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.

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

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

Expression of CLEC4A in porcine tissues and leukocyte populations and characterization of mRNA splice variants

CLECs are a group of molecules of the superfamily of C-type lectin domain containing receptors. Several receptors of this group have been described in humans and mice, as well as in other species. Many of them are expressed in immune cells, and have been shown to be involved in immune response modulation. Several molecules of this family have been proposed as targets for antigen delivery, which is what drew our interest in studying them in the pig. In this species only CLEC7A (also named Dectin-1) had been studied in some detail, and we have characterized two other members, CLEC12A and CLEC12B. Another molecule of interest was CLEC4A, for which we could not find any expression studies in pigs, although up to 5 different mRNA variants had been predicted by bioinformatics analysis of the genomic sequence in databases. Here we present an analysis of the expression of CLEC4A mRNA isoforms in tissues and blood cell subsets by PCR. Cloning and sequencing of cDNA of the different isoforms allowed us to identify all 5 predicted isoforms, in addition to characterizing 5 additional isoforms expressed in alveolar macrophages, of which the form coding for a canonical CLEC4A molecule was apparently the most abundant isoform. Analysis of the sequences of the 10 cDNA cloned allowed us to determine their exon usage and to identify their potential for protein coding. Only 8 of the characterized variants contain a recognizable coding sequence. The sequences of the coded proteins show both proteins with a putative transmembrane segment, and others without this feature, as well as proteins with the complete CLEC domain or with diverse truncated forms. We also prove that most of the cDNA can drive protein expression upon transfection in the CHO cell line. We discuss the relevance that the diversity of products of the porcine CLEC4A gene may have in the regulation of the expression and function of these molecules.

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

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

Porcine CLEC12B is expressed on alveolar macrophages and blood dendritic cells

CLEC12B is a C-type lectin-like receptor expressed on myeloid cells. In this study, we have characterized the porcine homologue of CLEC12B (poCLEC12B). To this end, we have generated constructs encoding a c-myc tagged version of the whole receptor, or its ectodomain fused to the Fc portion of human IgG1, from a cDNA clone obtained from an alveolar macrophage library, and raised monoclonal antibodies (mAb) against this molecule. Using these mAbs, poCLEC12B was found to be expressed on alveolar macrophages and, at lower levels, on blood conventional type 1 dendritic cells (cDC1) and plasmacytoid DCs. No binding was detected on monocytes, monocyte-derived macrophages or monocyte-derived DCs. Engagement of CLEC12B on alveolar macrophages with mAbs had no apparent effect on cytokine production (TNF-α, IL-8) induced by LPS. These results provide the basis for future investigations aimed to assess the role of poCLEC12B in different microbial infections and to evaluate its potential in vaccination strategies targeting DCs.

Expression of Siglec-1, -3, -5 and -10 in porcine cDC1 and cDC2 subsets from blood, spleen and lymph nodes and functional capabilities of these cells

Dendritic cells are professional antigen-presenting cells that play a critical role in the development of immune responses. DCs express a variety of Siglecs on their surface, which play a regulatory role modulating their activation through interaction with sialylated structures expressed by cells or pathogens. Here, we characterized the phenotype of porcine conventional dendritic cells subsets from blood, spleen and lymph nodes, emphasizing the analysis of the expression of Siglecs. Siglec-1 was detected in type 1 cDC and, at lower levels, in type 2 cDC in the spleen, being low to negative in blood and lymph node cDC. Siglec-3 and Siglec-5 were expressed in cDC1 at lower levels than in cDC2. Porcine cDCs did not express Siglec-10. cDC2 showed a higher capacity to phagocytose microspheres and to process DQ™-OVA than cDC1, but none of these functions was affected by engagement of Siglec-3 and -5 with antibodies on blood cDC.

Activation of pro- and anti-inflammatory responses in lung tissue injury during the acute phase of PRRSV-1 infection with the virulent strain Lena

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Lena virulent strain caused an increase in sera levels of IFN-γ and IL-6.

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Lung viral load and PRRSV-N-protein⁺ cells were inversely correlated with CD163⁺ macrophages in the lung.

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CD14⁺ cells infiltrated interstitium to possibly replenish macrophages subsets.

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Lena-induced microscopic lung injury was linked to an increase of iNOS⁺ cells.

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The increase of CD200R1⁺ and FoxP3⁺ cells was associated with the course of lung injury.

