A nested set of eight RNAs is formed in macrophages infected with lactate dehydrogenase-elevating virus

Dynamics of Feline Coronavirus and FIP: A Compartmental Modeling Approach

The investigation of infectious agents invading human and nonhuman populations represents a rich research domain within the framework of mathematical biology, captivating the interest of scientists across various disciplines. In this work, we examine the endemic equilibrium of feline coronavirus and feline infectious peritonitis by using a modified susceptible-infected-susceptible epidemiological model. We incorporate the concept of mutations from FCoV to FIP to enrich our analysis. We establish that the model, when subjected to reasonable parameter ranges, supports an endemic equilibrium wherein the FCoV group dominates. To demonstrate the stability of the equilibria under typical parameters and initial conditions, we employ the model SCF presented by Dobie in 2022 (Dobie, 2022). We ascertain that the equilibrium values reside within the interior domains of stability. Additionally, we displayed perturbed solutions to enhance our understanding. Remarkably, our findings align qualitatively with existing literature, which reports the prevalence of seropositivity to FCoV among stray cats (Tekelioglu et al. 2015, Oğuzoğlu et al. 2010, Pratelli 2008, Arshad et al. 2004).

Identification of the RNA Pseudoknot within the 3' End of the Porcine Reproductive and Respiratory Syndrome Virus Genome as a Pathogen-Associated Molecular Pattern To Activate Antiviral Signaling via RIG-I and Toll-Like Receptor 3

Once infected by viruses, cells can detect pathogen-associated molecular patterns (PAMPs) on viral nucleic acid by host pattern recognition receptors (PRRs) to initiate the antiviral response. Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of porcine reproductive and respiratory syndrome (PRRS), characterized by reproductive failure in sows and respiratory diseases in pigs of different ages. To date, the sensing mechanism of PRRSV has not been elucidated. Here, we reported that the pseudoknot region residing in the 3' untranslated regions (UTR) of the PRRSV genome, which has been proposed to regulate RNA synthesis and virus replication, was sensed as nonself by retinoic acid-inducible gene I (RIG-I) and Toll-like receptor 3 (TLR3) and strongly induced type I interferons (IFNs) and interferon-stimulated genes (ISGs) in porcine alveolar macrophages (PAMs). The interaction between the two stem-loops inside the pseudoknot structure was sufficient for IFN induction, since disruption of the pseudoknot interaction powerfully dampened the IFN induction. Furthermore, transfection of the 3' UTR pseudoknot transcripts in PAMs inhibited PRRSV replication in vitro Importantly, the predicted similar structures of other arterivirus members, including equine arteritis virus (EAV), lactate dehydrogenase-elevating virus (LDV), and simian hemorrhagic fever virus (SHFV), also displayed strong IFN induction activities. Together, in this work we identified an innate recognition mechanism by which the PRRSV 3' UTR pseudoknot region served as PAMPs of arteriviruses and activated innate immune signaling to produce IFNs that inhibit virus replication. All of these results provide novel insights into innate immune recognition during virus infection.IMPORTANCE PRRS is the most common viral disease in the pork industry. It is caused by PRRSV, a positive single-stranded RNA virus, whose infection often leads to persistent infection. To date, it is not yet clear how PRRSV is recognized by the host and what is the exact mechanism of IFN induction. Here, we investigated the nature of PAMPs on PRRSV and the associated PRRs. We found that the 3' UTR pseudoknot region of PRRSV, which has been proposed to regulate viral RNA synthesis, could act as PAMPs recognized by RIG-I and TLR3 to induce type I IFN production to suppress PRRSV infection. This report is the first detailed description of pattern recognition for PRRSV, which is important in understanding the antiviral response of arteriviruses, especially PRRSV, and extends our knowledge on virus recognition.

Disulfide linkages mediating nucleocapsid protein dimerization are not required for porcine arterivirus infectivity

