Possible interactions between the NS-1 protein and tumor necrosis factor alpha pathways in erythroid cell apoptosis induced by human parvovirus B19

Small Genomes, Big Disruptions: Parvoviruses and the DNA Damage Response

Parvoviruses are small, single-stranded DNA viruses that have evolved sophisticated mechanisms to hijack host cell machinery for replication and persistence. One critical aspect of this interaction involves the manipulation of the host's DNA Damage Response (DDR) pathways. While the viral genome is comparatively simple, parvoviruses have developed strategies that cause significant DNA damage, activate DDR pathways, and disrupt the host cell cycle. This review will explore the impact of parvovirus infections on host genome stability, focusing on key viral species such as Adeno-Associated Virus (AAV), Minute Virus of Mice (MVM), and Human Bocavirus (HBoV), and their interactions with DDR proteins. Since parvoviruses are used as oncolytic agents and gene therapy vectors, a better understanding of cellular DDR pathways will aid in engineering potent anti-cancer agents and gene therapies for chronic diseases.

Lymphocytic Myocarditis in Children with Parvovirus B19 Infection: Pathological and Molecular Insights

BACKGROUND

This study aims to evaluate the role of parvovirus B19 (B19V) in the pathogenesis of myocarditis in a paediatric population, including post-mortem samples from two children.

METHODS

From 2004 to 2023, endomyocardial biopsies (EMBs) from children under 16 years of age were analyzed using histology, immunohistochemistry, and molecular pathology. A total of 306 children with acute and 1060 children with chronic lymphocytic myocarditis were identified.

RESULTS

B19V infection was more frequent in acute myocarditis than in chronic myocarditis (43% vs. 14%), with higher viral loads in acute cases regardless of age. The most prominent cardiac CD3+ T cell infiltration was noted in children < 2 years, correlating with high cardiac B19V loads. In two male infants who died from B19V infection, B19V DNA was localized in the endothelial cells of multiple organs using in situ hybridization. Virus replication was found in the endothelial cells of small cardiac arterioles and venules but not in capillaries. B19V DNA/mRNA was also detected in immune cells, especially in the spleen and lymph nodes, revealing virus replication in B lymphocytes.

CONCLUSIONS

B19V can induce severe lymphocytic myocarditis, especially in young children. The simultaneous histopathological and molecular assessment of EMBs is important for early diagnosis of viral myocarditis, preventing severe disease, and ensuring appropriate therapy.

The Novel Porcine Parvoviruses: Current State of Knowledge and Their Possible Implications in Clinical Syndromes in Pigs

Parvoviruses (PVs) affect various animal species causing different diseases. To date, eight different porcine parvoviruses (PPV1 through PPV8) are recognized in the swine population, all of which are distributed among subfamilies and genera of the Parvoviridae family. PPV1 is the oldest and is recognized as the primary agent of SMEDI, while the rest of the PPVs (PPV2 through PPV8) are called novel PPVs (nPPVs). The pathogenesis of nPPVs is still undefined, and whether these viruses are putative disease agents is unknown. Structurally, the PPVs are very similar; the differences occur mainly at the level of their genomes (ssDNA), where there is variation in the number and location of the coding genes. Additionally, it is considered that the genome of PVs has mutation rates similar to those of ssRNA viruses, that is, in the order of 10-5-10-4 nucleotide/substitution/year. These mutations manifest mainly in the VP protein, constituting the viral capsid, affecting virulence, tropism, and viral antigenicity. For nPPVs, mutation rates have already been established that are similar to those already described; however, within this group of viruses, the highest mutation rate has been reported for PPV7. In addition to the mutations, recombinations are also reported, mainly in PPV2, PPV3, and PPV7; these have been found between strains of domestic pigs and wild boars and in a more significant proportion in VP sequences. Regarding affinity for cell types, nPPVs have been detected with variable prevalence in different types of organs and tissues; this has led to the suggestion that they have a broad tropism, although proportionally more have been found in lung and lymphoid tissue such as spleen, tonsils, and lymph nodes. Regarding their epidemiology, nPPVs are present on all continents (except PPV8, only in Asia), and within pig farms, the highest prevalences detecting viral genomes have been seen in the fattener and finishing groups. The relationship between nPPVs and clinical manifestations has been complicated to establish. However, there is already some evidence that establishes associations. One of them is PPV2 with porcine respiratory disease complex (PRDC), where causality tests (PCR, ISH, and histopathology) lead to proposing the PPV2 virus as a possible agent involved in this syndrome. With the other nPPVs, there is still no clear association with any pathology. These have been detected in different systems (respiratory, reproductive, gastrointestinal, urinary, and nervous), and there is still insufficient evidence to classify them as disease-causing agents. In this regard, nPPVs (except PPV8) have been found to cause porcine reproductive failure (PRF), with the most prevalent being PPV4, PPV6, and PPV7. In the case of PRDC, nPPVs have also been detected, with PPV2 having the highest viral loads in the lungs of affected pigs. Regarding coinfections, nPPVs have been detected in concurrence in healthy and sick pigs, with primary PRDC and PRF viruses such as PCV2, PCV3, and PRRSV. The effect of these coinfections is not apparent; it is unknown whether they favor the replication of the primary agents, the severity of the clinical manifestations, or have no effect. The most significant limitation in the study of nPPVs is that their isolation has been impossible; therefore, there are no studies on their pathogenesis both in vitro and in vivo. For all of the above, it is necessary to propose basic and applied research on nPPVs to establish if they are putative disease agents, establish their effect on coinfections, and measure their impact on swine production.

Identification of AXL as a co-receptor for human parvovirus B19 infection of human erythroid progenitors

Parvovirus B19 (B19V) infects human erythroid progenitor cells (EPCs) and causes several hematological disorders and fetal hydrops. Amino acid (aa) 5-68 of minor capsid protein VP1 (VP1u5-68aa) is the minimal receptor binding domain for B19V to enter EPCs. Here, we carried out a genome-wide CRISPR-Cas9 guide RNA screen and identified tyrosine protein kinase receptor UFO (AXL) as a proteinaceous receptor for B19V infection of EPCs. AXL gene silencing in ex vivo expanded EPCs remarkably decreased B19V internalization and replication. Additions of the recombinant AXL extracellular domain or a polyclonal antibody against it upon infection efficiently inhibited B19V infection of ex vivo expanded EPCs. Moreover, B19V VP1u interacted with the recombinant AXL extracellular domain in vitro at a relatively high affinity (KD = 103 nM). Collectively, we provide evidence that AXL is a co-receptor for B19V infection of EPCs.

Prevalence, Cell Tropism, and Clinical Impact of Human Parvovirus Persistence in Adenomatous, Cancerous, Inflamed, and Healthy Intestinal Mucosa

Parvoviruses are single-stranded DNA viruses, infecting many animals from insects to humans. Human parvovirus B19 (B19V) causes erythema infectiosum, arthropathy, anemia, and fetal death, and human bocavirus (HBoV) 1 causes respiratory tract infections, while HBoV2-4 are enteric. Parvoviral genomes can persist in diverse non-permissive tissues after acute infection, but the host-cell tropism and the impact of their tissue persistence are poorly studied. We searched for parvoviral DNA in a total of 427 intestinal biopsy specimens, as paired disease-affected and healthy mucosa, obtained from 130 patients with malignancy, ulcerative colitis (UC), or adenomas, and in similar intestinal segments from 55 healthy subjects. Only three (1.6%) individuals exhibited intestinal HBoV DNA (one each of HBoV1, 2, and 3). Conversely, B19V DNA persisted frequently in the intestine, with 50, 47, 31, and 27% detection rates in the patients with malignancy, UC, or adenomas, and in the healthy subjects, respectively. Intra-individually, B19V DNA persisted significantly more often in the healthy intestinal segments than in the inflamed colons of UC patients. The highest loads of B19V DNA were seen in the ileum and colon specimens of two healthy individuals. With dual-RNAscope in situ hybridization and immunohistochemistry assays, we located the B19V persistence sites of these intestines in mucosal B cells of lymphoid follicles and vascular endothelial cells. Viral messenger RNA transcription remained, however, undetected. RNA sequencing (RNA-seq) identified 272 differentially expressed cellular genes between B19V DNA-positive and -negative healthy ileum biopsy specimens. Pathway enrichment analysis revealed that B19V persistence activated the intestinal cell viability and inhibited apoptosis. Lifelong B19V DNA persistence thus modulates host gene expression, which may lead to clinical outcomes.

