Summary of workshop findings for porcine T-lymphocyte-specific monoclonal antibodies

MITOCHONDRIA IN BIODOSIMETRY: FLOW CYTOMETRY ASSESMENT IN VITRO

The JC-1 dye is widely used in apoptosis studies to monitor mitochondrial health. The probe was tested in vitro on two established cell lines and peripheral porcine blood lymphocytes after gamma irradiation (IR) to assess its potential in biodosimetric evaluation. In brief, we stained irradiated and non-irradiated cells with the JC-1 dye to determine the existing changes in mitochondrial membrane potential and monitor cell health through flow cytometry. The stage of injury in these cells was evaluated through an irradiated versus non-irradiated ratio (IVNIR), comparing the relative proportion of polarised cells containing red JC-1 aggregates. We observed a decreasing IVNIR as the radiation dose increased (i.e. 0.5; 1; 2; 4; 6; 8 and 10 Gy), performing the analysis at 4, 8 and 24 h after IR in all the tested cells. The results from the JC1-dye test showed that CD4 T lymphocytes were more sensitive to irradiation than other subpopulations.

Pig peripheral blood mononuclear leucocyte subsets are heritable and genetically correlated with performance

Indicator traits used to select pigs for increased resistance to infection or improved health must be heritable and, preferably, be associated with improved performance. We estimated the heritability of a range of immune traits and their genetic and phenotypic correlations with growth performance. We measured immune traits on 589 pigs and performance on 1941 pigs from six farms, three of which were classified as 'high health status' (i.e. specific pathogen-free) and three were of lower health status. All pigs were apparently healthy. Immune traits were total white blood cells (WBC), and peripheral blood mononuclear leucocyte (PBML) subsets positive for CD4, CD8α, gamma delta (γδ) T cell receptor, CD11R1 (natural killer cell marker), B cell and monocyte markers at the start and the end of standard growth performance tests. At both time points, all immune traits were moderately to highly heritable except for CD8α+ cells. At end of test, heritability estimates (h2) (±s.e.) were 0.18 (±0.11) for total WBC count. For PBML subset proportions, the heritabilities were 0.52 (±0.14) for γδ TCR+ cells, 0.62 (±0.14) for CD4+ cells, 0.44 (±0.14) for CD11R1+ cells, 0.58 (±0.14) for B cells and 0.59 (±0.14) for monocytes. Farm health status affected the heritabilities for WBC, being substantially higher on lower health status farms, but did not have consistent effects on heritabilities for the PBML subsets. There were significant negative genetic correlations between numbers and proportions of various PBML subsets and performance, at both start and end of test. In particular, the proportion of PBML cells that were CD11R1+ cells, at end of test, was strongly correlated with daily gain (rg = -0.72; P < 0.01). There were also weaker but significant negative phenotypic correlations between PBML subsets measured at end of test and performance, for γδ+ T cells, CD8α+, CD11R1+ cells, B cells or monocytes. Phenotypic correlations with daily gain were generally lower at the start of test than at the end of test. These results show that most of the major pig PBML subsets are heritable, and that systemic levels of several of these PBML subsets are genetically negatively correlated with performance. This approach provides a basis for using immune trait markers when selecting boars that can produce higher-performing progeny.

Feeding of the probiotic bacterium Enterococcus faecium NCIMB 10415 differentially affects shedding of enteric viruses in pigs

