Apoptosis in lymphoid organs of pigs naturally infected by porcine circovirus type 2

Severe Inflammation Caused by Coinfection of PCV2 and Glaesserella parasuis Is Associated with Pyroptosis via Noncanonical Inflammasome Pathway

Coinfections of porcine circovirus type 2 (PCV2) and Glaesserella parasuis (G. parasuis) are widely existing in the swine industry worldwide. However, the mechanisms for this coinfection remain unclear. The aim of this study is to assess whether the coinfection PCV2 and G. parasuis would affect the inflammatory response and related mechanisms. In this study, BALB/c mice and RAW264.7 cells were used to study the inflammation and related mechanism caused by the coinfection of PCV2 and G. parasuis. Coinfection with PCV2 and G. parasuis significantly increased the mortality of mice and led to the development of more severe lung and spleen lesions compared with single agent infection. Especially, coinfection significantly increased the bacterial loads in the lungs. Coinfection with PCV2 and G. parasuis can enhance RAW264.7 cell phagocytosis and elimination to G. parasuis. Cell death rate of cells increased in coinfection was measured with Flow cytometry. Moreover, coinfection led to the downregulation of the expression of TNFα and IL-8 in comparison with G. parasuis infection, but the maturation of interleukin-1β (IL-1β) was significantly upregulated. Our study firstly revealed that coinfection of PCV2 and G. parasuis can increase the phagocytosis of cells to G. parasuis, and LPS in the cytoplasm will induce the maturation of caspase-11 and lead to the cleavage of Gasdermin D (GSDMD) to cause pyroptosis by noncanonical pathway. The revealing of mechanisms associated with coinfection with PCV2 and G. parasuis will provide a scientific basis for investigating the synergistic infection mechanisms between viruses and bacteria.

A Triple Gene-Deleted Pseudorabies Virus-Vectored Subunit PCV2b and CSFV Vaccine Protects Pigs against PCV2b Challenge and Induces Serum Neutralizing Antibody Response against CSFV

Porcine circovirus type 2 (PCV2) is endemic worldwide. PCV2 causes immunosuppressive infection. Co-infection of pigs with other swine viruses, such as pseudorabies virus (PRV) and classical swine fever virus (CSFV), have fatal outcomes, causing the swine industry significant economic losses in many if not all pig-producing countries. Currently available inactivated/modified-live/vectored vaccines against PCV2/CSFV/PRV have safety and efficacy limitations. To address these shortcomings, we have constructed a triple gene (thymidine kinase, glycoprotein E [gE], and gG)-deleted (PRVtmv) vaccine vector expressing chimeric PCV2b-capsid, CSFV-E2, and chimeric E^rns-fused with bovine granulocytic monocyte-colony stimulating factor (E^rns-GM-CSF), designated as PRVtmv+, a trivalent vaccine. Here we compared this vaccine’s immunogenicity and protective efficacy in pigs against wild-type PCV2b challenge with that of the inactivated Zoetis Fostera Gold PCV commercial vaccine. The live PRVtmv+ prototype trivalent subunit vaccine is safe and highly attenuated in pigs. Based on PCV2b-specific neutralizing antibody titers, viremia, viral load in lymphoid tissues, fecal-virus shedding, and leukocyte/lymphocyte count, the PRVtmv+ yielded better protection for vaccinated pigs than the commercial vaccine after the PCV2b challenge. Additionally, the PRVtmv+ vaccinated pigs generated low to moderate levels of CSFV-specific neutralizing antibodies.

Host immune response to infection with porcine circoviruses

Porcine circovirus type 2 (PCV2), which serves as a major causative agent of PCV2-associated diseases and causes severe loss to the pig industry worldwide, can dysregulate the immune response and induce immunosuppression in PCV2-infected pigs. Similar to PCV2, porcine circovirus type 3 (PCV3), a newly identified swine circovirus which might be closely associated with porcine dermatitis and nephropathy syndrome, reproductive disorder, and multisystemic inflammatory responses, also interferes with host immune defense. Interaction between host immune system and PCVs is considered to be a crucial determinant of pathogenicity in pigs. Here, we sought to briefly discuss the current knowledge regarding the interaction of porcine circovirus type 2 and/or 3 with host immune cells and immune responses to better depict the viral immunomodulatory capacity, pathogenic mechanisms, and the future research direction in host immune responses to infection with PCV2 and PCV3.

The Monoclonal Antibody Recognized the Open Reading Frame Protein in Porcine Circovirus Type 2-Infected Peripheral Blood Mononuclear Cells

The purpose of this study in the context of the open reading frame 3 (ORF3) protein of porcine circovirus type 2 (PCV2) was especially its location and its relation to the capsid protein and the apoptosis protein in PCV2-infected porcine peripheral blood mononuclear cells (PBMCs). To detect the ORF3 protein, monoclonal antibodies (mAbs) were generated in this study. The mAb 7D3 binds to the ORF3 peptide (residues 35–66) and the native ORF3 protein in PCV2-infected PBMCs, as shown by immunofluorescence assay (IFA). The data show that 3–5% of PBMCs were positive for ORF3 protein or p53 protein. Further, 78–82% of PBMCs were positive for the capsid. This study confirmed the ORF3 protein not only colocalized with the capsid protein but also colocalized with the p53 protein in PBMCs. Immunoassays were conducted in this study to detect the capsid protein, the ORF3 protein, anti-capsid IgG, and anti-ORF3 IgG. The data show the correlation (r = 0.758) of the ORF3 protein and the capsid protein in the blood samples from the PCV2-infected herd. However, each anti-viral protein IgG had a different curve of the profile in the same herd after vaccination. Overall, this study provides a blueprint to explore the ORF3 protein in PCV2-infected PBMCs.

Dissecting clinical outcome of porcine circovirus type 2 with in vivo derived transcriptomic signatures of host tissue responses

Background

Porcine Circovirus Type 2 (PCV2) is a pathogen that has the ability to cause often devastating disease manifestations in pig populations with major economic implications. How PCV2 establishes subclinical persistence and why certain individuals progress to lethal lymphoid depletion remain to be elucidated.

Results

Here we present PorSignDB, a gene signature database describing in vivo porcine tissue physiology that we generated from a large compendium of in vivo transcriptional profiles and that we subsequently leveraged for deciphering the distinct physiological states underlying PCV2-affected lymph nodes. This systems genomics approach indicated that subclinical PCV2 infections suppress a myeloid leukocyte mediated immune response. However, in contrast an inflammatory myeloid cell activation is promoted in PCV2 patients with clinical manifestations. Functional genomics further uncovered STAT3 as a druggable PCV2 host factor candidate. Moreover, IL-2 supplementation of primary lymphocytes enabled ex vivo study of PCV2 replication in its target cell, the lymphoblast.