Molecular Detection of Parvovirus in Manchurian Chipmunks (Tamias sibiricus asiaticus) Captured in Korea

Cross-species transmission of viral diseases alarms our global community for its potential of novel pandemic events. Of various viral pathogens noted recently, parvoviruses have posed public health threats not only to humans but also to wild animals. To investigate the prevalence of parvoviruses in wild Manchurian chipmunks, here we detected genetic fragments of the nonstructural protein of parvovirus by polymerase chain reaction in wild Manchurian chipmunk specimens captured in the central and southern regions of South Korea and compared their sequence homology with references. Of a total of 348 specimens examined, chipmunk parvovirus (ChpPV)-specific gene fragments were detected with a 31.32% rate (109 chipmunks of 348) in their kidney, liver, lung, and spleen samples, and the chipmunks captured in Gangwon Province exhibited the highest positive rate (45.37%), followed by Gyeongsang (35.29%), Gyeonggi (31.03%), Chungcheong (20.00%), and Jeolla (19.70%). When compared with the reference sequences, a partial ChpPV sequence showed 97.70% identity to the previously reported Korean strain at the nucleic acid level. In the phylogenetic analysis, ChpPV exhibited closer relationship to primate parvoviruses, erythroviruses, and bovine parvovirus than to adeno-associated viruses. Despite limited sample size and genetic sequences examined in this study, our results underline the prevalence of ChpPV in Korea and emphasize the need of close surveillance of parvoviruses in wild animals.

High throughput screening identifies inhibitors for parvovirus B19 infection of human erythroid progenitor cells

Parvovirus B19 (B19V) infection can cause hematological disorders and fetal hydrops during pregnancy. Currently, no antivirals or vaccines are available for the treatment or the prevention of B19V infection. To identify novel small-molecule antivirals against B19V replication, we developed a high throughput screening assay, which is based on an in vitro nicking assay using recombinant N-terminal 1-176 amino acids of the viral large nonstructural protein (NS1N) and a fluorescently labeled DNA probe (OriQ) that spans the nicking site of the viral DNA replication origin. We collectively screened 17,040 compounds and identified 2,178 (12.78%) hits that possess >10% inhibition of the NS1 nicking activity, among which 84 hits were confirmed to inhibit nicking in a dose-dependent manner. Using ex vivo expanded primary human erythroid progenitor cells (EPCs) infected by B19V, we validated 24 compounds demonstrated >50% in vivo inhibition of B19V infection at 10 μM, which can be categorized into 7 structure scaffolds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, the top 4 compounds were chosen to examine their inhibitions of B19V infection in EPCs at two times of the 90% maximal effective concentration (EC₉₀). A purine derivative (P7), demonstrated an antiviral effect (EC₅₀=1.46 μM) without prominent cytotoxicity (CC₅₀=71.8 μM) in EPCs, exhibited 92% inhibition of B19V infection in EPCs at 3.32 μM, which can be used as the lead compound in future studies for the treatment of B19V infection caused hematological disorders. Importance B19V encodes a large non-structural protein NS1. Its N-terminal domain (NS1N) consisting of 1-176 amino acids binds to viral DNA and serves as an endonuclease to nick the viral DNA replication origins, which is a pivotal step in rolling hairpin-dependent B19V DNA replication. For high throughput screening (HTS) of anti-B19V antivirals, we miniaturized a fluorescence-based in vitro nicking assay, which employs a fluorophore-labeled probe spanning the trs and the NS1N protein, into a 384-well plate format. The HTS assay showed a high reliability and capability in screening 17,040 compounds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, a purine derivative demonstrated an antiviral effect of 92% inhibition of B19V infection in EPCs at 3.32 μM (two times EC₉₀). Our study demonstrated a robust HTS assay for screening antivirals against B19V infection.

Ceramide and Related Molecules in Viral Infections

Ceramide is a lipid messenger at the heart of sphingolipid metabolism. In concert with its metabolizing enzymes, particularly sphingomyelinases, it has key roles in regulating the physical properties of biological membranes, including the formation of membrane microdomains. Thus, ceramide and its related molecules have been attributed significant roles in nearly all steps of the viral life cycle: they may serve directly as receptors or co-receptors for viral entry, form microdomains that cluster entry receptors and/or enable them to adopt the required conformation or regulate their cell surface expression. Sphingolipids can regulate all forms of viral uptake, often through sphingomyelinase activation, and mediate endosomal escape and intracellular trafficking. Ceramide can be key for the formation of viral replication sites. Sphingomyelinases often mediate the release of new virions from infected cells. Moreover, sphingolipids can contribute to viral-induced apoptosis and morbidity in viral diseases, as well as virus immune evasion. Alpha-galactosylceramide, in particular, also plays a significant role in immune modulation in response to viral infections. This review will discuss the roles of ceramide and its related molecules in the different steps of the viral life cycle. We will also discuss how novel strategies could exploit these for therapeutic benefit.

Canine Parvovirus and Its Non-Structural Gene 1 as Oncolytic Agents: Mechanism of Action and Induction of Anti-Tumor Immune Response

The exploration into the strategies for the prevention and treatment of cancer is far from complete. Apart from humans, cancer has gained considerable importance in animals because of increased awareness towards animal health and welfare. Current cancer treatment regimens are less specific towards tumor cells and end up harming normal healthy cells. Thus, a highly specific therapeutic strategy with minimal side effects is the need of the hour. Oncolytic viral gene therapy is one such specific approach to target cancer cells without affecting the normal cells of the body. Canine parvovirus (CPV) is an oncolytic virus that specifically targets and kills cancer cells by causing DNA damage, caspase activation, and mitochondrial damage. Non-structural gene 1 (NS1) of CPV, involved in viral DNA replication is a key mediator of cytotoxicity of CPV and can selectively cause tumor cell lysis. In this review, we discuss the oncolytic properties of Canine Parvovirus (CPV or CPV2), the structure of the NS1 protein, the mechanism of oncolytic action as well as role in inducing an antitumor immune response in different tumor models.

Screening for Human Parvovirus B19 Infection in Egyptian Family Replacement Blood Donors

Up till now, screening for human parvovirus B19 is not routine in national Egyptian blood bank strategy. Blood samples were collected from 500 healthy blood donors within the age range from 18 to 45 years old attending the blood bank of Suez Canal University Hospital, Ismailia, Egypt. Sera were separated and stored at - 20 °C. Serum samples were screened for anti-human parvovirus B19 IgM and IgG antibodies and B19 genome using ELISA and real-time PCR respectively. Frequency of B19 IgM and B19 IgG antibodies was 6.20%, and 80.20% respectively, and the prevalence of B19 genome was 3.00%. There is a high frequency of human parvovirus B19 among Egyptian blood donors; therefore, serological screening for B19 is warranted.

