Phenotypic and functional modulations of porcine macrophages by interferons and interleukin-4

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.

The scene of lung pathology during PRRSV-1 infection

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases for the pig industry worldwide. The disease was firstly reported in 1987 and became endemic in many countries. Since then, outbreaks caused by strains of high virulence have been reported several times in Asia, America and Europe. Interstitial pneumonia, microscopically characterised by thickened alveolar septa, is the hallmark lesion of PRRS. However, suppurative bronchopneumonia and proliferative and necrotising pneumonia are also observed, particularly when a virulent strain is involved. This raises the question of whether the infection by certain strains results in an overstimulation of the proinflammatory response and whether there is some degree of correlation between the strain involved and a particular pattern of lung injury. Thus, it is of interest to know how the inflammatory response is modulated in these cases due to the interplay between virus and host factors. This review provides an overview of the macroscopic, microscopic, and molecular pathology of PRRSV-1 strains in the lung, emphasising the differences between strains of different virulence.

Type I and II interferons, transcription factors and major histocompatibility complexes were enhanced by knocking down the PRRSV-induced transforming growth factor beta in monocytes co-cultured with peripheral blood lymphocytes

The innate and adaptive immune responses elicited by porcine reproductive and respiratory syndrome virus (PRRSV) infection are known to be poor. This study investigates the impact of PRRSV-induced transforming growth factor beta 1 (TGFβ1) on the expressions of type I and II interferons (IFNs), transcription factors, major histocompatibility complexes (MHC), anti-inflammatory and pro-inflammatory cytokines in PRRSV-infected co-cultures of monocytes and peripheral blood lymphocytes (PBL). Phosphorothioate-modified antisense oligodeoxynucleotide (AS ODN) specific to the AUG region of porcine TGFβ1 mRNA was synthesized and successfully knocked down TGFβ1 mRNA expression and protein translation. Monocytes transfected with TGFβAS1 ODN, then simultaneously co-cultured with PBL and inoculated with either classical PRRSV-2 (cPRRSV-2) or highly pathogenic PRRSV-2 (HP-PRRSV-2) showed a significant reduction in TGFβ1 mRNA expression and a significant increase in the mRNA expressions of IFNα, IFNγ, MHC-I, MHC-II, signal transducer and activator of transcription 1 (STAT1), and STAT2. Additionally, transfection of TGFβAS1 ODN in the monocyte and PBL co-culture inoculated with cPRRSV-2 significantly increased the mRNA expression of interleukin-12p40 (IL-12p40). PRRSV-2 RNA copy numbers were significantly reduced in monocytes and PBL co-culture transfected with TGFβAS1 ODN compared to the untransfected control. The yields of PRRSV-2 RNA copy numbers in PRRSV-2-inoculated monocytes and PBL co-culture were sustained and reduced by porcine TGFβ1 (rTGFβ1) and recombinant porcine IFNα (rIFNα), respectively. These findings highlight the strategy employed by PRRSV to suppress the innate immune response through the induction of TGFβ expression. The inclusion of TGFβ as a parameter for future PRRSV vaccine and vaccine adjuvant candidates is recommended.

Evolutionary-Related High- and Low-Virulent Classical Swine Fever Virus Isolates Reveal Viral Determinants of Virulence

