Characterization of monoclonal antibodies specific for monocytes, macrophages and granulocytes from porcine peripheral blood and mucosal tissues

Porcine Macrophage Markers and Populations: An Update

Besides its importance as a livestock species, pig is increasingly being used as an animal model for biomedical research. Macrophages play critical roles in immunity to pathogens, tissue development, homeostasis and tissue repair. These cells are also primary targets for replication of viruses such as African swine fever virus, classical swine fever virus, and porcine respiratory and reproductive syndrome virus, which can cause huge economic losses to the pig industry. In this article, we review the current status of knowledge on porcine macrophages, starting by reviewing the markers available for their phenotypical characterization and following with the characteristics of the main macrophage populations described in different organs, as well as the effect of polarization conditions on their phenotype and function. We will also review available cell lines suitable for studies on the biology of porcine macrophages and their interaction with pathogens.

The Attenuated Pseudorabies Virus Vaccine Strain Bartha Hyperactivates Plasmacytoid Dendritic Cells by Generating Large Amounts of Cell-Free Virus in Infected Epithelial Cells

Pseudorabies virus (PRV) is a porcine alphaherpesvirus and the causative agent of Aujeszky's disease. Successful eradication campaigns against PRV have largely relied on the use of potent PRV vaccines. The live attenuated Bartha strain, which was produced by serial passaging in cell culture, represents one of the hallmark PRV vaccines. Despite the robust protection elicited by Bartha vaccination, very little is known about the immunogenicity of the Bartha strain. Previously, we showed that Bartha-infected epithelial cells trigger plasmacytoid dendritic cells (pDC) to produce much higher levels of type I interferons than cells infected with wild-type PRV. Here, we show that this Bartha-induced pDC hyperactivation extends to other important cytokines, including interleukin-12/23 (IL-12/23) and tumor necrosis factor alpha (TNF-α) but not IL-6. Moreover, Bartha-induced pDC hyperactivation was found to be due to the strongly increased production of extracellular infectious virus (heavy particles [H-particles]) early in infection of epithelial cells, which correlated with a reduced production of noninfectious light particles (L-particles). The Bartha genome is marked by a large deletion in the US region affecting the genes encoding US7 (gI), US8 (gE), US9, and US2. The deletion of the US2 and gE/gI genes was found to be responsible for the observed increase in extracellular virus production by infected epithelial cells and the resulting increased pDC activation. The deletion of gE/gI also suppressed L-particle production. In conclusion, the deletion of US2 and gE/gI in the genome of the PRV vaccine strain Bartha results in the enhanced production of extracellular infectious virus in infected epithelial cells and concomitantly leads to the hyperactivation of pDC. IMPORTANCE The pseudorabies virus (PRV) vaccine strain Bartha has been and still is critical in the eradication of PRV in numerous countries. However, little is known about how this vaccine strain interacts with host cells and the host immune system. Here, we report the surprising observation that Bartha-infected epithelial porcine cells rapidly produce increased amounts of extracellular infectious virus compared to wild-type PRV-infected cells, which in turn potently stimulate porcine plasmacytoid dendritic cells (pDC). We found that this phenotype depends on the deletion of the genes encoding US2 and gE/gI. We also found that Bartha-infected cells secrete fewer pDC-inhibiting light particles (L-particles), which appears to be caused mainly by the deletion of the genes encoding gE/gI. These data generate novel insights into the interaction of the successful Bartha vaccine with epithelial cells and pDC and may therefore contribute to the development of vaccines against other (alphaherpes)viruses.

Alphaherpesvirus-induced activation of plasmacytoid dendritic cells depends on the viral glycoprotein gD and is inhibited by non-infectious light particles

Plasmacytoid dendritic cells (pDC) are important innate immune cells during the onset of viral infections as they are specialized in the production of massive amounts of antiviral type I interferon (IFN). Alphaherpesviruses such as herpes simplex virus (HSV) or pseudorabies virus (PRV) are double stranded DNA viruses and potent stimulators of pDC. Detailed information on how PRV activates porcine pDC is lacking. Using PRV and porcine primary pDC, we report here that PRV virions, so-called heavy (H-)particles, trigger IFNα production by pDC, whereas light (L-) particles that lack viral DNA and capsid do not. Activation of pDC requires endosomal acidification and, importantly, depends on the PRV gD envelope glycoprotein and O-glycosylations. Intriguingly, both for PRV and HSV-1, we found that L-particles suppress H-particle-mediated activation of pDC, a process which again depends on viral gD. This is the first report describing that gD plays a critical role in alphaherpesvirus-induced pDC activation and that L-particles directly interfere with alphaherpesvirus-induced IFNα production by pDC.

The pig as a medical model for acquired respiratory diseases and dysfunctions: An immunological perspective

By definition no model is perfect, and this also holds for biology and health sciences. In medicine, murine models are, and will be indispensable for long, thanks to their reasonable cost and huge choice of transgenic strains and molecular tools. On the other side, non-human primates remain the best animal models although their use is limited because of financial and obvious ethical reasons. In the field of respiratory diseases, specific clinical models such as sheep and cotton rat for bronchiolitis, or ferret and Syrian hamster for influenza and Covid-19, have been successfully developed, however, in these species, the toolbox for biological analysis remains scarce. In this view the porcine medical model is appearing as the third, intermediate, choice, between murine and primate. Herein we would like to present the pros and cons of pig as a model for acquired respiratory conditions, through an immunological point of view. Indeed, important progresses have been made in pig immunology during the last decade that allowed the precise description of immune molecules and cell phenotypes and functions. These progresses might allow the use of pig as clinical model of human respiratory diseases but also as a species of interest to perform basic research explorations.

Characterization and expression of DEC205 in the cDC1 and cDC2 subsets of porcine dendritic cells from spleen, tonsil, and submaxillary and mesenteric lymph nodes

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This study describes the characterization of cDCs, cDC1 and cDC2 in porcine lymphoid tissues.

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Results show that the spleen had the highest frequency of cDCs.

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The cDC1:cDC2 ratio showed a predominant presence of cDC1 in all lymphoid tissues.

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DEC205 was expressed on cDC1 and cDC2 cells from all analyzed tissues.

Conventional dendritic cells (cDCs) are divided into the following different subtypes: cDC1, which promotes a Th1 response, and cDC2, which stimulates a Th2 and Th17 response. These cells have not been characterized in porcine lymphoid tissues. DEC205 is a receptor that increases antigen presentation and allows DCs to cross-present antigens. The objectives of this work were to characterize cDCs subsets in the tonsil, submaxillary and mesenteric lymph nodes and spleen lymphoid tissues and to determine their expression of DEC205 by flow cytometry. The cDC1 (MHCII^highCADM1^highCD172a^−/low) and cDC2 (MHCII^highCADM1^highCD172a⁺) phenotypes were confirmed by the expression of characteristic cDC1 and cDC2 transcripts (FLT3, XCR1 and FCER1α). Among all lymphoid tissues, the spleen had the highest frequency of total cDCs. The cDC1:cDC2 ratio showed that all lymph tissues had higher levels of cDC1 than levels of cDC2. DEC205⁺ cDCs were found in all analyzed tissues, albeit with different frequencies. Our research will facilitate the study on the function of these cells and the investigation of the strategies for DEC205 targeting and functional studies.

