Porcine myelomonocytic markers and cell populations

Selective Depletion of Staphylococcus aureus Restores the Skin Microbiome and Accelerates Tissue Repair after Injury

Our skin is home to a diverse community of commensal microorganisms integral to cutaneous function. However, microbial dysbiosis and barrier perturbation increase the risk of local and systemic infection. Staphylococcus aureus is a particularly problematic bacterial pathogen, with high levels of antimicrobial resistance and direct association with poor healing outcome. Innovative approaches are needed to selectively kill skin pathogens, such as S aureus, without harming the resident microbiota. In this study, we provide important data on the selectivity and efficacy of an S aureus-targeted endolysin (XZ.700) within the complex living skin/wound microbiome. Initial cross-species comparison using Nanopore long-read sequencing identified the translational potential of porcine rather than murine skin for human-relevant microbiome studies. We therefore performed an interventional study in pigs to assess the impact of endolysin administration on the microbiome. XZ.700 selectively inhibited endogenous porcine S aureus in vivo, restoring microbial diversity and promoting multiple aspects of wound repair. Subsequent mechanistic studies confirmed the importance of this microbiome modulation for effective healing in human skin. Taken together, these findings strongly support further development of S aureus-targeted endolysins for future clinical management of skin and wound infections.

Characterizing the immune response to myocardial infarction in pigs

Though myocardial infarction (MI) in pigs is a well-established translational large animal model, it has not yet been widely used for immunotherapy studies, and a comprehensive description of the immune response to MI in this species is lacking. We induced MI in Landrace pigs by balloon occlusion of the left anterior descending artery over 90 min. Within 14 days, the necrotic myocardium was progressively replaced by scar tissue with involvement of myofibroblasts. We characterized the immune response in the heart ex vivo by (immuno)histology, flow cytometry, and RNA sequencing of myocardial tissue on days 3, 7, and 14 after MI. Besides a clear predominance of myeloid cells among heart-infiltrating leukocytes, we detected activated T cells and an increasing proportion of CD4+ Foxp3+ regulatory T cells (Treg), especially in the infarct core-findings that closely mirror what has been observed in mice and humans after MI. Transcriptome data indicated inflammatory activity that was persistent but markedly changing in character over time and linked to extracellular matrix biology. Analysis of lymphocytes in heart-draining lymph nodes revealed significantly higher proliferation rates of T helper cell subsets, including Treg on day 7 after MI, compared to sham controls. Elevated frequencies of myeloid progenitors in the spleen suggest that it might be a site of emergency myelopoiesis after MI in pigs, as previously shown in mice. We thus provide a first description of the immune response to MI in pigs, and our results can aid future research using the species for preclinical immunotherapy studies.

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.

Attenuated Porcine Reproductive and Respiratory Syndrome Virus Regains Its Fatal Virulence by Serial Passaging in Pigs or Porcine Alveolar Macrophages To Increase Its Adaptation to Target Cells

Porcine reproductive and respiratory syndrome (PRRS) is a globally important disease threatening the pork industry, and modified live-virus (MLV) vaccines are widely used for its prevention. However, PRRS MLV shows high potential for reversion to virulence, leading to a major concern about its safety. Yet the revertant mechanism is still poorly understood. Here, attenuated virus JXwn06-P80, derived from the highly pathogenic PRRS virus (PRRSV) strain JXwn06 by serial passaging in MARC-145 cells, was reversely passaged in pigs through intranasal inoculation to mimic natural infection for 13 rounds, and the pathogenicity of viruses at the 3rd, 5th, 9th, 10th, and 11th passages was evaluated in pigs. From the 9th passage, the viruses caused mortality, which was related to their increased adaptability and replication efficiency (100 times higher than those of JXwn06-P80) in porcine alveolar macrophage (PAM) target cells. Similarly, JXwn06-P80 could also regain fatal virulence through reverse passage in PAMs for 25 or more passages, indicating that the increased adaptability in PAMs directly contributes to its regained fatal virulence. Next, the full-genome sequences were analyzed to explore the genetic evolutionary processes during adaptation both in vivo and in vitro. Finally, by a reverse genetic operation, four reverse mutation sites, NSP12-W121R, ORF2b (open reading frame 2b)-H9D, ORF5-H15L, and ORF5-V189L, were finally identified to partially contribute to the ability of the virus to adapt to PAMs, which may be related to virulence reversion during reverse passage. These findings provided direct scientific evidence for the virulence reversion of PRRS MLV and provided valuable clues for exploring its molecular mechanism. IMPORTANCE Reversion to virulence of a live attenuated vaccine is a public concern; however, direct scientific evidence is limited, and the mechanism is still poorly understood. Here, we present direct evidence for the reversion to virulence of PRRS MLV after serial passaging in pigs or target cells and found a correlation between virulence reversion and increased replication fitness in primary PAMs. The genetic evolutionary process during adaptation will provide valuable clues for exploring the molecular mechanism of PRRS MLV virulence reversion and offer important implications for understanding the reversion mechanisms of other vaccines.

Systemic murine cathelicidin CRAMP safely attenuated colonic neutrophil infiltration in pigs

Post-weaning diarrheic colitis, often caused by enteropathogens, are severe and potentially lethal diseases in young pigs. Conventional treatment with antibiotics is problematic due to increasing prevalence of multi-drug resistant bacteria. Few alternative treatments exist, so development of antibiotic-free therapies is urgently needed for livestock. Cathelicidin peptides, produced by epithelial cells and neutrophils, are microbicidal compounds capable of modulating innate immune and inflammatory responses. However, the effects of exogenous cathelicidin on gut homeostasis is poorly understood in pigs. We administered the murine cathelicidin CRAMP systemically to healthy pigs, to establish the peptide's safety and assess its ability to modulate colonic mucosal defenses. A single intraperitoneal injection of CRAMP was well tolerated up to two weeks and pigs remained clinically healthy. CRAMP caused some alteration of mucus glycosylation patterns in the colon by increasing sialylated mucins (P < 0.05) and decreased neutrophil influx close to the epithelium (P < 0.001). This study supports further investigation of CRAMP as an immunomodulatory treatment for infectious colitis in pigs.

