Cytokine profiles of peripheral blood mononuclear cells from pigs with postweaning multisystemic wasting syndrome in response to mitogen, superantigen or recall viral antigens

PDZK1 upregulates nitric oxide production through the PI3K/ERK2 pathway to inhibit porcine circovirus type 2 replication

Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus-associated disease. Changes in host cell gene expression are induced by PCV2 infection. Here, we showed that porcine PDZ Domain-Containing 1 (PDZK1) expression was enhanced during PCV2 infection and that overexpression of PDZK1 inhibited the expression of PCV2 Cap protein. PCV2 genomic DNA copy number and viral titers were decreased in PDZK1-overexpressing PK-15B6 cells. PDZK1 knockdown enhanced the replication of PCV2. Overexpression of PDZK1 activated the phosphoinositide 3-kinase (PI3K)/ERK2 signaling pathway to enhance nitric oxide (NO) levels, while PDZK1 knockdown had the opposite effects. A PI3K inhibitor (LY294002) and a NO synthase inhibitor (L-NAME hydrochloride) decreased the activity of PDZK1 in restricting PCV2 replication. ERK2 knockdown enhanced the proliferation of PCV2 by decreasing levels of NO. Levels of interleukin (IL)- 4 mRNA were reduced in PDZK1 knockdown and ERK2 knockdown PK-15B6 cells. Increased IL-4 mRNA levels were unable to decrease NO production in PDZK1-overexpressing cells. Thus, we conclude that PDZK1 affected PCV2 replication by regulating NO production via PI3K/ERK2 signaling. PDZK1 affected IL-4 expression through the PI3K/ERK2 pathway, but PDZK1 modulation of PCV2 replication occurred independently of IL-4. Our results contribute to understanding the biological functions of PDZK1 and provide a theoretical basis for the pathogenic mechanisms of PCV2.

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.

Coinfections and their molecular consequences in the porcine respiratory tract

Understudied, coinfections are more frequent in pig farms than single infections. In pigs, the term “Porcine Respiratory Disease Complex” (PRDC) is often used to describe coinfections involving viruses such as swine Influenza A Virus (swIAV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and Porcine CircoVirus type 2 (PCV2) as well as bacteria like Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae and Bordetella bronchiseptica. The clinical outcome of the various coinfection or superinfection situations is usually assessed in the studies while in most of cases there is no clear elucidation of the fine mechanisms shaping the complex interactions occurring between microorganisms. In this comprehensive review, we aimed at identifying the studies dealing with coinfections or superinfections in the pig respiratory tract and at presenting the interactions between pathogens and, when possible, the mechanisms controlling them. Coinfections and superinfections involving viruses and bacteria were considered while research articles including protozoan and fungi were excluded. We discuss the main limitations complicating the interpretation of coinfection/superinfection studies, and the high potential perspectives in this fascinating research field, which is expecting to gain more and more interest in the next years for the obvious benefit of animal health.

Colonisation of mice and pigs by a chimeric porcine circovirus 1-2 prototype vaccine strain and a PCV2 isolate originating in China and their induction of cytokines

A chimeric porcine circovirus (PCV) 1-2b vaccine strain and its parental wild-type PCV2b strain from China (PCV2-J) were used separately to vaccinate BALB/c mice and tissue and serum samples were collected from the mice to investigate whether the replication properties of the viruses differed. The spleen lymphocytes from the infected mice were cultured in vitro; the amounts of interferon-γ-secreting cells (IFN-γ-SCs) and levels of interleukin (IL) 2, IL-4 and IL-10 in the culture fluids were monitored. The results showed that PCV1-2b induced higher levels of antibody production in the infected mice than the PCV2b-J isolate. Viremia declined gradually in both infection groups and the DNA copy numbers were nearly equal in both groups of mouse tissues tested. The IFN-γ-SC levels were clearly up-regulated in both the PCV1-2b- and PCV2b-J-infected mice. In both mouse groups, IL-2 was up-regulated, and IL-10 was detected at low levels, while IL-4 was always below the limit of detection. Similar experiments were performed in pigs and the results showed that when infected with either PCV1-2b or PCV2b-J the pigs experienced high-level antibody responses, with no significant differences between the infection groups. In the pig model, the development of IFN-γ-SCs in response to PCV1-2b and PCV2b-J infections was detected. However, the PCV1-2b strain tended to elicit more IFN-γ-SCs in the peripheral blood mononuclear cell population of the infected pigs from 21 to 28 days post infection than the PCV2b-J isolate did. The concentrations of IL-2 were transiently different between the PCV1-2b and PCV2b-J infected pigs, while those of IL-10 and IL-2 were similar in both groups, but were lower than those elicited in mice. These results indicated that BALB/c mouse could be used as an alternate model for evaluating the efficacy of attenuated PCV1-2b vaccines.