Porcine reproductive and respiratory syndrome virus (PRRSV) plays a key role in porcine respiratory disease complex modulating the host immune response and favouring secondary bacterial infections. Pulmonary alveolar macrophages (PAMs) are the main cells supporting PRRSV replication, with CD163 as the essential receptor for viral infection. Although interstitial pneumonia is by far the representative lung lesion, suppurative bronchopneumonia is described for PRRSV virulent strains. This research explores the role of several immune markers potentially involved in the regulation of the inflammatory response and sensitisation of lung to secondary bacterial infections by PRRSV-1 strains of different virulence. Conventional pigs were intranasally inoculated with the virulent subtype 3 Lena strain or the low virulent subtype 1 3249 strain and euthanised at 1, 3, 6 and 8 dpi. Lena-infected pigs exhibited more severe clinical signs, macroscopic lung score and viraemia associated with an increase of IL-6 and IFN-γ in sera compared to 3249-infected pigs. Extensive areas of lung consolidation corresponding with suppurative bronchopneumonia were observed in Lena-infected pigs. Lung viral load and PRRSV-N-protein⁺ cells were always higher in Lena-infected animals. PRRSV-N-protein⁺ cells were linked to a marked drop of CD163⁺ macrophages. The number of CD14⁺ and iNOS⁺ cells gradually increased along PRRSV-1 infection, being more evident in Lena-infected pigs. The frequency of CD200R1⁺ and FoxP3⁺ cells peaked late in both PRRSV-1 strains, with a strong correlation between CD200R1⁺ cells and lung injury in Lena-infected pigs. These results highlight the role of molecules involved in the earlier and higher extent of lung lesions in piglets infected with the virulent Lena strain, pointing out the activation of routes potentially involved in the restraint of the local inflammatory response.

Characterization of the Porcine CLEC12A and Analysis of Its Expression on Blood Dendritic Cell Subsets

CLEC12A has been proposed as a suitable target for delivering antigen to dendritic cells (DCs) to enhance vaccine efficacy both in human and mouse. In this study, we have characterized the porcine homolog of CLEC12A (poCLEC12A). Using new monoclonal antibodies (mAb), raised against its ectodomain, poCLEC12A was found to be expressed on alveolar macrophages, blood conventional type 1 and type 2 DCs and plasmacytoid DCs, but not on monocytes, T cells, B cells or NK cells, in contrast to its human and murine homologs. Western blot analysis showed that in alveolar macrophages this receptor is expressed both as a monomer and a dimer. After binding to DCs, anti- poCLEC12A mAb was efficiently internalized. No significant changes were observed in TNFα or IFNα secretion by plasmacytoid DCs stimulated with either CpGs (ODN2216) or polyinosinic-polycytidylic acid (poly I:C), upon incubation with mAb. These results provide the basis for future investigations aimed to assess the ability of anti-poCLEC12A mAbs to improve vaccine efficacy by targeting antigen to DCs.

Analysis of the expression of porcine CD200R1 and CD200R1L by using newly developed monoclonal antibodies

CD200R1 and CD200R1-like are paired receptors which modulate activation of immune cells. Here, we describe the characterisation of their porcine homologues. Analysis of database porcine sequences shows an exceptionally high homology between the extracellular Ig-like domains of these receptors, being the rest more dissimilar. We have obtained two mAbs, PCT1 and PCT3, against a CD200R1-Fc recombinant protein, that bind on CHO cells expressing GFP-tagged CD200R1. The specificity of these mAbs was analysed on CD200R1 L, and also on a CD200R1 splicing variant that lacks the V-type Ig domain. PCT1 bound to both CD200R1 and CD200R1L, but not to the splicing variant, what suggests that recognises an epitope in the V-type Ig domain. PCT3 reacted with both CD200R1 variants, but not CD200R1L, probably binding to an epitope in the N-terminal sequence of CD200R1. Analysis of porcine cells with these mAbs showed expression of CD200R1/CD200R1L on B cells, monocytes and alveolar macrophages.

Interaction of PRRS virus with bone marrow monocyte subsets

PRRSV can replicate for months in lymphoid organs leading to persistent host infections. Porcine bone marrow comprises two major monocyte subsets, one of which expresses CD163 and CD169, two receptors involved in the entry of PRRSV in macrophages. In this study, we investigate the permissiveness of these subsets to PRRSV infection. PRRSV replicates efficiently in BM CD163⁺ monocytes reaching titers similar to those obtained in alveolar macrophages, but with a delayed kinetics. Infection of BM CD163^- monocytes was variable and yielded lower titers. This may be related with the capacity of BM CD163^- monocytes to differentiate into CD163⁺ CD169⁺ cells after culture in presence of M-CSF. Both subsets secreted IL-8 in response to virus but CD163⁺ cells tended to produce higher amounts. The infection of BM monocytes by PRRSV may contribute to persistence of the virus in this compartment and to hematological disorders found in infected animals such as the reduction in the number of peripheral blood monocytes.