Cardiac Macrophages and Their Effects on Arrhythmogenesis

Cardiac electrophysiology is a complex system established by a plethora of inward and outward ion currents in cardiomyocytes generating and conducting electrical signals in the heart. However, not only cardiomyocytes but also other cell types can modulate the heart rhythm. Recently, cardiac macrophages were demonstrated as important players in both electrophysiology and arrhythmogenesis. Cardiac macrophages are a heterogeneous group of immune cells including resident macrophages derived from embryonic and fetal precursors and recruited macrophages derived from circulating monocytes from the bone marrow. Recent studies suggest antiarrhythmic as well as proarrhythmic effects of cardiac macrophages. The proposed mechanisms of how cardiac macrophages affect electrophysiology vary and include both direct and indirect interactions with other cardiac cells. In this review, we provide an overview of the different subsets of macrophages in the heart and their possible interactions with cardiomyocytes under both physiologic conditions and heart disease. Furthermore, we elucidate similarities and differences between human, murine and porcine cardiac macrophages, thus providing detailed information for researchers investigating cardiac macrophages in important animal species for electrophysiologic research. Finally, we discuss the pros and cons of mice and pigs to investigate the role of cardiac macrophages in arrhythmogenesis from a translational perspective.

Analyses of the Impact of Immunosuppressive Cytokines on Porcine Macrophage Responses and Susceptibility to Infection to African Swine Fever Viruses

African swine fever viruses (ASFV), currently a serious threat to the global pig industry, primarily target porcine macrophages. Macrophages are characterized by their remarkable plasticity, being able to modify their phenotype and functions in response to diverse stimuli. Since IL-10 and TGF-β polarize macrophages toward an anti-inflammatory phenotype, we analyzed their impact on porcine monocyte-derived macrophages’ (moMΦ) susceptibility to infection and their responses to two genotype I ASFV strains, virulent 26544/OG10 and attenuated NH/P68. At a low multiplicity of infection (MOI), NH/P68, but not 26544/OG10, presented a higher ability to infect moM(IL-10) compared to moMΦ and moM(TGF-β), but no differences were appreciated at a higher MOI. Both strains replicated efficiently in all moMΦ subsets, with no differences at later times post-infection. Both strains downregulated CD14 and CD16 expression on moMΦ, irrespective of the activation status. ASFV’s modulation of CD163 and MHC II DR expression and cytokine responses to NH/P68 or 26544/OG10 ASFV were not affected by either IL-10 or TGF-β pre-treatment. Our results revealed little impact of these anti-inflammatory cytokines on moMΦ interaction with ASFV, which likely reflects the ability of the virus to effectively modulate macrophage responses.

Cortical bone stem cells modify cardiac inflammation after myocardial infarction by inducing a novel macrophage phenotype

Acute damage to the heart, as in the case of myocardial infarction (MI), triggers a robust inflammatory response to the sterile injury that is part of a complex and highly organized wound-healing process. Cortical bone stem cell (CBSC) therapy after MI has been shown to reduce adverse structural and functional remodeling of the heart after MI in both mouse and swine models. The basis for these CBSC treatment effects on wound healing are unknown. The present experiments show that CBSCs secrete paracrine factors known to have immunomodulatory properties, most notably macrophage colony-stimulating factor (M-CSF) and transforming growth factor-β, but not IL-4. CBSC therapy increased the number of galectin-3+ macrophages, CD4+ T cells, and fibroblasts in the heart while decreasing apoptosis in an in vivo swine model of MI. Macrophages treated with CBSC medium in vitro polarized to a proreparative phenotype are characterized by increased CD206 expression, increased efferocytic ability, increased IL-10, TGF-β, and IL-1RA secretion, and increased mitochondrial respiration. Next generation sequencing revealed a transcriptome significantly different from M2a or M2c macrophage phenotypes. Paracrine factors from CBSC-treated macrophages increased proliferation, decreased α-smooth muscle actin expression, and decreased contraction by fibroblasts in vitro. These data support the idea that CBSCs are modulating the immune response to MI to favor cardiac repair through a unique macrophage polarization that ultimately reduces cell death and alters fibroblast populations that may result in smaller scar size and preserved cardiac geometry and function.NEW & NOTEWORTHY Cortical bone stem cell (CBSC) therapy after myocardial infarction alters the inflammatory response to cardiac injury. We found that cortical bone stem cell therapy induces a unique macrophage phenotype in vitro and can modulate macrophage/fibroblast cross talk.

Recombinant Antigen of Type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-2) Promotes M1 Repolarization of Porcine Alveolar Macrophages and Th1 Type Response

The polarization status of porcine alveolar macrophages (PAMs) determines the infectivity of porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV infection skews macrophage polarization toward an M2 phenotype, followed by T-cells inactivation. CD163, one of the scavenger receptors of M2 macrophages, has been described as a putative receptor for PRRSV. In this study, we examined two types of PRRSV-2-derived recombinant antigens, A1 (g6Ld10T) and A2 (lipo-M5Nt), for their ability to mediate PAM polarization and T helper (Th1) response. A1 and A2 were composed of different combination of ORF5, ORF6, and ORF7 in full or partial length. To enhance the adaptive immunity, they were conjugated with T cells epitopes or lipidated elements, respectively. Our results showed that CD163⁺ expression on PAMs significantly decreased after being challenged with A1 but not A2, followed by a significant increase in pro-inflammatory genes (TNF-α, IL-6, and IL-12). In addition, next generation sequencing (NGS) data show an increase in T-cell receptor signaling in PAMs challenged with A1. Using a co-culture system, PAMs challenged with A1 can induce Th1 activation by boosting IFN-γ and IL-12 secretion and TNF-α expression. In terms of innate and T-cell-mediated immunity, we conclude that A1 is regarded as a potential vaccine for immunization against PRRSV infection due to its ability to reverse the polarization status of PAMs toward pro-inflammatory phenotypes, which in turn reduces CD163 expression for viral entry and increases immunomodulation for Th1-type response.

