塩川 舞

Congenital tremor (CT) in piglets was first reported in 1922, and although the causative pathogen was unknown for many years, atypical porcine pestivirus (APPV) was recently shown to be the cause. APPV is difficult to isolate, and there have been few reports of APPV isolated from field materials. Here, we successfully isolated infectious particles from a tonsillar emulsion from a CT-affected piglet using the established swine-kidney-derived cell line SK-L. In addition, we produced APPV artificially using these cells. Thus, SK-L cells are useful for both isolation and artificial production of APPV.

Classical swine fever (CSF) live vaccine used in Japan, GPE- strain, is produced using guinea pig kidney (GPK)-derived primary culture cells. This means that a large number of guinea pigs are used to generate the primary GPK cells needed to produce the CSF live vaccine, and alternative solution is desired. Hence, we established two GPK cell lines capable of culturing the GPE- strain: spontaneously immortalized GPK (GPK-SI) cells were generated by repeated passaging of primary GPK cells, and the other cell line, artificially immortalized GPK (GPK-AI) cells, were obtained by introducing the SV40 large T antigen gene into primary GPK cells. Both cell lines were susceptible to the GPE- virus, and the virus grew more efficiently in GPK-SI cells at 37°C. When the culture temperature was set to 30°C, the virus titer reached 104.8 50% Tissue Culture Infectious Dose (TCID50)/mL in GPK-SI cells 7 days after virus inoculation at a multiplicity of infection (MOI) of 1, which was equivalent to that in cells cultured at 37°C. When the virus was inoculated at MOI <1, the virus titer 7 days after inoculation was higher when cultured at 30°C than when cultured at 37°C in both cell lines, reaching 105.63 TCID50/mL in GPK-SI cells. These results indicate that GPK-SI and GPK-AI cells can potentially replace primary GPK cells for the production of CSF live vaccines. This could also contribute to stable CSF vaccine production and animal welfare.

A novel picornavirus was isolated from the faeces of a diarrhoeic cow using MA-104 cells at the third blind passage. This virus, named Den1/2021/JPN, was completely sequenced using total RNA from the cell culture supernatant by deep sequencing. The genome of Den1/2021/JPN had a standard picornavirus genome organisation with conserved picornaviral motifs. The 5' untranslated region harboured a type-II internal ribosomal entry site. Den1/2021/JPN was most closely related to a bovine parechovirus (Bo_ParV) named cow/2018/4, which has been recently identified in publicly available databases. Phylogenetic analyses and pairwise sequence comparison revealed that Den1/2021/JPN and Bo_ParV cow/2018/4 clustered with parechoviruses and were most closely related to Parechovirus E identified in birds of prey, exhibiting nucleotide sequence similarity of 64.2-64.5 %, 58.6-59.7 % and 66.3-66.4 % in the polyprotein, P1 and 2C+3 CD coding regions, respectively. This study presents the first report on the isolation of Bo_ParV. Den1/2021/JPN and Bo_ParV cow/2018/4, which are candidates for a novel species in the genus Parechovirus.

Bovine-derived cultured cells, including Madin-Darby bovine kidney cells, are used worldwide; however, lipofection tend to result in low transfection efficiency, which has impeded the progress of veterinary research. We performed experiments to confirm the lipofection efficiency of bovine-derived cultured cells, to identify cells that suitable for lipofection. Several bovine tissues (endometrium, testis, ear tissue and foetal muscle) were collected, and primary cultured cells were prepared. Lipofection assay showed that only bovine endometrium (BE)-derived cells could be transfected efficiently (50‒70%). BE cells can be divided into at least two types of cell populations (BE-1 and BE-2). The BE-1 cells, which were suitable for lipofection, were obtained by passages at short intervals and were negative for cytokeratin- and positive for vimentin-expression; the BE-2 cells did not have these characteristics and were not suitable for lipofection. Furthermore, the BE-1 cells and artificially immortalised cells of BE-1, iBE-1 cells, were utilised in a reporter assay requiring the introduction of multiple DNAs. Endometrial tissues can be collected from living cows, and BE-1 cells can be obtained easily by controlling passaging timing. The production of BE-1 cells and sharing the methods required to prepare them will contribute to the development of veterinary research.