Phenotypic and functional characterization of porcine bone marrow monocyte subsets

Monocytes comprise several subsets with distinct phenotypes and functional capacities. Based on CD163 expression, two major monocyte subsets can be discriminated in the porcine bone marrow. The CD163⁺ cells expressed higher levels of SLA-DR, Siglec-1, CD11R1 and CD16 when compared to CD163^- monocytes, whereas no remarkable differences were observed in the expression of other markers analyzed. Gene expression analysis showed differential expression of several chemokine receptor and TLR genes. Both subsets phagocytosed microspheres with similar efficiency. However, CD163^- cells tended to produce higher levels of ROS in response to PMA, whereas CD163⁺ cells were more efficient in endocytosing and processing antigens (DQ-OVA). CD163^- monocytes produced higher levels of TNF-α and IL-10 than CD163⁺ cells when stimulated with LPS or Imiquimod. Both subsets produced similar amounts of IL-8 in response to LPS; however, CD163⁺ cells produced more IL-8 after Imiquimod stimulation. Whether these subsets represent different developmental stages, and how are they related remain to be investigated.

Splenic CD163+ macrophages as targets of porcine reproductive and respiratory virus: Role of Siglecs

CD169 and CD163 have been involved in the process of PRRS virus attachment and infection in macrophages, although recent studies have challenged the requirement for CD169. In addition to CD169, macrophages express other siglecs, whose role in PRRS virus infection is so far unknown. Splenic CD163⁺ macrophages express Siglec-3 and Siglec-5 but almost undetectable levels of CD169. Hence, we considered this cell population appropriate for analysing the role of these siglecs in the attachment and internalization of PRRS virus into macrophages. PRRS virus replicated efficiently in these macrophages, yielding even higher titres than in alveolar macrophages. Besides, a recombinant protein consisting in the ectodomain of porcine Siglec-3 fused to the Fc fragment of human IgG1 (Siglec3-Fc) was able to bind PRRS virus, while binding to Siglec-5-Fc was inconsistent. Antibodies to CD169 but not to Siglec-3 or Siglec-5 blocked the binding and infection of PRRS virus on alveolar macrophages. Unexpectedly, our antibody to CD169 also blocked the binding of PRRS virus to splenic CD163⁺ macrophages, whereas antibodies to Siglec-3 or Siglec-5 had no effect. These results show that very low levels of CD169 expression are enough to support the attachment and internalization of PRRS virus into macrophages, whereas Siglec-3 and Siglec-5 do not seem to contribute to the virus entry in these cells.

Molecular and functional characterization of porcine Siglec-3/CD33 and analysis of its expression in blood and tissues

A cDNA clone encoding a 380 a-a type 1 transmembrane protein with homology to human Siglec-3/CD33 was obtained from a swine small intestine library. An analysis of protein sequence identified two immunoglobulin-like domains, a transmembrane region, and a carboxi-terminal tail with two tyrosine-based signalling motifs. Binding assays of Siglec-3 transfected CHO cells to polyacrylamide glycoconjugates showed a preference for α2-6-linked sialic acids. Using mAbs raised against a fragment containing the two Ig-like domains, porcine Siglec-3 was found to be expressed on monocytes and granulocytes, and their bone marrow precursors. It was also detected in lymph node, splenic and alveolar macrophages. MAbs immunoprecipitated, from granulocyte lysates, a protein of 51-60 kDa under both non-reducing and reducing conditions. MAbs were also used to analyse functional activity of Siglec-3 on bone marrow and blood cells. Engagement of Siglec-3 by mAb had no apparent effect on cell proliferation or cytokine production.

Synthetic RNAs Mimicking Structural Domains in the Foot-and-Mouth Disease Virus Genome Elicit a Broad Innate Immune Response in Porcine Cells Triggered by RIG-I and TLR Activation

The innate immune system is the first line of defense against viral infections. Exploiting innate responses for antiviral, therapeutic and vaccine adjuvation strategies is being extensively explored. We have previously described, the ability of small in vitro RNA transcripts, mimicking the sequence and structure of different domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome (ncRNAs), to trigger a potent and rapid innate immune response. These synthetic non-infectious molecules have proved to have a broad-range antiviral activity and to enhance the immunogenicity of an FMD inactivated vaccine in mice. Here, we have studied the involvement of pattern-recognition receptors (PRRs) in the ncRNA-induced innate response and analyzed the antiviral and cytokine profiles elicited in swine cultured cells, as well as peripheral blood mononuclear cells (PBMCs).

Molecular characterization of porcine Siglec-10 and analysis of its expression in blood and tissues

Siglecs are sialic acid binding Ig-like proteins involved in the control of leukocyte responses. In this study we describe the characterization of a porcine orthologue of Siglec-10. A cDNA clone was obtained from a porcine library which encodes a protein with sequence homology to human Siglec-10. This cDNA codes for a type I transmembrane protein containing four Ig-like domains, a transmembrane region, and a cytoplasmic tail with three tyrosine-based motifs, including a membrane-proximal Grb2-binding motif, and two ITIM motifs. When expressed on transfected cells, porcine Siglec-10 was able to bind red blood cells in a sialic acid-dependent manner. Monoclonal antibodies were developed against this protein and used to examine its cell and tissue distribution in the pig. Siglec-10 was found to be expressed on blood B cells and B cell areas of the spleen and lymph nodes. A weak expression was also detected on monocytes.

