of IL-2R-alpha (CD25) is widely used to identify activated lymphocyte populations, while interferon-gamma (IFN-gamma) levels have been shown to be a good indicator of cell-mediated immunity (CMI) in pigs. To investigate the relationship between these two parameters, we developed an intracellular cytokine-staining assay and studied the kinetics of cytokine (IFN-gamma and interleukin-10, IL-10) production relative to CD25 expression in porcine lymphocyte subpopulations, following immunization with a classical swine fever (CSF) vaccine. The number of activated memory T cells (CD4(+)CD8(+)CD25(+) cells) increased slightly in the peripheral blood mononuclear cell (PBMC) population soon after vaccination, then diminished within a few weeks. The number of activated cytotoxic T cells (CD4(-)CD8(+)CD25(+) cells) peaked approximately 2 weeks after the memory population. Although the number of IFN-gamma producing cells detected in this experiment was relatively low, the CD4(+)CD8(+) T cells were major IFN-gamma producers in the PBMCs throughout the experiment. In another experiment, CSF-vaccinated pigs were challenged with a virulent classical swine fever virus (CSFV), and the kinetics of CD25 expression and cytokine productions were monitored. Following exposure to the virus, the number of IFN-gamma producing cells in the PBMCs increased markedly in both the vaccinated and unvaccinated groups. The CD4(-)CD8(+) cells were major IFN-gamma producing cells in vaccinated pigs, while both CD4(+)CD8(+) and CD4(-)CD8(+) populations contributed to the IFN-gamma production in the control group. Interestingly, the enhanced IFN-gamma production was not associated with the upregulation of CD25 expression following the CSFV challenge. In addition, exposure to the virulent CSFV significantly increased interleukin-10 production by the CD4(-)CD8(+) populations in PBMCs of the unvaccinated pigs. Taken together, our results indicated that CD25 expression and IFN-gamma production were not tightly associated in porcine lymphocytes. In addition, the CD4(-)CD8(+) lymphocytes of the PBMCs played a major role in cytokine productions following the CSFV challenge.

γδ Lymphocyte Response to Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be one of the most important diseases facing swine industry today. Following PRRSV infection pigs develop both humoral and cell-mediated responses following PRRSV exposure; however, the relative importance in protection and clearance of the virus is not yet completely understood. Swine contain a large percentage of gammadelta T-lymphocytes in peripheral circulation capable of responding to various pathogens in both an innate and specific immune response. The objectives of this study were to determine whether gammadelta lymphocytes functionally respond to PRRSV upon initial exposure and re-exposure. Four month old PRRSV free gilts were intranasally inoculated with a field isolate MN-30100 then assessed at various time points post infection. On day 120, pigs were re-exposed with MN-30100 PRRSV strain and subsequently were bled on days 0, 7, and 14 post re-exposure. Lymphocyte subpopulations, antigen specific proliferation, and IFN-gamma production were evaluated throughout the study. Circulating gammadelta lymphocytes in PRRSV exposed animals expanded between days 14 to 70 (d14-d70, p = 0.016); following antigen stimulation, gammadelta lymphocyte proliferated by day 14 (d0-d14, p = 0.001) continuing through day 60. gammadelta lymphocytes produced IFN-gamma by day 14 pi continuing through day 50 (d0-d50, p = 0.004). Following re-exposure both gammadelta+ and CD4+ lymphocytes increased in IFN-gamma production. These results are not fully conclusive on the role of gammadelta lymphocytes against PRRSV; the data indicate that gammadelta lymphocytes specifically respond to PRRSV.

Use of ELISPOT and ELISA to evaluate IFN-gamma, IL-10 and IL-4 responses in conventional pigs

ELISPOT and ELISA were standardised for pig interferon-gamma (IFN-gamma), interleukin-10 (IL-10) and interleukin-4 (IL-4) with the aim to study the evolution of the immune response in conventional pigs from birth to 6 months of age and also to compare results of both techniques. Five pigs were bled at 1, 6, 9, 12 and 22 weeks of age and peripheral blood mononuclear cells (PBMC) were stimulated with phytohemagglutinin. The frequencies of cytokine secreting cells (CSC) and the levels of secreted cytokines were compared. For IFN-gamma the mean of CSC increased with age (p<0.05) from an average of 486/10(6) PBMC at first week of age to 1256/10(6) PBMC at 22 weeks of age. No correlation was found between the number of IFN-gamma CSC and the cytokine levels obtained by ELISA. For IL-10, frequencies of CSC did not increase with age of pigs, having a low of 315/10(6) PBMC at first week of age and a high of 1485/10(6) PBMC at six weeks. Comparison of ELISA and ELISPOT results for IL-10 showed a certain degree of correlation (r=0.74; p<0.05). Spontaneous secretion was observed in unstimulated cultures. For IL-4, frequencies of CSC were low (50-70/10(6) PBMC). In this case, comparison of ELISA and ELISPOT could not be done because cytokine levels in culture supernatants were often below the detection limit of the IL-4 ELISA. All these values can serve as a reference for future studies and also, our observations suggest that ELISPOT and ELISA should be carefully interpreted and do not necessarily correlate.