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.

Subsets of CD1c+ DCs: Dendritic Cell Versus Monocyte Lineage

Currently three bona fide dendritic cell (DC) types are distinguished in human blood. Herein we focus on type 2 DCs (DC2s) and compare the three defining markers CD1c, CD172, and CD301. When using CD1c to define DC2s, a CD14⁺ and a CD14⁻ subset can be detected. The CD14⁺ subset shares features with monocytes, and this includes substantially higher expression levels for CD64, CD115, CD163, and S100A8/9. We review the current knowledge of these CD1c⁺CD14⁺ cells as compared to the CD1c⁺CD14⁻ cells with respect to phenotype, function, transcriptomics, and ontogeny. Here, we discuss informative mutations, which suggest that two populations have different developmental requirements. In addition, we cover subsets of CD11c⁺CD8⁻ DC2s in the mouse, where CLEC12A⁺ESAM^low cells, as compared to the CLEC12A⁻ESAM^high subset, also express higher levels of monocyte-associated markers CD14, CD3, and CD115. Finally, we summarize, for both man and mouse, the data on lower antigen presentation and higher cytokine production in the monocyte-marker expressing DC2 subset, which demonstrate that the DC2 subsets are also functionally distinct.

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.

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.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Impact of PRRSV strains of different in vivo virulence on the macrophage population of the thymus

The emergence of "highly pathogenic" isolates of porcine reproductive and respiratory syndrome virus (HP-PRRSV) has raised new concerns about PRRS control. Cells from the porcine monocyte-macrophage lineage represent the target for this virus, which replicates mainly in the lung, and especially in HP-PRRSV strains, also in lymphoid organs, such as the thymus. This study aimed at evaluating the impact of two PRRSV strains of different virulence on thymic macrophages as well as after heterologous vaccination. After experimental infection with PR11 and PR40 PRRSV1 subtype 1 strains (low and high virulent, respectively) samples from thymus were analysed by histopathology and immunohistochemistry for PRRSV N protein, TUNEL, CD172a, CD163, CD107a and BA4D5 expression. Mortality was similar in both infected groups, but lung lesions and thymus atrophy were more intense in PR40 group. Animals died at 10-14 dpi after PR11 or PR40 infection showed the most severe histopathological lesions, with a strong inflammatory response of the stroma and extensive cell death phenomena in the cortex. These animals presented an increase in the number of N protein, CD172a, CD163 and BA4D5 positive cells in the stroma and the cortex together with a decrease in the number of CD107a positive cells. Our results highlight the recruitment of macrophages in the thymus, the increase in the expression of CD163 and the regulation of the host cytotoxic activity by macrophages. However, no marked differences were observed between PR11- and PR40-infected animals. Heterologous vaccination restrained virus spread and lesions extent in the thymus of PR40-infected animals.

Cellular Innate Immunity against PRRSV and Swine Influenza Viruses

Porcine respiratory disease complex (PRDC) is a polymicrobial syndrome that results from a combination of infectious agents, such as environmental stressors, population size, management strategies, age, and genetics. PRDC results in reduced performance as well as increased mortality rates and production costs in the pig industry worldwide. This review focuses on the interactions of two enveloped RNA viruses—porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SwIV)—as major etiological agents that contribute to PRDC within the porcine cellular innate immunity during infection. The innate immune system of the porcine lung includes alveolar and parenchymal/interstitial macrophages, neutrophils (PMN), conventional dendritic cells (DC) and plasmacytoid DC, natural killer cells, and γδ T cells, thus the in vitro and in vivo interactions between those cells and PRRSV and SwIV are reviewed. Likewise, the few studies regarding PRRSV-SwIV co-infection are illustrated together with the different modulation mechanisms that are induced by the two viruses. Alterations in responses by natural killer (NK), PMN, or γδ T cells have not received much attention within the scientific community as their counterpart antigen-presenting cells and there are numerous gaps in the knowledge regarding the role of those cells in both infections. This review will help in paving the way for future directions in PRRSV and SwIV research and enhancing the understanding of the innate mechanisms that are involved during infection with these viruses.

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.

Intracellular replication of Streptococcus pneumoniae inside splenic macrophages serves as a reservoir for septicaemia

Bacterial septicaemia is a major cause of mortality, but its pathogenesis remains poorly understood. In experimental pneumococcal murine intravenous infection, an initial reduction of bacteria in the blood is followed hours later by a fatal septicaemia. These events represent a population bottleneck driven by efficient clearance of pneumococci by splenic macrophages and neutrophils, but as we show in this study, accompanied by occasional intracellular replication of bacteria that are taken up by a subset of CD169+ splenic macrophages. In this model, proliferation of these sequestered bacteria provides a reservoir for dissemination of pneumococci into the bloodstream, as demonstrated by its prevention using an anti-CD169 monoclonal antibody treatment. Intracellular replication of pneumococci within CD169+ splenic macrophages was also observed in an ex vivo porcine spleen, where the microanatomy is comparable with humans. We also showed that macrolides, which effectively penetrate macrophages, prevented septicaemia, whereas beta-lactams, with inefficient intracellular penetration, failed to prevent dissemination to the blood. Our findings define a shift in our understanding of the pneumococcus from an exclusively extracellular pathogen to one with an intracellular phase. These findings open the door to the development of treatments that target this early, previously unrecognized intracellular phase of bacterial sepsis.

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.