Classical swine fever (CSF) has been eradicated from Western and Central Europe but remains endemic in parts of Central and South America, Asia, and the Caribbean. CSF virus (CSFV) has been endemic in Cuba since 1993, most likely following an escape of the highly virulent Margarita/1958 strain. In recent years, chronic and persistent infections with low-virulent CSFV have been observed. Amino acid substitutions located in immunodominant epitopes of the envelope glycoprotein E2 of the attenuated isolates were attributed to positive selection due to suboptimal vaccination and control. To obtain a complete picture of the mutations involved in attenuation, we applied forward and reverse genetics using the evolutionary-related low-virulent CSFV/Pinar del Rio (CSF1058)/2010 (PdR) and highly virulent Margarita/1958 isolates. Sequence comparison of the two viruses recovered from experimental infections in pigs revealed 40 amino acid differences. Interestingly, the amino acid substitutions clustered in E2 and the NS5A and NS5B proteins. A long poly-uridine sequence was identified previously in the 3' untranslated region (UTR) of PdR. We constructed functional cDNA clones of the PdR and Margarita strains and generated eight recombinant viruses by introducing single or multiple gene fragments from Margarita into the PdR backbone. All chimeric viruses had comparable replication characteristics in porcine monocyte-derived macrophages. Recombinant PdR viruses carrying either E2 or NS5A/NS5B of Margarita, with 36 or 5 uridines in the 3'UTR, remained low virulent in 3-month-old pigs. The combination of these elements recovered the high-virulent Margarita phenotype. These results show that CSFV evolution towards attenuated variants in the field involved mutations in both structural and non-structural proteins and the UTRs, which act synergistically to determine virulence.

A sensitive luciferase reporter assay for the detection of infectious African swine fever virus

African swine fever virus (ASFV) is a complex DNA virus causing severe hemorrhagic disease in domestic pigs and wild boar. The disease has spread worldwide, with important socio-economic consequences. Early virus detection and control measures are crucial as there are no effective vaccines nor antivirals on the market. While the diagnosis of ASFV is fast and based primarily on qPCR, the detection of infectious ASFV is a labor-intensive process requiring susceptible macrophages and subsequent antibody-based staining or hemadsorption. The latter cannot detect ASFV isolates devoid of functional CD2v (EP402R) expression. Here, we report the development of a plasmid-based reporter assay (RA) for the sensitive detection and titration of infectious ASFV. To this end, we constructed a plasmid for secreted NanoLuc luciferase (secNluc) expression driven by the ASFV DNA polymerase gene G1211R promoter. Infection of plasmid-transfected immortalized porcine kidney macrophages (IPKM) followed by measurement of secNluc from cell culture supernatants allowed reliable automated quantification of infectious ASFV. The RA-based titers matched the titers determined by conventional p72-staining or hemadsorption protocols. The novel assay is specific for ASFV as it does not detect classical swine fever virus nor porcine reproductive and respiratory syndrome virus. It is applicable to ASFV of different genotypes, virulence, and sources, including ASFV from sera and whole blood from infected pigs as well as non-hemadsorbing ASFV.

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.

AVA-NP-695 Selectively Inhibits ENPP1 to Activate STING Pathway and Abrogate Tumor Metastasis in 4T1 Breast Cancer Syngeneic Mouse Model

Cyclic GMP-AMP synthase (cGAS) is an endogenous DNA sensor that synthesizes cyclic guanosine monophosphate–adenosine monophosphate (2′3′-cGAMP) from ATP and GTP. 2′3′-cGAMP activates the stimulator of interferon genes (STING) pathway, resulting in the production of interferons and pro-inflammatory cytokines. Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is the phosphodiesterase that negatively regulates the STING pathway by hydrolyzing 2′3′-cGAMP. It has been established that the cGAS–STING pathway plays a major role in inhibiting tumor growth by upregulating T cell response. Herein, we demonstrate that AVA-NP-695, a selective and highly potent ENPP1 inhibitor, apart from the immunomodulatory effect also modulates cancer metastasis by negatively regulating epithelial–mesenchymal transition (EMT). We established that the combined addition of 2′3′-cGAMP and AVA-NP-695 significantly abrogated the transforming growth factor beta (TGF-ꞵ)-induced EMT in MDA-MB-231 cells. Finally, results from the in vivo study showed superior tumor growth inhibition and impact on tumor metastasis of AVA-NP-695 compared to Olaparib and PD-1 in a syngeneic 4T1 breast cancer mouse model. The translation of efficacy from in vitro to in vivo 4T1 tumor model provides a strong rationale for the therapeutic potential of AVA-NP-695 against triple-negative breast cancer (TNBC) as an immunomodulatory and anti-metastatic agent.