Atypical porcine pestivirus (APPV), which has been confirmed to be associated with congenital tremor (CT) in pigs, is a newly discovered porcine virus that has been found in the Americas, Europe and Asia; however, no report of APPV in Japan has been published. We identified an APPV in the central nervous system of Japanese piglets with CT and firstly determined and analysed the complete genome sequence. Phylogenetic analysis using the complete genome nucleotide sequence of the Japanese APPV, named Anna/2020, and those of APPVs from the NCBI database showed that APPVs were divided into three genotypes (genotypes 1 to 3), and that Anna/2020 clustered with the genotype 3 APPV strains, but distantly branched from these strains. Pairwise complete coding region nucleotide sequence comparisons revealed that there was 94.0%- 99.7% sequence identity among the genotype 3 strains, while Anna/2020 showed 87.0%-89.3% identity to those genotype 3 strains, suggesting that Anna/2020 represents a novel APPV lineage within genotype 3. Retrospective examinations using RT-PCR revealed one genotype 1 and two novel genotype 3 APPVs from pigs without CT, and that novel genotype 3 APPVs have been prevalent in Japan since at least 2007.

Our previous study reported that persistently infected (PI) cattle of bovine viral diarrhea virus (BVDV) have co-infected with BVDV/END- and /END+ that promote and inhibit host's type-I interferon (IFN) production, respectively. However, the relationship between co-infection of immunologically distinct BVDVs and persistent infection as well as the biological significance of END- viruses remains unknown. Experiments using cultured cells revealed that END+ virus, which is unable to propagate in situations where the host's immune response is induced by IFN-α addition, is able to propagate under those conditions when co-infecting with END- virus. These results indicate that BVDV/END- can coexist with BVDV/END+ and that co-infection with END- viruses supports the propagation of END+ viruses. Our in vitro experiments strongly suggest that co-infection with END- virus is involved in the maintenance of persistent infection of BVDV.

Bovine abortion, diarrhea, and respiratory disease complexes, caused by infectious agents, result in high and significant economic losses for the cattle industry. These pathogens are likely transmitted by various vectors and reservoirs including insects, birds, and rodents. However, experimental data supporting this possibility are scarce. We collected 117 samples and screened them for 44 bovine abortive, diarrheal, and respiratory disease complex pathogens by using Dembo polymerase chain reaction (PCR), which is based on TaqMan real-time PCR. Fifty-seven samples were positive for at least one pathogen, including bovine viral diarrhea virus, bovine enterovirus, Salmonella enterica ser. Dublin, Salmonella enterica ser. Typhimurium, and Neospora caninum; some samples were positive for multiple pathogens. Bovine viral diarrhea virus and bovine enterovirus were the most frequently detected pathogens, especially in flies, suggesting an important role of flies in the transmission of these viruses. Additionally, we detected the N. caninum genome from a cockroach sample for the first time. Our data suggest that insects (particularly flies), birds, and rodents are potential vectors and reservoirs of abortion, diarrhea, and respiratory infectious agents, and that they may transmit more than one pathogen at the same time.

The purpose of this study was to investigate the prevalence of HoBi-like viruses in Japan and evaluate the immune response induced by bovine viral diarrhea virus (BVDV) vaccines available in Japan. No HoBi-like viruses were detected by RT-PCR and virus isolation in cattle sera collected in Japan between 2012 and 2017. Nevertheless, neutralizing antibody titers against HoBi-like viruses ranged from < 2 to 4,096, demonstrating cross-reactivity to HoBi-like viruses in cattle infected (naturally or vaccinated) with BVDV-1 and BVDV-2. These results suggest that continuous vaccination with both BVDV-1 and BVDV-2 contributes to the control of HoBi-like viruses in Japan.

Amphipathic alpha-helices of exchangeable apolipoproteins have shown to play crucial roles in the formation of infectious hepatitis C virus (HCV) particles through the interaction with viral particles. Among the Flaviviridae members, pestivirus and flavivirus possess a viral structural protein E-rns or a non-structural protein 1 (NS1) as secretory glycoproteins, respectively, while Hepacivirus including HCV has no secretory glycoprotein. In case of pestivirus replication, the C-terminal long amphipathic alpha-helices of E-rns are important for anchoring to viral membrane. Here we show that host-derived apolipoproteins play functional roles similar to those of virally encoded E-rns and NS1 in the formation of infectious particles. We examined whether E-rns and NS1 could compensate for the role of apolipoproteins in particle formation of HCV in apolipoprotein B (ApoB) and ApoE double-knockout Huh7 (BE-KO), and nonhepatic 293T cells. We found that exogenous expression of either E-rns or NS1 rescued infectious particle formation of HCV in the BE-KO and 293T cells. In addition, expression of apolipoproteins or NS1 partially rescued the production of infectious pestivirus particles in cells upon electroporation with an E-rns-deleted non-infectious RNA. As with exchangeable apolipoproteins, the C-terminal amphipathic alpha-helices of E-rns play the functional roles in the formation of infectious HCV or pestivirus particles. These results strongly suggest that the host-and virus-derived secretory glycoproteins have overlapping roles in the viral life cycle of Flaviviridae, especially in the maturation of infectious particles, while E-rns and NS1 also participate in replication complex formation and viral entry, respectively. Considering the abundant hepatic expression and liver-specific propagation of these apolipoproteins, HCV might have evolved to utilize them in the formation of infectious particles through deletion of a secretory viral glycoprotein gene.