The Pseudorabies Virus Glycoprotein gE/gI Complex Suppresses Type I Interferon Production by Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDC) play a central role in the antiviral immune response, both in the innate response and in shaping the adaptive response, mainly because of their ability to produce massive amounts of type I interferon (TI-IFN). Here, we report that cells infected with the live attenuated Bartha vaccine strain of porcine alphaherpesvirus pseudorabies virus (PRV) trigger a dramatically increased TI-IFN response by porcine primary pDC compared to cells infected with wild-type PRV strains (Becker and Kaplan). Since Bartha is one of the relatively few examples of a highly successful alphaherpesvirus vaccine, identification of factors that may contribute to its efficacy may provide insights for the rational design of other alphaherpesvirus vaccines. The Bartha vaccine genome displays several mutations compared to the genome of wild-type PRV strains, including a large deletion in the unique short (US) region, encompassing the glycoprotein E (gE), gI, US9, and US2 genes. Using recombinant PRV Becker strains harboring the entire Bartha US deletion or single mutations in the four affected US genes, we demonstrate that the absence of the viral gE/gI complex contributes to the observed increased IFN-α response. Furthermore, we show that the absence of gE leads to an enhanced extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in pDC, which correlates with a higher TI-IFN production by pDC. In conclusion, the PRV Bartha vaccine strain triggers strongly increased TI-IFN production by porcine pDC. Our data further indicate that the gE/gI glycoprotein complex suppresses TI-IFN production by pDC, which represents the first alphaherpesvirus factor that suppresses pDC activity.IMPORTANCE Several alphaherpesviruses, including herpes simpex virus, still lack effective vaccines. However, the highly successful Bartha vaccine has contributed substantially to eradication of the porcine alphaherpesvirus pseudorabies virus (PRV) in several countries. The impact of Bartha on the immune response is still poorly understood. Type I interferon (TI-IFN)-producing plasmacytoid dendritic cells (pDC) may play an important role in vaccine development. Here, we show that Bartha elicits a dramatically increased type I interferon (TI-IFN) response in primary porcine pDC compared to wild-type strains. In addition, we found that the gE/gI complex, which is absent in Bartha, inhibits the pDC TI-IFN response. This is the first description of an immune cell type that is differentially affected by Bartha versus wild-type PRV and is the first report describing an alphaherpesvirus protein that inhibits the TI-IFN response by pDC. These data may therefore contribute to the rational design of other alphaherpesvirus vaccines.

Characteristics of Porcine Circovirus—2 Replication in Lymphoid Organs of Pigs Inoculated in Late Gestation or Postnatally and Possible Relation to Clinical and Pathological Outcome of Infection

In this study, the characteristics of porcine circovirus–2 (PCV2) replication (infectious virus titrations, distribution, and immunophenotyping of infected cells) in lymphoid organs were examined and related to the development of clinical signs and histological lesions in 26 piglets that had been inoculated with PCV2 either in utero or at 1 day of age. Piglets inoculated in utero at 92 or 104 gestational days ( n = 12) were collected by Caesarean section at term and either sacrificed immediately or kept in isolators and allowed to live postnatally until 35 days postinoculation (PI). Caesarean-derived piglets inoculated at 1 day of age ( n = 14) were sacrificed at 10, 21, 35, 42, and 49 days PI. Spleen and lymph nodes were collected for virologic and histopathological examinations. Clinical signs were not observed in any of the piglets. High virus titers (104.5–5.7 TCID50/g [TCID refers to tissue culture infectious dose]) were detected in 6 of the 26 piglets. Three of these 6 piglets were euthanized at 10 days PI, and infected cells of the monocyte–macrophage lineage (SWC3+, CD14+, and sialoadhesin [Sa]+ cells) and infected cells bearing lymphocyte markers (CD4+, CD8+, and immunoglobulin M+ cells) were identified by double-immunofluorescence labeling on serial cryostat sections. The other 3 piglets were euthanized at 21 and 35 days PI, and the majority of infected cells were SWC3+, CD14+, and Sa–. The absence of Sa in these infected cells, together with their localization in lymphocyte-dependent regions, suggests that they were infiltrating monocytic cells. Sialoadhesin is highly expressed in differentiated macrophages and not in peripheral blood mononuclear cells. In all 6 piglets with high virus titers, lymphocyte depletion and infiltration of monocytic cells were observed. In the remaining 20 piglets with virus titers less than 1045 TCID50/g, the majority of infected cells were SWC3+, CD14+, and Sa+. In conclusion, it can be stated that high PCV2 titers in lymphoid organs may lead to the development of histological lesions similar to those observed in pigs with postweaning multisystemic wasting syndrome without causing disease. Furthermore, in lymphoid organs with high virus titers, infection occurs mainly in infiltrating monocytic cells and to a limited extent in cells bearing lymphocyte markers.

Pathogenesis and prevention of placental and transplacental porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV)-induced reproductive problems are characterized by embryonic death, late-term abortions, early farrowing and increase in number of dead and mummified fetuses, and weak-born piglets. The virus recovery from fetal tissues illustrates transplacental infection, but despite many studies on the subject, the means by which PRRSV spreads from mother to fetus and the exact pathophysiological basis of the virus-induced reproductive failure remain unexplained. Recent findings from our group indicate that the endometrium and placenta are involved in the PRRSV passage from mother to fetus and that virus replication in the endometrial/placental tissues can be the actual reason for fetal death. The main purpose of this review is to clarify the role that PRRSV replication and PRRSV-induced changes in the endometrium/placenta play in the pathogenesis of PRRSV-induced reproductive failure in pregnant sows. In addition, strategies to control placental and transplacental PRRSV infection are discussed.

Drug treatment combined with BCG vaccination reduces disease reactivation in guinea pigs infected with Mycobacterium tuberculosis

Bacillus-Calmette-Guerin (BCG), the only human tuberculosis vaccine, primes a partially protective immune response against Mycobacterium tuberculosis infection in humans and animals. In guinea pigs, BCG vaccination slows the progression of disease and reduces the severity of necrotic granulomas, which harbor a population of drug-tolerant bacilli. The objective of this study was to determine if reducing disease severity by BCG vaccination of guinea pigs prior to M. tuberculosis challenge enhanced the efficacy of combination drug therapy. At 20 days of infection, treatment of vaccinated and non-vaccinated animals with rifampin, isoniazid, and pyrizinamide (RHZ) was initiated for 4 or 8 weeks. On days 50, 80 and 190 of infection (10 weeks after drug were withdrawn), treatment efficacy was evaluated by quantifying clinical condition, bacterial loads, lesion severity, and dynamic changes in peripheral blood and lung leukocyte numbers by flow cytometry. In a separate, long-term survival study, treatment efficacy was evaluated by determining disease reactivation frequency post-mortem. BCG vaccination alone delayed pulmonary and extra-pulmonary disease progression, but failed to prevent dissemination of bacilli and the formation of necrotic granulomas. Drug therapy either alone or in combination with BCG, was more effective at lessening clinical disease and lesion severity compared to control animals or those receiving BCG alone. Fewer residual lesions in BCG vaccinated and drug treated animals, equated to a reduced frequency of reactivation disease and improvement in survival even out to 500 days of infection. The combining of BCG vaccination and drug therapy was more effective at resolving granulomas such that fewer animals had evidence of residual infection and thus less reactivation disease.

Innate defense regulator peptide synergizes with CpG ODN for enhanced innate intestinal immune responses in neonate piglets

The in vivo immunoadjuvant effects of the combination of CpG oligodeoxynucleotide (CpG ODN) and innate defense-regulator peptides (IDRs) have been studied in mice. However, little is known about the efficacy of these molecules in stimulating the innate intestinal immune system in neonatal piglets. In this study, we observed that intranasal (IN) administration of CpG-IDR (peptide HH2 (VQLRIRVAVIRA)) complex significantly increased intestinal mRNA expression of Th1 cytokines, CC chemokines and CXC chemokines when compared to HH2 and CpG ODN alone. Also an obvious cellular infiltration was observed in the intestine of CpG-HH2-treated neonatal piglets, which was associated with increased protection against Enterotoxigenic Escherichia coli (ETEC). Moreover, we showed that pro-inflammatory cytokine TNF-α was inhibited when CpG ODN combined with HH2. This was the first report that deciphered the role played by CpG-HH2 complex in the intestine of neonatal piglets. This work clearly demonstrated that efficiency of the IN route inducing intestinal responses in neonatal piglets might be taken into consideration for further vaccine development against neonatal intestinal diseases.