Assessment of the Impact of a Toll-like Receptor 2 Agonist Synthetic Lipopeptide on Macrophage Susceptibility and Responses to African Swine Fever Virus Infection

Toll-like receptor 2 (TLR2) ligands are attracting attention as prophylactic and immunopotentiator agents against pathogens, including viruses. We previously reported that a synthetic diacylated lipopeptide (Mag-Pam2Cys_P48) polarized porcine macrophages towards a proinflammatory antimicrobial phenotype. Here, we investigated its role in modulating monocyte-derived macrophage (moMΦ) responses against African swine fever virus (ASFV), the etiological agent of one of the greatest threats to the global pig industry. Two ASFV isolates were compared: the attenuated NH/P68 and the virulent 26544/OG10. No effect on virus infection nor the modulation of surface markers’ expression (MHC I, MHC II DR, CD14, CD16, and CD163) were observed when Mag-Pam2Cys_P48 treated moMΦ were infected using a multiplicity of infection (MOI) of 1. Mag-Pam2Cys_P48 treated moMΦ released higher levels of IL-1α, IL-1β, IL-1Ra, and IL-18 in response to infection with NH/P68 ASFV compared to 26544/OG10-infected and mock-infected controls. Surprisingly, when infected using a MOI of 0.01, the virulent ASFV 26544/OG10 isolate replicated even slightly more efficiently in Mag-Pam2Cys_P48 treated moMΦ. These effects also extended to the treatment of moMΦ with two other lipopeptides: Mag-Pam2Cys_P80 and Mag-Pam2Cys_Mag1000. Our data suggested limited applicability of TLR2 agonists as prophylactic or immunopotentiator agents against virulent ASFV but highlighted the ability of the virulent 26544/OG10 to impair macrophage defenses.

Cell Lines for the Development of African Swine Fever Virus Vaccine Candidates: An Update

African swine fever virus (ASFV) is the etiological agent of a highly lethal disease in both domestic and wild pigs. The virus has rapidly spread worldwide and has no available licensed vaccine. An obstacle to the construction of a safe and efficient vaccine is the lack of a suitable cell line for ASFV isolation and propagation. Macrophages are the main targets for ASFV, and they have been widely used to study virus-host interactions; nevertheless, obtaining these cells is time-consuming and expensive, and they are not ethically suitable for the production of large-scale vaccines. To overcome these issues, different virulent field isolates have been adapted on monkey or human continuous cells lines; however, several culture passages often lead to significant genetic modifications and the loss of immunogenicity of the adapted strain. Thus, several groups have attempted to establish a porcine cell line able to sustain ASFV growth. Preliminary data suggested that some porcine continuous cell lines might be an alternative to primary macrophages for ASFV research and for large-scale vaccine production, although further studies are still needed. In this review, we summarize the research to investigate the most suitable cell line for ASFV isolation and propagation.

Adaptive Cellular Immunity against African Swine Fever Virus Infections

African swine fever virus (ASFV) remains a threat to global pig populations. Infections with ASFV lead to a hemorrhagic disease with up to 100% lethality in Eurasian domestic and wild pigs. Although myeloid cells are the main target cells for ASFV, T cell responses are impacted by the infection as well. The complex responses remain not well understood, and, consequently, there is no commercially available vaccine. Here, we review the current knowledge about the induction of antiviral T cell responses by cells of the myeloid lineage, as well as T cell responses in infected animals, recent efforts in vaccine research, and T cell epitopes present in ASFV.

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.