Reduction of Postweaning Multisystemic Wasting Syndrome-Associated Clinical Symptoms by Virus-Like Particle Vaccine Against Porcine Parvovirus and Porcine Circovirus Type 2

The porcine circovirus type 2 (PCV2) capsid (Cap) protein and porcine parvovirus (PPV) VP2 protein have been studied in vaccines to control postweaning multisystemic wasting syndrome (PMWS). Virus-like particle (VLP) vaccines are nonreplicative vectors that deliver epitopes and induce immune responses. However, most VLP vaccines are recombinant proteins expressed in eukaryotic systems and are expensive and complex. In this study, the full-length PCV2-Cap and PPV-VP2 proteins were expressed in Escherichia coli, which self-assembled into VLPs. The highly soluble proteins were purified using Ni-chelating affinity chromatography. The proteins self-assembled into VLPs of ∼20 nm (Cap VLP) and 25 nm (VP2 VLP) in diameter. The immunogenicities of Cap VLP and VP2 VLP were determined in piglets coinfected with PPV and PCV2 postimmunization. The results suggested that Cap VLP and VP2 VLP did not antagonize each other. The combined vaccine induced stronger humoral and cellular immune responses and provided the best protection against PPV and PCV2 coinfection. On a farm containing PMWS-infected pigs, the combined Cap VLP and VP2 VLP vaccine significantly improved piglet growth indices; the average daily weight gains were significantly higher than those of the Cap VLP vaccine and nonimmunized groups. Thus, Cap and VP2 protein expression in E. coli is feasible for large-scale VLP vaccine production. The combined vaccine may be a promising candidate vaccine for better preventing PMWS-associated diseases coinfected with PCV2 and PPV.

Haemato-biochemical alterations and oxidative stress associated with naturally occurring porcine circovirus2 infection in pigs

Porcine circovirus2 (PCV2) infection in pigs is one of the major causes of economic loss to the farmers in terms of low production, slow growth and increase post-weaning mortality rate. The effect of PCV2 infection on haemogram, serum biochemical profile and oxidant/anti-oxidant status is not well established in pigs. In the present study, haemogram, serum biochemical profile and oxidant/anti-oxidant status were assessed in pigs confirmed positive for PCV2 infections as evidenced by commercially available enzyme-linked immunosorbent assay kit (n = 151) and polymerase chain reaction (PCR) (n = 42) among a total of 306 number of pigs included in the study. Non-infected healthy pigs (n = 6) served as healthy control. The total erythrocyte count (TEC), haemoglobin (Hb), packed cell volume (PCV), total leukocyte count (TLC), differential leukocyte count (DLC) and thrombocyte count were measured. The levels of total protein, albumin, globulin, total bilirubin, direct bilirubin, blood urea nitrogen (BUN), creatinine and glucose and enzymes viz. alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALP) were measured. Oxidative stress indicators such as plasma malondialdehyde (MDA) and total anti-oxidant activity (TAOA) were measured using commercially available kits. The mean values of TLC, lymphocytes and thrombocyte count were significantly (P < 0.05) low in PCV2-infected pigs. The levels of globulin, AST, GGT, BUN and creatinine were significantly increased (P < 0.05) whereas levels of albumin and glucose significantly (P < 0.05) decreased in PCV2-infected pigs. The significant increase (P < 0.05) in MDA level and significant decrease (P < 0.05) in TAOA level were noticed in PCV2-infected animals as compared with healthy control. The present study supports immunosuppression, possible multiple organ damage and oxidative stress associated with naturally occurring PCV2 infection in pigs. Timely vaccination and managemental practices can reduce PCV2 infection in farms. In spite of many research studies, there is still paucity of detailed systemic study on haemato-biochemical alteration and oxidative stress associated with PCV2 infection.

Herbal extracts as antiviral agents

Phytotherapy, or herbalism, is defined as the usage of plants or herbs as medication to treat or prevent diseases in human and animals. The usage is gaining more attention among medical practitioners as well as large-scale livestock producers. A number of reports have shown the positive effects of herbal extracts as an antiviral agent used in animal feed or as a prophylaxis and remedy. Besides being a cheaper and safer alternative, the use of herbs may reduce the incidence of drug resistance and may modulate the immune system in preventing viral-related diseases. In this chapter, the antiviral effects of several herbs and their extracts against viruses in terms of the mechanism of action in targeting viral replication steps, the effects in the host and the application in animals will be discussed. The information given may aid in improving the health and increase the production of animals.

Induction of Porcine Dermatitis and Nephropathy Syndrome in Piglets by Infection with Porcine Circovirus Type 3

Porcine circovirus type 3 (PCV3) is an emerging porcine circovirus that has been associated with porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, cardiac pathologies, and multisystemic inflammation in piglets and sows. Many aspects of PCV3 infection biology and pathogenesis, however, remain unknown. Here, we used a PCV3 virus stock from the rescue of an infectious PCV3 DNA clone to intranasally inoculate 4- and 8-week-old specific-pathogen-free piglets for evaluation of PCV3 pathogenesis. For 4-week-old piglets, typical clinical signs resembling those of PDNS-like disease were observed when piglets were inoculated with PCV3 alone or PCV3 combined with immunostimulation by keyhole limpet hemocyanin, with a mortality of 40% (2/5) for both types of inoculated piglets during a 28-day observation period postinoculation. Both types of inoculated piglets showed similar progressive increases in viral loads in the sera and had seroconverted to PCV3 capsid antibody after inoculation. Pathological lesions and PCV3-specific antigen were detected in various tissues and organs, including the lung, heart, kidney, lymph nodes, spleen, liver, and small intestine, in both types of inoculated piglets. The levels of proinflammatory cytokines and chemokines, including interleukin 1 beta (IL-1β), IL-6, IL-23α, gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and chemokine ligand 5 (CCL5), were significantly upregulated in both groups of inoculated piglets. Eight-week-old piglets also exhibited a similar PDNS-like disease but without death after PCV3 inoculation, as evidenced by pathological lesions and PCV3 antigen in various tissues and organs. These results show for the first time successful reproduction of PDNS-like disease by PCV3 infection and further provide significant information regarding the pathogenesis of PCV3 in piglets.IMPORTANCE Porcine circovirus type 3 (PCV3), an emerging porcine circovirus, is considered the cause of porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs and other systemic diseases in piglets and sows. To evaluate the pathogenesis of PCV3 infection in vivo, we used a PCV3 virus stock from the rescue of an infectious PCV3 DNA clone to intranasally inoculate 4- and 8-week-old specific-pathogen-free piglets and demonstrated successful reproduction of PDNS-like disease in animals that were inoculated with PCV3 alone or PCV3 combined with immunostimulation by keyhole limpet hemocyanin. Both 4- and 8-week-old PCV3-inoculated piglets showed similar increases in viral loads in the sera and had seroconverted to PCV3 capsid antibody. Pathological lesions and PCV3-specific antigen were detected in various tissues and organs, while numerous proinflammatory cytokines and chemokines in the sera were significantly upregulated after PCV3 inoculation. These results will provide significant information regarding the pathogenesis of PCV3 in piglets.

