Kinetics of UV(254) inactivation of selected viral pathogens in a static system.

AIMS: The objective of this study was to estimate UV(254) inactivation constants for four viral pathogens: influenza virus type A, porcine respiratory and reproductive syndrome virus (PRRSV), bovine viral diarrhoea virus (BVDV) and reovirus. METHODS AND RESULTS: Viruses in culture medium were exposed to one of nine doses of UV(254) and then titrated for infectious virus. Analysis showed that viral inactivation by UV(254) was more accurately described by a two-stage inactivation model vs a standard one-stage inactivation model. CONCLUSIONS: The results provided evidence for the existence of two heterogeneous viral subpopulations among the viruses tested, one highly susceptible to UV(254) inactivation and the other more resistant. Importantly, inactivation constants based on the one-stage inactivation model would have underestimated the UV(254) dose required for the inactivation of these viruses under the conditions of the experiment. SIGNIFICANCE AND IMPACT OF THE STUDY: To improve the accuracy of estimates, it is recommended that research involving the inactivation of micro-organisms evaluates inactivation kinetics using both one-stage and two-stage models. These results will be of interest to persons responsible for microbial agents under laboratory or field conditions.

Identification of two novel interferon-stimulated genes from cultured CAB cells induced by UV-inactivated grass carp hemorrhage virus.

Interferon (IFN) exerts its antiviral effect by inducing the expression of a number of IFN-stimulated genes (ISGs) to establish a host antiviral state. Earlier studies identified some important fish IFN system genes from IFN-induced CAB cells (crucian carp Carassius auratus L. embryonic blastulae cells) after treatment with UV-inactivated GCHV (grass carp hemorrhage virus). Herein, the cloning of 2 novel IFN-stimulated genes, termed Gig1 and Gig2, is described for the same cell system. The complete cDNA sequences of Gig1 and Gig2 contain 1244 bp encoding for a 194-amino-acid protein and 693 bp for a 158-amino-acid protein, respectively. A search of public databases revealed that these are 2 novel IFN-stimulated genes, since neither significant homologous genes nor conserved motifs were identified. Active GCHV, UV-inactivated GCHV and CAB IFN-containing supernatant (ICS) induced transcription of these genes and distinct kinetics were observed. An analysis of differences in expression between the 2 genes and the IFN signal factors CaSTAT1 and CaIRF7 indicated that GCHV infection activated different signal pathways for their up-regulation. Upon virus infection, the transcription of Gig1 but not of Gig2 is strongly suppressed by cycloheximide (CHX). In contrast, following treatment with CAB IFN-containing supernatant, CHX does not inhibit either gene transcription. The results suggest that GCHV infection can induce expression of both Gig1 and Gig2 via newly synthesized CAB IFN, most probably through the JAK-STAT signal pathway, and can also directly activate Gig2 transcription without ongoing protein synthesis.

Molecular characterization and IFN signal pathway analysis of Carassius auratus CaSTAT1 identified from the cultured cells in response to virus infection.

Type I interferon (IFN) exerts its pleiotropic effects mainly through the JAK-STAT signaling pathway, which is presently best described in mammals. By subtractive suppression hybridization, two fish signaling factors, JAK1 and STAT1, had been identified in the IFN-induced crucian carp Carassius auratus L. blastulae embryonic (CAB) cells after treatment with UV-inactivated grass carp hemorrhagic virus (GCHV). Further, the full-length cDNA of STAT1, termed CaSTAT1, was obtained. It contains 2926 bp and encodes a protein of 718 aa. CaSTAT1 is most similar to rat STAT1 with 59% identity overall and displays all highly conserved domains that the STAT family possesses. Like human STAT1beta, it lacks the C-terminus acting as transcriptional activation domain in mammals. By contrast, only a single transcript was detected in virus-induced CAB cells. Expression analysis showed that CaSTAT1 could be activated by stimulation of CAB cells with poly I:C, active GCHV, UV-inactivated GCHV or CAB IFN, and displayed diverse expression patterns similar to that of mammalian STAT1. Additionally, the expression of an antiviral gene CaMx1 was also induced under the same conditions, and expression difference between CaSTAT1 and CaMx1 was revealed by induction of CAB IFN. These results provide molecular evidence supporting the notion that the fish IFN signaling transduction pathway is similar to that in mammals. Fish IFN exerts its multiple functions, at least antiviral action, through a JAK-STAT pathway.

