Hijacking the translation apparatus by RNA viruses.
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As invading viruses do not harbor functional ribosomes in their virions, successful amplification of the viral genomes requires that viral mRNAs compete with cellular mRNAs for the host cell translation apparatus. Several RNA viruses have evolved remarkable strategies to recruit the host translation initiation factors required for the first steps in translation initiation by host cell mRNAs. This review describes the ways that three families of RNA viruses effectively usurp limiting translation initiation factors from the host. (+info)
Tipping the balance between necrosis and apoptosis in human and murine cells treated with interferon and dsRNA.
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Interferons enhance the cellular antiviral response by inducing expression of protective proteins. Many of these proteins are activated by dsRNA, a typical by-product of viral infection. Here we show that type-I and type-II interferons can sensitize cells to dsRNA-induced cytotoxicity. In caspase-8- or FADD-deficient Jurkat cells dsRNA induces necrosis, instead of apoptosis. In L929sA cells dsRNA-induced necrosis involves high reactive oxygen species production. The antioxidant butylated hydroxyanisole protects cells from necrosis, but shifts the response to apoptosis. Treatment with the caspase inhibitor benzyloxycarbonyl-Val-Ala-DL-Asp(OMe)-fluoromethylketone or overexpression of Bcl-2 prevent this shift and promote necrosis. Our results suggest that a single stimulus can initiate different death-signaling pathways, leading to either necrotic or apoptotic cell death. Inhibition of key events in these signaling pathways, such as caspase activation, cytochrome c release or mitochondrial reactive oxygen species production, tips the balance between necrosis and apoptosis, leading to dominance of one of these death programs. (+info)
Histologic and in situ viral findings in the myocardium in cases of sudden, unexpected death.
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The purpose of this study was to do in situ viral detection in myocardial tissues of individuals who suffered sudden unexpected death and to correlate the results with the postmortem histopathologic findings. Thirteen cases were identified and the heart tissues were analyzed for adenovirus, cytomegalovirus, Epstein Barr virus, herpes simplex virus 1 and 2, human immunodeficiency virus 1 (HIV-1), influenza A, influenza B, parvovirus, rotavirus, picornavirus (including separate primers for enterovirus and Coxsackie virus A and B), varicella zoster virus, and respiratory syncytial virus. Thirteen individuals aged 2 to 67 years were studied. In each case, polymerase chain reaction-amplified viral RNA was detected in situ: Coxsackie virus B (5 cases), rotavirus (4 cases), HIV-1 (2 cases), influenza A (1 case), and influenza B (1 case). Immunohistochemical detection of viral proteins was found in the five Coxsackie virus cases and four rotavirus cases. The mononuclear inflammatory infiltrate was diffuse and marked only in the cases of influenza A and HIV-1, as well as one of the Coxsackie virus and rotavirus cases, respectively. Immunohistochemical analysis showed that the most common cell type in the inflammatory infiltrates was CD68-positive macrophages. Direct myocyte infection was most prominent in the cases of Coxsackie virus infection. In summary, in situ viral detection was documented in each case of idiopathic myocarditis associated with sudden, unexpected death; in 6/13 cases, the myocarditis was focal and minimal. Although Coxsackie virus was, as expected, the most common virus noted, other viruses including rotavirus and HIV-1 were also observed, highlighting the need for comprehensive viral and histologic analyses in such cases. (+info)
Pathological changes in juvenile Atlantic halibut Hippoglossus hippoglossus persistently infected with nodavirus.