TNF-Mediated Inhibition of Classical Swine Fever Virus Replication Is IRF1-, NF-κB- and JAK/STAT Signaling-Dependent

The sera from pigs infected with virulent classical swine fever virus (CSFV) contain substantial amounts of tumor necrosis factor (TNF), a prototype proinflammatory cytokine with pleiotropic activities. TNF limits the replication of CSFV in cell culture. In order to investigate the signaling involved in the antiviral activity of TNF, we employed small-molecule inhibitors to interfere specifically with JAK/STAT and NF-κB signaling pathways in near-to-primary endothelial PEDSV.15 cells. In addition, we knocked out selected factors of the interferon (IFN) induction and signaling pathways using CRISPR/Cas9. We found that the anti-CSFV effect of TNF was sensitive to JAK/STAT inhibitors, suggesting that TNF induces IFN signaling. Accordingly, we observed that the antiviral effect of TNF was dependent on intact type I IFN signaling as PEDSV.15 cells with the disrupted type I IFN receptor lost their capacity to limit the replication of CSFV after TNF treatment. Consequently, we examined whether TNF activates the type I IFN induction pathway. With genetically modified PEDSV.15 cells deficient in functional interferon regulatory factor 1 or 3 (IRF1 or IRF3), we observed that the anti-CSFV activity exhibited by TNF was dependent on IRF1, whereas IRF3 was dispensable. This was distinct from the lipopolysaccharide (LPS)-driven antiviral effect that relied on both IRF1 and IRF3. In agreement with the requirement of IRF1 to induce TNF- and LPS-mediated antiviral effects, intact IRF1 was also essential for TNF- and LPS-mediated induction of IFN-β mRNA, while the activation of NF-κB was not dependent on IRF1. Nevertheless, NF-κB activation was essential for the TNF-mediated antiviral effect. Finally, we observed that CSFV failed to counteract the TNF-mediated induction of the IFN-β mRNA in PEDSV.15 cells, suggesting that CSFV does not interfere with IRF1-dependent signaling. In summary, we report that the proinflammatory cytokine TNF limits the replication of CSFV in PEDSV.15 cells by specific induction of an IRF1-dependent antiviral type I IFN response.

Proteome Analysis in PAM Cells Reveals That African Swine Fever Virus Can Regulate the Level of Intracellular Polyamines to Facilitate Its Own Replication through ARG1

In 2018, African swine fever broke out in China, and the death rate after infection was close to 100%. There is no effective and safe vaccine in the world. In order to better characterize and understand the virus–host-cell interaction, quantitative proteomics was performed on porcine alveolar macrophages (PAM) infected with ASFV through tandem mass spectrometry (TMT) technology, high-performance liquid chromatography (HPLC), and mass spectrometry (MS). The proteome difference between the simulated group and the ASFV-infected group was found at 24 h. A total of 4218 proteins were identified, including 306 up-regulated differentially expressed proteins and 238 down-regulated differentially expressed proteins. Western blot analysis confirmed changes in the expression level of the selected protein. Pathway analysis is used to reveal the regulation of protein and interaction pathways after ASFV infection. Functional network and pathway analysis can provide an insight into the complexity and dynamics of virus–host cell interactions. Further study combined with proteomics data found that ARG1 has a very important effect on ASFV replication. It should be noted that the host metabolic pathway of ARG1-polyamine is important for virus replication, revealing that the virus may facilitate its own replication by regulating the level of small molecules in the host cell.

Targeting Toll-Like Receptor 2: Polarization of Porcine Macrophages by a Mycoplasma-Derived Pam2cys Lipopeptide