Synthetic innate defence regulator peptide enhances in vivo immunostimulatory effects of CpG-ODN in newborn piglets

The in vivo immunoadjuvant effects of CpG oligodeoxynucleotides (CpG-ODN) have been studied extensively in mice and relatively fewer studies have been done in piglets. But so far, the innate immunostimulatory effects of CpG-ODN combination with innate defense-regulator peptides (IDRs) have not been demonstrated. The purpose of this study is to determine the potential effects of CpG-ODN with IDR in newborn piglets. The immunostimulatory abilities of four selected IDRs were compared, among them HH2 showed best immunostimulatory effects in newborn piglets. Hereafter, the abilities of CpG-ODN combined with HH2 to enhance innate immune responses were examined in newborn piglets. The complex of HH2 and CpG-ODN could induce much stronger Th1 cytokine and chemokine responses than HH2 or CpG-ODN alone. HH2-CpG-ODN immunized piglets showed higher B cell percentage in PBMCs than CpG-ODN alone. These in vivo data demonstrated for the first time that subcutaneously (SC) administration of CpG-ODN combined with HH2 is efficient to stimulate innate immune system in newborn piglets.

Porcine mononuclear phagocyte subpopulations in the lung, blood and bone marrow: dynamics during inflammation induced by Actinobacillus pleuropneumoniae

Mononuclear phagocytes (MP) are cells of nonspecific immunity, playing an essential role in defense against bacterial pathogens. Although various MP subpopulations have been described in the pig, relations among these populations in vivo are unknown to date. The present study was aimed at describing porcine MP subpopulations infiltrating inflamed tissue of pigs under in vivo conditions. Actinobacillus pleuropneumoniae (APP) infection was used to induce an inflammatory response. CD172α, CD14, CD163, MHCII and CD203α cell surface molecules were used to identify MP by flow cytometry. Changes in MP subpopulations in the peripheral blood (PB) and bone marrow (BM) compartments along with the analysis of MP appearing in the inflamed lungs were assessed to elucidate the possible origin and maturation stages of the infiltrating MP. The MP population migrating to the inflamed lungs was phenotype CD14⁺ CD163⁺ CD203α^+/− MHCII^+/−. Concomitantly, after APP infection there was an increase in the PB MP CD14⁺ CD163⁺ CD203α⁻ MHC II⁻ population, suggesting that these cells give rise to inflammatory monocytes/macrophages. The CD203α and MHCII molecules appear on these cells after leaving the PB. In healthy animals, the BM MP precursors were represented by CD14⁻ CD163⁻ cells maturing directly into CD14⁺ CD163⁻ that were then released into the PB. After infection, an altered maturation pathway of MP precursors appeared, represented by CD14⁻ CD163⁻ CD203α⁻ MHCII⁻ MP directly switching into CD14⁺ CD163⁺ CD203α⁻ MHCII⁻ MP. In conclusion, two different MP maturation pathways were suggested in pigs. The use of these pathways differs under inflammatory and noninflammatory conditions.

Administered CpG oligodeoxynucleotide induces mRNA expression of CXC and CC chemokines at the intestinal mucosa and PBMCs in piglets

Oligonucleotides containing CpG motifs (CpG ODN) are known to be potent stimulators of the innate immune system in vitro and in vivo. We therefore investigated if intranasal (IN)-mucosal or intramuscular (IM)-systemic administration of CpG ODN could enhance innate immunity in the intestinal mucosa and peripheral blood mononuclear cells (PBMCs) in piglets. Repeated IN or IM administration of CpG ODN significantly increased local/systemic mRNA expression of the CC chemokines macrophage inflammatory protein 1beta (MIP-1beta) and monocyte chemoattractant protein-1 (MCP-1) and CXC chemokine gamma interferon-inducible protein 10 (IP-10) and percentages of macrophages and cDCs in the intestine (jejunum, caecum and colon) and PBMCs by different kinetics. IN delivery of CpG ODN induced much stronger chemokine responses than IM delivery at intestinal mucosas, whereas IN delivery of CpG ODN induced some weaker chemokine responses than IM delivery in PBMCs. These findings suggest that IN administration of 100mug/kg-CpG ODN without antigen codelivery may represent a valuable strategy for induction of innate immunity against infection.

Evaluation of standard chemotherapy in the guinea pig model of tuberculosis

The purpose of this study was 2-fold. First, we evaluated standard chemotherapy in the guinea pig model of tuberculosis to determine if this animal species could productively be used for this purpose. Second, given the similarities of the pathology of disease in guinea pigs and humans, we wished to evaluate additional parameters, including magnetic resonance imaging, microscopy, and cytokine expression and lymphocyte phenotypes, in response to an infection treated with drug therapy. This study shows that conventional rifampin-isoniazid-pyrazinamide chemotherapy significantly decreased the numbers of the highly virulent Erdman K01 strain of Mycobacterium tuberculosis, with most of the bacilli being eliminated in a month. Despite this result, bacteria could still be detected in the lungs and other tissues for at least another 3 to 4 months. Resolution of the nonnecrotic granulomas in the lungs and lymph nodes could be clearly visualized by magnetic resonance imaging at the macroscopic level. Microscopically, the majority of the pulmonary and extrapulmonary inflammation resolved spontaneously, leaving residual lesions composed of dystrophic calcification and fibrosis marking the site of necrosis of the primary lesion. Residual calcified lesions, which were also associated with pulmonary lymphangitis, contained acid-fast bacilli even following aggressive chemotherapy. The presence of intact extracellular bacilli within these lesions suggests that these could serve as the primary sites of disease reactivation. The chemotherapy reduced the level of T-cell influx into infected tissues and was accompanied by a large and sustained increase in TH1 cytokine expression. Chemotherapy also prevented the emergence in lung tissues of high levels of interleukin-10 and Foxp3-positive cells, known markers of regulatory T cells.

Porcine myelomonocytic markers and cell populations

This review focuses in what is currently known about swine myeloid markers, the expression and function of these receptors in the biology of porcine myelomonocytic cells, the regulation of their expression along the different developmental stages of these cells and their utility to investigate the heterogeneity of monocyte and macrophage populations. Although the number of monoclonal antibodies recognizing surface antigens expressed on either swine granulocytes or monocytes is low compared with those available for human or mouse, they have contributed significantly to study the members of myeloid lineages in this species, allowing to discriminate different maturation stages of these cells in bone marrow and to reveal the heterogeneity of blood monocytes and tissue macrophages. Porcine myeloid cells share many similarities with humans, highlighting the relevance of the pig as a biomedical model.