Antiviral and Immunoregulatory Role Against PCV2 in Vivo of Chinese Herbal Medicinal Ingredients

Introduction

The aim of the research was to investigate the antiviral and immunoregulatory effects of saikosaponin A, saikosaponin D, Panax notoginseng saponins, notoginsenoside R1, and anemoside B4 saponins commonly found in Chinese herbal medicines.

Material and Methods

control mice were challenged intramuscularly (im) with 0.2 mL of porcine circovirus 2 (PCV2) solution containing 10⁷ TCID₅₀ of the virus/mL. Mice of high-, middle-, and low-dose saponin groups were initially challenged im with 0.2 mL of PCV2 solution and three days later treated intraperitoneally (ip) with one of five saponins at one of three doses (10, 5, or 1 mg/kg b.w.). In the drug control group, mice were dosed ip with 10 mg/kg b.w. of a given saponin, and mice in a blank control group were administered the same volume of normal saline.

Results

The results revealed that the saponins could reduce the incidence and severity of PCV2-induced immunopathological damage, e.g. body temperature elevation, weight loss, anaemia, and internal organ swelling. In addition, it was seen that the saponins could affect the immunoglobulin levels and protein absorption.

Conclusion

The data suggested that the saponins might effectively regulate immune responses.

Effect of porcine circovirus type 2 (PCV2) on the function of splenic CD11c+ dendritic cells in mice

Porcine circovirus-associated disease (PCVAD) caused by porcine circovirus type 2 (PCV2) is an important disease in the global pig industry. Dendritic cells (DCs) are the primary immune cells capable of initiating adaptive immune responses as well as major target cells of PCV2. To determine whether PCV2 affects the immune functions of DCs, we evaluated the expression of endocytosis and co-stimulatory molecules on DCs (CD11c⁺) from PCV2-infected mouse spleen by flow cytometry (FCM). We also analyzed the main cytokines secreted by DCs (CD11c⁺) and activation of CD4⁺ and CD8⁺ T cells by DCs (CD11c⁺) through measurement of cytokine secretion, using ELISA. Compared with control mice, PCV2 did not affect the endocytic activity of DCs but it significantly enhanced TNF-α secretion and markedly decreased IFN-α secretion. Subsets of CD40⁺, MHCII⁺ CD40⁺ and CD137L⁺ CD86⁺ DCs did not increase obviously, but MHCII⁺ CD40^- and CD137L^- CD80⁺/CD86⁺ DCs increased significantly in PCV2-infected mouse spleen. Under the stimulation of DCs from PCV2-infected mouse, secretion of IFN-γ by CD4⁺ and CD8⁺ T cells and of IL-12 by CD8⁺ T cells was significantly lower than in control mice, while secretion of IL-4 by CD4⁺ T cells was remarkably higher. These results indicate that PCV2 modulates cytokine secretion and co-stimulatory molecule expression of DCs, and alters activation of CD4⁺ and CD8⁺ T cells by DCs. The immunomodulatory effects of PCV2 on DCs might be related to the host's immune dysfunction and persistent infection with this virus.

RNA-Seq Analysis Reveals Genes Underlying Different Disease Responses to Porcine Circovirus Type 2 in Pigs

Porcine circovirus type 2 (PCV2), an economically important pathogen, causes postweaning multisystemic wasting syndrome (PMWS) and other syndrome diseases collectively known as porcine circovirus-associated disease (PCVAD). Previous studies revealed breed-dependent differences in porcine susceptibility to PCV2; however, the genetic mechanism underlying different resistance to PCV2 infection remains largely unknown. In this study, we found that Yorkshire × Landrace (YL) pigs exhibited serious clinical features typifying PCV2 disease, while the Laiwu (a Chinese indigenous pig breed, LW) pigs showed little clinical symptoms of the disease during PCV2 infection. At 35 days post infection (dpi), the PCV2 DNA copy in YL pigs was significantly higher than that in LW pigs (P < 0.05). The serum level of IL-4, IL-6, IL-8, IL-12 and TGF-β1 in LW pigs and TNF-α in YL pigs increased significantly at the early infected stages, respectively; while that of IL-10 and IFN-γ in YL pigs was greatly increased at 35 dpi. RNA-seq analysis revealed that, at 35 dpi, 83 genes were up-regulated and 86 genes were down-regulated in the lung tissues of LW pigs, while in YL pigs, the numbers were 187 and 18, respectively. In LW pigs, the differentially expressed genes (DEGs) were mainly involved in complement and coagulation cascades, metabolism of xenobiotics by cytochrome P450, RIG-I-like receptor signaling and B cell receptor signaling pathways. Four up-regulated genes (TFPI, SERPNC1, SERPNA1, and SERPNA5) that are enriched in complement and coagulation cascades pathway were identified in the PCV2-infected LW pigs, among which the mRNA expression of SERPNA1, as well as three genes including TGF-β1, TGF-β2 and VEGF that are regulated by SERPNA1 was significantly increased (P < 0.05). We speculate that higher expression of SERPNA1 may effectively suppress excessive inflammation reaction and reduce the pathological degree of lung tissue in PCV2-infected pigs. Collectively, our findings indicate that the susceptibility to PCV2 infection depends on a genetic difference between LW and YL pigs, and SERPNA1 likely plays an important role in the resistance of LW pigs to PCV2 infection.