Toll-like receptor 2 (TLR2) ligands are attracting increasing attention as prophylactic and immunotherapeutic agents against pathogens and tumors. We previously observed that a synthetic diacylated lipopeptide based on a surface protein of Mycoplasma agalactiae (Mag-Pam2Cys) strongly activated innate immune cells, including porcine monocyte-derived macrophages (moMΦ). In this study, we utilized confocal microscopy, flow cytometry, multiplex cytokine ELISA, and RT-qPCR to conduct a comprehensive analysis of the effects of scalar doses of Mag-Pam2Cys on porcine moMΦ. We observed enhanced expression of activation markers (MHC class I, MHC class II DR, CD25), increased phagocytotic activity, and release of IL-12 and proinflammatory cytokines. Mag-Pam2Cys also upregulated the gene expression of several IFN-α subtypes, p65, NOS2, and molecules with antimicrobial activities (CD14, beta defensin 1). Overall, our data showed that Mag-Pam2Cys polarized porcine macrophages towards a proinflammatory antimicrobial phenotype. However, Mag-Pam2Cys downregulated the expression of IFN-α3, six TLRs (TLR3, -4, -5, -7, -8, -9), and did not interfere with macrophage polarization induced by the immunosuppressive IL-10, suggesting that the inflammatory activity evoked by Mag-Pam2Cys could be regulated to avoid potentially harmful consequences. We hope that our in vitro results will lay the foundation for the further evaluation of this diacylated lipopeptide as an immunopotentiator in vivo.

Comparative Phenotypic and Functional Analyses of the Effects of IL-10 or TGF-β on Porcine Macrophages

Simple Summary

Macrophages play a central role in innate immune response to both infectious and non-infectious stressors. They respond to different agonists modifying their phenotype and functions. In humans and mice, the regulatory cytokines IL-10 or TGF-β are both known to drive macrophage polarization into an anti-inflammatory phenotype, referred to as M2c. However, the immune systems of animal species each have their own peculiarities and the M2c subsets has never been investigated in pigs. A deep knowledge of the porcine immune system is required to design vaccines or control strategies against pathogens, which are a major constraint to pork production. Due to anatomical, physiological, and immunological similarities, swine are attracting increasing attention as a model for human diseases. To better characterize porcine macrophages, we evaluated the effects of IL-10 or TGF-β on the phenotype and function of monocyte-derived macrophages. Both cytokines downregulated the expression of MHC II DR and CD14. IL-10, but not TGF-β, statistically significantly reduced the ability of macrophages to respond to Toll-like receptor 2 (TLR2) or TLR4 agonists. Whilst these data suggest differentiation to an M2c-like immunosuppressive phenotype, the responses, and differences between IL-10 and TGF-β also reveals species-specific differences.

Abstract

Macrophages are phagocytic cells involved in maintaining tissue homeostasis and defense against pathogens. Macrophages may be polarized into different functionally specialized subsets. M2c macrophages arise following stimulation with IL-10 or TGF-β and mediate anti-inflammatory and tissue repair functions. M2c macrophages remain poorly characterized in the pig, thus we investigated the impact of these regulatory cytokines on porcine monocyte-derived macrophages (moMΦ). The phenotype and functionality of these cells was characterized though confocal microscopy, flow cytometry, ELISA, and RT-qPCR. Both cytokines induced CD14 and MHC II DR down-regulation and reduced IL-6, TNF-α, and CD14 expression, suggestive of an anti-inflammatory phenotype. Interestingly, neither IL-10 or TGF-β were able to trigger IL-10 induction or release by moMΦ. Differences between these cytokines were observed: stimulation with IL-10, but not TGF-β, induced up-regulation of both CD16 and CD163 on moMΦ. In addition, IL-10 down-regulated expression of IL-1β and IL-12p40 4h post-stimulation and induced a stronger impairment of moMΦ ability to respond to either TLR2 or TLR4 agonists. Overall, our results provide an overview of porcine macrophage polarization by two immunosuppressive cytokines, revealing differences between IL-10 and TGF-β, and reporting some peculiarity of swine, which should be considered in translational studies.