The nucleocapsid (N) proteins of the North American (type II) and European (type I) genotypes of porcine reproductive and respiratory syndrome virus (PRRSV) share only approximately 60% genetic identity, and the functionality of N in both genotypes, especially its role in virion assembly, is still poorly understood. In this study, we demonstrated that the ORF7 3' untranslated region or ORF7 of type I is functional in the type II PRRSV background. Based on these results, we postulated that the cysteine at position 90 (Cys90) of the type II N protein, which corresponds to an alanine in the type I protein, is nonessential for virus infectivity. The replacement of Cys90 with alanine confirmed this hypothesis. We then hypothesized that all of the cysteines in the N protein could be replaced by alanines. Mutational analysis revealed that, in contradiction to previously reported findings, the replacement of all of the cysteines, either singly or in combination, did not impair the growth of either type II or type I PRRSV. Treatment with the alkylating agent N-ethylmaleimide inhibited cysteine-mediated N dimerization in living cells but not in released virions. Additionally, bimolecular fluorescence complementation assays revealed noncovalent interactions in living cells among the N and C termini and between the N-terminal and C-terminal regions of the N proteins of both genotypes of PRRSV. These results demonstrate that the disulfide linkages mediating the N dimerization are not required for PRRSV viability and help to promote our understanding of the mechanism underlying arterivirus particle assembly.

RNA interference protects horse cells in vitro from infection with Equine Arteritis Virus

Equine Arteritis Virus (EAV) belongs to the Arteriviridae and causes viral arteritis in horses. In an attempt to develop novel and save therapies against the infection it was tested whether EAV is susceptible to RNA interference (RNAi) in an equine in vitro system. Horse cells were transfected with chemically synthesized small interfering RNA oligonucleotides (siRNAs) and challenged with EAV. Application of these siRNAs led to a significant protection of the cells, and virus titers decreased drastically. siRNAs derived from DNA plasmids expressing small hairpin RNAs (shRNAs) were also effective. The protection was most pronounced with two siRNAs targeting the open reading frame 1 (coding for non-structural proteins), whereas siRNAs targeting sequences for several structural proteins had less or no effect. In addition, it was investigated whether RNAi could be used to treat cells with an already established viral infection. Only application of the siRNAs shortly after viral challenge led to significant survival rates of the cells, whereas transfection at later time points caused much less benefit for the cells. These findings are discussed in a perspective of using RNAi as a therapeutic approach to combat EAV.

A DNA-launched reverse genetics system for porcine reproductive and respiratory syndrome virus reveals that homodimerization of the nucleocapsid protein is essential for virus infectivity

Reverse genetic systems were developed for a highly virulent 'atypical' porcine reproductive and respiratory syndrome virus (PRRSV). The full-length genome of 15395 nucleotides was assembled as a single cDNA clone and placed under either the prokaryotic T7 or eukaryotic CMV promoter. Transfection of cells with the RNA transcripts or the DNA clone induced cytopathic effects and produced infectious progeny. The reconstituted virus was stable and grew to the titer of the parental virus in cells. Upon infection, pigs produced clinical signs and lung pathology typical for PRRSV and induced viremia and specific antibodies. Previously, we showed that the PRRSV nucleocapsid (N) protein forms homodimers via both noncovalent and covalent interactions and that cysteine at position 23 is responsible for the covalent interaction. The functional significance of cysteines of N for PRRSV infectivity was assessed using the infectious cDNA clone. Each cysteine of N at positions 23, 75, and 90 was replaced with serine and the individual mutation was incorporated into the cDNA clone such that three independent cysteine mutants were constructed. When transfected, the wild type and C75S clones induced cytopathic effects and produced infectious virus with indistinguishable plaque morphology. In contrast, the C23S mutation completely abolished infectivity of the clone, indicating that C23-mediated N protein homodimerization plays a critical role in PRRSV infectivity. Unexpectedly, the C90S mutation also appeared to be lethal for virus infectivity. Genome replication and mRNA transcription were both positive for the replication-defective C23S and C90S mutants. The data suggest that, in addition to homodimerization, the PRRSV N protein may also undergo heterodimerization with another structural protein using cysteine 90 and that the N protein heterodimerization is essential for PRRSV infectivity.

Detection of bovine torovirus and other enteric pathogens in feces from diarrhea cases in cattle

The objectives of this study were to determine the prevalence of bovine torovirus (BoTV) in bovine fecal samples from diarrhea cases submitted to the Ohio Animal Disease Diagnostic Laboratory (ADDL) and to assess if a relationship exists between BoTV and the other enteric pathogens detected. From November 1999 to May 2001, 259 specimens from 53 calves (< or = 6 months old), 27 young adults (52 years), 125 adults (> or = 2 years), and 54 animals of unknown age were examined by an antigen-capture enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) assay developed to detect BoTV. Testing for other enteric pathogens was performed by ADDL, and the results were analyzed with the BoTV data. The BoTV was detected using ELISA or RT-PCR in 9.7% (25/259) of the clinical samples, 56% (14/25) of which were from calves (P < 0.001) representing 26.4% (14/53) of the calves tested. Of the BoTV-positive calves, 71% (10/14) were less than 3 weeks of age. In 11/25 positive specimens, BoTV was the only pathogen detected among those examined. Other enteric organisms detected alone or in combination with BoTV in calf samples were rotavirus, coronavirus, Salmonella spp., Cryptosporidium spp., and Giardia spp.; but no consistent association between BoTV and these organisms was observed. In summary, BoTV was detected in fecal samples from cattle with diarrhea, principally in young calves less than 3 weeks of age. Future studies of infectious diarrhea in cattle should also include assays for this etiologic agent.