Identification and expression analysis of two IFN-inducible genes in crucian carp (Carassius auratus L.).

Interferon (IFN) exerts its antiviral effects mainly through activation of a subset of IFN-stimulated genes (ISG), but relatively few of fish ISGs have been isolated and characterized so far. Here, we report two fish ISGs, termed CaIFI58 and CaIFI56, cloned from a subtractive cDNA library constructed with mRNAs obtained from crucian carp (Carassius auratus L.) blastulae embryonic (CAB) cells infected by UV-inactivated GCHV and mock-infected cells. Database search revealed that both ISGs had a high-level homology with all members of a well conserved gene family with multiple tetratricopeptide repeat (TPR) motifs, including human IFI60, IFI58, IFI56, IFI54 and their homologues in some other mammalian species. The transcripts of CaIFI58 and CaIFI56 were undetectable in CAB cells but could be induced by active GCHV, UV-inactivated GCHV or CAB IFN. Analysis of expression difference between them and IFN signal factors, CaSTAT1 and CaIRF7, indicated that their transcriptions were mediated possibly through JAK-STAT signal pathway, which was further supported by the induction analysis in UV-inactivated GCHV infected, IFN-treated and untreated cells in the presence or absence of cycloheximide (CHX), a potent inhibitor of protein synthesis. In addition, a pufferfish (Fugu rubrides) DNA sequence representing putative FrIFI56 was also revealed when CaIFI58 and CaIFI56 were used to search the pufferfish genome database. Phylogenetic analysis showed that these fish ISGs form a unique clad independent of mammalian homologues, reflecting a distant evolutionary relationship from mammals. These studies identified the first teleost IFI56 and IFI58 orthologues.

Channel catfish reovirus (CRV) inhibits replication of channel catfish herpesvirus (CCV) by two distinct mechanisms: viral interference and induction of an anti-viral factor.

Catfish reovirus (CRV), a double stranded RNA virus, inhibited channel catfish herpes-virus (CCV) replication by 2 different mechanisms: (1) directly as a consequence of its own replication, and (2) indirectly due to the induction of an anti-viral factor. In the former, prior infection with CRV significantly reduced subsequent CCV protein synthesis and virus yield. CRV mediated-interference was greatest when CRV infection preceded CCV infection by 16 h, and was least when cell cultures were simultaneously infected with both viruses. in the latter case, the infection of channel catfish ovary (CCO) cultures with UV-inactivated CRV resulted in the synthesis (or release) of an anti-viral factor. Cells producing the factor were protected from CCV infection, as were cells which had been treated with spent culture medium containing anti-viral activity. Interestingly an anti-viral activity was constitutively present in long-term cultures of catfish T-cells and macrophages. Whether this factor and the one induced by UV-inactivated CRV are identical is not known, but analogy to mammalian systems suggests that the former may be similar to type II interferon, whereas the latter may be the piscine equivalent of type I interferon. These results suggest that UV-inactivated CRV may prove useful in the induction and characterization of interferon-like anti-viral proteins in the channel catfish and that long-term cultures of catfish T-cells and monocytes may serve as a ready source of additional anti-viral factors.

Molecular and functional characterization of turkey interferon.

The turkey interferon (TkIFN) gene encodes a signal peptide and a mature protein of 30 and 162 amino acids, respectively. TkIFN mRNA expression was induced by reoviral double-stranded RNA in fibroblasts. The recombinant TkIFN protein possessed species-specific antiviral activity and in synergy with lipopolysaccharide (LPS) induced bone marrow macrophages to produce nitric oxide (NO). LPS or TkIFN alone did not induce bone marrow macrophages to produce significant amounts of NO, which showed that TkIFN provided one of the two signals necessary to induce NO production in turkey macrophages. Unlike the anti-inflammatory nature of mammalian alpha/beta IFNs, TkIFN augmented the LPS-induced expression of interleukin-8, a proinflammatory cytokine. This finding suggests a role for TkIFN in inflammatory conditions.

Differences in the capacity of reovirus strains to induce apoptosis are determined by the viral attachment protein sigma 1.