Conclusion

Our systematic dissection of the mechanistic basis of PCV2 reveals that subclinical and clinical PCV2 display two diametrically opposed immunotranscriptomic recalibrations that represent distinct physiological states in vivo, which suggests a paradigm shift in this field. Finally, our PorSignDB signature database is publicly available as a community resource (http://www.vetvirology.ugent.be/PorSignDB/, included in Gene Sets from Community Contributors http://software.broadinstitute.org/gsea/msigdb/contributed_genesets.jsp) and provides systems biologists with a valuable tool for catalyzing studies of human and veterinary disease. Finally, a primary porcine lymphoblast cell culture system paves the way for unraveling the impact of host genetics on PCV2 replication.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5217-5) contains supplementary material, which is available to authorized users.

Regulation of Apoptosis During Porcine Circovirus Type 2 Infection

Apoptosis, an indispensable innate immune mechanism, regulates cellular homeostasis by removing unnecessary or damaged cells. It contains three signaling pathways: the mitochondria-mediated pathway, the death receptor pathway and the endoplasmic reticulum pathway. The importance of apoptosis in host defenses is stressed by the observation that multiple viruses have evolved various strategies to inhibit apoptosis, thereby blunting the host immune responses and promoting viral propagation. Porcine Circovirus type 2 (PCV2) utilizes various strategies to induce or inhibit programmed cell death. In this article, we review the latest research progress of the apoptosis mechanisms during infection with PCV2, including several proteins of PCV2 regulate apoptosis via interacting with host proteins and multiple signaling pathways involved in PCV2-induced apoptosis, which provides scientific basis for the pathogenesis and prevention of PCV2.

Caspase-Dependent Apoptosis Induction via Viral Protein ORF4 of Porcine Circovirus 2 Binding to Mitochondrial Adenine Nucleotide Translocase 3

Apoptosis is an essential strategy of host defense responses and is used by viruses to maintain their life cycles. However, the apoptotic signals involved in virus replication are poorly known. In the present study, we report the molecular mechanism of apoptotic induction by the viral protein ORF4, a newly identified viral protein of porcine circovirus type 2 (PCV2). Apoptosis detection revealed not only that the activity of caspase-3 and -9 is increased in PCV2-infected and ORF4-transfected cells but also that cytochrome c release from the mitochondria to the cytosol is upregulated. Subsequently, ORF4 protein colocalization with adenine nucleotide translocase 3 (ANT3) was observed using structured illumination microscopy. Moreover, coimmunoprecipitation and pulldown analyses confirmed that the ORF4 protein interacts directly with mitochondrial ANT3 (mtANT3). Binding domain analysis further confirmed that N-terminal residues 1 to 30 of the ORF4 protein, comprising a mitochondrial targeting signal, are essential for the interaction with ANT3. Knockdown of ANT3 markedly inhibited the apoptotic induction of both ORF4 protein and PCV2, indicating that ANT3 plays an important role in ORF4 protein-induced apoptosis during PCV2 infection. Taken together, these data indicate that the ORF4 protein is a mitochondrial targeting protein that induces apoptosis by interacting with ANT3 through the mitochondrial pathway.IMPORTANCE The porcine circovirus type 2 (PCV2) protein ORF4 is a newly identified viral protein; however, little is known about its functions. Apoptosis is an essential strategy of the host defense response and is used by viruses to maintain their life cycles. In the present study, we report the molecular mechanism of the apoptosis induced by the ORF4 protein. The ORF4 protein contains a mitochondrial targeting signal and is an unstable protein that is degraded by the proteasome-dependent pathway. Viral protein ORF4 triggers caspase-3- and -9-dependent cellular apoptosis in mitochondria by directly binding to ANT3. We conclude that the ORF4 protein is a mitochondrial targeting protein and reveal a mechanism whereby circovirus recruits ANT3 to induce apoptosis.

Vimentin modulates infectious porcine circovirus type 2 in PK-15 cells

Porcine circovirus type 2 (PCV2) is the pathogen that causes postweaning multisystemic wasting syndrome, which leads to significant economic losses for swine farms worldwide. However, the infection mechanism of PCV2 is not completely understood yet. Vimentin is a part of the cytoskeleton network and plays an important role in several virus infections. It is not clear whether vimentin has a role in PCV2 infection nor how it affects PCV2 infection. In this study, the function of vimentin in PK-15 cells infected with PCV2 has been elucidated. We found that vimentin had a restrictive effect on the replication of PCV2 in PK-15 cells. Overexpression of vimentin by transferred pCAGGS-vimentin and down-regulation by the respective scrambled small interfering RNA showed that vimentin restricted the replication and virion production of PCV2. A special interaction between vimentin and PCV2 Cap protein was observed using laser confocal microscopy and immunoprecipitation assay. Moreover, overexpression of vimentin could decrease NF-κB activity and increase PCV2-induced caspase-3 activity in PK-15 cells. These data suggest that vimentin is involved in the replication of PCV2 and has a restrictive effect on it, which is helpful in the study of the replication mechanism of PCV2.

Depletion of follicular dendritic cells in tonsils collected from PMWS-affected pigs

Post-weaning multisystemic wasting syndrome (PMWS) is a relevant, worldwide disease caused by porcine circovirus type 2 (PCV2). Microscopically, PMWS is mainly characterized by lymphocytic depletion, macrophage infiltration and syncytia in lymphoid tissues. Some data suggest that follicular dendritic cells (FDCs) could be infected by PCV2, thus likely playing a role in the pathogenesis of PMWS. The present paper aims at assessing, qualitatively and quantitatively, the FDCs' network in the soft palate tonsils of clinically healthy and PMWS-affected pigs. Consecutive tissue sections were tested by immunohistochemistry to detect PCV2, FDCs and macrophages. FDCs and PCV2 antigens were quantitatively assessed by means of the Image J software and results submitted to statistical analysis. Our data demonstrated that FDCs are significantly reduced in PMWS-affected pigs compared with healthy pigs and that FDCs' depletion should be considered among microscopic features of PMWS. It is reasonable to hypothesize that depletion of FDCs further compromises the immune response and enhances the occurrence and the severity of secondary infections, which are relevant for the clinical manifestation of PMWS.

Immunohistochemical MHC-II and Interleukin 2-R (CD25) Expression in Lymph Nodes of Pigs with Spontaneous Postweaning Multisystemic Wasting Syndrome (PMWS)

Immunohistochemical expression of immunocompetent cells bearing major histocompatibility complex (MHC-II) and interleukin 2-R (IL2-R) (CD25) molecules was performed on lymph nodes with spontaneous postweaning multisystemic wasting syndrome (PMWS). control lymph nodes displayed intense diffuse immunoreactivity to MHC-II in both follicles and interfollicular areas. A marked reduction of follicular MHC-II immunoreactivity and inconsistent staining of histiocytes in interfollicular areas was observed in PMWS cases with a slight lymphoid depletion; in those cases with moderate to severe lymphoid depletion, there was a progressive decrease in MHC-II expression. In controls and in slightly depleted nodes, IL2-R was equally expressed in interfollicular tissue and in follicles, whereas in moderate and severe cases, it was detected in interfollicular remnants only. Immunohistochemical staining was scored semiquantitatively. The mean MHC-II score was significantly reduced in PMWS cases compared with controls (Spearman test), whereas there was no difference in the IL2-R score. The evident reduction of MHC-II immunoreactivity suggests an impairment in MHC-II linked antigen presenting cell expression.

