Structural proteins of two salmonid rhabdoviruses

A soluble nonglycosylated recombinant infectious hematopoietic necrosis virus (IHNV) G-protein induces IFNs in rainbow trout (Oncorhynchus mykiss)

Viral glycoproteins interact with cell-surface receptors to mediate virus entry and innate immune system activation. We found that a soluble recombinant infectious hematopoietic necrosis virus G-protein (rIHNV-G) stimulated an early innate immune response mediated by proinflammatory cytokines, IFN1 and IFN-gamma in rainbow trout (Oncorhynchus mykiss) fry. Expression of both IFN1 and IFN-gamma mRNA transcripts was an early event and was rIHNV-G dose-dependent. In addition, preliminary evidence revealed that the innate immune response induced by rIHNV-G protein could protect rainbow trout fry from a subsequent IHNV virus challenge. Finally, the binding and distribution of FITC-rIHNV-G protein on rainbow trout spleen and head kidney leukocytes resemble morphological changes which occur on the cell membrane during antigen-receptor interaction including membrane reorganization, patching, polarization and capping. Thus a soluble nonglycosylated rIHNV-G protein could mediate the activation of rainbow trout leukocytes, with concomitant production of proinflammatory cytokines and IFNs.

Comparative analysis of the acute response of the trout, O. mykiss, head kidney to in vivo challenge with virulent and attenuated infectious hematopoietic necrosis virus and LPS-induced inflammation

BACKGROUND

The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray.

RESULTS

The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed.

CONCLUSION

In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

Analysis of DNA-vaccinated fish reveals viral antigen in muscle, kidney and thymus, and transient histopathologic changes

A highly efficacious DNA vaccine against a fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV), was used in a systematic study to analyze vaccine tissue distribution, persistence, expression patterns, and histopathologic effects. Vaccine plasmid pIHNw-G, containing the gene for the viral glycoprotein, was detected immediately after intramuscular injection in all tissues analyzed, including blood, but at later time points was found primarily in muscle tissue, where it persisted to 90 days. Glycoprotein expression was detected in muscle, kidney, and thymus tissues, with levels peaking at 14 days and becoming undetectable by 28 days. Histologic examination revealed no vaccine-specific pathologic changes at the standard effective dose of 0.1 mug DNA per fish, but at a high dose of 50 mug an increased inflammatory response was evident. Transient damage associated with needle injection was localized in muscle tissue, but by 90 days after vaccination no damage was detected in any tissue, indicating the vaccine to be safe and well tolerated.

Fast neutralization/immunoperoxidase assay for viral haemorrhagic septicaemia with anti-nucleoprotein monoclonal antibody

An enzyme-immunohistochemical procedure was employed to facilitate neutralization/diagnostic tests for viral haemorrhagic septicaemia virus (VHSV), a significant pathogen in trout farms throughout Europe. The method described can be used for trout or mice antibodies; increases speed (1 day), simplicity, and minimizes the use of reagents compared to other neutralization assays. Furthermore, the test requires a minimum handling of the cell cultures under sterile conditions, decreasing frequent contamination due to the non-sterile conditions of the fish pathological samples. Foci of 5-20 infected epithelioma papillosum carp (EPC) cells are detected and counted with an inverted microscope in under 16 h after infection of EPC monolayers using a high titre anti-N VHSV monoclonal antibody (MAb) 2C9. MAb 2C9 recognizes different viral haemorrhagic septicaemia virus serotypes and VHSV isolates from different host species (trout, salmon and barbel) and Spanish geographical locations. The high titre and specificity of MAb 2C9 favour its conjugation to peroxidase and also make it possible to use in direct immunoperoxidase staining of the VHSV infected EPC monolayers. This neutralization/immunoperoxidase assay should improve diagnostics that use currently agarose or methylcellulose plaque reduction neutralization assays.

The complete genome structure and phylogenetic relationship of infectious hematopoietic necrosis virus