Production, characterization, and uses of monoclonal antibodies against porcine reproductive and respiratory syndrome virus 3' untranslated region and nucleoprotein RNA binding proteins

Previous studies in our laboratory of interactions between the 3' untranslated region of porcine reproductive and respiratory syndrome virus (PRRSV) and MARC 145 cell cytoplasmic proteins have identified 11 RNA binding proteins. Here, we report the production and characterization of monoclonal antibodies (MAbs) against a 67-kD RNA binding protein of MARC 145 tissue cultured cells. Of the MAbs produced, 11 were reactive in ELISA with 67-kD protein. Immunoprecipitation tests showed that six clones precipitated a protein of 67 kD, and one clone recognized a multiple protein bands of 45, 37, and 27 kD. Western blotting showed that these clones detected two proteins of 67 and 55 kD. Indirect fluorescent antibody staining of testing of PRRSV-infected cells with these MAbs revealed diffuse cytoplasmic staining and intense perinuclear staining to one side of the nucleus. The presence of the double membrane vesicles in the same region in PRRSV-infected alveolar macrophages suggests that these RNA binding proteins might have a role in their formation.

Genetic variation in the PRRS virus

Porcine reproductive and respiratory syndrome (PRRS) is characterized by late-term abortions and stillbirths in sows and respiratory difficulties in nursery pigs. The disease appeared in Europe and North America at approximately the same time between 1985 and 1990. The PRRS virus was isolated shortly thereafter and demonstrated unexpectedly profound differences between European (Lelystad) and North American (VR2332) isolates as measured by serological crossreactivity and nucleotide sequence similarity. In order to determine the amount of genetic variation in the PRRS virus and to understand the molecular mechanisms of viral evolution, nucleotide sequences of PRRS virus strains were determined. Comparisons among ten U.S. strains showed that variation in primary nucleotide sequence between isolates ranged from 2.5% to 7.9% for ORFs 2-7. In contrast, Lelystad virus was, on average, 35% different from US clones. These results provided direct molecular evidence that US and European PRRSV isolates represented genetically distinct groups of the same viral family. A further analysis of more than 150 isolates in the United States and Canada demonstrated that the PRRS virus in North America represents a single large and diverse genetic group that is distinct from European forms of the virus.

Porcine reproductive and respiratory syndrome

In 1987, porcine reproductive and respiratory syndrome (PRRS) was recognized in the USA as a new disease of swine causing late-term reproductive failure and severe pneumonia in neonatal pigs. The syndrome is caused by an RNA virus referred to as PRRS virus (PRRSV), which is classified in the family Arteriviridae. Swine macrophages are the only indigenous cell type known to support PRRSV replication. Direct contact between infected and naive pigs is the predominant route of PRRSV transmission. Exposure of a mucosal surface to PRRSV leads to virus replication in regional macrophages, a prolonged viremia and systemic distribution of virus to other macrophage populations. Reproductive failure induced by PRRSV infection in late-gestation sows is characterized by premature farrowing of stillborn, partially autolyzed, and mummified fetuses. Pneumonia caused by PRRSV infection is more severe in young pigs compared to adults and may be complicated by concurrent bacterial infections. Gross lung lesions associated with PRRSV infection vary from none to diffuse consolidation. In addition, multiple lymph nodes may be markedly enlarged. Microscopically, PRRSV-pneumonia is characterized by multifocal, interstitial thickening by macrophages and necrotic cell debris in alveoli. Other less common microscopic lesions of PRRSV infection include myocarditis, vasculitis, encephalitis, and lymphoid hypertrophy and hyperplasia. In acute or subacute PRRSV infections, serum and lung are the best specimens for diagnosis. Persistent PRRSV infections can be produced by transplacental or intranasal infection. Persistent PRRSV infections are an important factor for virus survival and transmission within a swine herd and will complicate control programs.