Molecular characterization and expression of porcine Siglec-5

In this study we describe the characterization of the porcine orthologue of Siglec-5. A cDNa clone was obtained from a porcine cDNa library derived from swine small intestine which encodes a 555 a-a type 1 transmembrane protein with sequence homology to human Siglec-5. This protein consists of four Ig-like domains, a transmembrane region, and a cytoplasmic tail with two tyrosine-based signalling motifs. When expressed as a recombinant protein fused to the Fc region of human IgG1, porcine Siglec-5 was able to bind porcine red blood cells in a sialic acid-dependent manner. Monoclonal antibodies (mAb) were developed against porcine Siglec-5 and used to analyse its expression in bone marrow and blood cells, and lymphoid tissues. Porcine Siglec-5 expression was mainly restricted to myelomonocytic cells and their precursors, being detected also, although at low levels, on plasmacytoid dendritic cells and B lymphocytes. In lymphoid tissues, ellipsoids of the spleen and subcapsular and medullar sinuses of lymph nodes were positive for Siglec-5. These mAbs were able to precipitate, from granulocyte lysates, a protein of approximately 85 kDa under non-reducing conditions, indicating that porcine Siglec-5 is expressed as a monomer in the plasma membrane.

Phenotypic and functional heterogeneity of CD169⁺ and CD163⁺ macrophages from porcine lymph nodes and spleen

Secondary lymphoid organ macrophages are involved in the establishment of innate and acquired immunity. Here, we have isolated and characterized porcine lymph node and spleen CD169(+) and spleen CD163(+) macrophages. Lymph node and spleen CD169(+) macrophages can be both identified as CD172a(+)SLA-DR(hi)CD80/86(hi)CD14(int)TLR2(+)TLR4(+). On the other side, spleen CD163(+) macrophages are CD172a(+)SLA-DR(int)CD80/86(int)CD14(-)/(lo)TLR2(int)TLR4(int). In addition, these macrophages can be subdivided based on the expression of CD11R1 or CD11R3. Lymph node CD169(+) macrophages phagocytozed polystyrene microspheres more efficiently than spleen CD163(+) and CD169(+) macrophages. All macrophages exhibited low capacity to take up and process the soluble antigen DQ-OVA. Finally, spleen CD163(+) macrophages displayed the highest ability to present lysozyme to CD4(+) T cells in a secondary in vitro response, followed by lymph node and spleen CD169(+) macrophages.

Antigen targeting to APC: from mice to veterinary species

Antigen delivery to receptors expressed on antigen presenting cells (APC) has shown to improve immunogenicity of vaccines in mice. An enhancement of cytotoxic T lymphocyte (CTL), helper T cell or humoral responses was obtained depending on the type of APC and the surface molecule targeted. Although this strategy is being also evaluated in livestock animals with promising results, some discrepancies have been found between species and pathogens. The genetic diversity of livestock animals, the different pattern of expression of some receptors among species, the use of different markers to characterize APC in large animals and sometimes the lack of reagents make difficult to compare results obtained in different species. In this review, we summarize the data available regarding antigen targeting to APC receptors in cattle, sheep and pig and discuss the results found in these animals in the context of what has been obtained in mice.

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

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

DNA immunization of pigs with foot-and-mouth disease virus minigenes: from partial protection to disease exacerbation

Despite several attempts to design new vaccines, there are as of yet no available alternatives to the conventional FMDV vaccines. Here, we present the divergent results obtained in pigs after immunization with two experimental DNA vaccines encoding one B and two T cell FMDV epitopes, either expressed alone (pCMV-BTT) or fused to a strong signal peptide (pCMV-spBTT). While all pigs vaccinated with pCMV-spBTT showed both a delay in the disease onset and reduced severity of signs and lesions after FMDV challenge, pigs immunized with pCMV-BTT showed an exacerbation of the disease and most of the pigs remained viremic at 10 days post-infection, the end-point of the experiment, thus opening concerns about FMDV-suboptimal immunization. Interestingly, only one of the four pigs vaccinated with pCMV-spBTT showed neutralizing antibodies before challenge, demonstrating that partial protection against FMDV could be afforded in the absence of preexisting neutralizing antibodies.