Reoviruses are important models for studies of viral pathogenesis; however, the mechanisms by which these viruses produce cytopathic effects in infected cells have not been defined. In this report, we show that murine L929 (L) cells infected with prototype reovirus strains type 1 Lang (TIL) and type 3 Dearing (T3D) undergo apoptosis and that T3D induces apoptosis to a substantially greater extent than T1L. Using T1L x T3D reassortant viruses, we found that differences in the capacity of T1L and T3D to induce apoptosis are determined by the viral S1 gene segment, which encodes the viral attachment protein sigma 1 and the non-virion-associated protein sigma 1s. Apoptosis was induced by UV-inactivated, replication-incompetent reovirus virions, which do not contain sigma 1s and do not mediate its synthesis in infected cells. Additionally, T3D-induced apoptosis was inhibited by anti-reovirus monoclonal antibodies that inhibit T3D cell attachment and disassembly. These results indicate that sigma 1, rather than sigma 1s, is required for induction of apoptosis by the reovirus and suggest that interaction of virions with cell surface receptors is an essential step in this mechanism of cell killing.

Immunogenicity of bluetongue virus inactivated by gamma irradiation.

The immunogenicity of vaccines prepared from bluetongue viruses inactivated by gamma irradiation was tested by their ability to stimulate the production of neutralizing antibody in mice. Antibody titres induced by monovalent and polyvalent vaccines, vaccines prepared from virus produced in mice and cell cultures and vaccines containing virus exposed to six, eight and ten megarads of irradiation indicated that immunogenicity was not adversely affected by the inactivation procedure. The results suggest that gamma irradiation would be an effective means of inactivating bluetongue virus without affecting antigenic determinants for neutralizing antibody.

Immunologic tolerance after oral administration of reovirus: requirement for two viral gene products for tolerance induction.

We have demonstrated that reovirus type 1, but not type 3, generates serotype-specific immunologic tolerance for DTH responses following oral administration of UV-inactivated virus. As shown by adoptive transfer experiments, the tolerance is secondary to the generation of viral-specific suppressor T cells that are present in spleen and mesenteric lymph nodes. No tolerance was generated when live virus was administered orally. Using recombinant viral clones, it was found that 2 viral gene products were required for tolerance induction; serotype specificity is a property of the viral hemagglutinin (the product of the S1 dsRNA segment). The inability of type 3 reovirus to induce suppression following oral administration is a property of the mu 1C polypeptide (the product of the M2 dsRNA genome segment).

Reovirus inhibition of cellular DNA synthesis: role of the S1 gene.

Type 3 reovirus inhibits L cell DNA synthesis, whereas type 1 reovirus exerts little or no effect on L cell DNA synthesis. By using recombinant viruses containing both type 1 and type 3 double-standard RNA segments, we determined that one double-stranded RNA segment, the reovirus type 3 S1 double-stranded RNA segment which encodes the viral hemagglutinin, segregates with and is responsible for the capacity of reovirus type 3 to inhibit L cell DNA synthesis.

Interferon induction by viruses. VI. Reovirus: virion genome dsRNA as the interferon inducer in aged chick embryo cells.

The interferon-inducing particle (IFP) activity of avian and human reoviruses in aged chick embryo cells was determined by analyzing dose (multiplicity)-response (interferon yield) curves. These curves fit best a model in which each cell infected with greater than or equal to 1 IFP produces a quantum yield of interferon. Avian reovirus stocks contained as many as 60 times more IFP than plaque-forming particles (PFP). Upon UV-irradiation the ratio of IFP:PFP became 197, suggesting that virtually every physical particle of avian reovirus could function as an interferon-inducing particle. Thus, about one-third of the non-infectious particles were intrinsically IFP and the other two-thirds could be converted to IFP status at an optimal dose of UV radiation, the equivalent of 9.4 lethal hits, i.e., 8000 ergs/mm2. UV-irradiated avian reovirus induced about twice the usual yield of interferon on a per cell basis. Wildtype human reovirus (type 3) and mutants ts201(A,RNA+) and ts447(C,RNA-) were excellent inducers of interferon, but only about 1 in 3 infectious particles functioned as an interferon-inducing particle, meaning that virtually all physical particles failed to function as IFP, UV-irradiation of human reoviruses resulted in a slight loss of IFP activity. Our data support the hypothesis that virion genome dsRNA constitutes the interferon inducer moiety of avian reoviruses and that in its permissive host cell the processing of genome dsRNA from most particles to a putative recognition site in the cytoplasm occurs naturally with a high probability. For human reovirus this is a much rarer event which may be intrinsic only to infectious virus, and may require limited transcription for expression. The sensitivity of the avian reovirus-aged chick embryo cell system recommends it for further study on the mechanism of interferon induction by virions containing pre-existing dsRNA.