Posttranslational processing and identification of a neutralization domain of the GP4 protein encoded by ORF4 of Lelystad virus

GP4 is a minor structural glycoprotein encoded by ORF4 of Lelystad virus (LV). When it was immunoprecipitated from cell lysates and extracellular virus of CL2621 cells infected with LV, it was shown to have an apparent molecular mass of approximately 28 and 31 kDa, respectively. This difference in size occurred because its core N-glycans were modified to complex type N-glycans during the transport of the protein through the endoplasmic reticulum and Golgi compartment. A panel of 15 neutralizing monoclonal antibodies (MAbs) reacted with the native GP4 protein expressed by LV and the recombinant GP4 protein expressed in a Semliki Forest virus expression system. However, these MAbs did not react with the GP4 protein of U.S. isolate VR2332. To map the binding site of the MAbs, chimeric constructs composed of ORF4 of LV and VR2332 were generated. The reactivity of these constructs indicated that all the MAbs were directed against a region spanning amino acids 40 to 79 of the GP4 protein of LV. Six MAbs reacted with solid-phase synthetic dodecapeptides. The core of this site consists of amino acids 59 to 67 (SAAQEKISF). Comparison of the amino acid sequences of GP4 proteins from various European and North American isolates indicated that the neutralization domain spanning amino acids 40 to 79 is the most variable region of GP4. The neutralization domain of GP4, described here, is the first identified for LV.

Differential glycosylation of the ectodomain of the primary envelope glycoprotein of two strains of lactate dehydrogenase-elevating virus that differ in neuropathogenicity

ORF 5 encoding the primary envelope glycoprotein, VP-3P, of a highly neuropathogenic isolate of lactate dehydrogenase-elevating virus (LDV-v) has been sequenced. It exhibits 92% nucleotide identity with the ORF 5 of an LDV isolate that lacks neuropathogenicity, LDV-P, and the amino acid identities of the predicted VP-3Ps of the two strains is 90%. Most striking, however, is the absence in the ectodomain of LDV-v VP-3P of two out of three potential N-glycosylation sites present in the ectodomain of VP-3P of LDV-P. The ectodomain of VP-3P has been implicated to play an important role in host receptor interaction. VP-3P of another neuropathogenic LDV strain, LDV-C, lacks the same two N-glycosylation sites (Godeny et al., 1993). In vitro transcription/translation of the ORFs 5 of LDV-P and LDV-v indicated that all three N-glycosylation sites in the ectodomain of LDV-P VP-3P became glycosylated when synthesized in the presence of microsomal membranes, whereas the glycosylation of the ORF 5 proteins of LDV-v and LDV-C was consistent with glycosylation at a single site. No other biological differences between the neuropathogenic and non-neuropathogenic strains have been detected. They replicate with equal efficiency in mice and in primary macrophage cultures.

Detection of related positive-strand RNA virus genomes by reverse transcription/polymerase chain reaction using degenerate primers for common replicase sequences

A set of degenerate sense and antisense primers were designed on the basis of short segments with identical amino acids in the predicted ORF 1b replicase proteins of lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus, strain Lelystad virus (PRRSV-LV), which are members of a new group of positive-strand RNA viruses. Reverse transcription/polymerase chain reaction amplification using this set of degenerate primers yielded products of the expected size from the genomes of all three viruses. It also yielded a product of appropriate size from the genome of another strain of PRRSV (VR2332), the ORF 1b sequence of which is unknown, but the 3' end of the genome of which differs from that of the PRRSV-LV genome by about 50%. No products were generated from the genome of simian hemorrhagic fever virus (SHFV), another member of this virus group. However, an appropriate product was generated with a second set of degenerate primers which was designed from the same ORF 1b segments of LDV, EAV and PRRSV-LV as the first set but on the basis of human codon preferences. Sequence analysis showed that the amplified SHFV ORF 1b segment exhibited about 50% nucleotide identity with the corresponding segments of ORF 1b of LDV, EAV and PRRSV. The results show that these and other degenerate primer sets might be useful for the search of related viruses in other mammalian species.

Molecular characterization of the 3' terminus of the simian hemorrhagic fever virus genome

The 3' end of the simian hemorrhagic fever virus (SHFV) single-stranded RNA genome was cloned and sequenced. Adjacent to the 3' poly(A) tract, we identified a 76-nucleotide noncoding region preceded by two overlapping reading frames (ORFs). The ultimate 3' ORF of the viral genome encodes the capsid protein, and the penultimate ORF encodes the smallest SHFV envelope protein. These two ORFs overlap each other by 26 nucleotides. Northern (RNA) blot hybridization analyses of cytoplasmic RNA extracts from SHFV-infected MA-104 cells with gene-specific probes revealed the presence of full-length genomic RNA as well as six subgenomic SHFV-specific mRNA species. The subgenomic mRNAs are 3' coterminal. In its virion morphology and size, genome structure and length, and replication strategy, SHFV is most similar to lactate dehydrogenase-elevating virus, equine arteritis virus, and porcine reproductive and respiratory syndrome virus.