Ferulic Acid Protects against Porcine Parvovirus Infection-Induced Apoptosis by Suppressing the Nuclear Factor-κB Inflammasome Axis and Toll-Like Receptor 4 via Nonstructural Protein 1

Background

Porcine parvovirus (PPV) infection-induced apoptosis was recently identified as an important pathological factor in PPV-induced placental tissue damage, resulting in reproduction failure. In the present study, we demonstrate the possible involvement of toll-like receptor (TLR) 4 and nuclear factor (NF)-κB inflammasome activation in PPV infection-induced apoptosis and the protective potential of ferulic acid (FA). PPV infection significantly activated the expression levels of TLR4, NF-κB, MyD88, and interleukin (IL)-6. However, FA ameliorated the pathological process, prevented histological alterations, and inhibited the apoptosis rate in porcine kidney (PK-15) cells infected with PPV.

Results

FA inhibited PPV infection-induced inflammasome activation as shown by decreases in the expression of NF-κB, MyD88, and IL-6. FA also downregulated nonstructural (NS) 1 protein expression in infected PK-15 cells.

Conclusions

FA downregulated NS1 and TLR4 signaling, prevented the overproduction of reactive oxygen species, and suppressed the NF-κB inflammasome axis to inhibit PPV-induced apoptosis in PK-15 cells.

RNA Binding Motif Protein RBM45 Regulates Expression of the 11-Kilodalton Protein of Parvovirus B19 through Binding to Novel Intron Splicing Enhancers

Human parvovirus B19 (B19V) is a human pathogen that causes severe hematological disorders in immunocompromised individuals. B19V infection has a remarkable tropism with respect to human erythroid progenitor cells (EPCs) in human bone marrow and fetal liver. During B19V infection, only one viral precursor mRNA (pre-mRNA) is transcribed by a single promoter of the viral genome and is alternatively spliced and alternatively polyadenylated, a process which plays a key role in expression of viral proteins. Our studies revealed that a cellular RNA binding protein, RBM45, binds to two intron splicing enhancers and is essential for the maturation of the small nonstructural protein 11-kDa-encoding mRNA. The 11-kDa protein plays an important role not only in B19V infection-induced apoptosis but also in viral DNA replication. Thus, the identification of the RBM45 protein and its cognate binding site in B19V pre-mRNA provides a novel target for antiviral development to combat B19V infection-caused severe hematological disorders.

During infection of human parvovirus B19 (B19V), one viral precursor mRNA (pre-mRNA) is transcribed by a single promoter and is alternatively spliced and alternatively polyadenylated. Here, we identified a novel cis-acting sequence (5′-GUA AAG CUA CGG GAC GGU-3′), intronic splicing enhancer 3 (ISE3), which lies 72 nucleotides upstream of the second splice acceptor (A2-2) site of the second intron that defines the exon of the mRNA encoding the 11-kDa viral nonstructural protein. RNA binding motif protein 45 (RBM45) specifically binds to ISE3 with high affinity (equilibrium dissociation constant [K_D] = 33 nM) mediated by its RNA recognition domain and 2-homo-oligomer assembly domain (RRM2-HOA). Knockdown of RBM45 expression or ectopic overexpression of RRM2-HOA in human erythroid progenitor cells (EPCs) expanded ex vivo significantly decreased the level of viral mRNA spliced at the A2-2 acceptor but not that of the mRNA spliced at A2-1 that encodes VP2. Moreover, silent mutations of ISE3 in an infectious DNA of B19V significantly reduced 11-kDa expression. Notably, RBM45 also specifically interacts in vitro with ISE2, which shares the octanucleotide (GGGACGGU) with ISE3. Taken together, our results suggest that RBM45, through binding to both ISE2 and ISE3, is an essential host factor for maturation of 11-kDa-encoding mRNA.

Establishment of a Parvovirus B19 NS1-Expressing Recombinant Adenoviral Vector for Killing Megakaryocytic Leukemia Cells

Adenoviral viral vectors have been widely used for gene-based therapeutics, but commonly used serotype 5 shows poor transduction efficiency into hematopoietic cells. In this study, we aimed to generate a recombinant adenovirus serotype 5 (rAd5) vector that has a high efficiency in gene transfer to megakaryocytic leukemic cells with anticancer potential. We first modified the rAd5 backbone vector with a chimeric fiber gene of Ad5 and Ad11p (rAd5F11p) to increase the gene delivery efficiency. Then, the nonstructural protein NS1 of human parvovirus B19 (B19V), which induces cell cycle arrest at the G2/M phase and apoptosis, was cloned into the adenoviral shuttle vector. As the expression of parvoviral NS1 protein inhibited Ad replication and production, we engineered the cytomegalovirus (CMV) promoter, which governs NS1 expression, with two tetracycline operator elements (TetO₂). Transfection of the rAd5F11p proviral vectors in Tet repressor-expressing T-REx-293 cells produced rAd in a large quantity. We further evaluated this chimeric rAd5F11p vector in gene delivery in human leukemic cells, UT7/Epo-S1. Strikingly, the novel rAd5F11p-B19NS1-GFP vector, exhibited a transduction efficiency much higher than the original vector, rAd5-B19NS1-GFP, in UT7/Epo-S1 cells, in particular, when they were transduced at a relatively low multiplicity of infection (100 viral genome copies/cell). After the transduction of rAd5F11p-B19NS1-GFP, over 90% of the UT7/Epo-S1 cells were arrested at the G2/M phase, and approximately 40%–50% of the cells were undergoing apoptosis, suggesting the novel rAd5F11P-B19NS1-GFP vector holds a promise in therapeutic potentials of megakaryocytic leukemia.

Parvovirus B19 Infection in Human Bone Marrow Mesenchymal Stem Cells Affects Gene Expression of IL-6 and TNF-α and also Affects Hematopoietic Stem Cells Differentiation

Parvovirus B19 (B19V) has been known to induce transient erythroid aplasia, cytopenia and aplastic anemia. This virus persists in bone marrow mesenchymal stem cells (HBMSCs) of some immunocompetent individuals several years after primary infection. In B19V infected erythroid progenitor cells, the virus induces transactivation of Interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) gene expression. Due the critical role of HBMSCs in bone marrow niche and inhibitory effect of inflammatory cytokines on hematopoiesis, the aim of this study was to investigate the effect of B19V on IL-6 and TNF-α gene expression intransfected cells. In addition we assessed the clonogenicity potential of cord blood CD34+ stem cells that were co-cultured with infected cells. After 24 h of transfection, quantitative mRNA expression of IL-6 and TNF-α was evaluated and human cord blood CD34+ HSC were cultured with the transfected cells. At the end of 7 days of culture, HSCs colony forming units (CFUs) assay was performed. Our findings demonstrated statistically significant (18.1 and 21.9 fold) increase of TNF-α and IL-6 gene expression respectively and decrease in burst forming unit-erythrocyte (BFU-E) and colony forming unit-erythrocyte (CFU-E) enumeration(p < 0.05). We concluded that, inducing inflammatory cytokines gene expression in B19V-infected HBMSCs might influence on bone marrow microenvironment and hematopoiesis.