Activation of regulated cell death in the lung of piglets infected with virulent PRRSV-1 Lena strain occurs earlier and mediated by cleaved Caspase-8

PRRSV-1 virulent strains cause high fever, marked respiratory disease and severe lesions in lung and lymphoid organs. Regulated cell death (RCD), such as apoptosis, necroptosis and pyroptosis, is triggered by the host to interrupt viral replication eliminating infected cells, however, although it seems to play a central role in the immunopathogenesis of PRRSV, there are significant gaps regarding their sequence and activation upon PRRSV-infection. The present study evaluated RCD events by means of caspases expression in the lung of PRRSV-1-infected pigs and their impact on pulmonary macrophage subpopulations and lung lesion. Conventional piglets were intranasally inoculated with the virulent subtype 3 Lena strain or the low virulent subtype 1 3249 strain and euthanised at 1, 3, 6, 8 and 13 dpi. Lena-infected piglets showed severe and early lung damage with a high frequency of PRRSV-N-protein⁺ cells, depletion of CD163⁺ cells and high viral load in the lung. The number of TUNEL⁺ cells was significantly higher than cCasp3⁺ cells in Lena-infected piglets during the first week post-infection. cCasp8 and to a lesser extent cCasp9 were activated by both PRRSV-1 strains after one week post-infection together with a replenishment of both CD163⁺ and Arg-1⁺ pulmonary macrophages. These results highlight the induction of other forms of RCD beyond apoptosis, such as, necroptosis and pyroptosis during the first week post-infection followed by the activation of, mainly, extrinsic apoptosis during the second week post-infection. The recovery of CD163⁺ macrophages at the end of the study represents an attempt to restore pulmonary macrophage subpopulations lost during the early stages of the infection but also a macrophage polarisation into M2 macrophages.

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.

Comparison of Macrophage Responses to African Swine Fever Viruses Reveals that the NH/P68 Strain is Associated with Enhanced Sensitivity to Type I IFN and Cytokine Responses from Classically Activated Macrophages

African swine fever (ASF) poses a severe threat to the global pig industry for which currently there is no available vaccine. The aetiological ASF virus (ASFV) has a predilection for cells of the myeloid lineage, however little is known about its interaction with polarised macrophages. This study focused on the in vitro interactions of porcine monocyte-derived un-activated (moMΦ), classically (moM1), alternatively (moM2), and IFN-α-activated macrophages with two genotype I ASFV strains: virulent 22653/14 and attenuated NH/P68. At a high multiplicity of infection, NH/P68, but not 22653/14, presented a reduced ability to infect moM1 and IFN−α-activated moMΦ compared to moMΦ. IFN-α activation resulted in a dose-dependent reduction in the proportion of ASFV-infected cells. Both strains replicated efficiently in all the subsets. While higher levels of IL-1α, IL-1β, and IL-18 were secreted by NH/P68-infected moM1 compared to 22653/14, both strains negatively affected moMΦ ability to release IL-6, IL-12, TNF-α in response to classical activation or stimulation with a TLR2 agonist. Our results suggest that ASFV 22653/14 covertly replicates in macrophages, compromising the development of effective immune responses. Attenuated NH/P68 has partially lost these mechanisms, which may enhance immune surveillance. A better understating of these mechanisms should aid the rational design of live attenuated ASFV vaccines.

Differential innate immune responses induced by Mycoplasma hyopneumoniae and Mycoplasma hyorhinis in various types of antigen presenting cells

Mycoplasma (M.) hyopneumoniae is the etiological agent of enzootic pneumonia in pigs and is closely related to M. hyorhinis, which can be isolated from the healthy mucosal surfaces of the upper respiratory tract. In rare cases it can also cause arthritis and polyserositis. Since the innate immune system is an important first line of defense and promotes adaptive immune responses, we characterized the innate immune response of various antigen presenting cells (APCs) to M. hyopneumoniae and M. hyorhinis, which differ in their pathogenicity in vivo. Porcine peripheral blood mononuclear cells were infected with different multiplicities of infection (MOI) of live and inactivated porcine mycoplasmas. Both Mycoplasma species induced strong tumour necrosis factor (TNF) responses in monocytes, with a stronger activation by M. hyorhinis. This higher stimulatory activity was also confirmed for CD40 upregulation. Conventional and plasmacytoid dendritic cells (cDC and pDC, respectively) did not or poorly respond to mycoplasmas in terms of TNF expression but more efficiently in terms of CD40 upregulation. Again, these responses were generally stronger with M. hyorhinis than with M. hyopneumoniae. Both Mycoplasma species also activated B cells in terms of CD25 upregulation, proliferation, and IgM secretion. Interestingly, while the induction of CD25 and in particular proliferation was higher with M. hyorhinis, the IgM secretion did not differ between the two species with the exception of the highest dose of M. hyopneumoniae,which appeared to suppress IgM responses. Taken together, our results provide a comparative analysis of innate immune response with different porcine APCs and demonstrate Mycoplasma species-dependent differences, which could relate to their different pathogenicity in vivo.