Infection of central nervous system cells by ecotropic murine leukemia virus in C58 and AKR mice and in in utero-infected CE/J mice predisposes mice to paralytic infection by lactate dehydrogenase-elevating virus

Certain mouse strains, such as AKR and C58, which possess N-tropic, ecotropic murine leukemia virus (MuLV) proviruses and are homozygous at the Fv-1n locus are specifically susceptible to paralytic infection (age-dependent poliomyelitis [ADPM]) by lactate dehydrogenase-elevating virus (LDV). Our results provide an explanation for this genetic linkage and directly prove that ecotropic MuLV infection of spinal cord cells is responsible for rendering anterior horn neurons susceptible to cytocidal LDV infection, which is the cause of the paralytic disease. Northern (RNA) blot hybridization of total tissue RNA and in situ hybridization of tissue sections demonstrated that only mice harboring central nervous system (CNS) cells that expressed ecotropic MuLV were susceptible to ADPM. Our evidence indicates that the ecotropic MuLV RNA is transcribed in CNS cells from ecotropic MuLV proviruses that have been acquired by infection with exogenous ecotropic MuLV, probably during embryogenesis, the time when germ line proviruses in AKR and C58 mice first become activated. In young mice, MuLV RNA-containing cells were found exclusively in white-matter tracts and therefore were glial cells. An increase in the ADPM susceptibility of the mice with advancing age correlated with the presence of an increased number of ecotropic MuLV RNA-containing cells in the spinal cords which, in turn, correlated with an increase in the number of unmethylated proviruses in the DNA extracted from spinal cords. Studies with AKXD recombinant inbred strains showed that possession of a single replication-competent ecotropic MuLV provirus (emv-11) by Fv-1n/n mice was sufficient to result in ecotropic MuLV infection of CNS cells and ADPM susceptibility. In contrast, no ecotropic MuLV RNA-positive cells were present in the CNSs of mice carrying defective ecotropic MuLV proviruses (emv-3 or emv-13) or in which ecotropic MuLV replication was blocked by the Fv-1n/b or Fv-1b/b phenotype. Such mice were resistant to paralytic LDV infection. In utero infection of CE/J mice, which are devoid of any endogenous ecotropic MuLVs, with the infectious clone of emv-11 (AKR-623) resulted in the infection of CNS cells, and the mice became ADPM susceptible, whereas littermates that had not become infected with ecotropic MuLV remained ADPM resistant.

Low levels of poliovirus replication in primary human monocytes: possible interactions with lymphocytes

To investigate the molecular mediators of poliovirus tissue tropism, the correlation between poliovirus replication and poliovirus receptor expression was examined in a primary human tissue system. Earlier work [M. Freistadt, H. Fleit, and E. Wimmer, Virology 195: 798-803 (1993)] showed that the cellular receptor for poliovirus is present in 87% of primary human monocytes and that peripheral blood mononuclear cells support poliovirus replication. In the current work, monocytes, obtained by adherence or by a novel negative selection procedure using specific monoclonal antibodies to lymphocyte surface antigens, supported poliovirus replication. However, total virus yield was low and infectious centers assays revealed that a minority (6%) of monocytes become productively infected. Viral yield from monocytes was lower than from the heterogeneous mononuclear cells; however, when uninfected lymphocytes were added back to infected monocytes, the higher viral yield was restored. The purity of the cells did not significantly affect the number of cells infected. These results suggest that more poliovirus is produced per cell from activated rather than unactivated monocytes. Furthermore, poliovirus replication in monocytes may reflect genuine in vivo replication and comprise a system in which to determine molecular mediators of poliovirus tissue tropism.

