Nucleocapsid-glycoprotein interactions required for assembly of alphaviruses.

We have studied interactions between nucleocapsids and glycoproteins required for budding of alphaviruses, using Ross River virus-Sindbis virus chimeras in which the nucleocapsid protein is derived from one virus and the envelope glycoproteins are derived from the second virus. A virus containing the Ross River virus genome in which the capsid protein had been replaced with that from Sindbis virus was almost nonviable. Nucleocapsids formed in normal numbers in the infected cell, but very little virus was released from the cell. There are 11 amino acid differences between Ross River virus and Sindbis virus in their 33-residue E2 cytoplasmic domains. Site-specific mutagenesis was used to change 9 of these 11 amino acids in the chimera from the Ross River virus to the Sindbis virus sequence in an attempt to adapt the E2 of the chimera to the nucleocapsid. The resulting mutant chimera grew 4 orders of magnitude better than the parental chimeric virus. This finding provides direct evidence for a sequence-specific interaction between the nucleocapsid and the E2 cytoplasmic domain during virus budding. The mutated chimeric virus readily gave rise to large-plaque variants that grew almost as well as Ross River virus, suggesting that additional single amino acid substitutions in the structural proteins can further enhance the interactions between the disparate capsid and the glycoproteins. Unexpectedly, change of E2 residue 394 from lysine (Ross River virus) to glutamic acid (Sindbis virus) was deleterious for the chimera, suggesting that in addition to its role in nucleocapsid-E2 interactions, the N-terminal part of the E2 cytoplasmic domain may be involved in glycoprotein-glycoprotein interactions required to assemble the glycoprotein spikes. The reciprocal chimera, Sindbis virus containing the Ross River virus capsid, also grew poorly. Suppressor mutations arose readily in this chimera, producing a virus that grew moderately well and that formed larger plaques.     

Nucleotide sequence analysis and expression from recombinant vectors demonstrate that the attachment protein G of bovine respiratory syncytial virus is distinct from that of human respiratory syncytial virus

Bovine respiratory syncytial (BRS) virus causes a severe lower respiratory tract disease in calves similar to the disease in children caused by human respiratory syncytial (HRS) virus. While there is antigenic cross-reactivity among the other major viral structural proteins, the major glycoprotein, G, of BRS virus and that of HRS virus are antigenically distinct. The G glycoprotein has been implicated as the attachment protein for HRS virus. We have carried out a molecular comparison of the glycoprotein G of BRS virus with the HRS virus counterparts. cDNA clones corresponding to the BRS virus G glycoprotein mRNA were isolated and analyzed by dideoxynucleotide sequencing. The BRS virus G mRNA contained 838 nucleotides exclusive of poly(A) and had a major open reading frame coding for a polypeptide of 257 amino acid residues. The deduced amino acid sequence of the BRS virus G polypeptide showed only 29 to 30% amino acid identity with the G protein of either the subgroup A or B HRS virus. However, despite this low level of identity, there were strong similarities in the predicted hydropathy profiles of the BRS virus and HRS virus G proteins. A cDNA molecule containing the complete BRS virus G major open reading frame was inserted into the thymidine kinase gene of vaccinia virus by homologous recombination, and a recombinant virus containing the BRS virus G protein gene was isolated. This recombinant virus expressed the BRS virus G protein, as demonstrated by Western immunoblot analysis and immunofluorescence of infected cells. The BRS virus G protein expressed from the recombinant vector was transported to and expressed on the surface of infected cells. Antisera to the BRS virus G protein made by using the recombinant vector to immunize animals recognized the BRS virus attachment protein but not the HRS virus G protein and vice versa, confirming the lack of antigenic cross-reactivity between the BRS and HRS virus attachment proteins. On the basis of the data presented here, we conclude that BRS virus should be classified within the genus Pneumovirus in a group separate from HRS virus and that it is no more closely related to HRS virus subgroup A than it is to HRS virus subgroup B.     

Role of Interferon in the Propagation of MM Virus in L Cells

MM virus propagated in mouse brain replicates to low titers in L cells without production of cytopathic effect (CPE). After growing the virus in BHK-21 cells, however, the virus replicates to high titers in L cells with complete CPE. It was found that suspensions of MM virus propagated in L cells directly from the mouse brain contained much more interferon than did suspensions of virus which had first been grown in BHK-21 cells. Mouse brain suspensions of the virus were also found to contain high interferon titers. Treatment of L cells with actinomycin D before infection with mouse brain-grown virus resulted in full virus replication with CPE. BHK-21 cell-grown virus diluted in L cell interferon behaved like mouse brain-grown virus in L cells. It is concluded that the presence of interferon in the inoculum is largely responsible for the suppression of MM virus replication in L cells.     