Genotype 2 Strains of Porcine Reproductive and Respiratory Syndrome Virus Dysregulate Alveolar Macrophage Cytokine Production via the Unfolded Protein Response

Porcine reproductive and respiratory syndrome virus (PRRSV) infects alveolar macrophages (AMϕ), causing dysregulated alpha interferon (IFN-α) and tumor necrosis factor alpha (TNF-α) production through a mechanism(s) yet to be resolved. Here, we show that AMϕ infected with PRRSV secreted a reduced quantity of IFN-α following exposure of the cell to synthetic double-stranded RNA (dsRNA). This reduction did not correlate with reduced IFNA1 gene transcription. Rather, it coincided with two events that occurred late during infection and that were indicative of translational attenuation, specifically, the activation of eukaryotic translation initiation factor 2α (eIF2α) and the appearance of stress granules. Notably, the typical rapid production of TNF-α by AMϕ exposed to lipopolysaccharide (LPS) was suppressed or enhanced by PRRSV, depending on when the LPS exposure occurred after virus infection. If exposure was delayed until 6 h postinfection (hpi) so that the development of the cytokine response coincided with the time in which phosphorylation of eIF2α by the stress sensor PERK (protein kinase RNA [PKR]-like ER kinase) occurred, inhibition of TNF-α production was observed. However, if LPS exposure occurred at 2 hpi, prior to a detectable onset of eIF2α phosphorylation, a synergistic response was observed due to the earlier NF-κB activation via the stress sensor IRE1α (inositol-requiring kinase 1α). These results suggest that the asynchronous actions of two branches of the unfolded protein response (UPR), namely, IRE1α, and PERK, activated by ER stress resulting from the virus infection, are associated with enhancement or suppression of TNF-α production, respectively.IMPORTANCE The activation of AMϕ is controlled by the microenvironment to deter excessive proinflammatory cytokine responses to microbes that could impair lung function. However, viral pneumonias frequently become complicated by secondary bacterial infections, triggering severe inflammation, lung dysfunction, and death. Although dysregulated cytokine production is considered an integral component of the exacerbated inflammatory response in viral-bacterial coinfections, the mechanism responsible for this event is unknown. Here, we show that PRRSV replication in porcine AMϕ triggers activation of the IRE1α branch of the UPR, which causes a synergistic TNF-α response to LPS exposure. Thus, the severe pneumonias typically observed in pigs afflicted with PRRSV-bacterial coinfections could result from dysregulated, overly robust TNF-α production in response to opportunistic pathogens that is not commensurate with the typical restrained reaction by uninfected AMϕ. This notion could help in the design of therapies to mitigate the severity of viral and bacterial coinfections.

African Swine Fever Virus Biology and Vaccine Approaches

African swine fever (ASF) is an acute and often fatal disease affecting domestic pigs and wild boar, with severe economic consequences for affected countries. ASF is endemic in sub-Saharan Africa and the island of Sardinia, Italy. Since 2007, the virus emerged in the republic of Georgia, and since then spread throughout the Caucasus region and Russia. Outbreaks have also been reported in Belarus, Ukraine, Lithuania, Latvia, Estonia, Romania, Moldova, Czech Republic, and Poland, threatening neighboring West European countries. The causative agent, the African swine fever virus (ASFV), is a large, enveloped, double-stranded DNA virus that enters the cell by macropinocytosis and a clathrin-dependent mechanism. African Swine Fever Virus is able to interfere with various cellular signaling pathways resulting in immunomodulation, thus making the development of an efficacious vaccine very challenging. Inactivated preparations of African Swine Fever Virus do not confer protection, and the role of antibodies in protection remains unclear. The use of live-attenuated vaccines, although rendering suitable levels of protection, presents difficulties due to safety and side effects in the vaccinated animals. Several African Swine Fever Virus proteins have been reported to induce neutralizing antibodies in immunized pigs, and vaccination strategies based on DNA vaccines and recombinant proteins have also been explored, however, without being very successful. The complexity of the virus particle and the ability of the virus to modulate host immune responses are most likely the reason for this failure. Furthermore, no permanent cell lines able to sustain productive virus infection by both virulent and naturally attenuated African Swine Fever Virus strains exist so far, thus impairing basic research and the commercial production of attenuated vaccine candidates.

Release of pig leukocytes and reduced human NK cell recruitment during ex vivo perfusion of HLA-E/human CD46 double-transgenic pig limbs with human blood

BACKGROUND

In pig-to-human xenotransplantation, interactions between human natural killer (NK) cells and porcine endothelial cells (pEC) are characterized by recruitment and cytotoxicity. Protection from xenogeneic NK cytotoxicity can be achieved in vitro by the expression of the non-classical human leukocyte antigen-E (HLA-E) on pEC. Thus, the aim of this study was to analyze NK cell responses to vascularized xenografts using an ex vivo perfusion system of pig limbs with human blood.

METHODS

Six pig forelimbs per group, respectively, stemming from either wild-type (wt) or HLA-E/hCD46 double-transgenic (tg) animals, were perfused ex vivo with heparinized human blood for 12 hours. Blood samples were collected at defined time intervals, cell numbers counted, and peripheral blood mononuclear cells analyzed for phenotype by flow cytometry. Muscle biopsies were analyzed for NK cell infiltration. In vitro NK cytotoxicity assays were performed using pEC derived from wt and tg animals as target cells.

RESULTS

Ex vivo, a strong reduction in circulating human CD45 leukocytes was observed after 60 minutes of xenoperfusion in both wt and tg limb groups. NK cell numbers dropped significantly. Within the first 10 minutes, the decrease in NK cells was more significant in the wt limb perfusions as compared to tg limbs. Immunohistology of biopsies taken after 12 hours showed less NK cell tissue infiltration in the tg limbs. In vitro, NK cytotoxicity against hCD46 single tg pEC and wt pEC was similar, while lysis of double tg HLA-E/hCD46 pEC was significantly reduced. Finally, circulating cells of pig origin were observed during the ex vivo xenoperfusions. These cells expressed phenotypes mainly of monocytes, B and T lymphocytes, NK cells, as well as some activated endothelial cells.