Scavenger receptor class B type 1 (SR-B1) and low-density lipoprotein receptor (LDLR) are known to be involved in entry of hepatitis C virus (HCV), but their precise roles and their interplay are not fully understood. In this study, deficiency of both SR-B1 and LDLR in Huh7 cells was shown to impair the entry of HCV more strongly than deficiency of either SR-B1 or LDLR alone. In addition, exogenous expression of not only SR-B1 and LDLR but also very low-density lipoprotein receptor (VLDLR) rescued HCV entry in the SR-B1 and LDLR double-knockout cells, suggesting that VLDLR has similar roles in HCV entry. VLDLR is a lipoprotein receptor, but the level of its hepatic expression was lower than those of SR-B1 and LDLR. Moreover, expression of mutant lipoprotein receptors incapable of binding to or uptake of lipid resulted in no or slight enhancement of HCV entry in the double-knockout cells, suggesting that binding and/or uptake activities of lipid by lipoprotein receptors are essential for HCV entry. In addition, rescue of infectivity in the double-knockout cells by the expression of the lipoprotein receptors was not observed following infection with pseudotype particles bearing HCV envelope proteins produced in non-hepatic cells, suggesting that lipoproteins associated with HCV particles participate in the entry through their interaction with lipoprotein receptors. Buoyant density gradient analysis revealed that HCV utilizes these lipoprotein receptors in a manner dependent on the lipoproteins associated with HCV particles. Collectively, these results suggest that lipoprotein receptors redundantly participate in the entry of HCV.

To gain further insight into the genomic features of bovine viral diarrhea virus 1 (BVDV-1) subgenotypes, we sequenced the complete genome of BVDV-1n Shitara/02/06 and BVDV-1o IS26NCP/01. The complete genome of Shitara/02/06 and IS26NCP/01 shared 77.7 to 79.3% and 78.0 to 85.7% sequence identities with other BVDV-1 subgenotype strains, respectively.

We identified novel viruses in feces from cattle with diarrhea collected in 2009 in Hokkaido Prefecture, Japan, by using a metagenomics approach and determined the (near) complete sequences of the virus. Sequence analyses revealed that they had a standard picornavirus genome organization, i.e. 5' untranslated region (UTR) - L-P1 (VP4- VP3- VP2- VP1) - P2 (2A- 2B- 2C) - P3 (3A- 3B- 3C-3D) - 3'UTR- poly(A). They are closely related to other unclassified Chinese picornaviruses; bat picornaviruses group 1-3, feline picornavirus, and canine picornavirus, sharing 45.4-51.4% (P1), 38.0-44.9% (P2), and 49.6-53.3% (P3) amino acid identities, respectively. The phylogenetic analyses and detailed genome characterization showed that they, together with the unclassified Chinese picornaviruses, grouped as a cluster for the P1, 2C, 3CD and VP1 coding regions. These viruses had conserved features (e.g. predicted protein cleavage sites, presence of a leader protein, 2A, 2C, 3C, and 3D functional domains), suggesting they have a common ancestor. Reverse-transcription-PCR assays, using specific primers designed from the 5'UTR sequence of these viruses, showed that 23.0% (20/87) of fecal samples from cattle with diarrhea were positive, indicating the prevalence of these picornavirus in the Japanese cattle population in Hokkaido Prefecture. However, further studies are needed to investigate the pathogenic potential and etiological role of these viruses in cattle. (C) 2015 Elsevier B.V. All rights reserved.