Isolation of a new rhabdovirus in Australia related to Tibrogargan virus

A virus isolated from the blood of a healthy steer and designated DPP53 was shown to have rhabdovirus morphology. Although DPP53 virus was antigenically related to Tibrogargan virus by reciprocal immunofluorescence and neutralization tests, the viruses were distinguishable by neutralization tests. DPP53 virus contained RNA and was sensitive to both ether and chloroform. The geographical distribution of neutralizing antibody to DPP53 virus in Australian cattle corresponded to the distribution of Culicoides brevitarsis indicating that this virus may be arthropod-borne with this midge as a possible vector. Antibody to DPP53 virus was detected in serum from cattle, buffalo, dogs and one horse, but not in serum from deer, pigs, humans or wallabies. Highest virus titres were obtained by growth in Vero and BHK21 cell cultures, but the virus could also be grown in Aedes albopictus cell cultures. Higher virus titres were obtained when the multiplicity of infection was low. The name advanced for DPP53 virus is 'Coastal Plains' virus.     

Detection of multiple viruses in queens of the honey bee Apis mellifera L

Individual honey bee Apis mellifera L. queens were examined for the presence of six honey bee viruses including acute bee paralysis virus, chronic bee paralysis virus, black queen cell virus, deformed wing virus, Kashmir bee virus, and sacbrood virus. All viruses, except ABPV, were detected in the samples. Among queens examined for virus infections, 93% had multiple virus infections. The detection of viruses in queens raises the possibility of a vertical transmission pathway wherein infected queens can pass virus through their eggs to their offspring.     

RNAi的抗病毒研究进展

RNA干扰(RNA interference,RNAi)是真核生物中的特异核苷酸序列产生的基因沉默现象,被认为有抑制病毒复制的功能。最近的研究表明,通过诱导RNAi可以抑制多种病毒的复制,包括人类免疫缺陷病毒Ⅰ型,乙型肝炎病毒,丙型肝炎病毒,登革热病毒,脊髓灰质炎病毒,流感病毒,口蹄疫病毒和重症急性呼吸综合征病毒等。总结了目前运用RNA干扰技术抑制病毒复制的研究进展,展望基于RNAi技术的抗病毒治疗的可能性。     

Rabies virus infection of cultured rat sensory neurons.

The axonal transport of rabies virus (challenge virus strain of fixed virus) was studied in differentiated rat embryonic dorsal root ganglion cells. In addition, we observed the attachment of rabies virus to neuronal extensions and virus production by infected neurons. A compartmentalized cell culture system was used, allowing infection and manipulation of neuronal extensions without exposing the neural soma to the virus. The cultures consisted of 60% large neuronal cells whose extensions exhibited neurofilament structures. Rabies virus demonstrated high binding affinity to unmyelinated neurites, as suggested by assays of virus adsorption and immunofluorescence studies. The rate of axoplasmic transport of virus was 12 to 24 mm/day, including the time required for internalization of the virus into neurites. The virus transport could be blocked by cytochalasin B, vinblastine, and colchicine, none of which negatively affected the production of virus in cells once the infection was established. It was concluded that, for the retrograde transfer of rabies virus by neurites from the periphery to the neuronal soma, the integrity of tubulin- and actin-containing structures is essential. The rat sensory neurons were characterized as permissive, moderately susceptible, but low producers of rabies virus. These neurons were capable of harboring rabies virus for long periods of time and able to release virus into the culture medium without showing any morphological alterations. The involvement of sensory neurons in rabies virus pathogenesis, both in viral transport and as a site for persistent viral infection, is discussed.     

Performance of 3 successive generations of specified-pathogenfree chickens maintained as a closed flock

No antibodies against Salmonella pullorum, Mycoplasma gallisepticum, Mycoplasma synoviae, Haemophilus gallinarum, fowl pox virus, Marek's disease virus, herpes virus of turkey, infectious laryngotracheitis virus, avian adenovirus, avian reovirus, infectious bursal disease virus, reticuloendotheliosis virus, avian leukosis virus, avian encephalomyelitis virus and Newcastle disease virus were detectable in the sera obtained from these chickens in 3 generations at various ages. Antibodies against infectious bronchitis virus were detected in the sera of the 3rd generations at 66, 74 and 108 weeks of age. The performances of these chickens was nearly the same as that of conventional healthy chickens in the poultry industry, with no tendency to decline.     