CONCLUSIONS

Ex vivo perfusion of pig forelimbs using whole human blood represents a powerful tool to study humoral and early cell-mediated rejection mechanisms of vascularized pig-to-human xenotransplantation, although there are several limitations of the model. Here, we show that (i) transgenic expression of HLA-E/hCD46 in pig limbs provides partial protection from human NK cell-mediated xeno responses and (ii) the emergence of a pig cell population during xenoperfusions with implications for the immunogenicity of xenografts.

Long-term culture and differentiation of porcine red bone marrow hematopoietic cells co-cultured with immortalized mesenchymal cells

Mesenchymal cells are multipotent stromal cells with self-renewal, differentiation and immunomodulatory capabilities. We aimed to develop a co-culture model for differentiating hematopoietic cells on top of immortalized mesenchymal cells for studying interactions between hematopoietic and mesenchymal cells, useful for adequately exploring the therapeutic potential of mesenchymal cells. In this study, we investigated the survival, proliferation and differentiation of porcine red bone marrow hematopoietic cells co-cultured with immortalized porcine bone marrow mesenchymal cells for a period of five weeks. Directly after collection, primary porcine bone marrow mesenchymal cells adhered firmly to the bottom of the culture plates and showed a fibroblast-like appearance, one week after isolation. Upon immortalization, porcine bone marrow mesenchymal cells were continuously proliferating. They were positive for simian virus 40 (SV40) large T antigen and the mesenchymal cell markers CD44 and CD55. Isolated red bone marrow cells were added to these immortalized mesenchymal cells. Five weeks post-seeding, 92±6% of the red bone marrow hematopoietic cells were still alive and their number increased 3-fold during five weekly subpassages on top of the immortalized mesenchymal cells. The red bone marrow hematopoietic cells were originally small and round; later, the cells increased in size. Some of them became elongated, while others remained round. Tiny dendrites appeared attaching hematopoietic cells to the underlying immortalized mesenchymal cells. Furthermore, weekly differential-quick staining of the cells indicated the presence of monoblasts, monocytes, macrophages and lymphocytes in the co-cultures. At three weeks of co-culture, flow cytometry analysis showed an increased surface expression of CD172a, CD14, CD163, CD169, CD4 and CD8 up to 37±0.8%, 40±8%, 41±4%, 23±3% and 19±5% of the hematopoietic cells, respectively. In conclusion, continuous mesenchymal cell cultures were successfully established and characterized and they supported the proliferation of red bone marrow hematopoietic cells, which finally differentiated into monocytic cells and CD4⁺ and CD8⁺ cells.

Phenotyping and susceptibility of established porcine cells lines to African Swine Fever Virus infection and viral production

African swine fever virus (ASFV) is a highly pathogenic, double-stranded DNA virus with a marked tropism for cells of the monocyte-macrophage lineage, affecting swine species and provoking severe economic losses and health threats. In the present study, four established porcine cell lines, IPAM-WT, IPAM-CD163, C∆2+ and WSL, were compared to porcine alveolar macrophage (PAM) in terms of surface marker phenotype, susceptibility to ASFV infection and virus production. The virulent ASFV Armenia/07, E70 or the naturally attenuated NHV/P68 strains were used as viral models. Cells expressed only low levels of specific receptors linked to the monocyte/macrophage lineage, with low levels of infection overall, with the exception of WSL, which showed more efficient production of strain NHV/P68 but not of strains E70 and Armenia/07.

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.

The respiratory DC/macrophage network at steady-state and upon influenza infection in the swine biomedical model

Human and mouse respiratory tracts show anatomical and physiological differences, which will benefit from alternative experimental models for studying many respiratory diseases. Pig has been recognized as a valuable biomedical model, in particular for lung transplantation or pathologies such as cystic fibrosis and influenza infection. However, there is a lack of knowledge about the porcine respiratory immune system. Here we segregated and studied six populations of pig lung dendritic cells (DCs)/macrophages (Mθs) as follows: conventional DCs (cDC) 1 and cDC2, inflammatory monocyte-derived DCs (moDCs), monocyte-derived Mθs, and interstitial and alveolar Mθs. The three DC subsets present migratory and naive T-cell stimulation capacities. As observed in human and mice, porcine cDC1 and cDC2 were able to induce T-helper (Th)1 and Th2 responses, respectively. Interestingly, porcine moDCs increased in the lung upon influenza infection, as observed in the mouse model. Pig cDC2 shared some characteristics observed in human but not in mice, such as the expression of FCɛRIα and Langerin, and an intra-epithelial localization. This work, by unraveling the extended similarities of the porcine and human lung DC/Mθ networks, highlights the relevance of pig, both as an exploratory model of DC/Mθ functions and as a model for human inflammatory lung pathologies.

Establishing Porcine Monocyte-Derived Macrophage and Dendritic Cell Systems for Studying the Interaction with PRRSV-1

Monocyte-derived macrophages (MoMØ) and monocyte-derived dendritic cells (MoDC) are two model systems well established in human and rodent systems that can be used to study the interaction of pathogens with host cells. Porcine reproductive and respiratory syndrome virus (PRRSV) is known to infect myeloid cells, such as macrophages (MØ) and dendritic cells (DC). Therefore, this study aimed to establish systems for the differentiation and characterization of MoMØ and MoDC for subsequent infection with PRRSV-1. M-CSF differentiated MoMØ were stimulated with activators for classical (M1) or alternative (M2) activation. GM-CSF and IL-4 generated MoDC were activated with the well established maturation cocktail containing PAMPs and cytokines. In addition, MoMØ and MoDC were treated with dexamethasone and IL-10, which are known immuno-suppressive reagents. Cells were characterized by morphology, phenotype, and function and porcine MØ subsets highlighted some divergence from described human counterparts, while MoDC, appeared more similar to mouse and human DCs. The infection with PRRSV-1 strain Lena demonstrated different replication kinetics between MoMØ and MoDC and within subsets of each cell type. While MoMØ susceptibility was significantly increased by dexamethasone and IL-10 with an accompanying increase in CD163/CD169 expression, MoDC supported only a minimal replication of PRRSV These findings underline the high variability in the susceptibility of porcine myeloid cells toward PRRSV-1 infection.