Inhibition of complement and CD14 attenuates the Escherichia coli-induced inflammatory response in porcine whole blood

The innate immune response is a double-edged sword in systemic inflammation and sepsis. Uncontrolled or inappropriate activation can damage and be lethal to the host. Several studies have investigated inhibition of downstream mediators, including tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta). Emerging evidence indicates that upstream inhibition is a better therapeutic approach for attenuating damaging immune activation. Therefore, we investigated inhibition of two central innate immune pathways, those of complement and CD14/Toll-like receptor 4 (TLR4)/myeloid differentiation protein 2 (MD-2), in a porcine in vitro model of Escherichia coli-induced inflammation. Porcine whole blood anticoagulated with lepuridin, which did not interfere with the complement system, was incubated with E. coli lipopolysaccharide (LPS) or whole bacteria. Inhibitors of complement and CD14 and thus the LPS CD14/TLR4/MD-2 receptor complex were tested to investigate the effect on the inflammatory response. A broad range of inflammatory readouts were used to monitor the effect. Anti-CD14 was found to saturate the CD14 molecule on granulocytes and completely inhibited LPS-induced proinflammatory cytokines in a dose-dependent manner. Anti-CD14 significantly reduced the levels of the E. coli-induced proinflammatory cytokines TNF-alpha and IL-1beta, but not IL-8, in a dose-dependent manner. No effect on bacterial clearance was seen. Vaccinia complement control protein and smallpox inhibitor of complement enzymes, two Orthopoxvirus-encoded complement inhibitors, completely inhibited complement activation. Furthermore, these agents almost completely inhibited the expression of wCD11R3, which is associated with CD18 as a beta2 integrin, on porcine granulocytes and decreased IL-8 levels significantly in a dose-dependent manner. As expected, complement inhibition reduced bacterial clearance. We conclude that inhibition of complement and CD14 attenuates E. coli-induced inflammation and might be used as a therapeutic regimen in gram-negative sepsis along with appropriate treatment with antibiotics.

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.

Influence of Mycobacterium bovis BCG vaccination on cellular immune response of guinea pigs challenged with Mycobacterium tuberculosis

Mycobacterium bovis bacillus Calmette-Guérin (BCG) currently remains the only licensed vaccine for the prevention of tuberculosis. In this study, we used a newly described flow cytometric technique to monitor changes in cell populations accumulating in the lungs and lymph nodes of naïve and vaccinated guinea pigs challenged by low-dose aerosol infection with virulent Mycobacterium tuberculosis. As anticipated, vaccinated guinea pigs controlled the growth of the challenge infection more efficiently than controls did. This early phase of bacterial control in immune animals was associated with increased accumulation of CD4 and CD8 T cells, including cells expressing the activation marker CD45, as well as macrophages expressing class II major histocompatibility complex molecules. As the infection continued, the numbers of T cells in the lungs of vaccinated animals waned, whereas the numbers of these cells expressing CD45 increased. Whereas BCG vaccination reduced the influx of heterophils (neutrophils) into the lungs, an early B-cell influx was observed in these vaccinated animals. Overall, vaccine protection was associated with reduced pathology and lung damage in the vaccinated animals. These data provide the first direct evidence that BCG vaccination accelerates the influx of protective T-cell and macrophage populations into the infected lungs, diminishes the accumulation of nonprotective cell populations, and reduces the severity of lung pathology.

Lactic acid bacterial colonization and human rotavirus infection influence distribution and frequencies of monocytes/macrophages and dendritic cells in neonatal gnotobiotic pigs

Despite accumulating knowledge of porcine macrophages and dendritic cells (DCs) from in vitro studies, information regarding monocytes/macrophages and DCs in lymphoid tissues of enteric pathogen-infected neonatal animals in vivo is limited. In this study we evaluated the influence of commensal bacterial [two strains of lactic acid bacteria (LAB), Lactobacillus acidophilus and L. reuteri] colonization and rotavirus infection on distribution and frequencies of monocytes/macrophages and conventional DCs (cDCs) in ileum, spleen and blood. Gnotobiotic pigs were inoculated with LAB and virulent Wa strain human rotavirus (HRV) (LAB+HRV+), HRV only (LAB−HRV+), LAB only (LAB+HRV−) or mock (LAB−HRV−). The cDCs were characterized as SWC3⁺CD11R1⁺, whereas monocytes/macrophages were identified as SWC3⁺CD11R1⁻ by flow cytometry in the gnotobiotic pigs at 10 days of age. Infection with HRV alone activated/recruited significantly more monocytes/macrophages to the intestine than LAB colonization and 56% versus 28% of these cells expressed CD14. Colonization with LAB alone also significantly increased the frequencies of monocytes/macrophages and cDCs and the CD14 expression on monocytes/macrophages in ileum and spleen compared to the controls. LAB colonization plus HRV infection significantly reduced macrophage and cDC frequencies in spleen compared to LAB colonization or HRV infection alone, suggesting that LAB colonization down-regulated HRV− infection-induced monocyte/macrophage activation/recruitment at the systemic lymphoid tissue. These results illustrated the distribution of porcine monocytes/macrophages and cDCs and the frequencies of CD14 expression on these cells in intestinal and systemic lymphoid tissues in the early stage of immune responses to intestinal colonization by LAB versus infection by an enteric pathogen HRV and will facilitate further in vivo studies on functional characterization of these immune cells in neonates.

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.

Ontogeny of systemic cellular immunity in the neonatal pig: Correlation with the development of post-weaning multisystemic wasting syndrome

The aetiology of porcine post-weaning multisystemic wasting syndrome (PMWS) is poorly understood. Porcine circovirus type 2 (PCV-2) is an essential component of the experimental disease model for PMWS: however, evidence from experimental and field studies indicates that additional factors play a critical role in the aetiopathogenesis of PMWS. Current candidates include (1) immune stimulation (for example, via co-infection or vaccination), and (2) a novel infectious agent. A prospective, longitudinal case-control study was designed to investigate molecular triggers in leucocytes of neonatal piglets that may predispose to the development of PMWS. Blood samples were collected weekly from pigs (n=125) within five farms, from 1 week to 8 weeks of age: that is, before the appearance of clinical signs. Four colour flow cytometry was used to investigate changes in subsets of peripheral blood mononuclear cells, using monoclonal antibodies against the following cell associated markers; sIgG, CD3, MHCII dR, CD14, CD4a, CD8a, CD45RC, CD25, SWC3a, SWC8, CD163 and CD45. Sampling and laboratory analysis was supported by monitoring of clinical signs from 1 week to 20 weeks of age, or until disease supervened. At the conclusion of the study, 68 pigs (54%) were classified in Group 1 (no signs of clinical disease), 34 pigs (27%) in Group 2 (signs of clinical disease but not characteristic of PMWS), 17 pigs (14%) in Group 3 (suspect PMWS case) and 5 pigs (4%) in Group 4 (PMWS case). A single case of Porcine Dermatitis and Nephropathy syndrome (PDNS) was also diagnosed. Significant changes with age were demonstrated in clinically normal, neonatal pigs (Group 1), including an increase in B-cells and T-cells, and an increase in the proportion of total T-cells expressing MHCII. Within the T-cell subset, the proportion of CD8(+high) CD4(-) T-cells increased, in addition to the proportion of CD4(+) T-cells co-expressing CD8. Of the factors recorded, farm was found to have a highly significant effect on immune system development in the neonate. Comparison of Groups 1 and 4 cases identified significant differences between pigs which remained normal and those which subsequently developed PMWS. Pigs which went on to develop PMWS had a greater proportion of T-cells expressing MHCII in early life, higher mean intensity of expression of MHCII on T-cells, higher mean intensity of expression of MHCII on B cells and higher expression of CD25 on CD45RC(-) T-cells. These findings suggest that lymphocyte activation may be a key early event in the aetiology of PMWS.

Cloning, characterization and mapping of porcine CD14 reveals a high conservation of mammalian CD14 structure, expression and locus organization

The cell surface protein CD14 plays a central role in innate immunity as a pattern recognition receptor. CD14 is part of a receptor complex also including toll-like receptor 4 and MD2 proteins. Binding of the ligand lipopolysaccharide to the complex on myeloid cells leads to release of pro-inflammatory cytokines and mediators from the cell. In this study, we present the cloning, characterization and tissue expression pattern of a porcine CD14 encoding cDNA, and the chromosomal localization of the porcine CD14 gene. The open reading frame is predicted to encode a protein of 373 amino acids, which shows conservation of structural as well as functional regions when compared to other mammalian species. The CD14 gene was localized to porcine chromosome 2 in a region syntenic to human chromosome 5q. Transcription analysis shows that CD14 is widely expressed in tissues examined in this study, which correlates well with expression primarily on myeloid cells.