Evaluation of the Suitability of Monoclonal Antibodies for Flow Cytometric Intracellular Cytokine Detection in Porcine Peripheral Blood Lymphocytes

Panels of monoclonal antibodies (mAbs) specific for porcine interleukin (IL)-2, IL-4, IL-6, IL-12, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha were evaluated for their applicability in flow cytometric intracellular cytokine detection. Peripheral blood mononuclear cells were short-time stimulated in the presence of brefeldin-A, ionomycin and phorbol-12-myristate-13-acetate, fixed and incubated with the respective mAbs as well as phycoerythrin-conjugated second-step antibodies. Suitability of mAbs was judged by use of statistical data and by visual control of scattergrams, considering the capability of mAbs to discriminate between cytokine-positive and cytokine-negative cell populations. The number of suitable clones differed to a high degree between the investigated cytokines, but at least one mAb fitting for flow cytometric intracellular cytokine detection could be identified within each panel. Monoclonal Abs producing scattergrams with a clear demarcation between positive and negative cell populations were found within the anti-IL-2, IL-6 and IFN-gamma panels, whereas less well defined positive and negative cell populations could be generated by use of mAbs within the anti-IL-4 and TNF-alpha panels. Only one moderately fitting mAb was identified within the anti-IL-12 panel. After having evaluated the best fitting mAbs, these were used to obtain reference levels for the physiological range of porcine lymphocytic cytokine production in a second set of experiments. For that reason, 13 clinically healthy pigs aged between 6 weeks and 6 months were investigated. Data presented are given as mean +/- SD of the percentage of positive-staining lymphocytes: IL-2, 45.5 +/- 27.6; IL-4, 34.1 +/- 21.3; IL-6, 45.4 +/- 23.8; IL-12, 13.9 +/- 8.6; TNF-alpha, 43.4 +/- 11.3; IFN-gamma, 65.5 +/- 14.8.

Crossing the bridge: large animal models in translational transplantation research

Many methods for reducing the immunosuppressive requirements of allotransplantation have been proposed based on a growing understanding of physiological and allospecific immunity. As these regimens are developed for clinical application, they require validation in models that are reasonably predictive of their performance in humans. This article provides an overview of the large animal models commonly used to test immunomodulatory organ transplant protocols. The rationale for the use of large animals and the effects of common immunosuppressants in the dog, pig, and non-human primate are reviewed. Promising methods for the induction of allospecific tolerance are surveyed with references to early human trials where appropriate.

The level of virus-specific T-cell and macrophage recruitment in porcine reproductive and respiratory syndrome virus infection in pigs is independent of virus load

Porcine reproductive and respiratory syndrome virus (PRRSV) is the most important infectious disease agent of pigs worldwide, causing reproductive failure in pregnant sows and respiratory problems in nursing and growing pigs. PRRSV infection is characterized by a prolonged viremia of 30 or more days and an extended persistent infection of lymphoid tissues. To better understand the immunological basis for prolonged acute and persistent PRRSV infection, we have examined the cell-mediated immune (CMI) response throughout the course of infection and compared the results to the local distribution and abundance of PRRSV in infected tissues. PRRSV-specific T cells, enumerated by gamma interferon enzyme-linked immunospot assay, did not appear until 2 weeks after PRRSV inoculation, and their abundance exhibited substantial variation over time and among animals. In all cases the T-cell response was transient. High levels of viral RNA were present in lymphoid tissues of all animals in the acute phase of infection. Viral loads were decreased 1,000-fold or more in persistent infections, with the primary sites of persistence being tonsil, sternal lymph node, and inguinal lymph node. The abundance of virus-specific T cells in either acutely or persistently infected animals was highly variable and showed no correlation to the level of virus in lymphoid tissues. No significant difference in antigen-specific T-cell abundance was observed in secondary lymphoid tissues in either acute or persistent infection except for tonsil, in which the number of responding cells was extremely low. CD4(+)- and CD8(+)-T-cell frequencies did not change after PRRSV infection, though a decrease in gammadelta T cells was observed. Macrophages, the permissive cell type for PRRSV, were present in various levels in all tissue preparations and were not in proportion to local virus load. These findings indicate that a weak CMI response contributes to prolonged PRRSV infection and suggests that PRRSV suppresses T-cell recognition of infected macrophages. Thus, the slow but eventual resolution of PRRSV infection may be dependent on limiting permissive macrophages and on innate immune factors.