A viral metagenomics approach was used to investigate fecal samples of Japanese calves with and without diarrhea. Of the different viral pathogens detected, read counts gave nearly complete astrovirus-related RNA sequences in 15 of the 146 fecal samples collected in three distinct areas (Hokkaido, Ishikawa, and Kagoshima Prefectures) between 2009 and 2015. Due to the lack of genetic information about bovine astroviruses (BoAstVs) in Japan, these sequences were analyzed in this study. Nine of the 15 Japanese BoAstVs were closely related to Chinese BoAstVs and clustered into a lineage (tentatively named lineage 1) in all phylogenetic trees. Three of 15 strains were phylogenetically separate from lineage 1, showing low sequence identities, and clustered instead with an American strain isolated from cattle with respiratory disease (tentatively named lineage 2). Interestingly, two of 15 strains clustered with lineage 1 in the open reading frame (ORF)1a and ORF1b regions, while they clustered with lineage 2 in the ORF2 region. Remarkably, one of 15 strains exhibited low amino acid sequence similarity to other BoAstVs and was clustered separately with porcine astrovirus type 5 in all trees, and ovine astrovirus in the ORF2 region, suggesting past interspecies transmission.

Hepatitis C virus (HCV) is a major etiologic agent of chronic liver diseases. Although the HCV life cycle has been clarified by studying laboratory strains of HCV derived from the genotype 2a JFH-1 strain (cell culture-adapted HCV [HCVcc]), the mechanisms of particle formation have not been elucidated. Recently, we showed that exogenous expression of a liver-specific microRNA, miR-122, in nonhepatic cell lines facilitates efficient replication but not particle production of HCVcc, suggesting that liver-specific host factors are required for infectious particle formation. In this study, we screened human cancer cell lines for expression of the liver-specific alpha -fetoprotein by using a cDNA array database and identified liver-derived JHH-4 cells and stomach-derived FU97 cells, which express liver-specific host factors comparable to Huh7 cells. These cell lines permit not only replication of HCV RNA but also particle formation upon infection with HCVcc, suggesting that hepatic differentiation participates in the expression of liver-specific host factors required for HCV propagation. HCV inhibitors targeting host and viral factors exhibited different antiviral efficacies between Huh7 and FU97 cells. Furthermore, FU97 cells exhibited higher susceptibility for propagation of HCVcc derived from the JFH-2 strain than Huh7 cells. These results suggest that hepatic differentiation participates in the expression of liver-specific host factors required for complete propagation of HCV.

Hepatitis C virus (HCV) is one of the most common etiologic agents of chronic liver diseases, including liver cirrhosis and hepatocellular carcinoma. In addition, HCV infection is often associated with extrahepatic manifestations (EHM), including mixed cryoglobulinemia and non-Hodgkin's lymphoma. However, the mechanisms of cell tropism of HCV and HCV-induced EHM remain elusive, because in vitro propagation of HCV has been limited in the combination of cell culture-adapted HCV (HCVcc) and several hepatic cell lines. Recently, a liver-specific microRNA called miR-122 was shown to facilitate the efficient propagation of HCVcc in several hepatic cell lines. In this study, we evaluated the importance of miR-122 on the replication of HCV in nonhepatic cells. Among the nonhepatic cell lines expressing functional HCV entry receptors, Hec1B cells derived from human uterus exhibited a low level of replication of the HCV genome upon infection with HCVcc. Exogenous expression of miR-122 in several cells facilitates efficient viral replication but not production of infectious particles, probably due to the lack of hepatocytic lipid metabolism. Furthermore, expression of mutant miR-122 carrying a substitution in a seed domain was required for efficient replication of mutant HCVcc carrying complementary substitutions in miR-122-binding sites, suggesting that specific interaction between miR-122 and HCV RNA is essential for the enhancement of viral replication. In conclusion, although miR-122 facilitates efficient viral replication in nonhepatic cells, factors other than miR-122, which are most likely specific to hepatocytes, are required for HCV assembly.

The robust cell culture systems for hepatitis C virus (HCV) are limited to those using cell culture-adapted clones (HCV in cell culture [HCVcc]) and cells derived from the human hepatoma cell line Huh7. However, accumulating data suggest that host factors, including innate immunity and gene polymorphisms, contribute to the variation in host response to HCV infection. Therefore, the existing in vitro systems for HCV propagation are not sufficient to elucidate the life cycle of HCV. A liver-specific microRNA, miR122, has been shown to participate in the efficient replication of HCV. In this study, we examined the possibility of establishing a new permissive cell line for HCV propagation by the expression of miR122. A high level of miR122 was expressed by a lentiviral vector placed into human liver cell lines at a level comparable to the endogenous level in Huh7 cells. Among the cell lines that we examined, Hep3B cells stably expressing miR122 (Hep3B/miR122) exhibited a significant enhancement of HCVcc propagation. Surprisingly, the levels of production of infectious particles in Hep3B/miR122 cells upon infection with HCVcc were comparable to those in Huh7 cells. Furthermore, a line of "cured" cells, established by elimination of HCV RNA from the Hep3B/miR122 replicon cells, exhibited an enhanced expression of miR122 and a continuous increase of infectious titers of HCVcc in every passage. The establishment of the new permissive cell line for HCVcc will have significant implications not only for basic HCV research but also for the development of new therapeutics.