No Evidence for a Role for Antibodies during Vaccination-Induced Enhancement of Porcine Reproductive and Respiratory Syndrome

Vaccination is one of the most important tools to protect pigs against infection with porcine reproductive and respiratory syndrome virus 1 (PRRSV-1). Although neutralizing antibodies are considered to represent an important mechanism of protective immunity, anti-PRRSV antibodies, in particular at subneutralizing concentrations, have also been reported to exacerbate PRRSV infection, probably through FcγR-mediated uptake of antibody-opsonized PRRSV, resulting in enhanced infection of, and replication in, target cells. Therefore, we investigated this pathway using sera from an animal experiment in which vaccine-mediated enhancement of clinical symptoms was observed. Three groups of six pigs were vaccinated with an inactivated PRRSV vaccine based on the PRRSV-1 subtype 3 strain Lena and challenged after a single or a prime-boost immunization protocol, or injected with PBS. We specifically tested if sera obtained from these animals can enhance macrophage infections, viral shedding, or cytokine release at different dilutions. Neither the presence of neutralizing antibodies nor general anti-PRRSV antibodies, mediated an enhanced infection, increased viral release or cytokine production by macrophages. Taken together, our data indicate that the exacerbated disease was not caused by antibodies.

The regulatory actions of retinoic acid on M2 polarization of porcine macrophages

We previously demonstrated that the most bioactive vitamin A metabolite, all-trans retinoic acid (ATRA), increased T helper 2-associated responses induced in pigs by infection with the parasitic nematode Ascaris suum We also showed that ATRA potentiated the mRNA expression of several IL-4 induced chemokines (chemokine (CC motif) ligand 11 [(CCL11), CCL17, CCL22 and CCL26] associated with alternative activation (M2a) in porcine macrophages in vitro. Herein, several mechanisms whereby ATRA affects IL-4 signaling are profiled using large-scale real time PCR and RNA-Seq analysis. Twenty-three genes associated with M2a markers in other species were independently upregulated by both IL-4 and ATRA, including the adenosine receptor A2B (ADORA2B), cysteinyl leukotriene receptor 2 (CYSLTR2) and the vitamin D receptor (VDR). ATRA synergistically enhanced IL-4 up-regulation of Hepatitis A virus cellular receptor 2 (HAVCR2) and transglutaminase 2 (TGM2) and further repressed IL-4 down-regulated CD163 and Cytochrome b-245, beta polypeptide (CYBB) mRNA. Macrophages treated with ATRA exhibited a dose-dependent reduction in phagocytosis of opsonized Staphylococcus aureus. In addition, the combination of IL-4 and ATRA up-regulated the anti-inflammatory protein, IL-1R antagonist (IL1RN) and TGM2. These data indicate that ATRA induces a state of partial alternative activation in porcine macrophages, and amplifies certain aspects of M2a activation induced by IL-4. Given the prevalence of allergic and parasitic diseases worldwide and the close similarities in the porcine and human immune responses, these findings have important implications for the nutritional regulation of allergic inflammation at mucosal surfaces.