Distribution of the Receptor Sites for Sindbis Virus on the Surface of Chicken and BHK Cells

Sindbis virus was adsorbed to chicken cells or to BHK cells, and the distribution of virus over the surface of the cell was examined by electron microscopy of surface replicas. The distribution of virus particles on the cell was used to indicate the position of virus receptors at the cell surface. When purified Sindbis virus was adsorbed at 37 C to cells prefixed with glutaraldehyde, the virus particles were evenly distributed over the surface of most cells. There was a large variability from cell to cell, however, in the number of virus particles adsorbed, and regions with different concentrations of virus particles were sometimes observed on the same cell. The concentration of virus receptors observed varied from 20 to 160/mum(2) of cell surface, and, thus, the total number of virus receptors per chicken cell is on the order of 10(5). When virus was adsorbed to unfixed cells at 4 C, the virus particles were clustered into aggregates varying from a few particles to large crystalline arrays (the latter seen only in chicken cells). These conditions are apparently conducive to virus aggregation, and this, coupled with free lateral diffusion of the virus-receptor complex in the cell membrane at 4 C, leads to the observed clustering.     

Effect of Ionic Strength on the Binding of Sindbis Virus to Chick Cells

Sindbis virus can adsorb to chicken embryo fibroblasts in two different ways. "Loosely" bound virus can be washed off the cell with buffers of ionic strength 0.2 or greater, whereas "tightly" bound virus remains attached under these conditions. When Sindbis virus is adsorbed to chick cells at 4 C from a buffer of ionic strength 0.17, 40 to 50% of the adsorbed virus is loosely bound, the remainder tightly bound. Infection of chick cells by Sindbis virus has only small effects on the total amount of virus that can be bound to the cells. However, the amount of Sindbis virus that can be tightly bound declines rapidly beginning at 2 to 3 h after infection. By 7 h after infection, the amount of virus that can be tightly bound is only 10 to 20% of the amount bound to uninfected cells. The adsorption (and penetration) of virus at 37 C is most efficient at an ionic strength of 0.15 to 0.17; at this ionic strength most of the adsorbed virus is tightly bound. At higher ionic strengths the virus adsorbs poorly. At lower ionic strengths most of the virus is loosely bound. A second enveloped virus, vesicular stomatitis virus, has been studied for the purposes of comparison; its adsorption behavior differs from that of Sindbis virus.     

Transfection of RNA from Organ Samples of Infected Animals Represents a Highly Sensitive Method for Virus Detection and Recovery of Classical Swine Fever Virus

Translation and replication of positive stranded RNA viruses are directly initiated in the cellular cytoplasm after uncoating of the viral genome. Accordingly, infectious virus can be generated by transfection of RNA genomes into susceptible cells. In the present study, efficiency of conventional virus isolation after inoculation of cells with infectious sample material was compared to virus recovery after transfection of total RNA derived from organ samples of pigs infected with Classical swine fever virus (CSFV). Compared to the conventional method of virus isolation applied in three different porcine cell lines used in routine diagnosis of CSF, RNA transfection showed a similar efficiency for virus rescue. For two samples, recovery of infectious virus was only possible by RNA transfection, but not by the classical approach of virus isolation. Therefore, RNA transfection represents a valuable alternative to conventional virus isolation in particular when virus isolation is not possible, sample material is not suitable for virus isolation or when infectious material is not available. To estimate the potential risk of RNA prepared from sample material for infection of pigs, five domestic pigs were oronasally inoculated with RNA that was tested positive for virus rescue after RNA transfection. This exposure did not result in viral infection or clinical disease of the animals. In consequence, shipment of CSFV RNA can be regarded as a safe alternative to transportation of infectious virus and thereby facilitates the exchange of virus isolates among authorized laboratories with appropriate containment facilities.     

Inoculation of bulls with bovine virus diarrhea virus: Excretion of virus in semen and effects on semen quality

Bovine virus diarrhea (BVD) virus was inoculated into 9 bulls. Semen samples were collected to determine if BVD virus could be isolated from semen and to determine if the virus affected semen quality. The reproductive tracts of 6 bulls were recovered following slaughter and subjected to virus isolation procedures and histologic examination.BVD virus was detected in 4 of 98 semen samples following inoculation. The virus was also recovered from the testicle of one bull following slaughter. Inoculation of BVD virus into bulls did not affect semen quality and did not cause gross or microscopic lesions in the reproductive tract. This experiment indicates that following inoculation of BVD virus into bulls, the virus may be shed in the semen. However, the probability of this occurring is low.     