Photochemical cross-linking of reovirus genome RNA in situ and inactivation of viral transcriptase.

Reovirus infectivity and core-associated RNA polymerase activity were decreased by irradiation with long wavelength ultraviolet light in the presence of the 4'-substituted psoralen derivatives, 4'-aminomethyl-4,5',8-trimethylpsoralen and 4'-hydroxymethyl-4,5',8-trimethylpsoralen. Monoadduct formation occurred after photoreaction with low psoralen concentrations or brief irradiation times, and the presence of KCl or magnesium acetate had a protective effect. Under the mild reaction conditions in which 1 molecule of 4'-aminomethyl-4,5',8-trimethylpsoralen was bound covalently per 160 to 290 base-pairs, the polymerase activity was decreased by greater than 90%. At higher drug concentrations or longer times of photoreaction of reovirus cores, the viral RNA was extensively cross-linked indicating that the reovirus genome in situ is double-stranded.

The preferential cytotoxicity of reovirus for certain transformed cell lines.

The susceptibility of a variety of cell lines of different mammalian origin to cytotoxic (CT) induction by either ultraviolet light-irradiated reovirus type 2 (UVR2) or viable reovirus type 2 plus the protein synthesis inhibitor, cycloheximide, was examined. The following groups of cells were found to be susceptible to CT-induction: certain tumor cells and spontaneously transformed cell lines of human origin and certain virally and spontaneously transformed cell lines of murine origin. The following groups of cells were found to be resistant: normal human diploid cell lines, primary and continuous cell cultures of subhuman primates, primary mouse cells, normal rat kidney cells and baby hamster kidney cells. Susceptibility to CT-induction could not be related to the adsorption of virus to cells, nor to the capacity of the cell to support virus replication.

Effect of polycations on the early stages of reovirus infection.

The polycation DEAE-dextran treatment of HeLa cells was found to interfere with the production of reovirus, appearance of viral cytopathology, and the induction of cytotoxicity by UV-irradiated reovirus. The data obtained showed that while the polycation pre-treatment of cells enhanced virus adsorption to cells, its addition early during virus adsorption or 2 h after infection markedly interfered with virus production. The interference was decreasingly effective when the polycation was added during the later stages of the infectious cycle. Isopycnic CsCl buoyant density ultracentrifugation analyses of infected cytoplasmic extracts revealed that there were more subviral particles formed in untreated infected cells than there were in polycation-treated cells. In vitro uncoating studies with infected cytoplasmic extracts indicated that the polycation did not interfere with the removal of the outer capsid structure of the complete virus, and uncoating occurred only in the presence of the polycation. Electron microscopical examination revealed significantly fewer virus particles present in polycation-treated infected cells. The accumulated data strongly indicate that interference by DEAE-dextran is an early event involving viral penetration. Corollary studies using other polycations, such as polybrene (hexadimethrine bromide and poly-l-lysine, revealed that while they also enhanced virus adsorption, they did not interfere with reovirus production, appearance of viral cytopathology, and the induction of cytotoxicity by UV-irradiated reovirus.

Comparison of the sensitivity to ultraviolet irradiation of reovirus 3 and some viruses of the Kemerovo group.

The kinetics of UV inactivation of the tick-borne Kemerovo (strain R-10) and Lipovnik (strain Lip-91) viruses which have been preliminarily classified as possible members of the Reovirus group was examined. Reovirus 3 and Sindbis virus served as reference double-stranded RNA and single-stranded RNA viruses, respectively. The parameters of UV inresembled those of Reovirus 3. This is consistent with their tentative classification as reovirus-like viruses.