In vitro characterization of PRRSV isolates with different in vivo virulence using monocyte-derived macrophages

The recent emergence of highly pathogenic porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) strains has caused severe economic losses. The biological elements defining virulence and pathogenicity are still unclear. In vitro characteristics using natural target cells of PRRSV provide important information to understand the basis of virulence at the cellular level, and provide a mean to reduce animal experimentations to achieve this goal. Here, we compared PRRSV strains from two geographically different regions, with varying in vivo characteristics, in terms of their interactions with monocyte-derived macrophages (MDMs). The strains included Lena and BOR59 from Belarus, and ILI6 from Russia, as well as PR11 and PR40, both from Italy. As a reference, we used a cell culture-adapted version of Lelystad, LVP. MDMs were pre-treated with IFNγ, IL-4 or IFNβ, in order to understand responses in polarized and antiviral MDMs. In general, independent of the geographical origin, the strains with high virulence infected a higher percentage of MDMs and replicated to higher titers. These virulence-dependent differences were most pronounced when the MDMs had been treated with IFNβ. Differentiation between intermediate and low virulent PRRSV was difficult, due to variations between different experiments, but LVP differed clearly from all field strains. IFNα and IL-10 were not detected in any experiment, but PR40 induced TNF and IL-1β. Taken together, these results validate the MDM model to understand pathogenicity factors of PRRSV and confirm the importance of the escape from type I and II IFN-mediated effects for PRRSV virulence.

Targeting of the Nasal Mucosa by Japanese Encephalitis Virus for Non-Vector-Borne Transmission

JEV, a main cause of severe viral encephalitis in humans, has a complex ecology composed of a mosquito-waterbird cycle and a cycle involving pigs, which amplifies virus transmission to mosquitoes, leading to increased human cases. JEV can be transmitted between pigs by contact in the absence of arthropod vectors. Moreover, virus or viral RNA is found in oronasal secretions and the nasal epithelium. Using nasal mucosa tissue explants and three-dimensional porcine nasal epithelial cells cultures and macrophages as ex vivo and in vitro models, we determined that the nasal epithelium could be a route of entry as well as exit for the virus. Infection of nasal epithelial cells resulted in apical and basolateral virus shedding and release of monocyte recruiting chemokines and therefore infection and replication in macrophages, which is favored by epithelial-cell-derived cytokines. The results are relevant to understand the mechanism of non-vector-borne direct transmission of JEV.

The mosquito-borne Japanese encephalitis virus (JEV) causes severe central nervous system diseases and cycles between Culex mosquitoes and different vertebrates. For JEV and some other flaviviruses, oronasal transmission is described, but the mode of infection is unknown. Using nasal mucosal tissue explants and primary porcine nasal epithelial cells (NEC) at the air-liquid interface (ALI) and macrophages as ex vivo and in vitro models, we determined that the nasal epithelium could represent the route of entry and exit for JEV in pigs. Porcine NEC at the ALI exposed to with JEV resulted in apical and basolateral virus shedding and release of monocyte recruiting chemokines, indicating infection and replication in macrophages. Moreover, macrophages stimulated by alarmins, including interleukin-25, interleukin-33, and thymic stromal lymphopoietin, were more permissive to the JEV infection. Altogether, our data are important to understand the mechanism of non-vector-borne direct transmission of Japanese encephalitis virus in pigs.

IMPORTANCE JEV, a main cause of severe viral encephalitis in humans, has a complex ecology composed of a mosquito-waterbird cycle and a cycle involving pigs, which amplifies virus transmission to mosquitoes, leading to increased human cases. JEV can be transmitted between pigs by contact in the absence of arthropod vectors. Moreover, virus or viral RNA is found in oronasal secretions and the nasal epithelium. Using nasal mucosa tissue explants and three-dimensional porcine nasal epithelial cells cultures and macrophages as ex vivo and in vitro models, we determined that the nasal epithelium could be a route of entry as well as exit for the virus. Infection of nasal epithelial cells resulted in apical and basolateral virus shedding and release of monocyte recruiting chemokines and therefore infection and replication in macrophages, which is favored by epithelial-cell-derived cytokines. The results are relevant to understand the mechanism of non-vector-borne direct transmission of JEV.