Characterization of bovine respiratory syncytial virus proteins and mRNAs and generation of cDNA clones to the viral mRNAs.

We have characterized the proteins and mRNAs of bovine respiratory syncytial (BRS) virus strain 391-2 and constructed cDNA clones corresponding to 9 of the 10 BRS virus mRNAs. The proteins of BRS virus-infected cells were compared with the proteins from human respiratory syncytial (HRS) virus-infected cells. Nine proteins specific to BRS virus-infected cells, corresponding to nine HRS virus proteins, were identified. Only a BRS virus polymerase protein remains to be identified. The BRS virus G glycoprotein showed major antigenic differences from the HRS virus G glycoprotein by immunoprecipitation and Western (immuno-) blot analysis, whereas the BRS virus F, N, M, and P proteins showed antigenic cross-reactivity with their HRS virus counterparts. Analysis of RNAs from BRS virus-infected cells showed virus-specific RNAs which had electrophoretic mobilities similar to those of mRNAs of HRS virus but which hybridized poorly or not at all with HRS virus-specific probes in Northern (RNA) blot analysis. To analyze the BRS virus RNAs further, cDNA clones to the BRS virus mRNAs were generated. Nine separate groups of clones were identified and shown to correspond to nine BRS virus mRNAs by Northern blot analysis. A 10th BRS virus large mRNA was identified by analogy with the HRS virus polymerase mRNA. These data show that like HRS virus, BRS virus has 10 genes coding for 10 mRNAs.     

Four Categories of Viral Infection Describe the Health Status of Honey Bee Colonies

Honey bee virus prevalence data are an essential prerequisite for managing epidemic events in a population. A survey study was carried out for seven viruses in colonies representing a healthy Danish honey bee population. In addition, colonies from apiaries with high level Varroa infestation or high level of winter mortality were also surveyed. Results from RT-qPCR showed a considerable difference of virus levels between healthy and sick colonies. In the group of healthy colonies, no virus was detected in 36% of cases, while at least one virus was found in each of the sick colonies. Virus titers varied among the samples, and multiple virus infections were common in both groups with a high prevalence of Sacbrood virus (SBV), Black queen cell virus (BQCV) and Deformed wing virus (DWV). Based on the distribution of virus titers, we established four categories of infection: samples free of virus (C = 0), samples with low virus titer (estimated number of virus copies 0 < C < 10³), samples with medium virus titer (10³ ≤ C < 10⁷) and samples with high virus titer (C ≥ 10⁷). This allowed us to statistically compare virus levels in healthy and sick colonies. Using categories to communicate virus diagnosis results to beekeepers may help them to reach an informed decision on management strategies to prevent further spread of viruses among colonies.     

针对多种强致病性病毒的基因芯片检测方法的建立

为了制备灵敏的可检测多种烈性病毒性病原体的基因芯片,本研究设计了针对21种烈性病毒性病原体的基因芯片检测探针,每种5条,长50 bp.并以甲病毒属的基孔肯亚病毒和黄病毒属的黄热病毒细胞培养物为检测模型,摸索了合适的病毒基因处理与扩增方法.将提取的病毒RNA先用DNase Ⅰ处理,以去除掉其中的DNA分子,然后利用病毒属特异性引物进行反转录,以引导病毒基因组的合成,从而尽可能地减少宿主细胞基因成分的干扰.进行随机PCR扩增后将扩增产物与基因芯片进行杂交,分别出现了4条基孔肯亚病毒探针信号和5条黄热病毒的探针信号,说明所设计的检测探针具有较好的特异性,可用于这2种病毒的特异性检测.这种病毒基因样品的处理和扩增方法也为此基因芯片的临床应用奠定了基础.     