Effects of probiotic bacteria on viral infections have been described previously. Here, two groups of sows and their piglets were fed with or without feed supplementation of the probiotic bacterium Enterococcus faecium NCIMB 10415. Shedding of enteric viruses naturally occurring in these pigs was analyzed by quantitative real-time RT-PCR. No differences between the groups were recorded for hepatitis E virus, encephalomyocarditis virus and norovirus. In contrast, astrovirus was exclusively detected in the non-supplemented control group. Rotavirus was shedded later and with lower amounts in the probiotic piglet group (p < 0.05); rotavirus-shedding piglets gained less weight than non-infected animals (p < 0.05). Serum titres of anti-rotavirus IgA and IgG antibodies were higher in piglets from the control group, whereas no difference was detected between sow groups. Phenotype analysis of immune cell antigens revealed significant differences of the CD4 and CD8β (p < 0.05) as well as CD8α and CD25 (p < 0.1) T cell populations of the probiotic supplemented group compared to the non-supplemented control group. In addition, differences were evident for CD21/MHCII-positive (p < 0.05) and IgM-positive (p < 0.1) B cell populations. The results indicate that probiotic bacteria could have effects on virus shedding in naturally infected pigs, which depend on the virus type. These effects seem to be caused by immunological changes; however, the distinct mechanism of action remains to be elucidated.

Contribution of large pig for renal ischemia-reperfusion and transplantation studies: the preclinical model

Animal experimentation is necessary to characterize human diseases and design adequate therapeutic interventions. In renal transplantation research, the limited number of in vitro models involves a crucial role for in vivo models and particularly for the porcine model. Pig and human kidneys are anatomically similar (characterized by multilobular structure in contrast to rodent and dog kidneys unilobular). The human proximity of porcine physiology and immune systems provides a basic knowledge of graft recovery and inflammatory physiopathology through in vivo studies. In addition, pig large body size allows surgical procedures similar to humans, repeated collections of peripheral blood or renal biopsies making pigs ideal for medical training and for the assessment of preclinical technologies. However, its size is also its main drawback implying expensive housing. Nevertheless, pig models are relevant alternatives to primate models, offering promising perspectives with developments of transgenic modulation and marginal donor models facilitating data extrapolation to human conditions.

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.

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.

The association between plasma levels of acute phase proteins, haptoglobin, alpha-1 acid glycoprotein (AGP), Pig-MAP, transthyretin and serum amyloid A (SAA) in Large White and Meishan pigs

During infection, the acute phase response triggers the release of acute phase proteins (APP), alpha-(1) acid glycoprotein (AGP), serum amyloid A (SAA) and Pig-MAP into the circulation, accompanied by a decrease in plasma levels of transthyretin. We quantified the association between these APP in 26 apparently healthy pigs from two breeds, 13 Large White and 13 Meishan (16 male; 10 female). There was a significant correlation between plasma levels of haptoglobin and Pig-MAP (r=0.57; p<0.05), but no significant associations between any of the other APP tested. We also measured the relationship between PigMAP, transthyretin and SAA, and the proportions of peripheral blood mononuclear sub-sets, CD8(+) cells, CD4(+) cells, CD11R1(+) cells, MHC DQ(+) cells, and monocytes. There were correlations between both plasma levels of Pig-MAP and the proportion of monocytes (r=0.55; p<0.05) and plasma levels of transthyretin and the proportion of MHC DQ(+) cells (r=0.40; p<0.01). Breed and sex influenced plasma levels of Pig-MAP but not plasma levels of transthyretin. Overall, these results suggest closer links between the mechanisms that regulate the release haptoglobin, Pig-MAP and monocytes compared to those that regulate the release of AGP, SAA and transthyretin.

Selection for lean growth and food intake leads to correlated changes in innate immune traits in Large White pigs