Porcine monocyte subsets differ in the expression of CCR2 and in their responsiveness to CCL2

Monocyte subsets have been shown to differ in the pattern of chemokine receptor expression and their migratory properties, both in human and mouse. Previously we have characterized in the swine several monocyte subpopulations, based on the expression of CD163, Tük4 and SLA-II, which share features with the populations described in human and mouse. Here, we have analysed the expression of different chemokine receptors in the CD163⁻Tük4⁺SLA-II⁻ and CD163⁺Tük4⁻SLA-II⁺ populations of porcine monocytes. CD163⁺Tük4⁻SLA-II⁺ monocytes expressed higher CX₃CR1 but lower CCR2 and CXCR4 mRNA levels than CD163⁻Tük4⁺SLA-II⁻ monocytes. Moreover, porcine CCL2 binding on Tük4⁺SLA-II⁻ but not on Tük4⁻SLA-II⁺ cells was detected by using a CCL2-green fluorescence protein (pCCL2-GFP) fusion protein. Finally, flow cytometric analyses of monocytes recovered after chemotaxis assays show a clear increase in the proportion of Tük4⁺SLA-II⁻ cells in the fraction migrating toward CCL2, consistent with the polarized CCR2 expression in this monocyte population. The pattern of expression of these chemokine receptors reinforces the similarities of these porcine subsets with their human and mouse counterparts.

Targeting to porcine sialoadhesin receptor improves antigen presentation to T cells

Antibody-mediated targeting of antigen to specific antigen presenting cells (APC) receptors is an attractive strategy to enhance T cell immune responses to weak immunogenic antigens. Here, we describe the characterization of two monoclonal antibodies (mAb) against different epitopes of porcine sialoadhesin (Sn) and evaluate in vitro the potential of targeting this receptor for delivery of antigens to APC for T cell stimulation. The specificity of these mAb was determined by amino acid sequence analysis of peptides derived from the affinity purified antigen. Porcine Sn is expressed by macrophages present in the border between white and red pulp of the spleen and in the subcapsular sinus of lymph nodes, an appropriate location for trapping blood and lymph-borne antigens. It is also expressed by alveolar macrophages and monocyte-derived dendritic cells (MoDC). Blood monocytes are negative for this molecule, but its expression can be induced by treatment with IFN-alpha. MAb bound to Sn is rapidly endocytosed. MAb to sialoadhesin induced in vitro T cell proliferation at concentrations 100-fold lower than the non-targeting control mAb when using T lymphocytes from pigs immunized with mouse immunoglobulins as responder cells and IFN-alpha treated monocytes or MoDC as APC, suggesting a role of sialoadhesin in antigen uptake and/or delivery into the presentation pathway in APC.

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.

Expression of toll-like receptor 2 (TLR2) in porcine leukocyte subsets and tissues

Toll-like receptors (TLR) are a group of pattern recognition molecules that play a crucial role in innate immunity. TLR2 recognises a variety of microbial components leading to the development of inflammatory and immune responses. To characterise the expression and functional properties of porcine TLR2 (pTLR2), we have raised a panel of monoclonal antibodies (mAb) against this molecule. Mouse 3T3 cell transfectants expressing pTLR2 were used for immunisation of mice. The specificity of these antibodies was confirmed by their reactivity with CHO cells transfected with pTLR2 but not with pTLR4 or with non-transfected cells. Using one of these mAbs, named 1H11, pTLR2 was found on cells of the innate immune system, including monocytes, macrophages, and granulocytes, but not on peripheral blood lymphocytes. Staining of tissue sections showed that pTLR2 is also expressed on epithelial cells lining the tracheobronchial and intestinal tracts, bile ducts in the liver and renal tubules, and on the basal layer of the epidermis. This distribution is consistent with a surveillance function at entry sites, allowing for early detection of microbial invasion.

Characterisation of porcine bone marrow progenitor cells identified by the anti-c-kit (CD117) monoclonal antibody 2B8/BM

c-kit (CD117) plays an important role in the early stages of haematopoiesis. Previous studies of porcine haematopoietic stem cells have relied for their identification on the use of the c-kit ligand stem cell factor. Here, we describe a new mAb, 2B8/BM, that recognizes a 155-kDa protein expressed on a small subset (2-8%) of bone marrow haematopoietic cells. 2B8/BM(+) cells have a blast appearance, and are mostly negative for lineage-specific markers or express low levels of CD172a or SLA-II. In in vitro colony-forming unit assays these cells were able to give rise to erythroid and myeloid colonies. Altogether these data suggested that the 2B8/BM antigen might be the porcine orthologue of the human c-kit. This specificity was confirmed by the binding of mAb 2B8/BM to CHO cells transfected with a plasmid encoding the porcine c-kit ectodomain. This antibody can facilitate the isolation and enrichment of porcine stem cells to be used in procedures aimed to induce xenograft tolerance or to test their potential to repair damaged tissues and organs.