Immunity Elicited by an Experimental Vaccine Based on Recombinant Flagellin-Porcine Circovirus Type 2 Cap Fusion Protein in Piglets

In a recent study, we reported that a recombinant protein from fusion expression of flagellin to porcine circovirus type 2 (PCV2) Cap induced robust humoral and cell-mediated immunity that afforded full protection for PCV2 infection using BALB/c mice. Here, we further evaluated the immunogenicity and protection of the recombinant protein using specific pathogen free (SPF) pigs. Twenty-five 3-week-old piglets without passively acquired immunity were divided into 5 groups. All piglets except negative controls were challenged with a virulent PCV2 at 21 days after booster vaccination and necropsied at 21 days post-challenge. Vaccination of piglets with the recombinant protein without adjuvant induced strong humoral and cellular immune responses as observed by high levels of PCV2-specific IgG antibodies and neutralizing antibodies, as well as frequencies of PCV2-specific IFN-γ-secreting cells that conferred good protection against PCV2 challenge, with significant reduced PCV2 viremia, mild lesions, low PCV2 antigen-positive cells, as well as improved body weight gain, comparable to piglets vaccinated with a commercial PCV2 subunit vaccine. These results further demonstrated that the recombinant flagellin-Cap fusion protein is capable of inducing solid protective humoral and cellular immunity when administered to pigs, thereby becoming an effective PCV2 vaccine candidate for control of PCV2 infection.

Porcine circovirus 2 immunology and viral evolution

Porcine circovirus 2 (PCV2) has and is still causing important economic losses to pig industry. This is due to PCV2-systemic disease (PCV2-SD), formerly known as postweaning multi-systemic wasting syndrome (PMWS), which increases mortality rates and slows down the growth of the animals, as well as other conditions collectively included within the so-called porcine circovirus diseases (PCVD). PCV2-SD affected pigs are considered to be immunosuppressed, with severe lymphocyte depletion and evidence of secondary infections. However, PCV2-infected pigs not developing the disease are able to mount humoral and cellular immune responses and clear the virus or limit the infection. On the contrary, insufficient amounts of neutralizing antibodies have been linked to increased PCV2 replication, severe lymphoid lesions and development of PCV2-SD. Central role in controlling PCV2 infection are played by the antigen specific memory T cells. These cells persist long term post-infection or vaccination and are able to expand rapidly after recall antigen recognition. Most farms in the main pig producing countries are applying vaccination against PCV2 to prevent the disease and improve the farm performance. Vaccines do not induce sterilizing immunity and PCV2 keeps on circulating even in farms applying vaccination. This, together with the high mutation rate of PCV2, world-wide fluctuations in the genotype dominance and emergence of novel genetic variants, warrant close molecular survey of the virus in the field.

T-cell reprogramming through targeted CD4-coreceptor and T-cell receptor expression on maturing thymocytes by latent Circoviridae family member porcine circovirus type 2 cell infections in the thymus

Although porcine circovirus type 2 (PCV2)-associated diseases have been evaluated for known immune evasion strategies, the pathogenicity of these viruses remained concealed for decades. Surprisingly, the same viruses that cause panzootics in livestock are widespread in young, unaffected animals. Recently, evidence has emerged that circovirus-like viruses are also linked to complex diseases in humans, including children. We detected PCV2 genome-carrying cells in fetal pig thymi. To elucidate virus pathogenicity, we developed a new pig infection model by in vivo transfection of recombinant PCV2 and the immunosuppressant cofactor cyclosporine A. Using flow cytometry, immunofluorescence and fluorescence in situ hybridization, we found evidence that PCV2 dictates positive and negative selection of maturing T cells in the thymus. We show for the first time that PCV2-infected cells reside at the corticomedullary junction of the thymus. In diseased animals, we found polyclonal deletion of single positive cells (SPs) that may result from a loss of major histocompatibility complex class-II expression at the corticomedullary junction. The percentage of PCV2 antigen-presenting cells correlated with the degree of viremia and, in turn, the severity of the defect in thymocyte maturation. Moreover, the reversed T-cell receptor/CD4-coreceptor expression dichotomy on thymocytes at the CD4⁺CD8^interm and CD4SP cell stage is viremia-dependent, resulting in a specific hypo-responsiveness of T-helper cells. We compare our results with the only other better-studied member of Circoviridae, chicken anemia virus. Our data show that PCV2 infection leads to thymocyte selection dysregulation, adding a valuable dimension to our understanding of virus pathogenicity.