The Role of Porcine Monocyte Derived Dendritic Cells (MoDC) in the Inflammation Storm Caused by Streptococcus suis Serotype 2 Infection

Background

Streptococcus suis is an important swine pathogen and zoonotic agent. Infection with this highly pathogenic strain can cause streptococcal toxic shock-like syndrome (STSLS), characterized by a Th-1 inflammatory cytokine storm, and a high mortality rate. Monocyte derived dendritic cells (MoDCs) are known to stimulate Th-1 cell differentiation, but the role of MoDCs in STSLS remains to be elucidated.

Methodology and Findings

Porcine CD14-positive monocytes, purified from peripheral blood mononuclear cells (PBMCs), were used to generate MoDCs using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). Highly pure MoDCs were generated, as proved by their morphology, phenotype analysis, phagocytic ability, and induction of T cells proliferation. The MoDCs were further stimulated by the virulent S. suis serotype 2 (SS2) SC19 strain which triggered a strong release of several pro-inflammatory cytokines, including IL-1β, IL-8, TNF-α, IFN-γ, and IL-12. Furthermore, the stimulated MoDCs induced CD4⁺ T cell differentiation towards Th-1 cells in vitro.

Conclusions

The results of this study indicated that the porcine MoDCs stimulated by SS2 could release high levels of Th-1 inflammatory cytokines and induce CD4⁺ T cell differentiation towards Th-1 cells. Hence, it is likely that porcine MoDCs play an important role in the STSLS caused by SS2.

Effect of O. porcinus Tick Salivary Gland Extract on the African Swine Fever Virus Infection in Domestic Pig

African swine fever is a haemorrhagic disease in pig production that can have disastrous financial consequences for farming. No vaccines are currently available and animal slaughtering or area zoning to restrict risk-related movements are the only effective measures to prevent the spread of the disease. Ornithodoros soft ticks are known to transmit the African swine fever virus (ASFV) to pigs in farms, following the natural epidemiologic cycle of the virus. Tick saliva has been shown to modulate the host physiological and immunological responses during feeding on skin, thus affecting viral infection. To better understand the interaction between soft tick, ASFV and pig at the bite location and the possible influence of tick saliva on pig infection by ASFV, salivary gland extract (SGE) of Ornithodoros porcinus, co-inoculated or not with ASFV, was used for intradermal auricular inoculation. Our results showed that, after the virus triggered the disease, pigs inoculated with virus and SGE presented greater hyperthermia than pigs inoculated with virus alone. The density of Langerhans cells was modulated at the tick bite or inoculation site, either through recruitment by ASFV or inhibition by SGE. Additionally, SGE and virus induced macrophage recruitment each. This effect was enhanced when they were co-inoculated. Finally, the co-inoculation of SGE and virus delayed the early local spread of virus to the first lymph node on the inoculation side. This study has shown that the effect of SGE was powerful enough to be quantified in pig both on the systemic and local immune response. We believe this model should be developed with infected tick and could improve knowledge of both tick vector competence and tick saliva immunomodulation.

Innate Immune Response of the Pig Laryngeal Mucosa to Endotracheal Intubation

Objective

The aim of this study was to measure the effects of endotracheal intubation on innate immune response within the pig laryngeal mucosa.

Study Design

Prospective controlled basic science study.

Setting

The animal experiments and analyses were conducted at the University of Bristol.

Samples and Methods

Eighteen pigs, matched at the major histocompatibility complex (MHC), were used in the study. The pigs were divided into 9 pairs. One of each pair (9 pigs in total) was intubated with an endotracheal tube under general anesthesia for 90 minutes. Two days later, pinch biopsies were taken from the supraglottis (specifically the false cords) and subglottis of both pigs. The experiment was repeated 8 more times. Based on quantitative immunohistochemistry, percentage areas of positive staining for CD172a, CD163, MHC class II, CD14, and CD16 were calculated separately for the epithelium and lamina propria of each biopsy.

Results

Total areas of laryngeal mucosa (epithelium and lamina propria) expressing CD172a and coexpressing CD163 and CD172a were significantly reduced at 2 days following endotracheal intubation ( P = .039 and P = .037, respectively). MHC class II expression and MHC class II coexpression with CD172a were similarly reduced following intubation ( P = .003 and P = .005, respectively). In the supraglottis, MHC class II coexpression with CD16 and CD14 was also reduced following endotracheal intubation ( P = .037).

Conclusions

Our results indicate that endotracheal intubation reduces the number of innate immune cells within the upper airway mucosa. This may be an important first step in a cascade leading to chronic wound and scar formation causing airway stenosis.

Oral antibiotics increase blood neutrophil maturation and reduce bacteremia and necrotizing enterocolitis in the immediate postnatal period of preterm pigs

Immature immunity may predispose preterm neonates to infections and necrotizing enterocolitis (NEC). Intravenous antibiotics are frequently given to prevent and treat sepsis, while oral antibiotics are seldom used. We hypothesized that oral antibiotics promote maturation of systemic immunity and delay gut bacterial colonization and thereby protect preterm neonates against both NEC and bacteremia in the immediate postnatal period. Preterm pigs were given formula and administered saline (CON) or broad-spectrum antibiotics orally (ORA) or systemically (SYS) for 5 d after birth. Temporal changes in blood parameters and bacterial composition in the intestine, blood and immune organs were analyzed. Newborn preterm pigs had few blood neutrophils and a high frequency of progenitor cells. Neutrophils gradually matured after preterm birth with increasing CD14 and decreasing CD172a expressions. Preterm neutrophil and monocyte TLR2 expression and TLR2-mediated blood cytokine responses were low relative to adults. ORA pigs showed enhanced blood neutrophil maturation with reduced cell size and CD172a expression. Only ORA pigs, but not SYS pigs, were protected from a high density of gut Gram-positive bacteria, high gut permeability, Gram-positive bacteremia and NEC. Neonatal oral antibiotics may benefit mucosal and systemic immunity via delayed gut colonization and enhanced blood neutrophil maturation just after preterm birth.