Infectious hematopoietic necrosis virus (IHNV), a member of the family Rhabdoviridae, causes a severe disease with high mortality in salmonid fish. The nucleotide sequence (11,131 bases) of the entire genome was determined for the pathogenic WRAC strain of IHNV from southern Idaho. This allowed detailed analysis of all 6 genes, the deduced amino acid sequences of their encoded proteins, and important control motifs including leader, trailer and gene junction regions. Sequence analysis revealed that the 6 virus genes are located along the genome in the 3' to 5' order: nucleocapsid (N), polymerase-associated phosphoprotein (P or M1), matrix protein (M or M2), surface glycoprotein (G), a unique non-virion protein (NV) and virus polymerase (L). The IHNV genome RNA was found to have highly complementary termini (15 of 16 nucleotides). The gene junction regions display the highly conserved sequence UCURUC(U)7RCCGUG(N)4CACR (in the vRNA sense), which includes the typical rhabdovirus transcription termination/polyadenylation signal and a novel putative transcription initiation signal. Phylogenetic analysis of M, G and L protein sequences allowed insights into the evolutionary and taxonomic relationship of rhabdoviruses of fish relative to those of insects or mammals, and a broader sense of the relationship of non-segmented negative-strand RNA viruses. Based on these data, a new genus, piscivirus, is proposed which will initially contain IHNV, viral hemorrhagic septicemia virus and Hirame rhabdovirus.

Recombinant infectious hematopoietic necrosis virus and viral hemorrhagic septicemia virus glycoprotein epitopes expressed in Aeromonas salmonicida induce protective immunity in rainbow trout (Oncorhynchus mykiss)

Fragments of the glycoprotein genes of viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV) were cloned into a bacterial broad-host-range expression vector under the control of the plac promoter. Western blot (immunoblot) analysis with monoclonal antibodies specific to the glycoproteins demonstrated the inducible expression of the fusion proteins in Escherichia coli. Aeromonas salmonicida is the causative agent of furunculosis in salmonid fish. It was confirmed that an avirulent strain of A. salmonicida, A440, which contains a deletion in the structural gene for the paracrystalline surface protein array, will provide protective immunity against furunculosis when used as a live attenuated vaccine. The plasmid-encoded viral epitopes were then mobilized into A440 for use as a shuttle system for the expression of fragments of the glycoprotein genes of IHNV and VHSV. Vaccination of rainbow trout with A440 containing the viral epitopes resulted in the development of protective immunity against both VHSV and IHNV. This indicates that the use of cloned fragments of the glycoproteins and the use of A. salmonicida as a shuttle system constitute a feasible approach to fish vaccine development.

The free nucleocapsids of the viral haemorrhagic septicaemia virus contain two antigenically related nucleoproteins

A protein of 34 kDa (Nx) was induced in vitro by the infection of fish cell cultures with the rhabdovirus agent of viral haemorrhagic septicaemia (VHS) of the trout. This protein only appeared as a major component in concentrated or intracellular labeled VHS virus but not in purified VHS or in the related infectious haematopoietic necrosis virus. That Nx protein is antigenically related to the nucleoprotein of purified virus was shown by its reaction with four anti-nucleoprotein monoclonal antibodies (at least 3 of them reacting non competitively against different epitopes) and by immunoprecipitation with polyvalent international reference sera. The Nx protein was shown to be specifically associated with free non-infective particles isolated by ultracentrifugation which were confirmed to be nucleocapsids by electron microscopy.

Epitope mapping and characterization of the infectious hematopoietic necrosis virus glycoprotein, using fusion proteins synthesized in Escherichia coli

A characterization of the antigenic determinants (epitopes) of the glycoprotein (G) of infectious hematopoietic necrosis virus was made by expressing different regions of the G gene in Escherichia coli. A cDNA copy of the G gene was divided into four fragments by TaqI digestion, and the fragments were subcloned into pATH vectors, placing the expression of each G gene fragment under control of the trpE promoter. The resulting plasmids, pXL2, pXL3, and pXL7, encoded trpE-G fusion proteins subsequently detected with anti-infectious hematopoietic necrosis virus sera by Western immunoblots. A comparison of reactivities of the fusion proteins encoded by these plasmids was made by Western immunoblot and radioimmunoassay with a number of anti-G specific monoclonal antibodies (MAbs). The nonneutralizing MAb 136J reacted with the trpE-G fusion protein encoded by pXL3 and fusion proteins encoded by plasmids p52G and p618G, which were described in previous studies (R. D. Gilmore, Jr., H. M. Engelking, D. S. Manning, and J. C. Leong. Bio/Technology 6:295-300, 1988). Another nonneutralizing MAb, 2F, bound to the pXL3 fusion protein, and the neutralizing MAb RB/B5 recognized the pXL7 fusion protein. All fusion proteins were tested as vaccines in rainbow trout fry. Although significant protection was induced by all fusion proteins, the pXL3 fusion protein was most effective as a vaccine.