Roles of neuraminidase in the initial stage of influenza virus infection

We propose a concept that neuraminidase (NA) promotes virus entry into target cells during the initial stage of viral infection, in addition to the generally accepted concept that influenza virus NA promotes the release of progeny virus from a host cell at the final stage of viral replication. When NA activity was inhibited with specific inhibitors such as zanamivir and oseltamivir carboxylate, infection efficiency of the virus to MDCK and A549 cells was reduced to approximately 1/4 and 1/8, respectively. NA inhibitors did not significantly affect virus binding and envelope fusion activities, when assessed using an erythrocyte and virus system. Since the initial stage of viral infection involves binding of the virus to the target cell, virus entry into an endosome and envelope fusion with the endosomal membrane, our results indicated that NA inhibitors interfered with the virus entry step. Thus, NA is thought to promote virus entry, and thereby enhances infection efficiency.     

Glycoprotein gIII of pseudorabies virus is multifunctional.

One of the major glycoproteins of pseudorabies virus, gIII, is nonessential for growth in cell culture. Mutants defective in gIII, however, consistently yield lower titers of infectious virus (3- to 20-fold) than does wild-type virus. The interactions of gIII- mutants with their host cells were compared with those of wild-type virus in an attempt to uncover the functions of gIII. We show that gIII plays a major role in the stable adsorption of the virus to its host cell; in the absence of gIII, the rate of adsorption is reduced and adsorption is easily reversed by washing. Thus, adsorption of pseudorabies virus can be said to occur in at least the following two ways: (i) a gIII-mediated rapid adsorption or (ii) a slower and more labile adsorption that is independent of gIII. After virions have been complexed with monoclonal antibodies against gIII (but not some monoclonal antibodies against other glycoproteins), both modes of adsorption were inhibited. Glycoprotein gIII affects virus stability and virus release, as well as adsorption. The effect on virus release is marked when the virus is defective in additional functions. Thus, although we found no obvious difference in the release of virus from gIII- or wild-type virus-infected rabbit kidney cells, release of a gIII-/gI- double mutant from the cells occurred less readily than did release of a gI- mutant. The gIII-/gI- and gIII- mutants, however, adsorbed to cells at a similar rate, indicating that the effects of gIII on adsorption and virus release constitute separate functions. The Bartha vaccine strain of pseudorabies virus has a defective gIII gene and is released poorly from rabbit kidney cells. After the resident Bartha gIII gene was replaced by the gIII gene of wild-type virus, virus release was enhanced considerably. Since inactivation of gIII in wild-type pseudorabies virus did not significantly affect virus release, the Bartha strain must be defective in another function which, in conjunction with gIII, significantly affects virus release. These results indicate again that gIII affects virus release in conjunction with other functions. Also, although the Bartha strain was functionally defective in virus release, it adsorbed to cells as well as wild-type virus did, showing that the effects of gIII on virus adsorption and release constitute separate functions. We conclude that gIII is a multifunctional glycoprotein.     

Morphogenesis of Bittner Virus

The morphogenesis of Bittner virus (mouse mammary tumor virus) was studied in sectioned mammary tumor cells. Internal components of the virus (type A particles) were seen being assembled in virus factories close to the nucleus and were also seen forming at the plasma membrane. The particles in virus factories became enveloped by budding through the membrane of cytoplasmic vacuoles which were derived from dilated endoplasmic reticulum. Complete virus particles were liberated from these vacuoles by cell lysis. Particles budding at the plasma membrane were released into intercellular spaces. Maturation of enveloped virus occurred after release, but mature internal components were rarely seen in the cytoplasm before envelopment. Direct cell-to-cell transfer of virus by pinocytosis of budding particles by an adjacent cell was observed, and unusual forms of budding virus which participated in this process are illustrated and described. There was evidence that some virus particles contained cytoplasmic constituents, including ribosomes. Certain features of the structure of internal components are discussed in relation to a recently proposed model for the internal component of the mouse leukemia virus. Intracisternal virus-like particles were occasionally seen in tumor cells, but there was no evidence that these structures were developmentally related to Bittner virus.     

Role of virus variants and cells in maintenance of persistent infection by measles virus.

Hamster embryo fibroblasts persistently infected with a derivative of the Schwarz vaccine strain of measles virus spontaneously released virus particles with an average buoyant density considerably lower than that of the parental virus. The released virus contained all of the measles virus structural proteins and interfered with replication of standard virus. All of the virus structural proteins were associated with a membrane-free cytoplasmic extract from the persistently infected cells. Membrane-free cytoplasmic extracts prepared from Vero cells lytically infected with Schwarz strain measles contained little or no virus envelope structural protein. Maintenance of persistent infection may involve both the presence of virus variants and a defect in the ability of the infected cell to replicate the virus efficiently.