Phenotypic and functional characterization of porcine granulocyte developmental stages using two new markers

Here, we describe two new surface antigens, named 6D10 and 2B2, whose expression is restricted to porcine granulocytes. 6D10 is only detected in neutrophils and its expression decreases from promyelocytes to mature cells. By contrast, 2B2 antigen is selectively expressed in mature neutrophils, eosinophils and basophils. The expression of these antigens along granulocyte maturation allows the discrimination of several developmental stages of granulocytes based on phenotypic, morphological and functional characteristics previously established. Moreover, these new markers are useful tools to easily characterize the different granulocytes lineages (neutrophils, eosinophils and basophils). By using multiparameter flow cytometric analysis, we have performed a phenotypic and functional characterization of the granulocyte subsets identified by the combination of 6D10 and 2B2 antigens.

Molecular cloning characterization and expression of porcine immunoreceptor SIRPalpha

SWC3 is a porcine CD that has been the reference marker of myeloid lineage. It is expressed in every myelomonocytic cell from early bone marrow precursors. We have identified the molecule recognized by anti-SWC3 antibodies as a member of the signal-regulatory proteins (SIRPs)alpha family. Here, we describe the cloning of a cDNA coding for a porcine SIRPalpha protein. The sequence is 2470 nucleotides long and contains an open reading frame encoding a 507 amino acid sequence. The predicted polypeptide was composed of a 30 amino acids putative signal peptide, a 342 amino acid extracellular region, a 23 amino acid transmembrane segment and a 112 amino acid cytoplasmic domain. Analysis of the sequence reveals a high degree of homology with known SIRPs in other species, being easily identified the three extracellular Ig type domains and two cytoplasmic ITIM motifs characteristic of this molecule. The gene coding for porcine SIRPalpha has been mapped to porcine chromosome 17, in a region syntenic to the human chromosome 20 where SIRP genes have been mapped. During the analysis of SIRP gene expression in tissues by RT-PCR, we noticed the existence of a shorter mRNA, and cloned the corresponding cDNA. This coded for a splicing variant of SIRPalpha that lacked the two membrane proximal Ig domains. In transfection experiments, we have been able to show that anti-SWC3 antibodies recognize both forms of the molecule, mapping the SWC3 epitopes to the N-terminal IgV type domain.

Molecular cloning, characterization and tissue expression of porcine Toll-like receptor 4

A cDNA containing the porcine Toll-like receptor 4 (TLR4) coding sequence has been cloned by RT-PCR from alveolar macrophages mRNA, and its complete sequence has been determined. The predicted amino acid sequence comprises an extracellular domain with 21 leucine-rich repeats (LRR) and a LRR-C-terminal (LRR-CT) motif, followed by a 30 amino acid transmembrane segment, and a 179 amino acid intracytoplasmic region containing the Toll/IL-1R domain. Pig TLR4 shows 63-80% amino acid sequence identity with those of cow, horse, cat, human, rabbit and mouse. The degree of sequence identity rises to over 90% in the TIR domain. The whole TLR4 sequence and its ectodomain were expressed as GFP fusion proteins in CHO cells. Using RT-PCR analysis, porcine TLR4 transcripts were detected in DCs, monocytes and macrophages, and in tissue samples of bone marrow, thymus, lymph node, spleen, brain, liver, kidney and ovary. The expressed protein will be used for the development of reagents. Knowledge of TLR4 expression will help to address mechanisms of immune induction by antigens and vaccines.

Differential expression of chemokine receptors and CD95 in porcine CD4+ T cell subsets

Among other differences, naïve and memory T cells show distinct migratory patterns and susceptibility to CD95-mediated cell death. We have recently characterised in the pig two subsets of CD4(+) T cells, based on the expression of the 2E3 marker, that display phenotypic and functional features of naïve (CD4(+)2E3(+)) and effector/memory (CD4(+)2E3(-)) T cells. In this study, we have analysed the expression of several chemokine receptors, as well as the distribution of CD95 antigen (APO-1/Fas) in these CD4(+) T cell subsets. CD4(+)2E3(-) T cells express high levels of CXCR3 and CCR4 transcripts but not of CCR7. On the contrary, CCR7 is clearly detected in CD4(+)2E3(+) T cells, whereas CXCR3 and CCR4 are negative or present at trace levels. These subsets also differ in the expression of CD95 antigen, being CD95 positive cells significantly more abundant in the CD4(+)2E3(-) cell subset. These findings, although based on a small number of animals, fit well with those reported for naïve and memory CD4(+) T cells in humans.

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.