Porcine Circovirus 2 Deploys PERK Pathway and GRP78 for Its Enhanced Replication in PK-15 Cells

Porcine circovirus type 2 (PCV2) infection induces autophagy and apoptosis. These cellular responses could be connected with endoplasmic reticulum (ER) stress. It remains unknown if PCV2 induces ER stress and if autophagy or apoptosis is primary to PCV2 infection or secondary responses following ER stress. Here, we demonstrate that PCV2 triggered unfolded protein response (UPR) in PK-15 cells by activating the PERK/eIF2α pathway without concomitant activation of IRE1 or ATF6. Since ATF4 and CHOP were induced later than PERK/eIF2α, it is clear that persistent PCV2 infection could lead to selective activation of PERK via the PERK-eIF2α-ATF4-CHOP axis. Therefore, PERK activation could be part of the pro-apoptotic signaling via induced expression of CHOP by PCV2. Since PERK inhibition by GSK2606414 or RNA silencing or suppression of eIF2α dephosphorylation by salubrinal limited viral replication, we suppose that PCV2 deploys UPR to enhance its replication. Over-expression of GRP78 or treatment with tauroursodeoxycholic acid could enhance viral capsid expression and/or viral titers, indicating that these chaperones, endogenous or exogenous, could help correct folding of viral proteins. Our findings provide the first evidence that ER stress plays a role in the pathogenesis of PCV2 infection probably as part of autophagic and apoptotic responses.

Characterization of specific antigenic epitopes and the nuclear export signal of the Porcine circovirus 2 ORF3 protein

Porcine circovirus 2 (PCV2) is the etiological agent of postweaning multisystemic wasting syndrome. PCV2 ORF3 protein is a nonstructural protein known to induce apoptosis, but little is known about the biological function of ORF3 protein. Therefore, we undertook this study to map ORF3 protein epitopes recognized by a panel of monoclonal antibodies (mAbs) and to characterize putative nuclear localization (NLS) and nuclear export (NES) sequences in ORF3. The linear epitopes targeted by two previously published mAbs 3B1 and 1H3 and a novel mouse mAb 3C3 were defined using overlapping pools of peptides. Here, we find that ORF3 in PCV2 infected cells contains a conformational epitope targeted by the antibody 3C3, which is distinct from linear epitopes recognized by the antibodies 3B1 and 1H3 in recombinant ORF3 protein. These results suggest that the linear epitope recognized by 3B1 and 1H3 is masked in PCV2 infected cells, and that the conformational epitope is unique to PCV2 infection. Furthermore, we find that ORF3 protein expressed in cytoplasm in early stages of PCV2 infection and then accumulated in nucleus over time. Moreover, we localize a NES at the N-terminus (residues 1-35aa) of ORF3 which plays critical role in nuclear export activity. These findings provide a novel insight that deepens our understanding of the biological function of PCV2 ORF3.

19-Norvitamin D analogs for breast cancer therapy

The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3 or calcitriol), is known to inhibit the proliferation and invasiveness of many types of cancer cells, including breast, colon, pancreatic, prostate, and liver cancer cells. These findings support the use of 1α,25(OH)2D3 for the treatment of these types of cancer. However, 1α,25(OH)2D3 can cause hypercalcemia, so analogs of 1α,25(OH)2D3 that are less calcemic but exhibit more potent anti-tumor activity would be good candidates as therapeutic agents. Therefore, a series of 19-norvitamin D analogs, in which the methylidene group on C19 is replaced with 2 hydrogen atoms, have been synthesized by several laboratories. In our laboratory, we have designed and synthesized a series of 2α-functional group substituted 19-norvitamin D3 analogs and examined their anti-proliferative activity. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D3 (MART-10 and MART-11) were found to be the most promising. Here, we review the rationale and approaches for the synthesis of different 19-norvitamin D analogs, and the pre-clinical studies using these analogs in breast cancer cells, in particular, we chose MART-10 for its potential application to the prevention and treatment of breast cancer.

Characterization of thymus atrophy in calves with subclinical BVD challenged with BHV-1

Since the thymus is a target organ for the bovine viral diarrhea virus (BVDV), our experiment aimed to understand its relationship with the immunosuppressive effect by studying the consequences of a previous infection with BVDV on the thymus of calves challenged with bovine herpesvirus 1.1 (BHV-1). For this purpose, 12 animals were inoculated intranasally with non-cytopathic BVDV-1; 12 days later, 10 of them were coinfected intranasally with BHV-1. These animals were euthanized in batches of two at 0, 1, 2, 4, 7 or 14 dpi with BHV-1. Another 10 calves were inoculated solely with BHV-1 and euthanized in batches of two at 1, 2, 4, 7 or 14 dpi with BHV-1; two uninoculated calves were used as negative controls. Thymus samples from these animals were processed for viral detection and histopathological, immunohistochemical, and ultrastructural studies focused on BVDV/BHV-1 antigens, cortex:medulla ratio, apoptosis (TUNEL and caspase-3), collagen deposition, and factor VIII endothelial detection. Our study revealed the immunohistochemical presence of BVDV antigen in all animals in the BVDV-infected group, unlike BHV-1 detection, which was observed in animals in both infection groups only by molecular techniques. BVDV-preinfected animals showed severe atrophic changes associated with reduced cortex:medulla ratio, higher presence of cortical apoptosis, and increased collagen deposition and vascularization. However, calves solely infected with BHV-1 did not show atrophic changes. These findings could affect not only the numbers of circulating and local mature T cells but also the T cell-mediated immunity, which seems to be impaired during infections with this virus, thus favoring pathogenic effects during secondary infections.