2E3, a new marker that selectively identifies porcine CD4+ naive T cells

We describe a novel antigen recognized by mAb 2E3 selectively expressed in the periphery by a subset of porcine CD4+ T cells. Both, CD4+CD8alpha- and CD4+CD8alphalow T cell subpopulations express this antigen. CD4+2E3+ T cells show phenotypical and functional characteristics of nai;ve cells. The majority of them are CD29low, CD45RAhigh, CD49dlow, CD11alow, CD18low, and SLA-II-. After mitogen activation CD4+2E3+ T cells express high levels of IL-2 mRNA, but only traces of IFN-gamma or IL-4 mRNA. Indeed a minor percentage of cells stained positive for IFN-gamma when assessed by flow cytometry. Moreover, CD4+2E3+ T cells did not proliferate in response to the recall antigen lysozyme, although they did efficiently to the mitogen ConA. By contrast, CD4+2E3- T cells show phenotypical and functional characteristics of primed cells. They express markers associated to a memory phenotype, respond to the recall antigen lysozyme, and produce high amounts of IFN-gamma and IL-4.

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.

Gradual development of the interferon-gamma response of swine to porcine reproductive and respiratory syndrome virus infection or vaccination

Infection of swine with virulent porcine reproductive and respiratory syndrome (PRRS) virus induced a rapid, robust antibody response that comprised predominantly nonneutralizing antibodies and waned after approximately 3 months. In contrast, the initial onset of virus-specific interferon (IFN)-gamma-secreting cells (SC) in the pig lymphocyte population remained at a fairly low level during this period and then increased gradually in frequency, plateauing at 6 months postinfection. A similar polarization of the host humoral and cellular immune responses was also observed in pigs immunized with a PRRS-modified live virus (MLV) vaccine. Even coadministration of an adjuvant that enhanced the immune response to a pseudorabies (PR) MLV vaccine failed to alter the induction of PRRS virus-specific IFN-gamma SC (comprising predominantly CD4/CD8 alpha double positive memory T cells with a minority being typical CD4(-)/CD8 alpha beta(+) T cells) and the generation of neutralizing antibodies. Moreover, unlike inactivated PR virus, nonviable PRRS virus did not elicit virus-neutralizing antibody production. Presumably, an intrinsic property of this pathogen delays the development of the host IFN-gamma response and preferentially stimulates the synthesis of antibodies incapable of neutralization.

Immunohistochemical staining of IFN-gamma positive cells in porcine reproductive and respiratory syndrome virus-infected lungs

Paraffin-embedded lungs were obtained from a previous porcine reproductive and respiratory syndrome virus (PRRSV)-challenged experiment involving three groups: an uninfected control group, a low virulence (LV, Resp PRRSV/Repro)-infected group, and a high virulence (HV, VR-2385)-infected group. Tissues were collected at 3, 7, 10, 14 or 28 days post-inoculation (DPI) (n=5). Lungs were examined to detect IFN-gamma positive cells by immunohistochemical staining using polyclonal antibodies to IFN-gamma. The microscopic lung lesions induced by the HV group were more severe than those in the LV group. A significant increase in number of lymphocytes in the HV group was observed at 10 DPI (24.90+/-9.79%), 14 DPI (22.00+/-11.47%) and 28 DPI (28.95+/-15.11%) (P<0.05). A relative decrease in macrophage numbers was observed and correlated well with the increase in lymphocyte numbers when the disease progressed. IFN-gamma positive cells were demonstrated in both lymphocytes and macrophages, particularly pulmonary alveolar macrophages. A significant increase in IFN-gamma positive cells was found at 7 DPI (15.90+/-13.65%), 10 DPI (46.95+/-13.79%), 14 DPI (10.90+/-5.13%) and 28 DPI (13.40+/-4.89%) in the HV group (P<0.05). The results suggested that the increase in IFN-gamma positive cells in the HV group correlated well with the severity of the lung lesions, which may be because of the presence of PRRSV in the lung.