Analysis of functional heterogeneity of porcine memory CD4+ T cells

Previous studies have identified swine helper memory T cells as CD4+CD8alpha+SLADR+. We have recently described a new porcine surface antigen (2E3) selectively expressed on CD4+ T cells that allows to divide these cells into naive (2E3+) and effector/memory (2E3-). However, although the majority of CD4+2E3- cells are CD8alpha+SLADR+, a minor proportion do not express SLADR and/or CD8alpha. Here, we have analyzed the functional capacity of these CD4+2E3- subsets to proliferate to a recall antigen. Both SLADR- and CD8alpha- cells proliferated in response to lysozyme, but at lower levels compared to the whole population CD4+2E3-. Besides, after activation with PMA plus ionomycin, CD4+2E3-SLADR- T cells produced IFNgamma and TNFalpha, although they did also in lower proportion than the whole CD4+2E3- population. Most of the IFNgamma-TNFalpha+, IFNgamma+TNFalpha+, IFNgamma+TNFalpha- cells were CD8alpha+ and CD45RA-, while IFNgamma-TNFalpha- cells showed a less differentiate phenotype.

In vitro effect of classical swine fever virus on a porcine aortic endothelial cell line

The effect of classical swine fever (CSF) virus on some phenotypic and functional features of an established porcine aortic endothelial cell (AOC) line was investigated. AOC cells show most of the characteristics of primary endothelial cells, avoiding the alterations and senescence that these cells undergo after a few passages in culture. AOC cells were susceptible to CSF virus infection to a high degree, reaching 90% of CSF virus positive cells after 24 h of infection; however as with other porcine susceptible cells, no cytopathic effect could be observed. In these conditions none of the surface molecules studied, including SLA-II MHC antigens, adhesion or co-stimulatory molecules, were altered by virus infection after 24 or 48 h. Functionally CSF virus infection induced a decrease in the pro-coagulant activity of the AOC cells, determined by the increase in the clot formation time shown by the lysates of these cells. This contrasts with the increase observed in the expression of mRNA corresponding to IL-1 alpha and IL-6, two proinflammatory and pro-coagulant cytokines, in CSF virus-infected AOC cells.

In vitro differentiation of porcine blood CD163− and CD163+ monocytes into functional dendritic cells

Swine monocytes constitute a heterogeneous cell population containing subsets with distinct functional capacities or representing different maturational stages. Based on the expression of CD163, we have recently identified two monocyte subpopulations. In this study, we investigate the ability of both CD163- and CD163+ monocytes to differentiate into dendritic cells (DCs) in the presence of GM-CSF and IL-4. Monocyte differentiation into DC is accompanied by an up-regulation of the expression of swine leukocyte antigen (SLA) I, SLA II and CD80/86 molecules, and a decrease in the expression of CD14, CD16 and CD163. These DC express the pan-myeloid marker SWC3 and display typical dendritic cytoplasmic projections. When monocytes are split into CD163+ and CD163- cells, both subsets give rise to DC. However, compared to CD163- monocyte-derived DC (MoDC), CD163+ MoDC appear to have reached a more advanced stage of maturation, expressing higher levels of SLA II and CD80/86 and inducing more efficiently proliferation of T cells to recall antigens and alloantigens.

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

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

Social integration of juvenile amputees: comparison with a general population

The objective was to assess the social integration of juvenile amputees according to marital status, schooling and occupation, and to compare it with the population of Asturias, Spain. A retrospective study was carried out of the juvenile amputees registered from 1976 to 1999 at the Prosthetics Unit of the Asturias Central Hospital (n=281 amputees). The proportion of single women amongst the amputees was greater than in the population of Asturias (p<0.05). Amongst the male amputees, relative to the general population, there was a larger proportion of the group with primary studies (p<0.001) and a smaller proportion with secondary studies (p<0.001). At the higher level (university) there were no differences, either in men or in women. As regards occupation, amongst the amputees a larger number was found who were retired or unemployed (p<0.05 and p<0.001). In conclusion, juvenile amputees do not show differences compared to the general population with regard to their attendance at a higher or university level of education. However, if their social integration is considered through occupation, male amputees show a greater proportion of unemployment, which is a clear reflection of their handicap.

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

We have developed a three-colour flow cytometric assay for phenotypic characterization of porcine IFN-gamma-producing lymphocytes. Analyses of activated swine peripheral blood mononuclear cells (PBMC) showed a significant difference in the proportion of IFN-gamma producing cells between young and adult animals (13.2+/-5.8% versus 34.2+/-5.7%). The majority of IFN-gamma producing cells were alphabeta T lymphocytes, although there was also an important proportion of gammadelta T cells particularly in young animals. Within the alphabeta T lymphocytes, the double positive CD4(+)CD8(lo) subset, that contains memory T cells, produced high levels of IFN-gamma, whereas the CD8(hi) T cells ranged from low to high levels of IFN-gamma. Also, consistent with a higher production by memory T cells, the CD45RA(-) subset of both CD4(+) and CD8(+) cells contained higher numbers of IFN-gamma producing cells than the CD45RA(+) subset. Finally, no production of IFN-gamma by either B cells (CD21(+)) or monocytes (SWC3(+)) was detected. This assay may be useful for the assessment of cell-mediated immunity in vaccine trials and may contribute to our understanding of the role of IFN-gamma in protective immunity against important viral diseases of the pig.