Antigen presenting cells in mucosal sites of veterinary species

The ability of antigen presenting cells, in particular dendritic cells, to integrate a variety of environmental signals, together with their ability to respond appropriately by initiating either tolerance or defensive immune responses make them cells of particular relevance and importance in the mucosal environment. They have been demonstrated in a variety of mucosal tissues in veterinary species and have been characterized to varying degrees, showing that fundamental immunological principles apply throughout all species, but also highlighting some species differences. A major advantage of carrying out immunological research in veterinary species is their size: it is possible to cannulate lymphatic ducts and obtain information about cell migration between different tissues. It is also possible to obtain pure populations of relatively rare cell types such as the plasmacytoid dendritic cells or mucosal dendritic cells ex vivo for the study of immune responses to diseases in their natural host and for other thorough functional studies. Two major myeloid antigen presenting cell (APC) (dendritic cells, DC) cell populations have been described in gut draining lymph and other mucosal sites in ruminants and pigs, characterised by the presence or absence of surface molecules, their enzyme profiles, their ability to phagocytose and their different potential as APC. There is evidence that one of these subsets has migrated from the diffuse mucosal tissue, where it is found as a phagocytic as well as stimulatory APC population, which in turn may be derived from blood macrophages. In addition, the presence and role in viral infection of the IFN-alpha producing plasmacytoid DC in mucosal tissue is discussed, based on studies in pigs.

Novel two-parameter flow cytometry (MIL4/SSC followed by MIL4/CT7) allows for identification of five fractions of guinea pig leukocytes in peripheral blood and lymphoid organs

Though the guinea pig has been an extremely useful animal model for a variety of diseases, the tools necessary to undertake a full-scale immunological analysis of the guinea pig have been lacking. For instance, traditional two-parameter forward/side scatter (FSC/SSC) flow cytometry, though effective in human and other animal models, is unable to adequately identify the distinct fractions of guinea pig peripheral blood leukocytes (PBL). We introduce here a new flow cytometric technique (MIL4/SSC followed by MIL4/CT7) which redresses this lack by identifying and characterizing five distinct fractions of PBL: neutrophils, lymphocytes, monocytes, eosinophils plus basophils, and the novel MIL4(-)SSC(large)CT7(high) population. The MIL4(-)SSC(large)CT7(high) cells possess cytoplasmic inclusion bodies of variable size that were positive for periodic acid Schiff (PAS). Their cell surface stained positive for the helper/inducer lymphocyte markers, T cell markers, CD45, Thy-1, asialo GM1 and FcR, but negative for B cell markers, such as membrane-type IgM, CD8 and MHC class II. The novel flow cytometric technique also allowed us to establish that the five leukocyte fractions were found in PBL, splenocytes, thymocytes and lymph node cells. Cells which were positive for inclusion bodies comprised 16.6% of splenocytes, 9.9% of PBL and 4.3% of liver cells, but were comparatively rare in lymph node cells, thymocytes, and BM cells. The novel flow cytometric technique introduced here will allow a better understanding of the response of each type of guinea pig leukocyte and thereby shed light on the diseases with which they are associated.

Validation of computer-assisted, pixel-based analysis of multiple-colour immunofluorescence histology

Developments in immunohistology allow the routine simultaneous use on tissue sections of three monoclonal antibodies, tagged with different fluorochromes. Such staining can identify seven different cell populations and the limiting factor is rapid, reliable and reproducible analysis. Future reliance on computer-assisted analysis of digitised images depends on validation against manual counting, often viewed as the 'gold standard'. In this study images were digitised from sections of normal porcine skin, inflamed skin and tonsil, simultaneously stained with three monoclonal antibodies. Combinations of staining were quantified by four manual counts and by pixel-based area measurement. On individual images, the correlation between automated and manual measurements was poor. Despite this, the concordance between manual and automated measurements in the means and variances of tissues was good, and both techniques identified the same changes in inflamed versus normal tissues. In addition, pixel-based counting permitted statistical analysis of co-localisation of cell types in tissue sections. We conclude that automated counting is acceptable for the assessment of tissues, is faster and provides less opportunity for observer variation than manual counting. We also demonstrate that the technique is applicable where more than three fluorochromes are used such that manual counting becomes essentially impossible.

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

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

Phenotypic and functional heterogeneity of porcine blood monocytes and its relation with maturation

Swine monocytes constitute a heterogeneous population of cells which can be divided into four subsets based on the expression of SWC3, CD14, CD163 and swine leucocyte antigen (SLA) DR markers. These subsets appear to represent different maturation stages in a pathway along which these cells up-regulate the expression of SLA DR and CD163 antigens and reduce that of CD14. Differences in the expression of adhesion and costimulatory molecules are also patent, with a progressive increase in the expression of CD11a, wCD11R1, CD29, CD49d, CD61, CD1a and CD80/86, and a concomitant decrease in that of wCD11R2. Besides, these subsets differ in their capacity for tumour necrosis factor-alpha (TNF-alpha) production in response to lipopolysaccharide + interferon-gamma. The CD163(+) CD14(-) SLA DR(+) subset produces higher amounts of TNF-alpha than the CD163(-) CD14(+) SLA DR(-) subset, whereas CD163(+) CD14(+) SLA DR(+) and CD163(-) CD14(+) SLA DR(+) subsets show intermediate values. CD163(+) monocytes also display a higher ability to present soluble antigens to T cells than CD163(-) monocytes.

Development of the palatine tonsil in conventional and germ-free piglets

Palatine tonsils, like the Peyer's patches, are considered to be major inductive sites for the mucosa-associated lymphoid tissue (MALT), providing sampling and effector functions for the upper respiratory tract. Consistent with this, they have the architecture required of a classic inductive site (B-cell follicles, immunoglobulin class switching and the presence of naïve and memory T-cells). Here we show that much of this architecture develops after birth in the neonatal piglet, the numbers of T-cells, B-cells and accessory cells increasing with age. Conventional piglets also had higher levels of activated and memory T-cell subsets than germ-free piglets, consistent with development occurring as a result of microbial stimulus. The results suggest that the microbial environment influences the development of the tonsil immunological architecture. Given the role of the tonsil in induction of mucosal responses, this raises questions as to the effectiveness of the tonsil in dealing with colonising organisms in the neonate.

The normalization of guinea pig leukocyte fractions and lymphocyte subsets in blood and lymphoid tissues using a flow cytometric procedure

Many hematological and immunological parameters remain unclear in the study of the guinea pig. In this study, we established the mean values of blood counts, the percentage of leukocyte fractions and lymphocyte subsets in blood and various lymphoid tissues of the guinea pig with a flow cytometric procedure using MIL4/SSC. The mean counts of WBC and RBC in the blood were lower, and MCV and MCH were higher than those of other rodents, resembling those of humans. Furthermore, the mean percentages of blood lymphocytes were smaller and that of granulocyte was larger than those of other rodents, resembling those of humans. We further established a flow cytometric procedure for lymphocyte subsets and clarified the mean percentages of T- and B-cells, CD4(+)-, CD8(+)- and MHC Class II(+)- T-cells, and CD4(-)CD8 (-) T-cells. The latter were morphologically larger in cell size and cytoplasm than CD4(+)- plus CD8(+) T-cells, and this subset had a significantly higher percentage in newborn animals. Furthermore, the appearance of the MHC Class II(+) T-cell subset was suggested to be a marker of hyper-activation of T-cells in BCG-immunized animals. Thus, both the novel flow cytometric procedure for leukocyte fractions and lymphocyte subsets, and the established normal values will be useful tools in studying guinea pigs as models of various diseases and biological phenomena.