The role of visfatin on the regulation of inflammation and apoptosis in the spleen of LPS-treated rats

The purpose of the present study is to determine if visfatin is involved in inflammation or apoptosis induced by LPS in rat. Forty Wistar rats were divided into four groups: saline group, LPS group, visfatin group and Visfatin + LPS co-stimulated group. Spleen samples from each group of rats were collected for study. The spleen structure was examined by histological imaging. Apoptosis was evaluated with TUNEL reaction. Caspase-3 was detected with immunohistochemistry and western blot. The apoptosis-related genes were detected by qPCR and inflammatory cytokines were tested by ELISA. Our main findings were as follows. (1) Macrophages were markedly increased in the visfatin group compared with the saline group. This finding was confirmed when spleen samples were examined with western blot using CD68 antibody. (2) Visfatin promoted the expression of CD68 and caspase-3 in rat spleen, whereas visfatin could inhibit the expression of CD68 and activated caspase-3 in spleen of LPS-induced acute inflammation. (3) Visfatin had a pro-apoptotic effect on normal rat spleen, whereas it exerted an anti-apoptotic effect during LPS-induced lymphocytes apoptosis in rat spleen. Moreover, the effect of visfatin on cell apoptosis was mediated by the mitochondrial pathway. (4) Visfatin could modulate both the anti-inflammatory cytokines and pro-inflammatory cytokines in rat spleen, such as IL-10, IL-4, IL-6, TNF-α and IL-1β. Taken together, we demonstrate that visfatin could participate in the inflammatory process in rat spleen by modulating the macrophages and inflammatory cytokines. Also, visfatin plays a dual role in the apoptosis in rat spleen, which is mediated by the mitochondrial pathway.

Hsp70 positively regulates porcine circovirus type 2 replication in vitro

The Hsp70 chaperone plays a central role in multiple processes within cells. Porcine circovirus type 2 (PCV2) is the essential causal agent of post-weaning multisystemic wasting syndrome (PMWS), which has spread worldwide. But the mechanism of PCV2 replication remains poorly understood. In this study, we firstly found the positive effect of heat stress on the replication of PCV2 in the continuous porcine monocytic cell line 3D4/31. Downregulation of Hsp70 by the specific chaperone inhibitor Quercetin or RNA interference and upregulation of Hsp70 by expression from a recombinant adenovirus showed that Hsp70 enhanced PCV2 genome replication and virion production. A specific interaction between Hsp70 and PCV2 Cap was confirmed by colocalization by confocal microscopy and co-immunoprecipitation. Furthermore, the NF-κB pathway was activated and caspase-3 activity was reduced when Hsp70 was overexpressed in PCV2-infected 3D4/31 cells. These data suggested that Hsp70 positively regulated PCV2 replication, which being helpful for understanding the molecular mechanism of PCV2 infection.

Potent 19-norvitamin D analogs for prostate and liver cancer therapy

The active form of vitamin D(3), 1α,25(OH)(2)D(3) or calcitriol, is known to inhibit the proliferation and invasiveness of many types of cancer cells, including prostate and liver cancer cells. These findings support the use of 1α,25(OH)(2)D(3) for prostate and liver cancer therapy. However, 1α,25(OH)(2)D(3) can cause hypercalcemia, thus, analogs of 1α,25(OH)(2)D(3) that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. We have developed 2α-functional group substituted 19-norvitamin D(3) analogs with and without 14-epimerization. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (MART-10 and -11, respectively) and 14-epi-2α- and 14-epi-2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (14-epi-MART-10 and 14-epi-MART-11, respectively) were found to be the most promising. In this review, we discuss the synthesis of this unique class of vitamin D analogs, the molecular mechanism of anticancer actions of vitamin D, and the biological evaluation of these analogs for potential application to the prevention and treatment of prostate and liver cancer.

Porcine circovirus type 2 (PCV2): pathogenesis and interaction with the immune system

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease (PCVAD). The virus preferentially targets the lymphoid tissues, which leads to lymphoid depletion and immunosuppression in pigs. The disease is exacerbated by immunostimulation or concurrent infections with other pathogens. PCV2 resides in certain immune cells, such as macrophage and dendritic cells, and modulates their functions. Upregulation of IL-10 and proinflammatory cytokines in infected pigs may contribute to pathogenesis. Pig genetics influence host susceptibility to PCV2, but the viral genetic determinants for virulence remain unknown. PCV2 DNA and proteins interact with various cellular genes that control immune responses to regulate virus replication and pathogenesis. Both neutralizing antibodies and cell-mediated immunity are important immunological correlates of protection. Despite the availability of effective vaccines, variant strains of PCV2 continue to emerge. Although tremendous progress has been made toward understanding PCV2 pathogenesis and immune interactions, many important questions remain.

Microarray analysis of mediastinal lymph node of pigs naturally affected by postweaning multisystemic wasting syndrome

Postweaning multisystemic wasting syndrome (PMWS) is one of the pig diseases with major economic impact worldwide. Clinical, pathologic and some immunologic aspects of this disease are relatively well-known, but the molecular mechanisms underlying the pathogenic mechanisms of the disease are still poorly understood. The objective of the present study was to investigate the global transcriptome changes in the mediastinal lymph nodes from pigs naturally affected by PMWS, as well as healthy counterparts, using the Affymetrix Porcine Genechip(®). From 366 transcripts showing significant differential abundance in the PMWS group of pigs relative to healthy animals, 229 showed higher and 137 lower abundance. A relative increased abundance of mRNAs coded by a large set of genes involved in the inflammatory responses (e.g. cytokines, acute phase proteins, and respiratory burst) was observed in PMWS affected pigs. The Gpnmb and Lgals3 genes, which have antagonistic functions in regulation of inflammatory processes, showed high mRNA levels in diseased pigs. The complement system was altered by PMWS, notably by the lower levels of Cr1 mRNA, which might favour both complement deposition and secondary infections by impairing phagocytosis. Decreased mRNA abundance of several genes involved in lymphocyte activation/differentiation, such as Cd79b, Cd19, Cd21 and MybL1, and the high level of Vsig4 mRNA, which can compromise the activation of residing T-cells, pointed towards a defective adaptive immunity. This is the first study on gene expression in pigs naturally affected by PMWS. The present results allowed identifying potential mechanisms underlying the inflammation and lymphocyte depletion in lymphoid tissues by complement mediated damage and immunosuppression, which are key features of PMWS.

The Porcine Circovirus Type 2 Nonstructural Protein ORF3 Induces Apoptosis in Porcine Peripheral Blood Mononuclear Cells

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases in pigs. To analyze whether the PCV2 nonstructural protein ORF3 is able to induce apoptosis in nature target cells, transient expression of ORF3 in porcine peripheral blood mononuclear cells (PBMC) was performed, and apoptosis was confirmed by terminal dexoynucleotidyl transferase (TdT)-mediated BrdUTP-nick end labeling (TUNEL) assay. The apoptotic responses induced by the full length or the C-terminal half of ORF3 were significantly higher (p < 0.001) than that of cells transfected with the control plasmid. In contrast, the N-terminal half of ORF3 restrictively localized in the cytoplasm and remarkably reduced its ability to induce apoptosis, the apoptotic activity might be correlated with the nuclear localization of ORF3. Furthermore, two clusters of basic residues on the C-terminal half region at the amino acid residues 53-68 and 85-104 could mediate the nuclear localization of fusion protein, confirming their potential role as a nuclear localization signal.