Endonuclease Activity Inhibition of the NS1 Protein of Parvovirus B19 as a Novel Target for Antiviral Drug Development

Human parvovirus B19 (B19V), a member of the genus Erythroparvovirus of the family Parvoviridae, is a small nonenveloped virus that has a single-stranded DNA (ssDNA) genome of 5.6 kb with two inverted terminal repeats (ITRs). B19V infection often results in severe hematological disorders and fetal death in humans. B19V replication follows a model of rolling hairpin-dependent DNA replication, in which the large nonstructural protein NS1 introduces a site-specific single-strand nick in the viral DNA replication origins, which locate at the ITRs. NS1 executes endonuclease activity through the N-terminal origin-binding domain. Nicking of the viral replication origin is a pivotal step in rolling hairpin-dependent viral DNA replication. Here, we developed a fluorophore-based in vitro nicking assay of the replication origin using the origin-binding domain of NS1 and compared it with the radioactive in vitro nicking assay. We used both assays to screen a set of small-molecule compounds (n = 96) that have potential antinuclease activity. We found that the fluorophore-based in vitro nicking assay demonstrates sensitivity and specificity values as high as those of the radioactive assay. Among the 96 compounds, we identified 8 which have an inhibition of >80% at 10 µM in both the fluorophore-based and radioactive in vitro nicking assays. We further tested 3 compounds that have a flavonoid-like structure and an in vitro 50% inhibitory concentration that fell in the range of 1 to 3 µM. Importantly, they also exhibited inhibition of B19V DNA replication in UT7/Epo-S1 cells and ex vivo-expanded human erythroid progenitor cells.

Recent Advances in Replication and Infection of Human Parvovirus B19

Parvovirus B19 (B19V) is pathogenic to humans and causes bone marrow failure diseases and various other inflammatory disorders. B19V infection exhibits high tropism for human erythroid progenitor cells (EPCs) in the bone marrow and fetal liver. The exclusive restriction of B19V replication to erythroid lineage cells is partly due to the expression of receptor and co-receptor(s) on the cell surface of human EPCs and partly depends on the intracellular factors essential for virus replication. We first summarize the latest developments in the viral entry process and the host cellular factors or pathways critical for B19V replication. We discuss the role of hypoxia, erythropoietin signaling and STAT5 activation in the virus replication. The B19V infection-induced DNA damage response (DDR) and cell cycle arrest at late S-phase are two key events that promote B19V replication. Lately, the virus infection causes G2 arrest, followed by the extensive cell death of EPCs that leads to anemia. We provide the current understanding of how B19V exploits the cellular resources and manipulate pathways for efficient virus replication. B19V encodes a single precursor mRNA (pre-mRNA), which undergoes alternate splicing and alternative polyadenylation to generate at least 12 different species of mRNA transcripts. The post-transcriptional processing of B19V pre-mRNA is tightly regulated through cis-acting elements and trans-acting factors flanking the splice donor or acceptor sites. Overall, in this review, we focus on the recent advances in the molecular virology and pathogenesis of B19V infection.

Human Parvovirus B19 Utilizes Cellular DNA Replication Machinery for Viral DNA Replication

Human parvovirus B19 (B19V) infection of human erythroid progenitor cells (EPCs) induces a DNA damage response and cell cycle arrest at late S phase, which facilitates viral DNA replication. However, it is not clear exactly which cellular factors are employed by this single-stranded DNA virus. Here, we used microarrays to systematically analyze the dynamic transcriptome of EPCs infected with B19V. We found that DNA metabolism, DNA replication, DNA repair, DNA damage response, cell cycle, and cell cycle arrest pathways were significantly regulated after B19V infection. Confocal microscopy analyses revealed that most cellular DNA replication proteins were recruited to the centers of viral DNA replication, but not the DNA repair DNA polymerases. Our results suggest that DNA replication polymerase δ and polymerase α are responsible for B19V DNA replication by knocking down its expression in EPCs. We further showed that although RPA32 is essential for B19V DNA replication and the phosphorylated forms of RPA32 colocalized with the replicating viral genomes, RPA32 phosphorylation was not necessary for B19V DNA replication. Thus, this report provides evidence that B19V uses the cellular DNA replication machinery for viral DNA replication.IMPORTANCE Human parvovirus B19 (B19V) infection can cause transient aplastic crisis, persistent viremia, and pure red cell aplasia. In fetuses, B19V infection can result in nonimmune hydrops fetalis and fetal death. These clinical manifestations of B19V infection are a direct outcome of the death of human erythroid progenitors that host B19V replication. B19V infection induces a DNA damage response that is important for cell cycle arrest at late S phase. Here, we analyzed dynamic changes in cellular gene expression and found that DNA metabolic processes are tightly regulated during B19V infection. Although genes involved in cellular DNA replication were downregulated overall, the cellular DNA replication machinery was tightly associated with the replicating single-stranded DNA viral genome and played a critical role in viral DNA replication. In contrast, the DNA damage response-induced phosphorylated forms of RPA32 were dispensable for viral DNA replication.

Human Parvovirus Infection of Human Airway Epithelia Induces Pyroptotic Cell Death by Inhibiting Apoptosis

Human bocavirus 1 (HBoV1) is a human parvovirus that causes acute respiratory tract infections in young children. In this study, we confirmed that, when polarized/well-differentiated human airway epithelia are infected with HBoV1 in vitro, they develop damage characterized by barrier function disruption and cell hypotrophy. Cell death mechanism analyses indicated that the infection induced pyroptotic cell death characterized by caspase-1 activation. Unlike infections with other parvoviruses, HBoV1 infection did not activate the apoptotic or necroptotic cell death pathway. When the NLRP3-ASC-caspase-1 inflammasome-induced pathway was inhibited by short hairpin RNA (shRNA), HBoV1-induced cell death dropped significantly; thus, NLRP3 mediated by ASC appears to be the pattern recognition receptor driving HBoV1 infection-induced pyroptosis. HBoV1 infection induced steady increases in the expression of interleukin 1α (IL-1α) and IL-18. HBoV1 infection was also associated with the marked expression of the antiapoptotic genes BIRC5 and IFI6 When the expression of BIRC5 and/or IFI6 was inhibited by shRNA, the infected cells underwent apoptosis rather than pyroptosis, as indicated by increased cleaved caspase-3 levels and the absence of caspase-1. BIRC5 and/or IFI6 gene inhibition also significantly reduced HBoV1 replication. Thus, HBoV1 infection of human airway epithelial cells activates antiapoptotic proteins that suppress apoptosis and promote pyroptosis. This response may have evolved to confer a replicative advantage, thus allowing HBoV1 to establish a persistent airway epithelial infection. This is the first report of pyroptosis in airway epithelia infected by a respiratory virus.IMPORTANCE Microbial infection of immune cells often induces pyroptosis, which is mediated by a cytosolic protein complex called the inflammasome that senses microbial pathogens and then activates the proinflammatory cytokines IL-1 and IL-18. While virus-infected airway epithelia often activate NLRP3 inflammasomes, studies to date suggest that these viruses kill the airway epithelial cells via the apoptotic or necrotic pathway; involvement of the pyroptosis pathway has not been reported previously. Here, we show for the first time that virus infection of human airway epithelia can also induce pyroptosis. Human bocavirus 1 (HBoV1), a human parvovirus, causes lower respiratory tract infections in young children. This study indicates that HBoV1 kills airway epithelial cells by activating genes that suppress apoptosis and thereby promote pyroptosis. This strategy appears to promote HBoV1 replication and may have evolved to allow HBoV1 to establish persistent infection of human airway epithelia.

Genetic characterization of the complete genome of a mutant canine parvovirus isolated in China

A field canine parvovirus (CPV) strain, CPV-SH14, was previously isolated from an outbreak of severe gastroenteritis in Shanghai in 2014. The complete genome of CPV-SH14 was determined by using PCR with modified primers. When compared to other CPV-2 strains, several insertions, deletions, and point mutations were identified in the 5' and 3' UTR, with key amino acid (aa) mutations (K19R, E572K in NS1 and F267Y, Y324I and T440A in VP2) also being observed in the coding regions of CPV-SH14. These results indicated that significant and unique genetic variations have occurred at key sites or residues in the genome of CPV-SH14, suggesting the presence of a novel genetic variant of new CPV-2a. Phylogenetic analysis of the VP2 gene revealed that CPV-SH14 may have the potential to spread worldwide. In conclusion, CPV-SH14 may be a novel genetic variant of new CPV-2a, potentially with a selective advantage over other strains.