Role of Chinese herbal medicinal ingredients in secretion of cytokines by PCV2-induced endothelial cells

While T-lymphocytes are the major cell type responsible for host responses to a virus (including induction of inflammatory responses to aid in ultimate removal of virus), other cells, including macrophages, epithelial and dendritic cells also have key roles. Endothelial cells also play important roles in physiologic/pathologic processes, like inflammation, during viral infections. As endothelial cells can be activated to release various endogenous compounds, including some cytokines, ex vivo measures of cytokine formation by the cells can be used to indirectly assess any potential endothelial dysfunction in situ. The research presented here sought to investigate potential immunolomodulatory effects of five saponins on endothelial cells: Saikosaponins A (SSA) and D (SSD), Panax Notoginseng Saponin (PNS) and Notoginsenoside R1 (SR1) and Anemoside B4 (AB4). For this, cells (porcine iliac artery endothelial line) were challenged with a virus isolate PCV2-AH for 24 h and then treated with the test saponin (at 1, 5 or 10 μg/ml) for an additional 24 h at 37 °C. The culture supernatants were then collected and analyzed for interleukin (IL)-2, -4 and -10, as well as interferon (IFN)-γ by ELISA. The results revealed that PNS and SR1 inhibited the production of IL-4; PNS, SR1 and AB4 inhibited the secretion of IL-10; SSA, SSD and PNS up-regulated IL-2 expression; SSA and SSD increased the level of IFNγ. All these changes were significant. Taken together, the data suggested these saponins might potentially have a capacity to regulate immune responses in vivo via changes in production of these select cytokines by infected endothelial cells. Nevertheless, the impact of these agents on other key cell types involved in anti-viral responses, including T-lymphocytes, remains to be determined.

Memory T cell proliferative responses and IFN-γ productivity sustain long-lasting efficacy of a Cap-based PCV2 vaccine upon PCV2 natural infection and associated disease

Porcine circovirus type 2 (PCV2) vaccination represents an important measure to cope with PCV2 infection; however, data regarding the modulation of the immune cell compartment are still limited, especially under field conditions. This study is aimed at investigating the features of the cellular immune response in conventional piglets induced by vaccination using a capsid (Cap) protein-based PCV2 vaccine compared to unvaccinated animals when exposed to PCV2 natural infection. Immune reactivity was evaluated by quantifying peripheral cell subsets involved in the anti-viral response and characterizing the interferon-gamma (IFN-γ) secreting cell (SC) responsiveness both in vivo and upon in vitro whole PCV2 recall. The vaccination triggered an early and intense IFN-γ secreting cell response and induced the activation of peripheral lymphocytes. The early increase of IFN-γ SC frequencies resulted in a remarkable and transient tendency to increased IFN-γ productivity in vaccinated pigs. In vaccinated animals, soon before the onset of infection occurred 15-16 weeks post-vaccination, the recalled PCV2-specific immune response was characterized by moderate PCV2-specific IFN-γ secreting cell frequencies and augmented productivity together with reactive CD4+CD8+ memory T cells. Conversely, upon infection, unvaccinated animals showed very high frequencies of IFN-γ secreting cells and a tendency to lower productivity, which paralleled with effector CD4-CD8+ cytotoxic cell responsiveness. The study shows that PCV2 vaccination induces a long-lasting immunity sustained by memory T cells and IFN-γ secreting cells that potentially played a role in preventing the onset of infection; the extent and duration of this reactivity can be an important feature for evaluating the protective immunity induced by vaccination.

Porcine circovirus type 2 decreases the infection and replication of attenuated classical swine fever virus in porcine alveolar macrophages

Recently, it has been noted that porcine circovirus type 2 (PCV2) infection adversely affects the protective efficacy of Lapinized Philippines Coronel (LPC) vaccine, an attenuated strain of classical swine fever virus (CSFV), in pigs. In order to investigate the possible mechanisms of the PCV2-derived interference, an in vitro model was established to study the interaction of LPC virus (LPCV) and PCV2 in porcine alveolar macrophages (AMs). The results showed that PCV2 reduced the LPCV infection in AMs and the levels of PCV2-derived interference were dose-dependent. The PCV2-derived interference also reduced the replication level of LPCV in AMs. The full-length PCV2 DNA and its fragment DNA C9 CpG-ODN were involved in the reduction of LPCV infection in AMs, whereas UV-inactivated PCV2 was not. In addition, a moderate negative correlation between the LPCV antigen-containing rate and IFN-γ production was observed, and had a dose-dependent trend with the level of PCV2-inoculation. The results of the present study may partially explain how PCV2 infection interferes with the efficacy of LPC vaccine.

Porcine CD74 is involved in the inflammatory response activated by nuclear factor kappa B during porcine circovirus type 2 (PCV-2) infection

Human CD74 induces a signalling cascade that results in the activation of nuclear factor kappa B (NF-κB); however, porcine CD74 has not been widely studied. In this study, we show that porcine CD74 is mainly expressed in cells of the macrophage lineage and can be induced by lipopolysaccharide (LPS), polyinosinic acid-polycytidylic acid [Poly(I:C)], and infection with porcine circovirus type 2 (PCV2) in vitro. In addition, we confirmed that porcine CD74 can activate NF-κB by promoting IκBα degradation and nuclear translocation of p65. Furthermore, the transcription of NF-κB-regulated genes [Interleukin-6 (IL-6), Interleukin-8 (IL-8), and COX-2] was upregulated in response to the overexpression of porcine CD74. In general, porcine CD74 significantly enhanced the inflammatory response by regulating the NF-κB signalling pathway during PCV2 infection, which suggests that porcine CD74 may be implicated in the pathogenesis of PCV2 infection.