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.

PRRSV-infected monocyte-derived dendritic cells express high levels of SLA-DR and CD80/86 but do not stimulate PRRSV-naïve regulatory T cells to proliferate

In vitro generated monocyte-derived dendritic cells (moDCs) have frequently been used to study the influence of porcine reproductive and respiratory syndrome virus (PRRSV) infection on antigen presenting cells. However, obtained results have often been conflicting in regard to expression of co-stimulatory molecules and interaction with T cells. In this study we performed a detailed phenotypic characterisation of PRRSV-infected moDCs and non-infected moDCs. For CD163 and CD169, which are involved in PRRSV-entry into host cells, our results show that prior to infection porcine moDCs express high levels of CD163 but only very low levels for CD169. Following infection with either PRRSV-1 or PRRSV-2 strains after 24 h, PRRSV-nucleoprotein (N-protein)⁺ and N-protein⁻ moDCs derived from the same microculture were analyzed for expression of swine leukocyte antigen-DR (SLA-DR) and CD80/86. N-protein⁺ moDCs consistently expressed higher levels of SLA-DR and CD80/86 compared to N-protein⁻ moDCs. We also investigated the influence of PRRSV-infected moDCs on proliferation and frequency of Foxp3⁺ regulatory T cells present within CD4⁺ T cells in in vitro co-cultures. Neither CD3-stimulated nor unstimulated CD4⁺ T cells showed differences in regard to proliferation and frequency of Foxp3⁺ T cells following co-cultivation with either PRRSV-1 or PRRSV-2 infected moDCs. Our results suggest that a more detailed characterisation of PRRSV-infected moDCs will lead to more consistent results across different laboratories and PRRSV strains as indicated by the major differences in SLA-DR and CD80/86 expression between PRRSV-infected and non-infected moDCs present in the same microculture.

African swine fever virus infects macrophages, the natural host cells, via clathrin- and cholesterol-dependent endocytosis

The main cellular target for African swine fever virus (ASFV) is the porcine macrophage. However, existing data about the early phases of infection were previously characterized in non-leukocyte cells such as Vero cells. Here, we report that ASFV enters the natural host cell using dynamin-dependent and clathrin-mediated endocytosis. This pathway is strongly pH-dependent during the first steps of infection in porcine macrophages. We investigated the effect of drugs inhibiting several endocytic pathways in macrophages and compared ASFV with vaccinia virus (VV), which apparently involves different entry pathways. The presence of cholesterol in cellular membranes was found to be essential for a productive ASFV infection while actin-dependent endocytosis and the participation of phosphoinositide-3-kinase (PI3K) activity were other cellular factors required in the process of viral entry. These findings improved our understanding of the ASFV interactions with macrophages that allow for successful viral replication.

Pulmonary intravascular macrophages: prime suspects as cellular mediators of porcine CARPA

Pigs provide a highly sensitive and quantitative in vivo model for complement (C) activation-related pseudoallergy (CARPA), a hypersensitivity reaction caused by some state-of-art nanomedicines. In an effort to understand the mechanism of the pigs’ unique sensitivity for CARPA, this review focuses on pulmonary intravascular macrophages (PIMs), which are abundantly present in the lung of pigs. These cells represent a macrophage subpopulation whose unique qualities explain the characteristic symptoms of CARPA in this species, most importantly the rapidly (within minutes) developing pulmonary vasoconstriction, leading to elevation of pulmonary arterial pressure. The unique qualities of PIM cells include the following; 1) they are strongly adhered to the capillary walls via desmosome-like intercellular adhesion plaques, which secure stable and lasting direct exposition of the bulk of these cells to the blood stream; 2) their ruffled surface engaged in intense phagocytic activity ensures efficient binding and phagocytosis of nanoparticles; 3) PIM cells express anaphylatoxin receptors, this way C activation can trigger these cells, 4) they also express pattern recognition molecules on their surface, whose engagement with certain coated nanoparticles may also activate these cells or act in synergy with anaphylatoxins and, finally 5) their high metabolic activity and capability for immediate secretion of vasoactive mediators upon stimulation explain the circulatory blockage and other robust physiological effects that their stimulation may cause. These qualities taken together with reports on liposome uptake by PIM cells during CARPA and the possible presence of these cells in human lung suggests that PIM cells may be a potential therapeutic target against CARPA.

The immunology of the porcine skin and its value as a model for human skin

The porcine skin has striking similarities to the human skin in terms of general structure, thickness, hair follicle content, pigmentation, collagen and lipid composition. This has been the basis for numerous studies using the pig as a model for wound healing, transdermal delivery, dermal toxicology, radiation and UVB effects. Considering that the skin also represents an immune organ of utmost importance for health, immune cells present in the skin of the pig will be reviewed. The focus of this review is on dendritic cells, which play a central role in the skin immune system as they serve as sentinels in the skin, which offers a large surface area exposed to the environment. Based on a literature review and original data we propose a classification of porcine dendritic cell subsets in the skin corresponding to the subsets described in the human skin. The equivalent of the human CD141(+) DC subset is CD1a(-)CD4(-)CD172a(-)CADM1(high), that of the CD1c(+) subset is CD1a(+)CD4(-)CD172a(+)CADM1(+/low), and porcine plasmacytoid dendritic cells are CD1a(-)CD4(+)CD172a(+)CADM1(-). CD209 and CD14 could represent markers of inflammatory monocyte-derived cells, either dendritic cells or macrophages. Future studies for example using transriptomic analysis of sorted populations are required to confirm the identity of these cells.