Parvovirus B19 integration into human CD36+ erythroid progenitor cells

The pathogenic autonomous human parvovirus B19 (B19V) productively infects erythroid progenitor cells (EPCs). Functional similarities between B19V nonstructural protein (NS1), a DNA binding endonuclease, and the Rep proteins of Adeno-Associated Virus (AAV) led us to hypothesize that NS1 may facilitate targeted nicking of the human genome and B19 vDNA integration. We adapted an integration capture sequencing protocol (IC-Seq) to screen B19V infected human CD36+ EPCs for viral integrants, and discovered 40,000 unique B19V integration events distributed throughout the human genome. Computational analysis of integration patterns revealed strong correlations with gene intronic regions, H3K9me3 sites, and the identification of 41 base pair consensus sequence with an octanucleotide core motif. The octanucleotide core has homology to a single region of B19V, adjacent to the P6 promoter TATA box. We present the first direct evidence that B19V infection of erythroid progenitor cells disrupts the human genome and facilitates viral DNA integration.

The SAT Protein of Porcine Parvovirus Accelerates Viral Spreading through Induction of Irreversible Endoplasmic Reticulum Stress

The SAT protein (SATp) of porcine parvovirus (PPV) accumulates in the endoplasmic reticulum (ER), and SAT deletion induces the slow-spreading phenotype. The in vitro comparison of the wild-type Kresse strain and its SAT knockout (SAT^-) mutant revealed that prolonged cell integrity and late viral release are responsible for the slower spreading of the SAT^- virus. During PPV infection, regardless of the presence or absence of SATp, the expression of downstream ER stress response proteins (Xbp1 and CHOP) was induced. However, in the absence of SATp, significant differences in the quantity and the localization of CHOP were detected, suggesting a role of SATp in the induction of irreversible ER stress in infected cells. The involvement of the induction of irreversible ER stress in porcine testis (PT) cell necrosis and viral egress was confirmed by treatment of infected cells by ER stress-inducing chemicals (MG132, dithiothreitol, and thapsigargin), which accelerated the egress and spreading of both the wild-type and the SAT^- viruses. UV stress induction had no beneficial effect on PPV infection, underscoring the specificity of ER stress pathways in the process. However, induction of CHOP and its nuclear translocation cannot alone be responsible for the biological effect of SAT, since nuclear CHOP could not complement the lack of SAT in a coexpression experiment.IMPORTANCE SATp is encoded by an alternative open reading frame of the PPV genome. Earlier we showed that SATp of the attenuated PPV NADL-2 strain accumulates in the ER and accelerates virus release and spreading. Our present work revealed that slow spreading is a general feature of SAT^- PPVs and is the consequence of prolonged cell integrity. PPV infection induced ER stress in infected cells regardless of the presence of SATp, as demonstrated by the morphological changes of the ER and expression of the stress response proteins Xbp1 and CHOP. However, the presence of SATp made the ER stress more severe and accelerated cell death during infection, as shown by the higher rate of expression of CHOP and alteration of the localization of CHOP. The beneficial effect of irreversible ER stress on PPV spread was confirmed by treatment of infected cells with ER stress-inducing chemicals.

Phosphorylated STAT5 directly facilitates parvovirus B19 DNA replication in human erythroid progenitors through interaction with the MCM complex

Productive infection of human parvovirus B19 (B19V) exhibits high tropism for burst forming unit erythroid (BFU-E) and colony forming unit erythroid (CFU-E) progenitor cells in human bone marrow and fetal liver. This exclusive restriction of the virus replication to human erythroid progenitor cells is partly due to the intracellular factors that are essential for viral DNA replication, including erythropoietin signaling. Efficient B19V replication also requires hypoxic conditions, which upregulate the signal transducer and activator of transcription 5 (STAT5) pathway, and phosphorylated STAT5 is essential for virus replication. In this study, our results revealed direct involvement of STAT5 in B19V DNA replication. Consensus STAT5-binding elements were identified adjacent to the NS1-binding element within the minimal origins of viral DNA replication in the B19V genome. Phosphorylated STAT5 specifically interacted with viral DNA replication origins both in vivo and in vitro, and was actively recruited within the viral DNA replication centers. Notably, STAT5 interacted with minichromosome maintenance (MCM) complex, suggesting that STAT5 directly facilitates viral DNA replication by recruiting the helicase complex of the cellular DNA replication machinery to viral DNA replication centers. The FDA-approved drug pimozide dephosphorylates STAT5, and it inhibited B19V replication in ex vivo expanded human erythroid progenitors. Our results demonstrated that pimozide could be a promising antiviral drug for treatment of B19V-related diseases.

Human parvovirus B19 (B19V) infection can cause severe hematological disorders, a direct consequence of the death of infected human erythroid progenitor cells (EPCs) of the bone marrow and fetal liver. B19V replicates autonomously in human EPCs, and the erythropoietin (EPO) and EPO-receptor (EPO-R) signaling is required for productive B19V replication. The Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) signaling plays a key role in B19V replication. Here, we identify that phosphorylated STAT5 directly interacts with B19V replication origins and with minichromosome maintenance (MCM) complex in human EPCs, and that it functions as a scaffold protein to bring MCM to the viral replication origins and thus plays a key role in B19V DNA replication. Importantly, pimozide, a STAT5 phosphorylation-specific inhibitor and an FDA-approved drug, abolishes B19V replication in ex vivo expanded human EPCs; therefore, pimozide has the potential to be used as an antiviral drug for treatment of B19V-caused hematological disorders.

Parvovirus B19 NS1 protein induces cell cycle arrest at G2-phase by activating the ATR-CDC25C-CDK1 pathway

Human parvovirus B19 (B19V) infection of primary human erythroid progenitor cells (EPCs) arrests infected cells at both late S-phase and G2-phase, which contain 4N DNA. B19V infection induces a DNA damage response (DDR) that facilitates viral DNA replication but is dispensable for cell cycle arrest at G2-phase; however, a putative C-terminal transactivation domain (TAD2) within NS1 is responsible for G2-phase arrest. To fully understand the mechanism underlying B19V NS1-induced G2-phase arrest, we established two doxycycline-inducible B19V-permissive UT7/Epo-S1 cell lines that express NS1 or NS1mTAD2, and examined the function of the TAD2 domain during G2-phase arrest. The results confirm that the NS1 TAD2 domain plays a pivotal role in NS1-induced G2-phase arrest. Mechanistically, NS1 transactivated cellular gene expression through the TAD2 domain, which was itself responsible for ATR (ataxia-telangiectasia mutated and Rad3-related) activation. Activated ATR phosphorylated CDC25C at serine 216, which in turn inactivated the cyclin B/CDK1 complex without affecting nuclear import of the complex. Importantly, we found that the ATR-CHK1-CDC25C-CDK1 pathway was activated during B19V infection of EPCs, and that ATR activation played an important role in B19V infection-induced G2-phase arrest.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

Cynomolgus monkeys (Macaca fascicularis) experimentally infected with B19V and hepatitis A virus: no evidence of the co-infection as a cause of acute liver failure

This study was conducted to analyse the course and the outcome of the liver disease in the co-infected animals in order to evaluate a possible synergic effect of human parvovirus B19 (B19V) and hepatitis A virus (HAV) co-infection. Nine adult cynomolgus monkeys were inoculated with serum obtained from a fatal case of B19V infection and/or a faecal suspension of acute HAV. The presence of specific antibodies to HAV and B19V, liver enzyme levels, viraemia, haematological changes, and necroinflammatory liver lesions were used for monitoring the infections. Seroconversion was confirmed in all infected groups. A similar pattern of B19V infection to human disease was observed, which was characterised by high and persistent viraemia in association with reticulocytopenia and mild to moderate anaemia during the period of investigation (59 days). Additionally, the intranuclear inclusion bodies were observed in pro-erythroblast cell from an infected cynomolgus and B19V Ag in hepatocytes. The erythroid hypoplasia and decrease in lymphocyte counts were more evident in the co-infected group. The present results demonstrated, for the first time, the susceptibility of cynomolgus to B19V infection, but it did not show a worsening of liver histopathology in the co-infected group.