19-Nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (MART-10) is a potent cell growth regulator with enhanced chemotherapeutic potency in liver cancer cells

The discovery that the active form of vitamin D, 1α,25-dihydroxyvitamin D [1α,25(OH)(2)D] can modulate cellular proliferation and differentiation of cancer cells has led to its potential application as a chemotherapeutic agent to treat a variety of cancers. However, the use of 1α,25(OH)(2)D is limited due to its lethal side effect of hypercalcemia upon systemic administration. To overcome this drawback, numerous analogs have been synthesized. In this report, we examined the anti-proliferative activity of a new analog, 19-nor-2α-(3-hydroxypropyl)-1α,25(OH)(2)D(3) (MART-10), in HepG2 liver cancer cells, and studied the potential mechanisms mediating this action. We found that MART-10 exhibited approximately 100-fold greater activity than 1α,25(OH)(2)D(3) in inhibiting HepG2 cell proliferation as determined by cell number counting method. MART-10 was also approximately 100-fold more potent than 1α,25(OH)(2)D(3) in the upregulation of p21 and p27, that in turn arrested HepG2 cells at the G(0)/G(1) phase to a greater extent. Given that no active caspase 3 was detected and treatment with 1α,25(OH)(2)D(3) or MART-10 did not further increase the fractions of apoptotic and necrosis cells over the controls, the growth-inhibitory effect of 1α,25(OH)(2)D(3) and MART-10 on HepG2 cells may not involve apoptosis. Overall, our findings suggest that MART-10 is a good candidate as a novel therapeutic regimen against liver cancer. Further pre-clinical studies using animal models and the subsequent human clinical trials are warranted.

Immunology of porcine circovirus type 2 (PCV2)

The emergence of porcine circovirus type 2 (PCV2) associated diseases and particularly postweaning multisystemic wasting syndrome (PMWS) was a shock for the swine industry and formulated a considerable challenge for researchers in the area of viral immunology in swine. The unique features of PMWS of which emaciation and lymphoid depletion were the most evident indicated a deep involvement of the immune system of the pig in the pathogenesis of this condition and indicated that PCV2 was a singular pathogen. Also, the multifactorial nature of the disease complicated the understanding of PMWS pathogenesis. Nowadays, it is known that PCV2 deeply affects the functionality of the immune system of the pig but also the industry has been able to produce efficacious vaccines. In the present paper some of the most relevant immunological features of PMWS and of PCV2 infection in general will be reviewed.

Viral distribution and lesions in Kunming mice experimentally infected with porcine circovirus type 2b

The viral distribution and lesions in Kunming mice experimentally infected with porcine circovirus type 2b (PCV-2b) were investigated. Seventy special pathogen free mice were divided into 2 groups with 35 mice in each group. The test group (TG) was infected with PCV-2b, the control group (CG) was inoculated with sterile cell cultures. Five mice in each group were sacrificed at 3, 7, 14, 21, 28, 35 and 42 dpi (day post infection), respectively. Necropsies were performed on all mice and tissues were collected for testing by histopathology, immunohistochemistry, transmission electron microscope (TEM) and polymerase chain reaction (PCR). Apoptosis and necrosis in lymphoid organs were observed in virus-infected mice, and became severe from 14 to 28 dpi. The proportion of PCV-2b antigen-positive cells was moderate in lung, heart, thymus, liver or kidney, and low in brain from TG. In spleen and cervical lymph node, the proportions of PCV-2b antigen-positive cells were low to high from 7 to 28 dpi, and moderate from 35 to 42 dpi. PCV-2b DNA was detected in all tissues examined in TG from 7 to 42 dpi. Viral inclusion bodies presented in the cytoplasm of lymphocytes, macrophages, hepatocytes, podocytes, neurocytes, spermatids and uterine epithelial cells in TG. In CG, no viruses and viral lesions were detected. PCV-2b could replicate in mice, and PCV-2b associated lesions in mice were similar to those observed in pigs. The present results indicate that it is possible to use Kunming mouse as an animal model for PMWS research.

ORF3 of porcine circovirus 2 enhances the in vitro and in vivo spread of the of the virus

The ORF3 protein of the pathogenic porcine circovirus 2 (PCV2) causes apoptosis of the virus-infected cells. In PCV2-infected piglets, ORF3 induces B and CD4 T lymphocyte depletion and lymphoid organ destruction and the ORF3-deficient PCV2 is attenuated in its pathogenicity (Virology, 383 (2009), 338). In addition to its role in causing the apoptosis of the immune cells, characteristic of the PCV2 infection associated disease conditions, the ORF3 also plays a role in the systemic dissemination of the PCV2 infection. Our experiments here show that ORF3 expedites the spread of the virus by inducing the early release of the virus from the infected cells. Further, in PCV2-infected mice, the ORF3-induced apoptosis also aids in recruiting macrophages to phagocytize the infected apoptotic cells leading to the systemic dissemination of the infection. The apoptotic activity of the ORF3 of PCV2 hence lends advantage to the spread of the virus.

Immunopathological characterization of porcine circovirus type 2 infection-associated follicular changes in inguinal lymph nodes using high-throughput tissue microarray

The immunopathogenesis of porcine circovirus type 2 (PCV2) infection in conventional pigs is complicated by various environmental factors and individual variation and is difficult to be completely reproduced experimentally. In the present field-based study, a tissue microarray (TMA) consisting of a series of lymphoid follicles having different PCV2-loads was constructed using formalin-fixed and paraffin-embedded superficial inguinal lymph nodes (LNs) from 102 pigs. Using the TMA, a wide range of parameters, including co-infected viral pathogens, immune cell subsets, and cell apoptosis/proliferation activity by immunohistochemical (IHC) staining or in situ hybridization (ISH) were measured, characterized, and compared. The signal location and area extent of each parameter were interpreted by pathologists, semi-quantified by automated image analysis software, and analyzed statistically. The results herein demonstrated a significant negative correlation between PCV2 and CD79a (p<0.001) and a significant positive correlation between PCV2 and lysozyme (p<0.001) or TUNEL (p<0.001) using Pearson correlation analysis. The amount of porcine respiratory and reproductive syndrome virus (PRRSV) and porcine parvovirus antigens did not correlate with the tissue loads of PCV2 nucleic acid. Multiple regression analysis further predicted that PCV2 contributed major effects on CD79a, lysozyme, and TUNEL but PRRSV showed relatively less effects on these parameters. In addition, the total signal intensity of Ki67 (index of cell proliferation activity) did not change significantly among cases with different PCV2 loads; however, as the loading of PCV2 nucleic acid increased, the main contribution of Ki67 signal gradually shifted from B cells in the germinal center to T cells and macrophages in the interfollicular regions. In the present study, the use of TMA to establish a mathematical model with a wider range of statistical analysis can bring us a step forward to understand the immunopathogenesis of PCV2 infection-associated follicular changes in LNs.