Transcription analysis of the porcine alveolar macrophage response to porcine circovirus type 2

BACKGROUND

Porcine circovirus type 2 (PCV2) is the causal agent of postweaning multisystemic wasting syndrome (PMWS), which has severely impacted the swine industry worldwide. PCV2 triggers a weak and atypical innate immune response, but the key genes and mechanisms by which the virus interferes with host innate immunity have not yet been elucidated. In this study, genes that control the response of primary porcine alveolar macrophages (PAMs), the main target of PCV2, were profiled in vitro.

RESULTS

PAMs were successfully infected by PCV2-WH strain, as evidenced quantitative real-time polymerase chain reaction (qPCR) and immunofluorescence assay (IFA) results. Infection-related differential gene expression was investigated using pig microarrays from the US Pig Genome Coordination Program and validated by real-time PCR and enzyme-linked immunosorbent assay (ELISA). Microarray analysis at 24 and 48 hours post-infection (HPI) revealed 266 and 175 unique genes, respectively, that were differentially expressed (false discovery rate <0.05; fold-change >2). Only six genes were differentially expressed between 24 and 48 HPI. The up-regulated genes were principally related to immune response, cytokine activity, locomotion, regulation of cell proliferation, apoptosis, cell growth arrest, and antigen procession and presentation. The down-regulated genes were mainly involved in terpenoid biosynthesis, carbohydrate metabolism, translation, proteasome degradation, signal transducer activity, and ribosomal proteins, which were representative of the reduced vital activity of PCV2-infected cells.

CONCLUSIONS

PCV2 infection of PAMs causes up-regulation of genes related to inflammation, indicating that PCV2 may induce systematic inflammation. PCV2 persistently induced cytokines, mainly through the Toll-like receptor (TLR) 1 and TLR9 pathways, which may promote high levels of cytokine secretion. PCV2 may prevent apoptosis in PAMs by up-regulating SERPINB9 expression, possibly to lengthen the duration of PCV2 replication-permissive conditions. The observed gene expression profile may provide insights into the underlying immunological response and pathological changes that occur in pigs following PCV2 infection.

[Genome-wide selective sweep analysis on Large White and Tongcheng pigs]

The production performance of pigs has been significantly improved due to long-term artificial selection, and the specific variation characterizations (selection signatures) emerged from the selected genome regions. Different types of breeds are subjected to different selection intensities and had different selection signatures. Selective sweep analysis is one of major methods to detect the selection signatures. In this study, based on the 60K BeadChip genotyping data of both commercial Large White (n=45) and local Tongcheng pigs (n=45), genetic differentiation coefficient Fst was applied to detect the selection signatures. Using gPLINK software to set quality control standards, a total of 34 304 SNPs were selected for statistical analysis. Fst values between two breeds were estimated with Genepop package and the average Fst value was 0.3209. Setting Fst>0.7036 (1% of total number of Fst values) as selection threshold, 344 SNPs were obtained and SNP location annotation indicated that there were 79 candidate genes (Sus scrofa Build 9). Furthermore, network analysis was performed using Ingenuity Pathway Analysis and the preliminary results suggested that most genes were involved in growth, reproduction, and immune response, such as NCOA6, ERBB4, RUNX2, and APOB genes. The findings from this study will contribute to further identification of candidate genes and causal mutations implying for meat production and disease resistance in pig.

Induction of mucosal immunity by intranasal immunization with recombinant adenovirus expressing major epitopes of Porcine circovirus-2 capsid protein

Porcine circovirus-2 (PCV-2) is primarily transmitted through mucosa, thus the mucosal immunity may constitute an essential feature of vaccination strategies against PCV-2 infection. Mucosal immunity elicited by recombinant replication-deficient adenovirus expressing the major epitopes of PCV-2 capsid protein (rAd/Cap/518) via intranasal (i.n.), intramuscular (i.m.) or oral routes in mice were evaluated. Immunization with rAd/Cap/518 via i.n. route induced higher titers of IgA in saliva, bronchoalveolar and intestinal lavage fluid compared with those immunized via i.m. route. The proportions of CD3+, CD3+CD4+ and CD3+CD8+ T cells were significantly increased in mice immunized with rAd/Cap/518 via i.n. route compared with the control group. Higher levels of IFN-γ were detected in the spleen and mesenteric lymph nodes of mice immunized with rAd/Cap/518 via i.n. route compared with other groups, yet IL-4 was not detected in any group. Real-time PCR analysis confirmed viral DNA loads in the i.m. or i.n. immunization group was lower than that seen in the rAd immunization. These results indicate that i.n. administration of rAd/Cap/518 can elicit humoral and Th1-type cellular protective immunity in both systemic and mucosal immune compartments in mice, representing a promising mucosal vaccine candidate against PCV-2.

Attenuation of porcine circovirus type-2b by replacement with the Rep gene of porcine circovirus type-1

Porcine circovirus type-2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases and has 4 main ORFs, ORF1 (Rep gene), ORF2 (Cap gene), ORF3 within ORF1, and ORF4, which is overlapped with ORF3, and 1 origin (Ori) of replication located between ORF1 and ORF2. The chimeric PCV1-2, containing the PCV2 capsid, PCV1 rep, and Ori genes, is attenuated in pigs. In order to verify the role of the Rep gene or Ori in the virulence of PCV2, 3 chimeric viruses [PCV2b-Ori1 (PCV1 Ori gene cloned into the backbone of PCV2b), PCV2b-rep1 (PCV1 Rep gene cloned into the backbone of PCV2b), and PCV2b-rep1-Ori1 (PCV1 Rep and Ori genes cloned into the backbone of PCV2b)] and 2 wild-type recombinant PCV2b and PCV1 were constructed and identified. The experimental results in piglets showed that clinical symptoms, viremia, viral load, lesions in lymphoid and lung tissues, and IL-10 and TNF-α expression levels in PBMCs in the PCV2b-rep1-Ori1 and PCV2b-rep1 groups were significantly decreased, compared to PCV2-infected piglets. Meanwhile, histological lesions of lymphoid and lung tissues, viral loads in lymphoid tissues, viremia, and TNF-α expression in PBMCs were not significantly different between groups PCV2b-Ori1 and PCV2b, suggesting that the Rep gene (ORF1) likely contributes to viral pathogenicity in vivo.