Molecular cloning of the mRNA coding for the G protein of the viral haemorrhagic septicaemia (VHS) of salmonids

Viral haemorrhagic septicaemia virus (VHSV), a rhabdovirus, is a major threat for continental European trout fish farming. The development of a recombinant subunit vaccine could solve that problem. The neutralizing epitopes are located on the glycoprotein or G protein, the surface antigen. The G protein has a molecular weight of 65 kDa, reduced to 55 kDa by deglycosylation. cDNA was synthetized from mRNA of VHS virus infected cells, and cloned in E. coli. The viral cDNA was recognized by positive hybridization with a labelled probe made from infected cell RNA, and negative hybridization with labelled cDNA made from cellular RNA. The Northern blot hybridization with different clones on VHS infected cell RNA revealed two VHS mRNA whose lengths, 2.0 and 1.5 kb, were compatible with the mRNA length for G and N proteins respectively. This mRNA must contain about 400 bp of untranslated sequence.

Expression of the glycoprotein gene from a fish rhabdovirus by using baculovirus vectors

A cDNA fragment containing the gene encoding the glycoprotein of infectious hematopoietic necrosis virus was inserted into Autographa californica baculovirus vectors under the control of the polyhedrin promoter. A 66-kilodalton protein, identical in size to the glycosylated glycoprotein of infectious hematopoietic necrosis virus, was expressed at high levels in Spodoptera frugiperda cells infected with the recombinant viruses. The expressed protein reacted with antiserum to the glycoprotein on Western blots (immunoblots).

Nucleotide sequence of a cDNA clone carrying the glycoprotein gene of infectious hematopoietic necrosis virus, a fish rhabdovirus

The nucleotide sequence of the mRNA encoding the glycoprotein of infectious hematopoietic necrosis virus was determined from a cDNA clone containing the entire coding region. The G-protein cDNA is 1,609 nucleotides long (excluding the polyadenylic acid) and encodes a protein of 508 amino acids. The predicted amino acid sequence was compared with that of the glycoprotein of the Indiana and New Jersey serotypes of vesicular stomatitis virus and with the glycoprotein of rabies virus, using a computer program which determined optimal alignment. An amino acid identity of approximately 20% was found between infectious hematopoietic necrosis virus and the two vesicular stomatitis virus serotypes and between infectious hematopoietic necrosis virus and rabies virus. The positions and sizes of the signal sequence and transmembrane domain and the possible glycosylation sites were determined.

Molecular cloning of the six mRNA species of infectious hematopoietic necrosis virus, a fish rhabdovirus, and gene order determination by R-loop mapping

Plasmids carrying cDNA sequences to the mRNA species of infectious hematopoietic necrosis virus were constructed and cloned into Escherichia coli. Characterization of 21 cloned plasmids by hybridization to mRNA blots identified sets of plasmids with homology to each of the six viral mRNA species. R-loop mapping with these cDNA plasmids determined that the gene order on the infectious hematopoietic necrosis virus genome is (3')N-M1-M2-G-NV-L(5').

Characterization of infectious hematopoietic necrosis virus mRNA species reveals a nonvirion rhabdovirus protein

The genome RNA and six mRNA species of infectious hematopoietic necrosis virus were analyzed by denaturing gel electrophoresis. The following molecular weights were determined: genome RNA, 3.7 X 10(6); mRNA 1, 2.26 X 10(6); mRNA 2, 5.63 X 10(5); mRNA 3, 4.84 X 10(5); mRNA 4 (containing two different mRNA species), 3.00 X 10(5); and mRNA 5, 1.95 X 10(5). Densitometer analyses of gels were used to calculate the molar ratios of the intracellular mRNA species: mRNA 1, 0.02; mRNA 2, 0.49; mRNA 3, 1.0; mRNA 4, 2.52; and mRNA 5, 0.41. Hybrid selection studies determined the mRNA coding assignments as follows: mRNA 1 encodes the viral polymerase, L; mRNA 2 encodes the glycoprotein, G; mRNA 3 encodes the nucleocapsid protein, N; mRNA 4 is composed of two comigrating mRNA species which encode the matrix proteins, M1 and M2; and mRNA 5 encodes a previously unrecognized viral protein which is induced in infected cells but is not present in mature virions. This nonvirion protein has been designated the NV protein.

Adsorption to fish sperm of vertically transmitted fish viruses

More than 99 percent of a vertically transmitted fish rhabdovirus, infectious hematopoietic necrosis virus, was removed from suspension in less than 1 minute by adsorption to the surface membrane of sperm from two genera of salmonid fishes. The vertically transmitted, infectious pancreatic necrosis virus adsorbed to a lesser degree, but no adsorption occurred with a second fish rhabdovirus that is not vertically transmitted. Such adsorption may be involved in vertical transmission of these viruses.