Virotherapy of digestive tumors with rodent parvovirus: overview and perspectives

INTRODUCTION

Toolan's H-1 parvovirus (H-1PV) exerts a cytotoxic/oncolytic effect, predominantly mediated by its non-structural protein (NS1). This rat parvovirus is harmless, unlike other parvoviruses, and its antitumor potential may be useful to clinicians as its oncolytic action appears to be true in numerous non-digestive and digestive cancers.

AREAS COVERED

After a brief review of parvovirus genus and biology, we summarize the proposed mechanisms to explain the cytotoxicity of H-1PV to tumors which results in dysregulation of cell transcription, cell-cycle arrest, termination of cell replication, activation of cellular stress response and induction of cell death. Viral oncolysis induces a strong tumor-specific immune response leading to the recognition and elimination of minimal residual disease. As the action of H-1PV is not limited to the digestive tract, we initially analyse studies performed in non-digestive cancers such as glioma (as the virus is able to cross the blood brain barrier), and then focused more particularly on the results in digestive cancers.

EXPERT OPINION

Based on the results of studies showing little H-1PV toxicity to living bodies, we advocate for the use of the parvovirus in cancers such as melanoma, glioma and pancreatic ductal adenocarcinoma in addition to conventional chemotherapy.

Parvovirus B19 Replication and Expression in Differentiating Erythroid Progenitor Cells

The pathogenic Parvovirus B19 (B19V) is characterized by a strict adaptation to erythroid progenitor cells (EPCs), a heterogeneous population of differentiating cells with diverse phenotypic and functional properties. In our work, we studied the dynamics of B19V infection in EPCs in dependence on the cell differentiation stage, in terms of distribution of infected cells, synthesis of viral nucleic acids and production of infectious virus. EPCs at early differentiation stage led to an abortive infection, without viral genome replication and a very low transcriptional activity. EPCs at later stages were permissive, with highest levels of viral replicative activity at day 9 (+3.0 Log from 2 to 48 hpi) and lower levels at day 18 (+1.5 Log from 2 to 48 hpi). B19V DNA increment was in accordance with the percentage of cells positive to flow-FISH assay (41.4% at day 9, 1.1% at day 18). Quantitation of total RNA indicated a close association of genome replication and transcription with viral RNA accumulation within infected cells related to viral DNA increase during the course of infection. Analysis of the different classes of mRNAs revealed two distinct pattern of genome expression profile with a fine regulation in the frequency utilization of RNA processing signals: an early phase, when cleavage at the proximal site leading to a higher relative production of mRNA for NS protein, and a late phase, when cleavage at the distal site was more frequent leading to higher relative abundance of mRNA for VP and 11 kDA proteins. Infectious virus was released from cells at day 6–15, but not at day 18. Our results, providing a detailed description of B19V replication and expression profile in differentiating EPCs, highlight the very tight adaptation of B19V to a specific cellular target defined both by its erythroid lineage and its differentiation stage.

Canine parvovirus NS1 induced apoptosis involves mitochondria, accumulation of reactive oxygen species and activation of caspases

The non-structural protein (NS1) of parvoviruses plays an important role in viral replication and is thought to be responsible for inducing cell death. However, the detailed mechanism and the pathways involved in canine parvovirus type 2 NS1 (CPV2.NS1) induced apoptosis are not yet known. In the present study, we report that expression of CPV2.NS1 in HeLa cells arrests cells in G1 phase of the cell cycle and the apoptosis is mitochondria mediated as indicated by mitochondrial depolarization, release of cytochrome-c and activation of caspase 9. Treatment of cells with caspase 9 inhibitor Z-LEHD-FMK reduced the induction of apoptosis significantly. We also report that expression of CPV2.NS1 causes accumulation of reactive oxygen species (ROS) and treatment with an antioxidant reduces the ROS levels and the extent of apoptosis. Our results provide an insight into the mechanism of CPV2.NS1 induced apoptosis, which might prove valuable in developing NS1 protein as an oncolytic agent.

Down-regulation of inwardly rectifying Kir2.1 K+ channels by human parvovirus B19 capsid protein VP1

Parvovirus B19 (B19V) has previously been shown to cause endothelial dysfunction. B19V capsid protein VP1 harbors a lysophosphatidylcholine producing phospholipase A2 (PLA2). Lysophosphatidylcholine inhibits Na(+)/K(+) ATPase, which in turn may impact on the activity of inwardly rectifying K(+) channels. The present study explored whether VP1 modifies the activity of Kir2.1 K(+) channels. cRNA encoding Kir2.1 was injected into Xenopus oocytes without or with cRNA encoding VP1 isolated from a patient suffering from fatal B19V-induced inflammatory cardiomyopathy or the VP1 mutant (H153A)VP1 lacking a functional PLA2 activity. K(+) channel activity was determined by dual electrode voltage clamp. In addition, Na(+)/K(+)-ATPase activity was estimated from K(+)-induced pump current (I(pump)) and ouabain-inhibited current (I(ouabain)). Injection of cRNA encoding Kir2.1 into Xenopus oocytes was followed by appearance of inwardly rectifying K(+) channel activity (I(K)), which was significantly decreased by additional injection of cRNA encoding VP1, but not by additional injection of cRNA encoding (H153A)VP1. The effect of VP1 on I K was mimicked by lysophosphatidylcholine (1 μg/ml) and by inhibition of Na(+)/K(+)-ATPase with 0.1 mM ouabain. In the presence of lysophosphatidylcholine, I K was not further decreased by additional treatment with ouabain. The B19V capsid protein VP1 thus inhibits Kir2.1 channels, an effect at least partially due to PLA2-dependent formation of lysophosphatidylcholine with subsequent inhibition of Na(+)/K(+)-ATPase activity.

Viral genes as oncolytic agents for cancer therapy

Many viruses have the ability to modulate the apoptosis, and to accomplish it; viruses encode proteins which specifically interact with the cellular signaling pathways. While some viruses encode proteins, which inhibit the apoptosis or death of the infected cells, there are viruses whose encoded proteins can kill the infected cells by multiple mechanisms, including apoptosis. A particular class of these viruses has specific gene(s) in their genomes which, upon ectopic expression, can kill the tumor cells selectively without affecting the normal cells. These genes and their encoded products have demonstrated great potential to be developed as novel anticancer therapeutic agents which can specifically target and kill the cancer cells leaving the normal cells unharmed. In this review, we will discuss about the viral genes having specific cancer cell killing properties, what is known about their functioning, signaling pathways and their therapeutic applications as anticancer agents.

Parvovirus B19 at the culprit coronary stenosis predicts outcome after stenting

BACKGROUND

Parvovirus (PV) B19 DNA is detected in endothelial cells and may cause endothelial dysfunction, which is involved in in-stent restenosis. We aimed at performing an exploratory analysis that evaluated if PVB19 DNA at the culprit coronary stenosis would be associated with an increased rate of major adverse cardiac events (MACE) after coronary stenting.