A robust and reliable cell culture system for serum-derived HCV (HCVser) has not been established yet because of the presence of neutralizing antibody and tropism for infection. To overcome this obstacle, we employed a lipid-mediated protein intracellular delivery reagent (PIDR) that permits internalization of proteins into cells. Although entry of HCVcc was not enhanced by the treatment with PIDR, entry of HCVser into hepatoma cell lines (Huh7 and HepG2) and immortalized primary hepatocytes (He and HuS/E2) was significantly enhanced by the PIDR treatment. The entry of HCVser into Huh7 cells in the presence of PIDR was resistant to the neutralization by an anti-hCD81 antibody, suggesting that PIDR is capable of internalizing HCVser in a receptor-independent manner. Interestingly, the PIDR-mediated entry of HCVser and HCVcc was enhanced by the addition of sera from chronic hepatitis C patients but not from healthy donors. In addition, neutralization of HCVcc infection by anti-E2 antibody was canceled by the treatment with PIDR. In conclusion, the PIDR is a valuable tool to get over the obstacle of neutralizing antibodies to internalize HCV into cells and might be useful for the establishment of in vitro propagation HCVser. (C) 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

A major obstacle to gene transduction by viral vectors is inactivation by human complement in vivo. One way to overcome this is to incorporate complement regulatory proteins, such as CD55/decay accelerating factor (DAF), into viral particles. Lentivirus vectors pseudotyped with the baculovirus envelope protein GP64 have been shown to acquire more potent resistance to serum inactivation and longer transgene expression than those pseudotyped with the vesicular stomatitis virus (VSV) envelope protein G. However, the molecular mechanisms underlying resistance to serum inactivation in pseudotype particles bearing the GP64 have not been precisely elucidated. In this study, we generated pseudotype and recombinant VSVs bearing the GP64. Recombinant VSVs generated in human cell lines exhibited the incorporation of human DAF in viral particles and were resistant to serum inactivation, whereas those generated in insect cells exhibited no incorporation of human DAF and were sensitive to complement inactivation. The GP64 and human DAF were detected on the detergent-resistant membrane and were coprecipitated by immunoprecipitation analysis. A pseudotype VSV bearing GP64 produced in human DAF knockdown cells reduced resistance to serum inactivation. In contrast, recombinant baculoviruses generated in insect cells expressing human DAF or carrying the human DAF gene exhibited resistance to complement inactivation. These results suggest that the incorporation of human DAF into viral particles by interacting with baculovirus GP64 is involved in the acquisition of resistance to serum inactivation.

Japanese encephalitis virus (JEV) is a mosquito-borne RNA virus and one of the most important flaviviruses in the medical and veterinary fields. Although cholesterol has been shown to participate in both the entry and replication steps of JEV, the mechanisms of infection, including the cellular receptors of JEV, remain largely unknown. To clarify the infection mechanisms of JEV, we generated pseudotype (JEVpv) and recombinant (JEVrv) vesicular stomatitis viruses bearing the JEV envelope protein. Both JEVpv and JEVrv exhibited high infectivity for the target cells, and JEVrv was able to propagate and form foci as did authentic JEV. Anti-JEV envelope antibodies neutralized infection of the viruses. Treatment of cells with inhibitors for vacuolar ATPase and clathrin-mediated endocytosis reduced the infectivity of JEVpv, suggesting that JEVpv enters cells via pH-and clathrin-dependent endocytic pathways. Although treatment of the particles of JEVpv, JEVrv, and JEV with cholesterol drastically reduced the infectivity as previously reported, depletion of cholesterol from the particles by treatment with methyl beta-cyclodextrin enhanced infectivity. Furthermore, treatment of cells with sphingomyelinase (SMase), which hydrolyzes membrane-bound sphingomyelin to ceramide, drastically enhanced infection with JEVpv and propagation of JEVrv, and these enhancements were inhibited by treatment with an SMase inhibitor or C-6-ceramide. These results suggest that ceramide plays crucial roles in not only entry but also egress processes of JEV, and they should assist in the clarification of JEV propagation and the development of novel therapeutics against diseases caused by infection with flaviviruses.