Immune cell infiltration of normal and impaired sow endometrium

The paper reviews the physiological infiltration of immune cells, leukocytes, in the sow endometrium during different stages of the normal oestrous cycle, after mating and during early pregnancy. The mechanisms for development of endometritis in relation to oestrous cycle stages are also described.

Flow cytometric analysis of bone marrow leukocytes in neonatal dogs

Dogs represent both an important veterinary species and a convenient model for allogeneic hematopoietic stem cell transplantation. Even though anti-canine CD34 antibodies have recently become available, little is known about hematopoietic lineages in dogs, partially because CD34- cells have been ignored in all analyses performed so far. In this study, we have focused on the bone marrow mononuclear compartment to provide an additional piece of information on the phenotype of CD34+ progenitors and to identify the dominant CD34- population. We have shown that, in contrast to the adults, mature lymphocytes are scarce in neonatal dog bone marrow. Using cross-reactive antibodies against CD79alpha we have shown that the B lineage of hematopoiesis strongly prevails. CD34+ cells were shown to be positive for MHC class II and SWC3, a member of the signal regulatory protein family.

Immunohistochemical detection of SWC3, CD2, CD3, CD4 and CD8 antigens in paraformaldehyde fixed and paraffin embedded porcine lymphoid tissue

Identification of the different cell types of the immune system is important for in situ studies on the pathogenesis of infectious diseases in various animals, including the pig. Unfortunately, many monoclonal anti-leukocyte antibodies are only useful for staining frozen tissue sections with inherent poor tissue morphology, and are not readily adapted to formaldehyde fixed and paraffin embedded tissue with well preserved morphology. Seven well characterised monoclonal antibodies against porcine leukocyte antigens were tested on neutral buffered paraformaldehyde fixed and paraffin embedded porcine tissue sections using the highly sensitive tyramide signal amplification system. Combining this method with different antigen retrieval techniques enabled us to detect CD2, CD3, CD4, CD8 and SWC3 antigen expressing cells in porcine lymphoid tissue. Thus, we describe herein methods for the detection of several major cell types of the porcine immune system in fixed tissue with optimal preservation of histological details.

Innate immune responses following emergency vaccination against foot-and-mouth disease virus in pigs

Inactivated "emergency" foot-and-mouth disease virus (FMDV) vaccine of high potency will induce early protection against the disease, implying a critical role for innate immune defences. At 3 and 6 days post-vaccination (dpv), there was no evidence of vaccine-induced specific anti-FMDV antibodies (Abs), nor enhanced uptake and destruction of opsonised virus by macrophages. Sera from vaccinates and control animals showed similar capacity to neutralise the virus, and were not different from the pre-vaccination sera. There were also no distinguishable changes in the distribution of the different peripheral blood leucocyte (PBL) subpopulations. Nor was any vaccine-induced increase in production of acute phase proteins noted. In contrast, chemotaxis assays identified an increase in PBL migratory activity which was vaccine-related. Furthermore, sera from 3 days post-vaccination contained elevated chemotactic potential. These results demonstrate that enhanced chemotaxis of cells of the innate immune defences, could play an important role during the early protection induced by emergency FMDV vaccines.

Model for experimental revascularized laryngeal allotransplantation

BACKGROUND

Although a human laryngeal transplant has been undertaken successfully, important questions remain that require a suitable animal model.

METHODS

A pig model for allotransplantation has been developed. Organ perfusion was studied in nine animals before four transplants were performed in congenic (unrecovered) animals and eight in unmatched (recovered) animals. Larynges were regularly examined endoscopically until death at 14 days. Immunosuppression included the use of tacrolimus. Revascularization was achieved by anastomosing the donor right cervical vascular tree to the recipient common carotid. In recovered animals, four allografts were placed orthotopically and four heterotopically.

RESULTS

The pig larynx was perfused adequately via the right cervical vascular tree and congenic grafts were well tolerated. Of eight allografts, seven were well tolerated and remained healthy for the duration of the study (14 days). One allograft became infected between days 4 and 7 after operation. Median operating time was 6 h, with a median cold ischaemia time of 3 h.

CONCLUSION

Revascularized allotransplants of the larynx can be undertaken reliably in pigs and this provides a preclinical model for studies of laryngeal transplantation.

Immunophenotyping of leukocyte subsets in peripheral blood and palatine tonsils of prefattening pigs

The quantitative and distribution patterns of porcine peripheral blood and tonsillar lymphoid/myeloid cell subsets were assessed in order to establish the immune status of farm pigs prior to their transfer to fattening units. Peripheral blood and tonsillar samples were taken from clinically healthy, nonvaccinated, 12-week-old pigs, either ex vivo or following euthanasia. Single-colour flow cytometry, using monoclonal antibodies (mAbs) reactive with the swine leukocyte cluster of differentiation (CD) antigens, gave the proportions of lymphoid (9.7% CD4+, 8.0% CD8+, 36.9% CD5a+, 20.3% CD16+, 6.9% CD21+, 86.3% CD45+, 41.8% CD45RA+, 48.3% CD45RC+), null cells (6.9%) and myeloid cells (23.7% CD11b+ and 5.4% SWC3a+) in peripheral blood. In situ identification and distribution of lymphoid cells in the tonsils (CD3a+, CD21+, CD45RA+, CD45RC+) was performed with anti-CD mAbs using the avidin-biotin complex method. Most CD3a+ cells were in the parafollicular areas, with many cells in the follicles. CD21+ cells were scattered throughout the parafollicular area, with only a few cells inside lymphoid follicles. CD45RA+ cells were mostly concentrated in the follicles but many positive cells were present in the parafollicular area. Many CD45RC+ cells were visible in the parafollicular area, a few positive cells were in the crypt epithelium, and single cells were inside the follicles.

The sow endometrium at different stages of the oestrous cycle: immunohistochemical study on the distribution of SWC3-expressing cells (granulocytes, monocytes and macrophages)

Uterine samples from sows taken immediately after slaughter at late di-oestrus, pro-oestrus, oestrus, early di-oestrus and di-ocstrus, were analysed by immunohistochemistry with an avidinbiotin-peroxidase method using a monoclonal antibody (anti-SWC3) to granulocyte, monocyte and macrophage populations. The endometrium was then examined by light microscopy. In the surface and glandular epithelium, the largest numbers of SWC3-expressing cells (P < or = 0.01 and P < or = 0.05) were found at oestrus, and at pro-oestrus and oestrus, respectively. The numbers of SWC3-expressing cells in the epithelium were positively correlated with the plasma levels of oestradiol-17beta. In the connective tissue of the subepithelial and glandular layers, no significant effect of the oestrous Cycle stage was found on the number of SWC3-expressing cells. The present study showed a variation in the distribution of SWC3-expressing cells in the sow endometrium, especially in the surface and glandular epithelium, during different stages of the oestrous cycle.