Immunohistochemical detection of extrinsic and intrinsic mediators of apoptosis in porcine paraffin-embedded tissues

Apoptosis is a strictly regulated mechanism of cell death that involves a complex network of biochemical pathways. Whether a cell undergoes apoptosis or not depends on a delicate balance of anti- and pro-apoptotic stimuli. This phenomenon can be induced by two different pathways: intrinsic and extrinsic pathways. The main aim of this study was to determine the ideal fixative and antigen retrieval method in porcine paraffin embedded tissues for the immunohistochemical detection of apoptosis mediators, from both extrinsic and intrinsic pathways. Tonsil, retropharyngeal lymph node and lung tissue samples were fixed in 10% neutral buffered formalin, Bouin solution and zinc salts fixative (ZSF) and different unmasking methods were carried out. Both 10% neutral buffered formalin and ZSF resulted as the fixatives of election to study apoptosis phenomena. Tween 20 (0.01% in PBS), citrate buffer (microwave, pH 6.0) and/or protease type XIV were the antigen retrieval methods which displayed better labelling. Our results allow to deep in the knowledge of apoptosis and its role in the pathogenesis of porcine diseases.

Cytotoxicity of ORF3 proteins from a nonpathogenic and a pathogenic porcine circovirus

Porcine circovirus type 2 (PCV2) infection is associated with significant and serious swine diseases worldwide, while PCV1 appears to be a nonpathogenic virus. Previous studies demonstrated that the ORF3 protein of PCV2 (PCV2ORF3) was involved in PCV2 pathogenesis via its proapoptotic capability (J. Liu, I. Chen, Q. Du, H. Chua, and J. Kwang, J. Virol. 80:5065-5073, 2006). If PCV2ORF3-induced apoptosis is a determinant of virulence, PCV1ORF3 is hypothesized to lack this ability. The properties of PCV1 and PCV2 ORF3, expressed as fusion proteins to an enhanced green fluorescent protein (eGFP), were characterized with regard to their ability to cause cellular morphological changes, detachment, death, and apoptosis. PCV1ORF3 significantly induced more apoptotic cell death and was toxic to more different cell types than PCV2ORF3 was. PCV1ORF3-associated cell death was caspase dependent. PCV1ORF3 also induced poly(ADP-ribose) polymerase 1 (PARP) cleavage; however, whether PARP was involved in cell death requires further studies. Truncation of PCV1 and elongation of PCV2 ORF3 proteins revealed that the first 104 amino acids contain a domain capable of inducing cell death, whereas the C terminus of PCV1ORF3 contains a domain possibly responsible for enhancing cell death. These results suggest that the pathogenicity of PCV2 for pigs is either not determined or not solely determined by the ORF3 protein.

Characterization of necrotizing lymphadenitis associated with porcine circovirus type 2 infection

Necrotizing lymphadenitis is observed in approximately 2% of pigs affected by post-weaning multisystemic wasting syndrome (PMWS). The pathogenesis of the lesion has been linked to apoptosis induced by porcine circovirus type 2 (PCV2). The aim of the present study was to gain further insights into PCV2-associated lymphoid necrosis in pigs with PMWS. Three groups of animals were studied: (1) PMWS-affected pigs with necrotizing lymphadenitis (n=5), (2) PMWS-affected pigs without necrotizing lymphadenitis (n=5) and (3) healthy pigs with no PMWS-related lesions (n=5). Investigations performed included immunohistochemical evaluation of the expression of cleaved caspase-3 and von Willebrand factor, Mallory's staining for fibrin and in-situ hybridization for detection of the PCV2 genome. The results of the study suggested that lymphoid necrosis in PMWS-affected pigs may be related to hypertrophy and hyperplasia of high endothelial venules (HEVs). The mechanism underlying these changes in HEVs was not clearly defined, but necrotizing lymphadenitis in pigs with PMWS may develop following vascular damage with thrombosis and subsequent follicular necrosis. Apoptosis was not found to be involved in lymphocyte depletion in PMWS or in PMWS-associated necrotizing lymphadenitis.

Porcine circovirus type 2 ORF3 protein competes with p53 in binding to Pirh2 and mediates the deregulation of p53 homeostasis

The ORF3 protein of porcine circovirus type 2 (PCV2) causes apoptosis in virus-infected cells and is not essential for virus replication. The ORF3 protein plays an important role in the pathogenesis of the PCV2 infection in mouse models and SPF piglets. The ORF3 protein interacts with the porcine homologue of Pirh2 (pPirh2), a p53-induced ubiquitin-protein E3 ligase, which regulates p53 ubiquitination. Here, we present our study analyzing the details of the molecular interaction between these three factors. Our experiments, in vitro and in vivo, show that ORF3 protein competes with p53 in binding to pPirh2. The amino acid residues 20 to 65 of the ORF3 protein are essential in this competitive interaction of ORF3 protein with pPirh2 over p53. The interaction of ORF3 protein with pPirh2 also leads to an alteration in the physiological cellular localization of pPirh2 and a significant reduction in the stability of pPirh2. These events contribute to the deregulation of p53 by pPirh2, leading to increased p53 levels and apoptosis of the infected cells.

The open reading frame 3 (ORF3) of porcine circovirus type 2 (PCV2) is dispensable for virus infection but evidence of reduced pathogenicity is limited in pigs infected by an ORF3-null PCV2 mutant

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVAD) in pigs. The open reading frame (ORF) 3 of PCV2 reportedly induces apoptosis and is associated with PCV2 pathogenicity. In this study, we first created an ORF3-null PCV2 mutant (muPCV2) by site-directed mutagenesis and demonstrated that the dimerized plasmid DNA of muPCV2 clone is infectious when injected intramuscularly (I.M.) into pigs. Subsequently, by using a well-characterized pig model we compared the pathogenicity of the muPCV2 and the wildtype PCV2. Thirty-one pigs were divided into 3 groups of 11, 10, and 10 each: group 1 pigs were each inoculated I.M. with PBS buffer as negative controls, group 2 pigs each with 200 microg of muPCV2 infectious DNA clone, and group 3 pigs each with 200 microg of wildtype PCV2 infectious DNA clone. Blood was collected prior to inoculation and weekly thereafter, and tested for PCV2 antibodies by ELISA and serum viral DNA loads by quantitative PCR. All pigs were necropsied at 35 days post-inoculation. The results showed that pigs inoculated with muPCV2 had a delayed seroconversion and lower serum viral load. However, there was no significant difference in the average scores of the histological or gross lesions or the amount of PCV2-specific antigen in tissues between wildtype PCV2- and muPCV2-inoculated groups. Thus, the data from this study do not fully support the conclusion of a previous report regarding PCV2 attenuation by abrogation of ORF3 although the results did show that ORF3 is dispensable for PCV2 replication in pigs.