In vivo tracking and immunological properties of pulsed porcine monocyte-derived dendritic cells

Cellular therapies using immune cells and in particular dendritic cells (DCs) are being increasingly applied in clinical trials and vaccines. Their success partially depends on accurate delivery of cells to target organs or migration to lymph nodes. Delivery and subsequent migration of cells to regional lymph nodes is essential for effective stimulation of the immune system. Thus, the design of an optimal DC therapy would be improved by optimizing technologies for monitoring DC trafficking. Magnetic resonance imaging (MRI) represents a powerful tool for non-invasive imaging of DC migration in vivo. Domestic pigs share similarities with humans and represent an excellent animal model for immunological studies. The aim of this study was to investigate the possibility using pigs as models for DC tracking in vivo. Porcine monocyte derived DC (MoDC) culture with superparamagnetic iron oxide (SPIO) particles was standardized on the basis of SPIO concentration and culture viability. Phenotype, cytokine production and mixed lymphocyte reaction assay confirmed that porcine SPIO-MoDC culture were similar to mock MoDCs and fully functional in vivo. Alike, similar patterns were obtained in human MoDCs. After subcutaneous inoculation in pigs, porcine SPIO-MoDC migration to regional lymph nodes was detected by MRI and confirmed by Perls staining of draining lymph nodes. Moreover, after one dose of virus-like particles-pulsed MoDCs specific local and systemic responses were confirmed using ELISPOT IFN-γ in pigs. In summary, the results in this work showed that after one single subcutaneous dose of pulsed MoDCs, pigs were able to elicit specific local and systemic immune responses. Additionally, the dynamic imaging of MRI-based DC tracking was shown using SPIO particles. This proof-of-principle study shows the potential of using pigs as a suitable animal model to test DC trafficking with the aim of improving cellular therapies.

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.

Genome-wide analysis of antiviral signature genes in porcine macrophages at different activation statuses

Macrophages (MФs) can be polarized to various activation statuses, including classical (M1), alternative (M2), and antiviral states. To study the antiviral activation status of porcine MФs during porcine reproductive and respiratory syndrome virus (PRRSV) infection, we used RNA Sequencing (RNA-Seq) for transcriptomic analysis of differentially expressed genes (DEGs). Sequencing assessment and quality evaluation showed that our RNA-Seq data met the criteria for genome-wide transcriptomic analysis. Comparisons of any two activation statuses revealed more than 20,000 DEGs that were normalized to filter out 153–5,303 significant DEGs [false discovery rate (FDR) ≤0.001, fold change ≥2] in each comparison. The highest 5,303 significant DEGs were found between lipopolysaccharide- (LPS) and interferon (IFN)γ-stimulated M1 cells, whereas only 153 significant DEGs were detected between interleukin (IL)-10-polarized M2 cells and control mock-activated cells. To identify signature genes for antiviral regulation pertaining to each activation status, we identified a set of DEGs that showed significant up-regulation in only one activation state. In addition, pathway analyses defined the top 20–50 significantly regulated pathways at each activation status, and we further analyzed DEGs pertinent to pathways mediated by AMP kinase (AMPK) and epigenetic mechanisms. For the first time in porcine macrophages, our transcriptomic analyses not only compared family-wide differential expression of most known immune genes at different activation statuses, but also revealed transcription evidence of multiple gene families. These findings show that using RNA-Seq transcriptomic analyses in virus-infected and status-synchronized macrophages effectively profiled signature genes and gene response pathways for antiviral regulation, which may provide a framework for optimizing antiviral immunity and immune homeostasis.

Correlation of cell surface marker expression with African swine fever virus infection

The expression of surface markers on African swine fever virus (ASFV) infected cells was evaluated to assess their involvement in infection. Previous findings indicated CD163 expression was correlated with ASFV susceptibility. However, in this study the expression of porcine CD163 on cell lines did not increase the infection rate of these cells indicating other factors are likely to be important in determining susceptibility to infection. On adherent porcine bone marrow (pBM) cells the expression of CD45 was strongly correlated with infection. CD163 and CD203a expression correlated at intermediate levels with infection, indicating cells expressing these markers could become infected but were not preferentially infected by the virus. Most of the cells expressing MHCII were infected, indicating that they may be preferentially infected although expression of MHCII was not essential for infection and a large percentage of the infected cells were MHCII negative. CD16 showed a marked decrease in expression following infection and significantly lower levels of infected cells were shown to express CD16. Altogether these results suggest CD163 may be involved in ASFV infection but it may not be essential; the results also highlight the importance of other cell markers which requiring further investigation.

Organic barn dust extract exposure impairs porcine macrophage function in vitro: implications for respiratory health

Respiratory diseases are responsible for a significant amount of animal morbidity and mortality in the swine industry, including the majority of nursery and grower/finisher deaths. Innate immunity, including the maintenance of lung macrophage health and function, is an important defense mechanism against respiratory pathogens and their associated losses. Chronic exposure of swine industry workers to airborne barn dust results in significant predisposition to airway diseases and impairment of alveolar macrophage (AMφ) function. Because of their importance in maintaining normal respiratory function, this study was designed to evaluate the impact of barn dust on swine macrophages. As measures of macrophage function, we evaluated the activation of NF-κB, cytokine production, cell surface marker expression and the phagocytic and antibacterial capabilities of porcine macrophages after in vitro exposure to an organic swine barn dust extract (ODE). ODE treatment induced AMφ secretion of both pro- and anti-inflammatory cytokines, suggesting a complex activation profile. Additionally, ODE induced expression of genes (TLR2, NOD2) involved in sensing Gram-positive bacteria, a major component of barn dust. ODE exposure also enhanced the expression of several cell surface markers of activation, including a receptor for the porcine reproductive and respiratory syndrome virus. Moreover, two key functions of AMϕ, phagocytosis and bacterial killing, were impaired after exposure to ODE. Treatment with ODE for the first 72 h of differentiation also inhibited the ability of monocyte-derived macrophages to translocate NF-κB to the nucleus following endotoxin stimulation. Taken together, these results demonstrate, for the first time, that organic dust extract exposure negatively affects pig macrophage activation and function, potentially enhancing host susceptibility to a variety of respiratory infections.