Immunohistological study of the immune system cells in paraffin-embedded tissues of conventional pigs

The distribution of different cells of the immune system has been studied in formalin-fixed paraffin-embedded tissues from conventionally reared healthy pigs, using immunohistological techniques. The samples collected were: lungs, tonsils, lymph nodes (mediastinal, mesenteric, inguinal and submandibular), pancreas, spleen, liver, kidney, adrenal gland, ileum and stomach. A total of six primary antibodies anti-CD3, anti-CD79alpha, Mac 387, anti-lysozyme, anti-CD45RA (3C3/9) and anti-SLA-II-DQ (BL2H5) were used with a standard avidin-biotin peroxidase (ABC) method. Anti-CD3 and anti-CD79alpha mAb-reacted, respectively with cells located in T cell areas and B cell areas. Mac 387 recognised circulating polymorphonuclear leukocytes, while anti-lysozyme-stained resident macrophages in all tissues. 3C3/9 and BL2H5, were assessed in formalin-fixed paraffin-embedded tissues for the first time. 3C3/9 identified B lymphocytes, in primary follicles and mantle zones, a subpopulation of T cells, especially located in the marginal zone of the spleen and a variable number of immunoblasts, in the germinal centres. BL2H5 reacted with B cells in the mantle zones of the follicles of lymphoid tissues, with dendritic and interdigitating cells in all studied lymphoid tissues and with a variable number of resting and activated T cells in the periarteriolar lymphoid sheath (PALs), marginal zone and red pulp of the spleen. Furthermore, it stained Kupffer and perivascular macrophages in the liver. This study represents a detailed histological study of the distribution of the most important subpopulations of immune system cells in conventional, healthy pigs. In our view, these tools should be useful for future comparative studies in disease conditions.

Summary of workshop findings for porcine myelomonocytic markers

About 65 monoclonal antibodies (mAb) including 17 internal controls were analyzed for their ability to recognize and bind to various cells of the myelomonocytic lineage. Flow cytometry (FCM) utilizing both single and double staining, and immunoprecipitation (IP) assays were used in the analysis. About 38 of the mAb were reactive with myelomonocytic cells, resulting in nine clusters of interest. Although the exact identity of many of the molecules on the cells bound by the mAb remains undetermined, information obtained about the mAb analyzed in this workshop should be helpful in further identifying various populations of myelomonocytic cells and their stages of differentiation. Out of 12 mAbs with potential CD11 specificity, seven were assigned to three different swine specific alpha chains of the CD11/CD18 integrin heterodimer, the assignment of the remaining four was tentative. One antibody had a binding specificity consistent with SWC3 and one with SWC8. CD14 expression on pig cells was characterized with a panel of CD14-positive antibodies, two of these antibodies were assigned to swine CD14. Two antibodies were assigned to CD163. Further work is required to determine the antigens recognized by many of the other mAb.

Overview of the Third International Workshop on Swine Leukocyte Differentiation Antigens

The aim of the Third International Workshop on Swine Leukocyte Differentiation Antigens (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, using nomenclature in accordance with human and ruminant CD nomenclature, as agreed at the summary meeting of the Second International Swine CD Workshop in Davis, 1995: only mAb with proven reactivity for the orthologous porcine gene product or cross-reactivity for the human gene products, were given the full CD nomenclature, all other allocations were prefixed with "w". As in previous workshops, the overall organization was entrusted to the chair and first author, with support by the chair of the previous workshop and second author. In addition to the existing 26 pig leukocyte CD/SWC determinants established in previous workshops, this workshop established/confirmed another 11 CDs for pig leukocytes, identified by a total of 21 mAb: CD11R1 (2 mAb), CD11R2 (1 mAb), CD11R3 (4 mAb), wCD40 (1 mAb), wCD46 (4 mAb), wCD47 (3 mAb), wCD49d (1 mAb), CD61 (1 mAb), wCD92 (1 mAb), wCD93 (1 mAb) and CD163 (2 mAb).

Monoclonal antibodies raised to human cells--specificity for pig leukocytes

A total of 27 monoclonal antibodies raised to human targets were included in the present Pig CD workshop. 14 of these had been tested in previous workshops and had been reported as cross-reactive, a further 13 had been reported as cross-reactive during the Human Leukocyte Differentiation Antigens Workshop VI (HLDA VI) and/or by the donor (a commercial company submitting these mAb for validation by the workshop community). Of the 27 antibodies, three antibodies with previously reported reactivity for pig cells were eliminated from the workshop following preliminary tests due to lack of reactivity. Nine antibodies, although initially positive, gave inconsistent results during the course of the workshop. We found consistent reactivity for 15 antibodies. However, the cellular distribution of the target molecules on pig and human cells was shown to be different for three of these antibodies. These findings have important implications for the usefulness of these antibodies as research tools in the pig.

Monoclonal antibodies putatively recognising activation and differentiation antigens

In the activation/maturation section, 46 monoclonal antibodies (mAbs) were analysed using freshly isolated as well as mitogen activated and recall antigen re-stimulated cells. A total of 10 internal standards as well as 6 antibodies with established reactivity for human cells, reported to cross-react with porcine leukocytes, were included in the panel. The standard antibodies were anti-CD25, CD44, CD45, SLA II, SWC1, SWC2, SWC7 and SWC8 reagents. The test panel contained antibodies with putative reactivity to CD25, SLA II and other mAbs directed against ill-defined targets. Single and double colour surface staining was performed in the attempt to group the mAbs tested into clusters of differentiation. Five new anti-class II reagents, two directed to SLA-DQ and three to SLA-DR, could be added to the previously established ones. One new anti-CD25 as well as two new antibodies with SWC7 and SWC8 specificities, respectively, could also be added to the previously established ones. The identity of the two latter antibodies was also confirmed in other sections of this workshop (B-cell section for SWC7 antibodies and myeloid section for the SWC8 antibodies). The antibody JM2F12, in our hands, has shown strong similarities to the cross-reactive anti human-CD49f reagent. No other clusters were identified, as all remaining antibodies behaved in a different way on different target leukocyte populations. The second purpose of the section was fulfilled: interesting staining profiles of several antibodies on differentiating lymphocytes were recorded and are discussed here.

Induction of apoptosis in bone marrow neutrophil-lineage cells by classical swine fever virus

The pathogenesis of bone marrow atrophy during classical swine fever (CSF) was investigated in vitro by using CSF virus (CSFV) infection of bone marrow haematopoietic cells (BMHC). The monocytic lineage had the highest susceptibility to CSFV infection, whereas the more mature SWC8+ granulocytic cells were not directly susceptible to infection. However, myelomonocytic precursors were targets for CSFV infection and continued to differentiate into SWC8+ granulocytic cells, which remained infected. This explains the occurrence of infected peripheral blood granulocytes during CSF. The infection of BMHC resulted in increased apoptosis and necrosis, mainly within the granulocytic lineage. Caspases 3 and 9 were particularly activated, relating to the mitochondrial pathway of apoptosis. Interestingly, the majority of infected cells were non-apoptotic, the apoptotic cells being primarily non-infected. This indicated an indirect mechanism for induction of apoptosis, but no role could be identified for bone marrow stroma cells such as macrophages or fibroblastoid cells. Furthermore, soluble factors including cytokines and reactive oxygen species were not primarily responsible. In contrast, contact between infected and non-infected BMHC was critical for increasing apoptosis in the latter. Taken together, these results in vitro relate to and help to explain further the apoptosis of BMHC that occurs in vivo during CSF. This experimental system will also be particularly useful for the study of CSFV gene products involved in leukocyte apoptosis.

Immunolocalization of matrix metalloproteinases in partial-thickness defects in pig articular cartilage. A preliminary report

BACKGROUND

Partial-thickness defects in mature articular cartilage do not heal spontaneously. Attempts at repair often result in limited integration between the repair tissue and the surrounding cartilage, with formation of chondrocyte clusters adjacent to a zone of cartilage necrosis. In wound repair, spatially and temporally controlled expression of matrix metalloproteinases and their inhibitors have been implicated in proteolytic degradation of damaged extracellular matrix components, but the sequence of events following damage to cartilage is unknown. To determine this sequence, we studied the distribution of matrix metalloproteinases and their inhibitors during early in vivo repair of partial-thickness defects in pig articular cartilage.