Ultrastructural Findings in Lymph Nodes from Pigs Suffering from Naturally Occurring Postweaning Multisystemic Wasting Syndrome

The aims of this study were to evaluate ultrastructural lesions in lymph nodes from postweaning multisystemic wasting syndrome (PMWS)-affected pigs and to correlate these alterations with detection of viral-like particles (VLPs). Samples of lymph nodes were taken from 4 PMWS-affected pigs and 2 healthy animals and processed by transmission electron microscopy. Significant ultrastructural alterations were only noted in PMWS-affected pigs, mainly in histiocytes and rarely in other cell types. Histiocytes showed severe swelling and proliferation of mitochondria, and proliferation and dilation of rough endoplasmic reticulum and Golgi complex. Infected histiocytes contained large numbers of intracytoplasmic inclusion (ICI) bodies with VLPs; some histiocytes also had intranuclear inclusions (INIs). Small inclusions were surrounded by double membrane, with a granular appearance or containing paracrystalline arrays; icosahedral VLPs were 8–17 nm in diameter. Large ICIs were double-membrane bounded or not and contained VLPs usually forming paracrystalline arrays. ICIs were often found next to mitochondria with severe swelling, and also inside them. INIs were not surrounded by membranes and contained virions of 10–13 nm diameter. Lymphocyte depletion was a striking finding of lymph nodes from PMWS-affected pigs. The inclusion bodies containing VLPs referred to in the present study should be classified as viral factories, suggesting that viral replication is probably a frequent event in macrophages, in which mitochondria might play a role.

Attenuation of porcine circovirus 2 in SPF piglets by abrogation of ORF3 function

Porcine circovirus 2 (PCV2), open reading frame 3 (ORF3) codes a 105 amino acid protein that causes apoptosis of PCV2 infected cells. In infected cells, the ORF3 causes the accumulation of p53 by interacting with pPirh2 and possibly by disrupting the association of p53 and pPirh2 (J.Virol.81(2007)9560). Mutant PCV2 lacking the expression of ORF3 are infectious and replicate in cells in vitro, but do not cause apoptosis of the infected cells. The ORF3 of PCV2 has been shown to be involved in pathogenesis of the virus in mice model (J. Virol. 80(2006)5065). Here we report the experimental inoculation of ORF3 deficient PCV2 in its natural host, the piglets. The pathogenicity of the ORF3 deficient virus is attenuated in the piglets. The mutant virus did not cause any observable disease or perturbation of the lymphocyte count in the inoculated piglets and elicited an efficient immune response. When compared with the wildtype virus infection, the mutant virus infection was characterized by mild viremia and absence of pathological lesions. The findings highlight the role of ORF3 in the pathogenesis of PCV2 infection in its host.

Porcine circoviruses: a minuscule yet mammoth paradox

Porcine circovirus type 2 (PCV2) is the primary causative agent for porcine circovirus-associated disease (PCVAD). PCVAD has been the cause of considerable economic losses to the pork industry worldwide. The disease is primarily characterized by wasting, enlarged lymph nodes, jaundice and weight loss in affected weanling pigs. Several other complex syndromes involving reproductive failure, enteritis, pneumonia and necrotizing dermatitis have also been associated with PCV2 infection. Lymphoid depletion, which is the hallmark lesion of PCVAD, predisposes the host to immunosuppression. Disease progression is further complicated by co-infections with other bacterial and viral pathogens. Despite the availability of effective vaccines for the last 2 years, newly emerging strains of the virus have been reported to cause more severe outbreaks in parts of the USA and Canada. While knowledge of the biology and pathogenesis of PCV2 has progressed considerably over the last 12 years since the disease was recognized, many questions still remain to be answered.

A meta-analysis on experimental infections with porcine circovirus type 2 (PCV2)

A meta-analysis was performed with the aim to identify factors with a relevant influence on the expression of clinical postweaning multisystemic wasting syndrome (PMWS) under experimental conditions. Data from 44 studies were included in the analysis. Several variables were studied: number of pigs in the experiment, intake of colostrum, serological status against porcine circovirus type 2 (PCV2), strain of PCV2 used for inoculation, the route and dose of inoculation, and use of potential triggering factors (such as co-infections, vaccinations, or immunomodulator products). Multiple correspondence analysis and log-linear regression methods were used to establish the relationships between the studied variables and the number of PCV2 infected pigs that developed PMWS. Based on the results of the meta-analysis, the most successful animal experiment aimed to develop PMWS should include: (1) colostrum-deprived pigs, (2) age of inoculation below 3 weeks, (3) high doses of PCV2 inoculum, (4) PCV2 strain from genotype 1, and (5) co-infection with another swine pathogen as a triggering factor.

Porcine circovirus type 2-associated cerebellar vasculitis in postweaning multisystemic wasting syndrome (PMWS)-affected pigs

Porcine circovirus type 2 (PCV2) is associated with several syndromes in growing pigs, including postweaning multisystemic wasting syndrome and porcine dermatitis and nephropathy syndrome. In the present study, a previously undescribed neurovascular disorder associated with a PCV2 infection is described. Sixteen pigs showed clinical signs of wasting and neurologic deficits. Acute hemorrhages and edema of cerebellar meninges and parenchyma due to a necrotizing vasculitis resulted in degeneration and necrosis of the gray and white matter. Few to numerous PCV2 DNA and antigen-bearing endothelial cells were detected in affected areas of the brain using in situ hybridization and immunohistochemistry. Conventional histochemical stains, as well as the detection of caspase 3 activity and DNA strand breaks by the terminal transferase dUTP nick end labeling assay, showed numerous apoptotic endothelial cells in the vascular lesions observed. Sequencing of various brain-derived PCV2-specific amplicons revealed a strong identity between different isolates and an 89 to 100% identity to previous isolates. The phylogenetic tree showed that there was no clustering of isolates correlating to clinical signs or geographic distribution. This previously undescribed PCV2-associated neurologic disease has features of both postweaning multisystemic wasting syndrome and, to a lesser extent, porcine dermatitis and nephropathy syndrome. The available evidence suggests that direct virus-induced apoptosis of endothelial cells plays a role in the pathogenesis of this unusual PCV2-associated cerebellar vasculitis.

Porcine circovirus diseases

Porcine circovirus type 2 (PCV2) is a member of the familyCircoviridae, a recently established virus family composed of small, non-enveloped viruses, with a circular, single-stranded DNA genome. PCV2, which is found all over the world in the domestic pig and probably the wild boar, has been recently associated with a number of disease syndromes, which have been collectively named porcine circovirus diseases (PCVD). Postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS) and reproductive disorders are the most relevant ones. Among them, only PMWS is considered to have a severe impact on domestic swine production. PMWS mainly affects nursery and/or fattening pigs; wasting is considered the most representative clinical sign in this disease. Diagnosis of this disease is confirmed by histopathological examination of lymphoid tissues and detection of a moderate to high amount of PCV2 in damaged tissues. Since PMWS is considered a multifactorial disease in which other factors in addition to PCV2 are needed in most cases to trigger the clinical disease, effective control measures have focused on the understanding of the co-factors involved in individual farms and the control or elimination of these triggers. PDNS, an immuno-complex disease characterized by fibrino-necrotizing glomerulonephritis and systemic necrotizing vasculitis, has been linked to PCV2, but a definitive proof of this association is still lacking. PCV2-associated reproductive disease seems to occur very sporadically under field conditions, but it has been characterized by late-term abortions and stillbirths, extensive fibrosing and/or necrotizing myocarditis in fetuses and the presence of moderate to high amounts of PCV2 in these lesions. Taking into account that scientific information on PCV2 and its associated diseases has been markedly expanded in the last 8 years, the objective of this review is to summarize the current state of knowledge of the most relevant aspects of PCV2 biology and PCVD.