Comparison of the structural protein coding sequences of the VR-2332 and Lelystad virus strains of the PRRS virus

The 3'-portion of the genome of a U.S. isolate of the porcine reproductive and respiratory syndrome (PRRS) virus, ATCCVR-2332, was cloned and sequenced. The resultant 3358 nucleotides contain 6 open reading frames (ORFs) with homologies to ORFs 2 through 7 of the European strain of the PRRS virus and other members of the free-standing genus of arteriviruses. Both VR-2332 and the European isolate (called the Lelystad virus) have been identified as infectious agents responsible for the swine disease called PRRS. Comparative sequence analysis indicates that there are degrees of amino acid identity to the Lelystad virus open reading frames ranging from 55% in ORF 5 to 79% in ORF 6. Hydropathy profiles indicate that the ORFs of VR-2332 and Lelystad virus correspond structurally despite significant sequence differences. These results are consistent with the biological similarities but distinct serological properties of North American and European isolates of the virus.

Phylogenetic analyses of the putative M (ORF 6) and N (ORF 7) genes of porcine reproductive and respiratory syndrome virus (PRRSV): implication for the existence of two genotypes of PRRSV in the U.S.A. and Europe

The putative membrane (M) protein (ORF 6) and nucleocapsid (N) protein (ORF 7) genes of five U.S. isolates of porcine reproductive and respiratory syndrome virus (PRRSV) with differing virulence were cloned and sequenced. To determine the genetic variation and the phylogenetic relationship of PRRSV, the deduced amino acid sequences of the putative M and N proteins from these isolates were aligned, to the extent known, with other PRRSV isolates, and also other members of the proposed arterivirus group including lactate dehydrogenase-elevating virus (LDV) and equine arteritis virus (EAV). There was 96-100% amino acid sequence identity in the putative M and N genes among U.S. and Canadian PRRSV isolates with differing virulence. However, their amino acid sequences varied extensively from those of European PRRSV isolates, and displayed only 57-59% and 78-81% identity, respectively. The phylogenetic trees constructed on the basis of the putative M and N genes of the proposed arterivirus group were similar and indicated that both U.S. and European PRRSV isolates were related to LDV and were distantly related to EAV. The U.S. and European PRRSV isolates fell into two distinct groups, suggesting that U.S. and European PRRSV isolates represent two distinct genotypes.

Lelystad virus belongs to a new virus family, comprising lactate dehydrogenase-elevating virus, equine arteritis virus, and simian hemorrhagic fever virus

Lelystad virus (LV) is an enveloped positive-stranded RNA virus, which causes abortions and respiratory disease in pigs. The complete nucleotide sequence of the genome of LV has been determined. This sequence is 15.1 kb in length and contains a poly(A) tail at the 3' end. Open reading frames that might encode the viral replicases (ORFs 1a and 1b), membrane-associated proteins (ORFs 2 to 6) and the nucleocapsid protein (ORF7) have been identified. Sequence comparisons have indicated that LV is distantly related to the coronaviruses and toroviruses and closely related to lactate dehydrogenase-elevating virus (LDV) and equine arteritis virus (EAV). A 3' nested set of six subgenomic RNAs is produced in LV-infected alveolar lung macrophages. These subgenomic RNAs contain a leader sequence, which is derived from the 5' end of the viral genome. Altogether, these data show that LV is closely related evolutionarily to LDV and EAV, both members of a recently proposed family of positive-stranded RNA viruses, the Arteriviridae.

Molecular biology of rubella virus

This chapter summarizes the present medical significance of rubella virus. Rubella virus infection is systemic in nature and the accompanying symptoms are generally benign, the most pronounced being a mild rash of short duration. The most common complication of rubella virus infection is transient joint involvement such as polyarthralgia and arthritis. The primary health impact of rubella virus is that it is a teratogenic agent. The vaccination strategy is aimed at elimination of rubella and includes both universal vaccination of infants at 15 months of age with the trivalent measles, mumps, rubella (MMR) vaccine and specific targeting with the rubella vaccine of seronegative women planning pregnancy and seronegative adults who could come in contact with women of childbearing age, although it is recommended that any individual over the age of 12 months without evidence of natural infection or vaccination be vaccinated. Medically, the current challenge posed by rubella virus is to achieve complete vaccination coverage to prevent resurgences.