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.

Innate pro-inflammatory and adaptive immune cytokines in PBMC of vaccinated and unvaccinated pigs naturally exposed to porcine circovirus type 2 (PCV2) infection vary with the occurrence of the disease and the viral burden

Pro-inflammatory (IL-8, TNF-α, IL-1β) and immune (IFN-γ, IL-10) cytokines were evaluated in PCV2-vaccinated and unvaccinated pigs exposed to natural PCV2 infection retrospectively selected according to the time of the onset of viremia and the viral burden, and the presence of PMWS clinical signs. In a farrow-to-finish herd with a history of PMWS in animals aged older than 15 weeks, at weaning (21 ± 3 days of age), vaccinated pigs were intramuscularly inoculated with one dose of Porcilis(®) PCV vaccine+adjuvant whereas the adjuvant alone was administered to the control animals. Thirty animals bled at 16 weeks of age (before the occurrence of the natural infection and the onset of the disease) and then at 19, 20, 22 and 26 weeks of age, were categorized as: (a) vaccinated non-infected and non-PMWS-affected (PCV2-vac), (b) unvaccinated spontaneously infected/non-PMWS-affected (Ctrl) and (c) unvaccinated spontaneously infected/PMWS-affected (Ctrl-PMWS+) pigs. A major evidence of this study is that PMWS-affected animals were not able to mount an efficient innate pro-inflammatory response to cope with PCV2 infection as demonstrated by the low levels of pro-inflammatory cytokines, namely IL-8, TNF-α and IL-1β, and IFN-γ. Conversely, significantly increased gene expression levels of IL-8, TNF-α and IL-1β were detected especially in the PCV2-vac group at the early phase of the infection. Moreover, in PMWS diseased animals, a significant increase of IL-10 occurred at the early phase of infection, while, vaccinated pigs, in addition to the low viremia burden and its frequency and the absence of PMWS disease, showed a more stable IFN-γ response.

Subclinical porcine circovirus type 2 infection does not modulate the immune response to an Aujeszky's disease virus vaccine

Porcine circovirus type 2 (PCV2) negatively modulates the immune response in vitro. The objective of this study was to investigate if PCV2 interferes with the development of the immune response to Aujeszky's disease virus (ADV) vaccine, using an in vivo experimental subclinical model. Pigs were divided into four groups: (group CC) not infected with PCV2 and not vaccinated against ADV; (group IC) infected with PCV2 but not vaccinated against ADV; (group CV) not infected with PCV2 but vaccinated against ADV, and (group IV) infected with PCV2 and vaccinated against ADV. Pigs in groups IC and IV were inoculated intranasally with PCV2 and 14 days later, pigs in the CV and IV groups were vaccinated IM with a gE(-)tk(-) attenuated ADV vaccine. Clinical signs and weight gains were recorded from days 0 to 35 post-PCV2 inoculation (PI), at which point the pigs were euthanased and examined post-mortem. Throughout the experiment the PCV2 load was quantified in serum, antibodies to PCV2 and ADV were determined and antigen-specific cellular responses against both viruses were measured using an interferon-γ ELISPOT. PCV2 inoculated animals developed subclinical infection and had lower weight gain relative to non-infected controls. No differences were observed between the CV and IV groups in terms of the humoral or cellular immune responses to vaccination against Aujeszky's disease, suggesting that subclinical infection with PCV2 does not alter the response to this vaccine.

Emerging and re-emerging swine viruses

In the past two decades or so, a number of viruses have emerged in the global swine population. Some, such as porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), cause economically important diseases in pigs, whereas others such as porcine torque teno virus (TTV), now known as Torque teno sus virus (TTSuV), porcine bocavirus (PBoV) and related novel parvoviruses, porcine kobuvirus, porcine toroviruses (PToV) and porcine lymphotropic herpesviruses (PLHV), are mostly subclinical in swine herds. Although some emerging swine viruses such as swine hepatitis E virus (swine HEV), porcine endogenous retrovirus (PERV) and porcine sapovirus (porcine SaV) may have a limited clinical implication in swine health, they do pose a potential public health concern in humans due to zoonotic (swine HEV) or potential zoonotic (porcine SaV) and xenozoonotic (PERV, PLHV) risks. Other emerging viruses such as Nipah virus, Bungowannah virus and Menangle virus not only cause diseases in pigs but some also pose important zoonotic threat to humans. This article focuses on emerging and re-emerging swine viruses that have a limited or uncertain clinical and economic impact on pig health. The transmission, epidemiology and pathogenic potential of these viruses are discussed. In addition, the two economically important emerging viruses, PRRSV and PCV2, are also briefly discussed to identify important knowledge gaps.

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.