Generation and immunogenicity of a recombinant pseudorabies virus expressing cap protein of porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is associated with post-weaning multisystemic wasting syndrome (PMWS), which is an important economical disease affecting the pig industry worldwide. In order to develop an effective vaccine for PMWS, a recombinant pseudorabies virus (PRV) was generated and tested in piglets in this study. The PCV2 open reading frame 2 (ORF2) gene was inserted into pIECMV plasmid and co-transfected with PRV Tk-/gE-/LacZ+ genome into IBRS-2 cells to generate a recombinant Tk-/gE-/ORF2(+) virus. The expression of PCV2 ORF2 gene in the recombinant virus was confirmed by Western blotting and indirect immunofluorescence assay (IFA). Four-week-old piglets were immunized by the recombinant virus, and the immunogenicity of PRV Tk-/gE-/ORF2(+) was tested by PRV-enzyme-linked immunosorbent assay (ELISA), PRV neutralizing assay, ORF2-ELISA and ORF2 specific lymphocyte proliferation response. PRV Tk-/gE-/ORF2(+) elicited significant humoral immune responses to both PRV and PCV2, and the PCV2-specific lymphocyte proliferation response could be detected on day 49 of this experiment. These findings suggest that the recombinant PRV Tk-/gE-/ORF2(+) may be a potential vaccine against both PCV2 and PRV.

Selective lymphocyte depletion during the early stage of the immune response to foot-and-mouth disease virus infection in swine

Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious vesicular disease of cloven-hoofed animals. In the present study we use FMDV serotype C infection of swine to determine, by analytical techniques, the direct ex vivo visualization of virus-infected immune cells during the first 17 days of infection. We report, for the first time, that FMDV C-S8c1 can infect T and B cells at short periods of time postinoculation, corresponding with the peak of the viremia. There is a significant lymphopenia that involves CD3(+) CD4(-) CD8(+/-), CD3(+) CD4(-) CD8(+)Tc, and CD3(+) CD4(+) CD8(+) memory Th but not CD3(+) CD4(+) CD8(-) naïve Th lymphocytes. In addition, a profound depletion of the vast majority of peripheral T cells in lymph nodes and spleen is observed. This selective depletion of T cells is not due mainly to in situ death via apoptosis as visualized by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) technique. Thus, early infection of T cells by FMDV may be the main cause of the observed T-cell depletion. Importantly, this lack of T cells is reflected in a reduced response to mitogen activation, which in many cases is totally eliminated. These data suggest a mechanism by which the virus causes a transient immunosuppression, subvert the immune systems, and spreads. These results have important implications for our understanding of early events in the development of a robust immune response against FMDV.

Porcine circovirus type 2 (PCV2) causes apoptosis in experimentally inoculated BALB/c mice

BACKGROUND

We have previously described microscopic and electron microscopic alterations in lymphoid organs of PCV2 inoculated mice as apoptosis. In this study we wanted to investigate the molecular pathogenetic mechanism of PCV2-induced apoptosis. Eight-week old BALB/c mice were either sham inoculated (control mice) or inoculated intraperitoneally (ip) and intranasally (in) with a single (sPCV mice) or multiple (mPCV mice) doses of PCV2. Four control mice and 4 sPCV mice were sacrificed 7, 14, 28 and 42 days post inoculation (PI). All 4 mPCV mice were sacrificed 42 days PI. Following necropsy, immunohistochemistry for caspase 3 and in-situ TUNEL assay were performed on sections of spleen, lymph nodes, thymus and ileum from control, sPCV and mPCV mice. In addition, total RNA was extracted from spleens of control, sPCV and mPCV mice for simultaneous detection and semiquantitation of bcl-2 homologues and various caspase mRNAs using a multiprobe RNase protection assay system.

RESULTS

PCV2 replicated and was associated with apoptosis in spleens, lymph nodes and Peyer's patches of infected BALB/c mice. Upregulation of caspase 1, 2, 3, 6, 7, 8, 11 and 12 and upregulation for the transcripts of apoptosis inhibitors bcl-2, bcl-w and bcl-X and apoptosis promoters' bax, bak and bad was detected in spleens of sPCV and mPCV mice, but not control mice. Apoptosis was further confirmed by light and electron microscopic morphology as well as by positive TUNEL assay and detection of activated caspase 3. PCV2 nucleic acid was detected by in-situ hybridization in the nuclei and cytoplasm of such apoptotic cells.

CONCLUSION

The data presented here support the hypothesis that PCV2 induces apoptosis mediated through the activation of caspases 8 and 3 in the spleens of infected mice.

Characterization of a previously unidentified viral protein in porcine circovirus type 2-infected cells and its role in virus-induced apoptosis

Porcine circovirus type 2 (PCV2) is the causative agent of postweaning multisystemic wasting syndrome in pigs. In this study, transcription and translation of a novel viral gene (termed ORF3 here) was detected during productive infection of PCV2 in PK15 cells. The results of infection with ORF3-deficient PCV2 by site-directed mutagenesis indicated that the protein is not essential for viral replication. To investigate the underlying mechanism of cell death caused by replication of PCV2, apoptosis characterized by chromosomal condensation and fragmentation, formation of apoptotic bodies, and significant increase in hypodiploids were detected in infected cells. We further demonstrated that PCV2-induced apoptosis required the activation of caspase-8 but not caspase-9. The activation of caspase-8 results in the activation of caspase-3 as shown by an increase in the cleavage of the caspase substrate in the infected cells. To determine whether ORF3 protein could trigger apoptosis, ORF3 as well as ORF1 and ORF2 genes were transiently expressed in PK15 and Cos-7 cells for apoptotic activity assay. Transfection of cells with the ORF3 alone induced apoptosis using a pathway similar to that described in the context of viral infection. This is further confirmed by a significant decrease in apoptotic activity of infected cells in the absence of the ORF3 expression, suggesting that the protein plays a major role in the induction of virus-induced apoptosis. Altogether, these results indicate that ORF3 is a novel PCV2 protein that is not essential for viral replication in cultured cells but is involved in PCV2-induced apoptosis by activating caspase-8 and caspase-3 pathways.