Comparison of the ability of lactate dehydrogenase-elevating virus and its virion RNA to infect murine leukemia virus-infected or -uninfected cell lines

Lactate dehydrogenase-elevating virus (LDV) has a strict species specificity. Cells or cell lines other than a particular subset of mouse primary macrophages which can support LDV replication in vitro have not been identified. LDV induces neurological disorders in old C58 or AKR strains, in which the involvement of multiple copies of the endogenous N-tropic murine leukemia virus (MuLV) genome and the Fv-1 locus of the mouse has been implicated. Our previous studies have demonstrated that LDV could infect and replicate in cell lines of the mouse or other species in vitro when they were infected with MuLV. The significance of and the precise mechanism underlying this phenomenon, however, remain unclear. We demonstrated in this study the efficient infection and replication of the virus in vitro by inoculation of its RNA mixed with liposome. No significant difference either in the efficiency of RNA transfection or in the ability to support its replication was observed among the various species' cell lines examined. In addition, by RNA transfection the virus replicated with equal efficiency in MuLV-infected and -uninfected cells or in macrophages derived from mice irrespective of their age. In contrast, the pattern of the infection by virus particles was quite different; LDV replication was observed only in macrophages (particularly from newborn mice) and MuLV-infected cells. By using various LDV isolates, it was demonstrated that the capability of replication between neurovirulent, LDV type C, and the other avirulent strains was almost the same in mouse cell lines when their RNA was introduced into the cells. Higher infectivity of LDV-C to MuLV-infected cells may be due to its efficient incorporation of the particles into MuLV-infected cells.

A review of feline infectious peritonitis virus: molecular biology, immunopathogenesis, clinical aspects, and vaccination

Feline infectious peritonitis (FIP) has been an elusive and frustrating problem for veterinary practitioners and cat breeders for many years. Over the last several years, reports have begun to elucidate aspects of the molecular biology of the causal virus (FIPV). These papers complement a rapidly growing base of knowledge concerning the molecular organization and replication of coronaviruses in general. The fascinating immunopathogenesis of FIPV infection and the virus' interaction with macrophages has also been the subject of several recent papers. It is now clear that FIPV may be of interest to scientists other than veterinary virologists since its pathogenesis may provide a useful model system for other viruses whose infectivity is enhanced in the presence of virus-specific antibody. With these advances and the recent release of the first commercially-available FIPV vaccine, it is appropriate to review what is known about the organization and replication of coronaviruses and the pathogenesis of FIPV infection.

The 5' end of the equine arteritis virus replicase gene encodes a papainlike cysteine protease

The presence of a papainlike cysteine protease (PCP) domain in the N-terminal region of the equine arteritis virus (EAV) replicase, which had been postulated on the basis of limited sequence similarities with cellular and viral thiol proteases, was confirmed by in vitro translation and mutagenesis studies. The EAV protease was found to direct an autoproteolytic cleavage at its C terminus which leads to the production of an approximately 30-kDa N-terminal replicase product (nsp1) containing the PCP domain. Amino acid residues Cys-164 and His-230 of the EAV replicase polyprotein were identified as the most likely candidates for the role of PCP catalytic residues. By means of N-terminal sequence analysis of a PCP cleavage product, derived from a bacterial expression system, it was shown that cleavage occurs between Gly-260 and Gly-261. No evidence for PCP-directed cleavages at other positions in the EAV replicase was obtained. In cotranslational and posttranslational trans-cleavage assays, neither EAV nsp1 nor its precursor was able to process the PCP cleavage site in trans.

Structural proteins of equine arteritis virus

We have recently shown that the genome of equine arteritis virus (EAV) contains seven open reading frames (ORFs). We now present data on the structural proteins of EAV and the assignment of their respective genes. Virions are composed of a 14-kDa nucleocapsid protein (N) and three membrane proteins designated M, GS, and GL. M is an unglycosylated protein of 16 kDa, and GS and GL are N-glycosylated proteins of 25 and 30 to 42 kDa, respectively. The broad size distribution of GL results from heterogeneous N-acetyllactosamine addition since it is susceptible to digestion by endo-beta-galactosidase. Using monospecific antisera as well as an antivirion serum, and by expression of individual ORFs, the genes for the structural proteins were identified: ORF 7 codes for N, ORF 6 for M, ORF 5 for GL, and ORF 2 for GS. With the exception of GS, the proteins are about equally abundant in EAV virions, being present at a molar ratio of 3 (N):2 (M):3 (GL). The GS protein, which is expressed at a level similar to that of M in infected cells, is strikingly underrepresented in virus particles (1 to 2%). Our data justify a distinct taxonomic position for EAV, together with lactate dehydrogenase-elevating virus and simian hemorrhagic fever virus; although coronavirus- and toroviruslike in features of transcription and translation, the virion architecture of EAV is fundamentally different.