Correction of insulin resistance in methimazole-treated patients with Graves disease

The effect of thyroid hormone excess on glucose tolerance as well as insulin secretion and its peripheral action has been a matter of debate for many years. Thyrotoxicosis caused by Graves' disease is associated in some patients with impaired glucose tolerance and insulin resistance. The objective of the present study was to investigate if the insulin sensitivity, assessed by the euglycemic insulin clamp technique, increase after correction of hyperthyroidism due to Graves' disease. After four months of medical treatment, patients became euthyroid and insulin sensitivity increased significantly from 3.47 to 6.39 mg/kg/min; therefore it was concluded that insulin resistance could be improved after successful treatment of hyperthyroidism. The precise mechanism underlying the effect of thyroid hormone excess on insulin sensitivity remains to be elucidated.

Phenotypic characterization of monocyte subpopulations in the pig

We have recently described the existence of two subsets of porcine monocytes based on the expression of CD163. In this study we compare the expression of a number of cell surface antigens in CD163+ and CD163- monocyte subsets using three-color flow cytometry. These monocyte subsets show differences with respect to the expression of MHC class II antigens (SLA-DR and DQ) and a variety of adhesion molecules (CD11a, wCD11c, wCD29, CD49d) that are expressed at higher levels on CD163+ monocytes, and of CD14 that is higher expressed by CD 163- cells. These differences on phenotype could reflect differences in the ability of these two subsets to migrate to tissues and may account for the higher allostimulatory capacity of CD163+ cells. In some aspects, the phenotype of CD163+ monocytes resembles that of mature macrophages. In vitro serum-induced maturation of monocytes into macrophages lead to the expression of SWC9 together with an increase in the expression of CD163 and a reduction in that of CD14. These results delineate a maturation pathway where CD14hiCD163-SWC9- monocytes develop into CD14loCD163+SWC9- monocytes and these cells into CD14loCD163+SWC9+ macrophages.

[Behavior disorders during REM sleep. Two clinical cases]

INTRODUCTION

The behavior disorder occurring during REM (Rapid Eye Movement) sleep is a parasomnia characterized by absence of atonia typical of this phase of sleep, although the other characteristics are maintained, namely rapid eye movements and desynchronization of cortical electrical activity. Clinically it is accompanied by abrupt, often violent movements, which may involve a limb or the trunk in relation to dreams typical of this phase of sleep, and which may interrupt sleep. Many pathological processes have been described, including: the Shy-Dragger syndrome, Parkinson's disease, olivopontocerebellar atrophy, multisystemic atrophy, in relation to certain antidepressant drugs, and most frequently the idiopathic form.

CLINICAL CASES

We present two cases, one diagnosed as olivopontocerebellar atrophy and another in which there were no pathological findings. Both were referred to our department for the study of possible sleep disorders. In both cases neurophysiological studies, basically polysomnography with monitorization of various muscle groups and video, led to the diagnosis.

CONCLUSIONS

We discuss the diagnostic and physiological criteria, and physiopathological explanations of each case, with special reference to N-Methyl-D-Aspartate (NMDA) and non-N-Methyl-D-Aspartate (non-NMDA) receptors. Finally we consider the pharmacological treatment of this disorder.

Acute effects of soft drink intake on calcium and phosphate metabolism in immature and adult rats

OBJECTIVE

To test the acute effects of the intake of a phosphoric acid containing soft drink on acid-base balance and on calcium and phosphate metabolism.

MATERIAL AND METHODS

We studied 14 young adult male Sprague-Dawley rats aged 90 days, and 14 immature animals aged 30 days. Half of the animals in each group were randomly assigned to receive either tap water (controls), or Coca-Cola ad libitum for seven days. After this period, the rats were individually placed in metabolic cages to collect 24 hours urine, and they were exsanguinated by aortic puncture. Immediately, pH and ionized calcium were measured in whole blood. Creatinine, phosphate and total calcium were determined in the urine and plasma. Plasma levels of PTH, 1 alpha, 25 (OH)2 D3 and 25 OH D3 were measured by IRMA and RIA commercial kits.

RESULTS

The animals receiving the soft drink, both adults and immature, developed significant hypercalciuria and hyperphosphaturia. In immature animals, the plasma pH dropped from 7.45 +/- 0.04 to 7.33 +/- 0.02 (p < 0.05) but did not change in adult animals. Ionized calcium dropped significantly from 1.06 +/- 0.04 to 0.80 +/- 0.06 meq/L (p < 0.05) in immature animals but not in the adult animals. Only immature rats developed significant reduction of 1 alpha, 25 (OH)2 D3 and 25 OH D3, whereas only the adult rats developed significant hyperparathyroidism. Immature animals showed more severe derangement of calcium and phosphate metabolism related to soft drink intake.