MATERIALS AND METHODS

Consecutive patients undergoing stent implantation for stable or unstable coronary artery disease were enroled. Serology for PVB19 infection and presence of DNA for PVB19 on balloons used for predilatation were assessed in all patients. MACE rate, as a composite of cardiac death, myocardial infarction (MI) or clinically driven target lesion revascularization (TLR) was obtained at 24 month follow-up. Adjusted hazard ratio (HR) with 95% confidence interval (CI) was calculated for variables associated with MACE.

RESULTS

One hundred and nine patients [age 66 ± 10, male sex 89 (82%)] were enroled. At 24-month follow-up, 18 patients experienced a MACE. Two patients (2%) experienced MI, while 16 patients (15%) experienced clinically driven TLR. At multiple Cox regression analysis, the presence of PVB19 DNA on the balloon and the use of bare-metal stents were independent predictors of MACE [HR 3·30, 95% CI (1·12-10·08), P = 0·03 and HR 4·19, 95% CI (1·60-10·94), P = 0·003].

CONCLUSIONS

PVB19 DNA detected on the balloon used for dilatation of coronary stenosis before stent implantation is associated with MACE rate at follow-up, mainly due to clinically driven TLR. The results of this exploratory analysis should be confirmed in a larger population.

Abnormal erythropoiesis and the pathophysiology of chronic anemia

Erythropoiesis, the bone marrow production of erythrocytes by the proliferation and differentiation of hematopoietic cells, replaces the daily loss of 1% of circulating erythrocytes that are senescent. This daily output increases dramatically with hemolysis or hemorrhage. When erythrocyte production rate of erythrocytes is less than the rate of loss, chronic anemia develops. Normal erythropoiesis and specific abnormalities of erythropoiesis that cause chronic anemia are considered during three periods of differentiation: a) multilineage and pre-erythropoietin-dependent hematopoietic progenitors, b) erythropoietin-dependent progenitor cells, and c) terminally differentiating erythroblasts. These erythropoietic abnormalities are discussed in terms of their pathophysiological effects on the bone marrow cells and the resultant changes that can be detected in the peripheral blood using a clinical laboratory test, the complete blood count.

Human parvovirus B19 infection causes cell cycle arrest of human erythroid progenitors at late S phase that favors viral DNA replication

Human parvovirus B19 (B19V) infection has a unique tropism to human erythroid progenitor cells (EPCs) in human bone marrow and the fetal liver. It has been reported that both B19V infection and expression of the large nonstructural protein NS1 arrested EPCs at a cell cycle status with a 4 N DNA content, which was previously claimed to be "G2/M arrest." However, a B19V mutant infectious DNA (M20(mTAD2)) replicated well in B19V-semipermissive UT7/Epo-S1 cells but did not induce G2/M arrest (S. Lou, Y. Luo, F. Cheng, Q. Huang, W. Shen, S. Kleiboeker, J. F. Tisdale, Z. Liu, and J. Qiu, J. Virol. 86:10748-10758, 2012). To further characterize cell cycle arrest during B19V infection of EPCs, we analyzed the cell cycle change using 5-bromo-2'-deoxyuridine (BrdU) pulse-labeling and DAPI (4',6-diamidino-2-phenylindole) staining, which precisely establishes the cell cycle pattern based on both cellular DNA replication and nuclear DNA content. We found that although both B19V NS1 transduction and infection immediately arrested cells at a status of 4 N DNA content, B19V-infected 4 N cells still incorporated BrdU, indicating active DNA synthesis. Notably, the BrdU incorporation was caused neither by viral DNA replication nor by cellular DNA repair that could be initiated by B19V infection-induced cellular DNA damage. Moreover, several S phase regulators were abundantly expressed and colocalized within the B19V replication centers. More importantly, replication of the B19V wild-type infectious DNA, as well as the M20(mTAD2) mutant, arrested cells at S phase. Taken together, our results confirmed that B19V infection triggers late S phase arrest, which presumably provides cellular S phase factors for viral DNA replication.

Parvovirus B19 Achievements and Challenges

Parvovirus B19 is a widespread human pathogenic virus, member of the Erythrovirus genus in the Parvoviridae family. Infection can be associated with an ample range of pathologies and clinical manifestations, whose characteristics and outcomes depend on the interplay between the pathogenetic potential of the virus, its adaptation to different cellular environments, and the physiological and immune status of the infected individuals. The scope of this review is the advances in knowledge on the biological characteristics of the virus and of virus-host relationships; in particular, the interactions of the virus with different cellular environments in terms of tropism and ability to achieve a productive replicative cycle, or, on the contrary, to establish persistence; the consequences of infection in terms of interference with the cell physiology; the process of recognition of the virus by the innate or adaptive immune system, hence the role of the immune system in controlling the infection or in the development of clinical manifestations. Linked to these issues is the continuous effort to develop better diagnostic algorithms and methods and the need for development of prophylactic and therapeutic options for B19V infections.

Human parvovirus B19 NS1 protein aggravates liver injury in NZB/W F1 mice

Human parvovirus B19 (B19) has been associated with a variety of diseases. However, the influence of B19 viral proteins on hepatic injury in SLE is still obscure. To elucidate the effects of B19 viral proteins on livers in SLE, recombinant B19 NS1, VP1u or VP2 proteins were injected subcutaneously into NZB/W F1 mice, respectively. Significant expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were detected in NZB/W F1 mice receiving B19 NS1 as compared to those mice receiving PBS. Markedly hepatocyte disarray and lymphocyte infiltration were observed in livers from NZB/WF 1 mice receiving B19 NS1 as compared to those mice receiving PBS. Additionally, significant increases of Tumor Necrosis Factor -α (TNF-α), TNF-α receptor, IκB kinase -α (IKK-α), nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor (IκB) and nuclear factor-kappa B (NF-κB) were detected in livers from NZB/W F1 mice receiving B19 NS1 as compared to those mice receiving PBS. Accordingly, significant increases of matrix metalloproteinase-9 (MMP9) and U-plasminogen activator (uPA) were also detected in livers from NZB/W F1 mice receiving B19 NS1 as compared to those mice receiving PBS. Contrarily, no significant variation on livers from NZB/W F1 mice receiving B19 VP1u or VP2 was observed as compared to those mice receiving PBS. These findings firstly demonstrated the aggravated effects of B19 NS1 but not VP1u or VP2 protein on hepatic injury and provide a clue in understanding the role of B19 NS1 on hepatic injury in SLE.

The nonstructural protein NP1 of human bocavirus 1 induces cell cycle arrest and apoptosis in Hela cells

Human bocavirus type 1 (HBoV1) is a newly identified pathogen associated with human respiratory tract illnesses. Previous studies demonstrated that proteins of HBoV1 failed to cause cell death, which is considered as a possible common feature of bocaviruses. However, our work showed that the NP1 of HBoV1 induced apoptotic cell death in Hela cells in the absence of viral genome replication and expression of other viral proteins. Mitochondria apoptotic pathway was involved in the NP1-induced apoptosis that was confirmed by apoptotic characteristics including morphological changes, DNA fragmentation and caspase activation. We also demonstrated that the cell cycle of NP1-transfected Hela cells was transiently arrested at G2/M phase followed by rapid appearance of apoptosis and that the N terminal domain of NP1 was critical to its nuclear localization and function in apoptosis induction in Hela cells. These findings might provide alternative information for further study of mechanism of HBoV1 pathogenesis.