Lactate dehydrogenase-elevating virus (LDV): subgenomic mRNAs, mRNA leader and comparison of 3'-terminal sequences of two LDV isolates

The 3'-terminal 1314 nucleotides of the genome of one isolate of lactate dehydrogenase-elevating virus, LDV-P, has been derived by sequence analyses of cDNAs from several genomic libraries and compared to that of another LDV isolate, LDV-C (Godeny et al. (1990) Virol. 177, 768-771). The 3'-non-coding segment of 80 nucleotides of the two LDV genomes is identical, whereas marked, but varying nucleotide and amino acid divergence is apparent in the three upstream overlapping open reading frames (ORF). The third ORF from the 3'-end exhibits only 82% nucleotide and 90% amino acid identity, whereas the 3'-terminal ORF, which encodes the nucleocapsid protein, exhibits approximately 99% amino acid identity. The second 3'-terminal ORF encodes an 18.8 kDa protein which lacks N-glycosylation sites but possesses 2 or 3 potential transmembrane helices in the N-terminal half of the molecule. A similar membrane organization is observed for the corresponding protein of equine arteritis virus and the M protein of mouse hepatitis virus. The sequence analyses combined with Northern hybridization analyses of RNA from LDV-infected macrophages and spleens of LDV-infected mice indicate that the three ORFs encoded by the 3'-terminal end of the LDV genome are expressed via the three smallest mRNAs (mRNAs 6-8) of the seven subgenomic mRNAs of LDV (mRNAs 2-8), which range in size from about 0.8 to 3.6 kb. All mRNAs have been shown to carry poly(A)-tracts and a common leader sequence. The seven mRNAs were produced in infected macrophage cultures concomitantly with genomic LDV RNA. Maximum LDV RNA synthesis was observed between 6 and 8 h post-infection. The same seven subgenomic mRNAs were detected in macrophages infected with three different isolates of LDV, but different relative amounts of some of the mRNAs were produced. The relative proportions of molecules of mRNAs 1-8 present in 6 h LDV-P-infected macrophages were about 13, 5, 5, 8, 6, 11, 11 and 27% of the total, respectively.

Lactate dehydrogenase-elevating virus, equine arteritis virus, and simian hemorrhagic fever virus: a new group of positive-strand RNA viruses

The last comprehensive reviews of nonarbotogaviruses included discussions on pestiviruses, rubella virus, lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV), simian hemorrhagic fever virus (SHFV), cell fusion agent, and nonarboflaviviruses. The inclusion of all these viruses in the family Togaviridae was largely based on the similarities in morphological and physical–chemical properties of these viruses, and in the sizes and polarities of their genomes. In the intervening years, considerable new information on the replication strategies of these viruses and the structure and organization of their genomes has become available that has led to the reclassification or suggestions for reclassification of some of them. The replication strategy of EAV resembles that of the coronaviruses, involving a 3'-coterminal nested set of mRNAs. Therefore, EAV has been suggested to be included in a virus superfamily, along with coronaviruses and toroviruses. Recent evidence indicates that LDV not only resembles EAV in morphology, virion and genome size, and number and size of their structural proteins, but also in genome organization and replication via a 3'-coterminal set of mRNAs. SHFV, although not fully characterized, exhibits properties resembling those of LDV and EAV, and the recent evidence suggest that it may possess the same genome organization as these viruses. The three viruses may, therefore, represent a new family of positive-strand RNA viruses and are reviewed together in this chapter. In this chapter, emphasis is on the recent information concerning their molecular properties and pathogenesis in vitro and in vivo and on the host immune responses to infections by these viruses.

Mode of neutralization of lactate dehydrogenase-elevating virus by polyclonal and monoclonal antibodies

Neutralization of the infectivity of [3H]uridine-labeled lactate dehydrogenase-elevating virus (LDV) by polyclonal mouse or rabbit antibodies to the envelope glycoprotein of LDV, VP-3, or by neutralizing monoclonal antibodies (mAb) that recognize a different epitope on VP-3 than the polyclonal antibodies correlated with an increase in the sedimentation rate of LDV from 230 S to greater than or equal to 270 S. Incubation of LDV with normal mouse plasma or non-neutralizing mAbs to LDV VP-3 had no effect on its sedimentation rate. Similarly, incubation of a neutralization escape variant of LDV with the mAb used in its selection had no effect on its sedimentation rate, whereas neutralization of this variant by polyclonal mouse or rabbit anti-VP3 antibodies increased the sedimentation rate. Neutralization of LDV infectivity was only observed at high antibody/virion ratios and often was followed by loss of the viral RNA. The results suggest that neutralization of LDV infectivity results from binding of multiple antibody molecules that recognize specific epitopes on the viral envelope glycoprotein and ultimately leads to disintegration of the virions.