Porcine circovirus type 2 (PCV2) infection decreases the efficacy of an attenuated classical swine fever virus (CSFV) vaccine

The Lapinized Philippines Coronel (LPC) vaccine, an attenuated strain of classical swine fever virus (CSFV), is an important tool for the prevention and control of CSFV infection and is widely and routinely used in most CSF endemic areas, including Taiwan. The aim of this study was to investigate whether PCV2 infection affects the efficacy of the LPC vaccine. Eighteen 6-week-old, cesarean-derived and colostrum-deprived (CDCD), crossbred pigs were randomly assigned to four groups. A total of 10^5.3 TCID₅₀ of PCV2 was experimentally inoculated into pigs through both intranasal and intramuscular routes at 0 days post-inoculation (dpi) followed by LPC vaccination 12 days later. All the animals were challenged with wild-type CSFV (ALD stain) at 27 dpi and euthanized at 45 dpi. Following CSFV challenge, the LPC-vaccinated pigs pre-inoculated with PCV2 showed transient fever, viremia, and viral shedding in the saliva and feces. The number of IgM⁺, CD4⁺CD8^-CD25⁺, CD4⁺CD8⁺CD25⁺, and CD4^-CD8⁺CD25⁺ lymphocyte subsets and the level of neutralizing antibodies against CSFV were significantly higher in the animals with LPC vaccination alone than in the pigs with PCV2 inoculation/LPC vaccination. In addition, PCV2-derived inhibition of the CSFV-specific cell proliferative response of peripheral blood mononuclear cells (PBMCs) was demonstrated in an ex vivo experiment. These findings indicate that PCV2 infection decreases the efficacy of the LPC vaccine. This PCV2-derived interference may not only allow the invasion of wild-type CSFV in pig farms but also increases the difficulty of CSF prevention and control in CSF endemic areas.

Effects of porcine circovirus type 2 on expression of mRNA associated with endogenous antigen processing and presentation in pulmonary alveolar macrophages and circulating T lymphocytes in piglets

Pulmonary alveolar macrophages (PAMs) are the major target cells of porcine circovirus type 2 (PCV2). This study examined cellular immunity and expression of molecules associated with endogenous antigen processing and presentation in porcine PAMs for 28 days following infection with PCV2. The numbers of total T cells and T lymphocyte subpopulations were measured by flow cytometry (FCM). The expression of mRNA of large multifunctional peptidase 7 (LMP7), ubiquitin-specific protease (UBP), heat shock proteins 70 and 90 (HSP70 and HSP90), major histocompatibility class I (MHC-I), β(2)-microglobulin, glucose-regulated protein 94 (GRP94), calnexin and calreticulin of PAMs from PCV2 infected and control pigs were determined by real-time reverse transcriptase PCR. The absolute numbers of total T cells, T helper (Th) cells, cytotoxic T cells and γδ T cells, but not memory/activated Th cells, decreased following PCV2 infection. There was decreased expression of LMP7 mRNA at 3days postinfection (DPI), whereas expression of UBP and calreticulin mRNA was increased at 3 DPI, expression of HSP90 and β(2)-microglobulin mRNA was increased at 3 and 7 DPI and expression of GRP94 mRNA was increased at 14 DPI. PAMs from PCV2-infected piglets had lower surface expression of CD80/CD86 at 7 and 14 DPI and MHC-II at 7 DPI. These findings suggest that there are alterations in cellular immune function and in the endogenous antigen presentation capacity of PAMs in PCV2-infected piglets.

Distribution and characterization of IL-10-secreting cells in lymphoid tissues of PCV2-infected pigs

Distribution and characterization of interlukin-10 (IL-10)-secreting cells in lymphoid tissues of pigs naturally infected with porcine circovirus type 2 (PCV2) were evaluated in accordance with PCV2 antigen detection. After screening a total of 56 pigs showing the symptoms of postweaning multisystemic wasting syndrome (PMWS), 15 pigs were PCV2 positive and 5 pigs, which showed stronger positive signals over multiples tissues were further investigated. This study showed that in PCV2-infected lymphoid tissues, particularly mandibular lymph node, spleen and tonsil, IL-10 expression was mainly localized in T-cell rich areas but rarely in B cell rich areas. IL-10 was highly expressed in bystander cells but rarely in PCV2-infected cells. Elevated IL-10 expression was predominantly associated with T cells, but rarely with B cells or with macrophages. The results of this study provide evidence for the role of IL-10 in chronic PCV2 infection and its relation to PCV2 antigen in affected tissues. Constantly elevated levels of IL-10 lead to immunosuppression in persistent and chronic viral infections. The increased IL-10 expression observed in PCV2 infection in this study suggests that IL-10-mediated immunosuppression may play an important role in the pathogenesis and maintenance of naturally occurring PCV2 infection.

Ear necrosis reduction in pigs after vaccination against PCV2

The influence of sows vaccination against PCV2 on the prevalence of ear necrosis syndrome (ENS) reduction among weaners was analyzed using 12,931 piglets from 45 consecutive batches, born to both, vaccinated and non-vaccinated sows. The results were statistically tested with a nonparametric Kruskal-Wallis and Chi-square tests. The results show that vaccination against PCV2 significantly reduced the prevalence of ENS (p<0.05). The percentage of affected pigs born to vaccinated sows was about over two times lower than in both groups of pigs born to non-vaccinated females (before the vaccination implementation and after its withdrawing). Even more distinct were the differences in the intensity of the lesions (p<0.05). In the group of pigs born to vaccinated sows, the percentage of severe lesions was three times lower than in the pigs born to non-vaccinated sows. It conclusion, it could statement that vaccination against PCV2 might be effective in reduction of ENS.