Parvovirus infection-induced DNA damage response

Parvoviruses are a group of small DNA viruses with ssDNA genomes flanked by two inverted terminal structures. Due to a limited genetic resource they require host cellular factors and sometimes a helper virus for efficient viral replication. Recent studies have shown that parvoviruses interact with the DNA damage machinery, which has a significant impact on the life cycle of the virus as well as the fate of infected cells. In addition, due to special DNA structures of the viral genomes, parvoviruses are useful tools for the study of the molecular mechanisms underlying viral infection-induced DNA damage response (DDR). This review aims to summarize recent advances in parvovirus-induced DDR, with a focus on the diverse DDR pathways triggered by different parvoviruses and the consequences of DDR on the viral life cycle as well as the fate of infected cells.

Human parvovirus B19 induced apoptotic bodies contain altered self-antigens that are phagocytosed by antigen presenting cells

Human parvovirus B19 (B19V) from the erythrovirus genus is known to be a pathogenic virus in humans. Prevalence of B19V infection has been reported worldwide in all seasons, with a high incidence in the spring. B19V is responsible for erythema infectiosum (fifth disease) commonly seen in children. Its other clinical presentations include arthralgia, arthritis, transient aplastic crisis, chronic anemia, congenital anemia, and hydrops fetalis. In addition, B19V infection has been reported to trigger autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. However, the mechanisms of B19V participation in autoimmunity are not fully understood. B19V induced chronic disease and persistent infection suggests B19V can serve as a model for viral host interactions and the role of viruses in the pathogenesis of autoimmune diseases. Here we investigate the involvement of B19V in the breakdown of immune tolerance. Previously, we demonstrated that the non-structural protein 1 (NS 1) of B19V induces apoptosis in non-permissive cells lines and that this protein can cleave host DNA as well as form NS1-DNA adducts. Here we provide evidence that through programmed cell death, apoptotic bodies (ApoBods) are generated by B19V NS1 expression in a non-permissive cell line. Characterization of purified ApoBods identified potential self-antigens within them. In particular, signature self-antigens such as Smith, ApoH, DNA, histone H4 and phosphatidylserine associated with autoimmunity were present in these ApoBods. In addition, when purified ApoBods were introduced to differentiated macrophages, recognition, engulfment and uptake occurred. This suggests that B19V can produce a source of self-antigens for immune cell processing. The results support our hypothesis that B19V NS1-DNA adducts, and nucleosomal and lysosomal antigens present in ApoBods created in non-permissive cell lines, are a source of self-antigens.

Human parvovirus B19 DNA replication induces a DNA damage response that is dispensable for cell cycle arrest at phase G2/M

Human parvovirus B19 (B19V) infection is highly restricted to human erythroid progenitor cells, in which it induces a DNA damage response (DDR). The DDR signaling is mainly mediated by the ATR (ataxia telangiectasia-mutated and Rad3-related) pathway, which promotes replication of the viral genome; however, the exact mechanisms employed by B19V to take advantage of the DDR for virus replication remain unclear. In this study, we focused on the initiators of the DDR and the role of the DDR in cell cycle arrest during B19V infection. We examined the role of individual viral proteins, which were delivered by lentiviruses, in triggering a DDR in ex vivo-expanded primary human erythroid progenitor cells and the role of DNA replication of the B19V double-stranded DNA (dsDNA) genome in a human megakaryoblastoid cell line, UT7/Epo-S1 (S1). All the cells were cultured under hypoxic conditions. The results showed that none of the viral proteins induced phosphorylation of H2AX or replication protein A32 (RPA32), both hallmarks of a DDR. However, replication of the B19V dsDNA genome was capable of inducing the DDR. Moreover, the DDR per se did not arrest the cell cycle at the G(2)/M phase in cells with replicating B19V dsDNA genomes. Instead, the B19V nonstructural 1 (NS1) protein was the key factor in disrupting the cell cycle via a putative transactivation domain operating through a p53-independent pathway. Taken together, the results suggest that the replication of the B19V genome is largely responsible for triggering a DDR, which does not perturb cell cycle progression at G(2)/M significantly, during B19V infection.

Oncolytic viruses & their specific targeting to tumour cells

Cancer is one of the major causes of death worldwide. In spite of achieving significant successes in medical sciences in the past few decades, the number of deaths due to cancer remains unchecked. The conventional chemotherapy and radiotherapy have limited therapeutic index and a plethora of treatment related side effects. This situation has provided an impetus for search of novel therapeutic strategies that can selectively destroy the tumour cells, leaving the normal cells unharmed. Viral oncotherapy is such a promising treatment modality that offers unique opportunity for tumour targeting. Numerous viruses with inherent anti-cancer activity have been identified and are in different phases of clinical trials. In the era of modern biotechnology and with better understanding of cancer biology and virology, it has become feasible to engineer the oncolytic viruses (OVs) to increase their tumour selectivity and enhance their oncolytic activity. In this review, the mechanisms by which oncolytic viruses kill the tumour cells have been discussed as also the development made in virotherapy for cancer treatment with emphasis on their tumour specific targeting.

Concise review: Anemia caused by viruses

Most of the viruses known to be associated with anemia in human tend to persistently infect their host and are noncytopathic or poorly cytopathic for blood cell progenitors. Infections with Epstein-Barr virus, cytomegalovirus, varicella-zoster virus, human herpes virus 6 (HHV-6), B19 parvovirus, human immunodeficiency virus, hepatitis A and C viruses and the putative viral agent associated with non-A-G post-hepatitis aplastic anemia have been reported in association with anemia. Nevertheless, a direct cytotoxic effect on erythroid progenitors has been clearly demonstrated only for human parvovirus B19 and evocated for HHV-6. A major role for destructive immunity is strongly suspected in the pathogenesis of anemia associated with the other viral infections. Host genes play a role in the occurrence of virus-induced anemia in animal models, and there are some evidences that genetic background could also influence the occurrence of virus-associated anemia in human.

Diagnosis, management and possibilities to prevent parvovirus B19 infection in pregnancy

Human parvovirus B19 (B19V) infection in pregnancy can cause severe fetal anemia and nonimmune hydrops fetalis, which may be associated with spontaneous abortion and fetal death. Approximately 30–40% of women of child-bearing age are not immune to B19V infection. The risk to fetal life is particularly high if maternal infection occurs during the first 20 weeks of gestation. In this article we intend to give an overview on the molecular biology, epidemiology and management of B19V infection during pregnancy. These data will be combined with an assessment of the clinical situation of the infected fetus and the possibilities for avoiding and/or preventing B19V infection in pregnant women. Currently B19V infection is the causative agent of one of the most frequently occurring infectious complications in pregnancy that endangers fetal life, and so the necessity to develop a preventive vaccine is discussed.

Human bocavirus: still more questions than answers

The human bocavirus was first detected in 2005 and since then has been found in both respiratory secretions from patients with airway infections and in stool samples from patients with gastroenteritis. Meanwhile, four different genotypes have been identified that most likely derive from recombination events. Although the modified Koch’s postulates have not yet been fulfilled completely, owing to the lack of an animal model or a simple cell culture system, there is increasing evidence that the human bocaviruses are serious participants in infectious diseases of the respiratory and the GI tracts. This article reviews the current status of the clinical features of human bocaviruses and provides an overview of the latest findings concerning the biology, phylogeny, epidemiology and diagnostic tools related to human bocaviruses. Furthermore, it discusses the potential pathogenicity of human bocavirus, as well as its persistence and reactivation in hosts.

[Acute erythroblastopenia due to Parvovirus B19 revealing hereditary spherocytosis]

Acute Parvovirus B19 infection is responsible for blocking the erythroblastic line, usually with no consequences on hematopoiesis except in patients with chronic hemolytic anemia in whom it can evolve to potentially serious acute anemia. We report 2 observations of acute erythroblastopenia revealing hereditary spherocytosis in 2 children (1 boy and 1 girl) of non-consanguineous parents.