The viral diseases of fish: a review through 1978. Part 1: Diseases of proven viral etiology

In this review, a survey is made of the published literature on the viral diseases of fish available up to and including the year 1978. It is divided into two main sections. Part 1 describes 11 diseases where a virus has been isolated and proven to be the causative agent. Part 2 discusses 16 diseases where there is reason to suspect viral etiology because of evidence deriving from electron microscopy or transmission experiments with bacteria-free filtrates of homogenates of diseased tissue, but where final proof of a causative relationship is lacking. The review attempts to provide the most significant information on the disease process itself, in most cases including external signs, fish species susceptible, pathology, geographic distribution, existence of carriers, methods of transmission, and control. It also gives the most recent and significant data concerning the nature of the causative virus, including its cultural, biological, and physicochemical properties, where such information is available.

Proteins of vesicular stomatitis virus. V. Identification of a precursor to the phosphoprotein of Piry virus

A metabolic precursor to the major phosphoprotein of Piry virus (NSv) has been identified in extracts of Piry virus-infected L cells. The conversion of the precursor NSi to NSv occurs with a half-life of 20 min and is independent of continued protein synthesis. NSi has a greater electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis than does the product NSv, suggesting an increase in molecular weight during maturation. The conversion is unaffected by cyclic AMP, cyclic GMP, or by theophilline and cordycepin. No decrease in isoelectric point of NSv relative to NSi was observed on isoelectric focusing acrylamide gels. These latter observations suggest that NSi and NSv do not differ in extent of phosphorylation. We also report, without further characterization, the identification of another phosphoprotein in Piry virus-infected cells having an electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis just slightly greater than the nucleocapsid N protein.

Spring viremia of carp virus RNA and virion-associated transcriptase activity

An RNA-dependent RNA polymerase activity has been demonstrated for spring viremia of carp virus (SVCV). The optimal temperature for in vitro synthesis of RNA was 20 to 25 degrees C. The SVCV enzyme activity was stimulated when the methyl donor S-adenosyl-L-methionine was included in the reaction mixture. S-adenosyl-L-methionine was not particularly effective in stimulating the virion RNA polymerase activity of vesicular stomatitis virus or pike fry rhabdovirus. The 5' nucleotide of the SVCV viral RNA is pppAp.

Virion RNA polymerases of two salmonid rhabdoviruses

RNA-dependent RNA polymerases were found to be associated with two salmonid rhabdoviruses: infectious hematopoietic necrosis (IHN) virus and the virus of hemorrhagic septicemia (VHS). The protein composition of these rhabdoviruses closely resembles that of rabies virus rather than that of vesicular stomatitis virus (McAllister and Wagner, 1975). The optimal temperature for in vitro transcription was found to be approximately 18 degrees C for IHN virus and approximately 15 degrees for VHS,, closely approximating optimal temperatures for growth of these viruses in salmonid cells. Unlike vesicular stomatitis virus, manganese ion (1 mM) could be used as a divalent cation substitute for magnesium ion (5 mM). The in vitro transcription products of IHN and VHS viruses hybridized completely to the homologous genome but not at all to the heterologous genome.

Structural proteins of La Crosse virus

Preparations of La Crosse virus, a member of the California encephalitis group of bunyaviruses, were found to possess three major virion proteins. Two of the proteins were glycosylated (G1 and G2) and were located on the surface of the virus particles. These two glycoproteins were present in equimolar amounts and possessed apparent molecular weights of 120 X 10(3) and 34 X 10(3). Virion nucleocapsids, isolated by a nonionic detergent and salt treatment, contained another major protein, N (molecular weight = 23 X 10(3)). A large, but minor, protein species L (molecular weight = 180 X 10(3)) was also found in virus preparations. The approximate number of protein molecules per virion has been determined. Electron microscopy of purified La Crosse virus indicated that the virus particle (mean diameter, 91 nm) is enveloped and possesses irregular surface projections (length, 10 nm).

Comparative membrane microviscosity of fish and mammalian rhabdoviruses studied by fluorescence depolarization

The microviscosity of the hydrophobic region of the membrane of infectious hematopoietic necrosis virus was determined using fluorescence depolarization analysis of the probe 1,6-diphenyl-1,3,5-hexatriene and was found to be much lower at 37 C than that of another rhabdovirus, vesicular stomatitis virus. However, the microviscosity of this fish virus at 18 C, the temperature at which it was grown, corresponded to the microviscosity of vesicular stomatitis virus at 37 C. Data obtained with the fish virus host cell (chinook salmon embryo cells) grown at 18 C suggest that its membranes have a lower microviscosity than either L-929 or BHK-21 cells (the vesicular stomatitis virus host cells) grown at 37 C.