METHODS

With use of a model that elicits the ingrowth of mesenchymal cells into partial-thickness defects, partial-thickness defects were created in knee joint cartilage. The distributions of matrix metalloproteinase-1, 2, 3, 9, 13, and 14; tissue inhibitors of metalloproteinase-1 and 2; and the neoepitope DIPEN341 specifically generated following matrix metalloproteinase cleavage of aggrecan were determined by immunolocalization of repair tissue and surrounding cartilage excised from immature pigs during the first eight weeks of repair and from adult minipigs at eight days and three weeks.

RESULTS

Synthesis of matrix metalloproteinase-13 was usually confined to hypertrophic chondrocytes in immature cartilage and to the radial zone in adult cartilage. Following injury, strong induction of matrix metalloproteinase-13 synthesis was observed in chondrocyte clusters surrounding lesions in all of the animals. The migration of macrophages into defects was prominent at two and eight days, with synthesis and deposition of matrix metalloproteinase-9 onto damaged cartilage matrix and newly synthesized matrix in the defect. The DIPEN341 neoepitope was localized to damaged cartilage matrix at eight days and six weeks, indicating partial degradation of aggrecan. Focal synthesis of matrix metalloproteinase-1, 3, and 14 and of tissue inhibitor of metalloproteinase-1 occurred at later times, suggesting continuous remodeling of the increasingly compact repair tissue.

CONCLUSIONS

The expression of matrix metalloproteinase-13 by normal hypertrophic chondrocytes and the induction of synthesis in chondrocyte clusters adjacent to the zone of cartilage necrosis suggest that this enzyme participates in the pericellular proteolysis required for lacunar expansion. The localization of matrix metalloproteinase-9 to damaged cartilage matrix suggested matrix proteolysis, which was confirmed with DIPEN341 localization. Reduced matrix metachromasia persisted and was colocalized with DIPEN341 at six weeks. However, under the conditions investigated, there was only limited proteolytic degradation in the zone of cartilage necrosis. This may render the zone mechanically weakened, thereby contributing to subsequent instability of the region, and may form a barrier to integration of repair tissue with viable cartilage.

CLINICAL RELEVANCE

Osteoarthritis initially involves the superficial layers of cartilage. The development of procedures to promote the healing or repair of early defects will have major advantages in terms of disease alleviation as well as economic importance. Identification of the enzymes involved in the early repair of partial-thickness defects in articular cartilage is clinically relevant because proteolysis of damaged matrix has to take place in order for repair tissue to integrate with surrounding healthy cartilage.

Characterization of lymphocyte subsets from mucosal tissues in neonatal swine

Monitoring differences in lymphocytes during neonatal development constitutes a key to understanding the developing piglet's natural and pathological immune responses. A survey was conducted to accumulate information on the phenotype of lymphocytes isolated from blood, lymph nodes, and lymphoid associated structures of the pig small intestine of conventional pigs from day 1 to 47 of age and inbred miniature pigs between 12 and 82days. The effect of weaning, and age before and after weaning, were also evaluated. Weaning had a significant effect on the number of CD4(+), CD8(+), double positive CD4(+)/CD8(+), CD21(+), deltagammaTCR(+), SWC3(+) and SLA-DQ(+) cells. Aging of the pig before and after weaning resulted in significant changes in lymphocytes isolated from mesenteric lymph nodes and ileal sites. These results constitute an important baseline for studying mucosal immune response of neonatal pigs and identifying factors that influence the ability of the neonate to respond to the stresses and antigenic exposure associated with weaning.

Depletion of CD4(+) and CD8(high+) T-cells before the onset of viraemia during classical swine fever

Leukopenia, in particular lymphopenia, is a characteristic early event during classical swine fever (CSF). This was the case in both highly virulent (CSF virus (CSFV) strain Brescia) and moderately virulent (CSFV Uelzen) infections. The leukopenia involved leukocyte sub-populations in a disparate manner, with B-lymphocytes, helper T-cells and cytotoxic T-cells being the most affected. Depletion of lymphocyte sub-populations occurred 1-4 days before virus could be detected by RT-PCR in the serum. With the virulent Brescia virus, depletion was evident by 2 days post-infection (p.i.) but not until 3 days p.i. with an equivalent dose of the low virulent Uelzen strain. A lower (1000-fold) dose of the latter virus delayed these kinetics. gammadelta-TCR(+) T-cells were also reduced, but more so with the virulent Brescia infection. The final level of B-and alphabeta-T-cell lymphopenia was similar for all animals, including those infected with the lower virus dose. AnnexinV staining revealed that cell viability was clearly diminished, particularly interesting, considering the clinical differences between infections by Brescia and Uelzen viruses. It was the time p.i. and rate of appearance of dying cells which was more rapid in the virulent Brescia infections. Interestingly, the repeated blood sampling resulted in depletion of some leukocyte populations also in non-infected control animals. Particularly neutrophils and NK cells, and to a lower extent CD4(+), CD8(+) T-lymphocytes and B-lymphocytes were affected. Taken together, the data show that the alphabeta-T-lymphocyte subsets are particularly susceptible to modulation during the acute phase of CSF, being detectable before the onset of viraemia. The pathogenic mechanism therein would involve indirect virus-host interactions, probably originating from the site of primary infection, rather than a direct effect of the virus or viral protein. Furthermore, these characteristics offer an explanation for the retardation of the cellular and humoral immune response observed during classical swine fever.

Morphologic and immunohistochemical features of experimentally induced allergic contact dermatitis in Göttingen minipigs

Many preclinical studies in investigative dermatology are performed preferably in pigs because pig skin is more similar to human skin than is rodent skin. A frequently used model is allergic contact dermatitis (ACD); however, this T-cell-mediated skin condition so far is not well characterized in pigs. The present study is aimed at the evaluation of morphologic and immunohistochemical features of experimentally induced acute ACD in Göttingen minipigs using 2,4-dinitrofluorobenzene (DNFB) as a hapten. Eight minipigs were sensitized with 10% DNFB and challenged 2 weeks later at different sites with 1% DNFB. In addition to clinical examinations, cutaneous blood flow was quantified by laser Doppler velocimetry (Periflux PF3). These examinations were performed before challenge and 8, 24, 48, and 72 hours after challenge. Skin biopsies were taken at the same time points, fixed, sectioned, and stained with Giemsa for histologic evaluation, or with mouse anti-swine monoclonal antibodies (CD1, CD2, CD4, CD5, CD8, CD25, CD45, MHCII) and with one mouse anti-human monoclonal antibody (CD62E) cross-reacting with swine for immunohistochemical evaluation. Positively stained cells were counted per square millimeter of epidermis and dermis by using a video image analyzing system (Videoplan Kontron). Erythema and cutaneous blood flow peaked at 24 hours. The major epidermal changes most pronounced at 48 hours were acanthosis, spongiosis, intracellular edema, exocytosis, and abscesses mainly containing neutrophils and mononuclear cells (MNC). Perivascular infiltrates of MNC as well as neutrophils and eosinophils were the most significant dermal changes, with peak levels at 24-48 hours. In biopsies taken before challenge, CD1+ dendritic cells were found in similar numbers and locations as MHCII+ cells in the epidermis. In the epidermis the maximum CD1+ cell decrease occurred at 24 hours whereas in the dermis the maximum increase in CD1+ stained cells was seen at 72 hours. The dermal infiltrate (CD2+, CD5+, CD25+, and CD45+) was most dense at 48 hours. Between 8 and 48 hours more CD4+ were present than CD8+, cells, whereas at 72 hours CD4+ and CD8+ cells were similar in numbers. These findings closely resemble changes in human ACD. Therefore, DNFB-induced ACD in Göttingen minipigs is considered to be an appropriate animal model to study immunopathologic mechanisms and pharmacologic intervention.