Genetic selection is well established as a means of improving productivity in pigs, but the effects of continued selection for increased performance on immunity are not well understood, nor are genetic relationships between performance and immunity. This study compared differences in the levels of a range of immune traits between lines of Large White pigs divergently selected for a number of productivity traits. Selection lines compared were highv. low lean growth under restricted feeding (31 high linev. 10 controlv. 38 low line pigs), high v. low lean growth underad libitumfeeding (18 high line v. 10 controlv. 19 low line pigs), and highv. low food intake (24 high linev. 26 low line pigs). Immune traits measured were total white blood cell numbers (WBC), and the numbers of leukocyte subsets: neutrophils, monocytes, eosinophils, lymphocytes, CD4+cells, CD8α+cells, B cells, γδ T cells and CD11R1+Natural killer (NK) cells. CD4+, γδ T cells and CD11R1+cells were subdivided into subpopulations that were positive or negative for the CD8α marker, and conventional CD8αhigh+cytotoxic T cells were also determined. Pigs were tested underad libitumfeeding conditions from 14 to 24 weeks, and immune traits were assessed at ages 18 and 24 weeks. Line differences were estimated using residual maximum likelihood techniques. Consistent differences in immune trait levels were evident between pigs previously selected for high and low lean growth under restricted feeding: at age 24 weeks, high line pigs had higher basal levels of WBC (39·6v. 27·8×106cells per ml, s.e.d. 2·09, for highv. low line pigs) mainly explained by higher levels of lymphocytes (25·5v. 17·3×106cells per ml, s.e.d. 1·54, for highv. low line pigs) with increased numbers of CD8α+cells (8·19v. 5·15×106cells per ml, s.e.d. 0·14) and CD11R1+cells (5·23v. 2·46×106cells per ml, s.e.d. 0·43), predominantly the CD11R1+CD8α?subpopulation ((3·20v. 1·64×106cells per ml, s.e.d. 0·11). High line pigs also had increased numbers of monocytes (2·64v. 1·83×106cells per ml, s.e.d. 0·35). Similar results were obtained at age 18 weeks. There were no consistent differences between divergent lines in pigs selected for lean growth underad libitumfeeding or food intake. This is the first report to demonstrate that selection for some aspects of performance can influence WBC and leukocyte subset numbers in pigs.

Innate immune traits differ between Meishan and Large White pigs

A panel of innate immune traits were compared between Meishan and Large White pigs. These pigs were of similar age and kept under the same environmental conditions to reduce non-genetically derived variation in immune traits. The animals were all apparently healthy and were not experimentally challenged with any pathogen during the study. The measures only required a small blood sample. Total white cell counts were similar between the pig breeds. However, the numbers of lymphocytes, neutrophils and monocytes differed significantly, with Meishans having higher neutrophil and monocyte counts and lower lymphocyte counts. Flow cytometric methods were used to determine quantitatively the characteristics and function of neutrophils and monocytes. Meishan neutrophils were smaller and less complex than Large White neutrophils, and phagocytosis of Escherichia coli and the ensuing oxidative burst was lower in Meishan neutrophils compared to Large White neutrophils. Monocyte phagocytosis of E. coli was significantly less than that of neutrophils in both breeds but the function of Meishan monocytes as measured by phagocytosis and tumour necrosis factor alpha (TNFalpha) release did not differ from that of Large White monocytes. Levels of acute phase proteins also differed between the breeds with a significantly higher proportion of Meishans having elevated serum amyloid A levels. However, Meishans had lower alpha(1)-acid glycoprotein levels than Large Whites and haptoglobin levels were similar. Such differences in innate immune traits may have implications in the resistance to infection by a broad range of pathogens and subsequent disease effects in these breeds. Further studies are warranted to investigate the genes underlying these traits.

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.

Porcine CD58: cDNA cloning and molecular dissection of the porcine CD58-human CD2 interface

The porcine ligands of human CD2 remain unknown in xenotransplantation despite being an important pathway of T cell costimulation. Of the two main candidates, i.e., CD48 and CD58, the cDNA of the most likely ligand poCD58 was cloned from CD48-negative endothelial cells costimulating human CD4(+) T cells through the CD2 pathway. The deduced protein sequence is 244 residues long and is 43% homologous to the human sequence. Based on similarity between porcine and human CD58 external V-set Ig-type domains, a structural model of poCD58-huCD2 interaction was built. Most of the charged residues located at the interface with huCD2 are highly conserved. Six putative hydrogen bonds between poCD58 and huCD2 were identified; five involve the same residues as in the syngeneic combination while the sixth is formed between an additional tyrosine in poCD58 and Arg48 in huCD2, increasing the complementarity between the two molecules. These structural data will help us to develop poCD58 blocking agents for xenotransplantation.

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.