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This is the first description of a persistent subclinical nodavirus infection in the Atlantic halibut Hippoglossus hippoglossus. Juvenile fish (1 to 5 g) were sampled at 4, 5 and 8 mo of age at a fish farm in Norway during and after weaning. None showed clinical signs of viral encephalopathy and retinopathy (VER) or other disease. Pathological changes and/or nodavirus were detected by light microscopy, immunohistochemistry, reverse transcriptase polymerase chain reaction (RT-PCR) and transmission electron microscopy in all fish examined. High numbers of virus particles were found in macrophage-like cells in the central nervous system, including brain and retina (CNS). The virus particles displayed the icosahedral shape and size (approximately 25 nm) characteristic of nodaviruses. The virus-infected cells formed focal cell aggregates and were seen in all regions of the brain and all nuclear cell layers of the retina. The cytoplasm of the infected cells was filled with membrane-enclosed inclusions packed with virus particles. Some virus particles lay along membranes and formed membrane-bound necklace-like arrangements. The virus-infected cells of the retina also contained pigment granula located generally inside virus inclusions and sometimes forming a coating around the virus particles. All frontal parts with the eyes and brain and 50% of the mid-parts, which included the abdominal organs, were found positive for nodavirus with RT-PCR. Pathological changes in these persistently nodavirus-infected fish differ from earlier descriptions in Atlantic halibut during outbreaks of VER. Vertical transmission from infected spawners is believed to be a major route for nodavirus infection. Detection of nodavirus in subclinical infected fish and a better understanding of its pathogenesis are important in order to prevent the spread of nodavirus in the fish-farming industry. (+info)
Interference of the life cycle of fish nodavirus with fish retrovirus.
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Interference of the life cycle of grouper nervous necrosis virus (GNNV), a member of the Nodaviridae, genus Betanodavirus, by snakehead retrovirus (SnRV) has been studied in vitro. SGF-1, a new fish cell line that is persistently infected with SnRV, was induced by inoculating SnRV into the grouper fin cell line GF-1. Culture supernatants and cell pellets from both GNNV-infected SGF-1 and GF-1 cells were collected and employed for virus productivity analysis. The yields of GNNV RNA and capsid protein in GNNV-infected SGF-1 cells were similar to those in GNNV-infected GF-1 cells. However, when GF-1 cells were used for titration, the titre of the culture supernatant from GNNV-infected SGF-1 cells was much higher than that from GNNV-infected GF-1 cells. The titration result suggested that SnRV enhanced the infection or cytopathic effect (CPE) of GNNV during GNNV and SnRV coinfection of the GF-1 cell titration system, although SnRV cannot induce any CPE in GF-1 cells alone, nor can it increase the yield of GNNV after GNNV superinfection of SGF-1 cells. Moreover, GNNV cDNA was detected in both the pellet and the supernatant from GNNV-infected SGF-1 cells. This result indicated that SnRV reverse-transcribed the GNNV single-stranded genomic RNA into cDNA during GNNV superinfection of SGF-1 cells and created a new cDNA stage in the life cycle of the fish nodavirus. (+info)
Sensitive detection of RNA viruses associated with gastroenteritis by a hanging-drop single-tube nested reverse transcription-PCR method.
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The detection of the human RNA viruses, calicivirus and astrovirus, requires high sensitivity and broad reactivity. A novel single-tube nested reverse transcription-PCR (RT-PCR) method is described here, in which all of the required reagents are included in the one tube; however, those required for the nested amplification are separated in a "hanging drop" in the cap to be introduced by centrifugation after the RT and first-round cDNA amplification steps. Broad reactivity was obtained by using primer cocktails covering the published sequence variation in the primer targets. The method was evaluated with clinical fecal samples from outbreak and sporadic cases. Norwalk-like virus types 1 and 2 and rotavirus were the causal agents in 10 of 12 outbreaks. A viral agent was detected in 44% of 197 samples from sporadic infections in patients presenting to community health centers and a children's hospital. Interestingly, whereas rotavirus was more common than astrovirus in patients presenting to the hospital (33 and 7.6%, respectively), the reverse was true for patients presenting to community health centers (4.2 and 34%, respectively). (+info)
Neuronal survival strategies in the face of RNA viral infection.
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Neurons of the mammalian central nervous system (CNS) are an essential and largely nonrenewable cell population. Thus, viral infections that result in neuronal depletion, either by viral lysis or by induction of the cytolytic immune response, would likely lead to profound neurologic impairment. However, many viral infections that result in tissue destruction elsewhere in the host produce few overt symptoms in the CNS, despite readily detectable virus expression. This observation has lead to the speculation that neurons possess strategies to limit the replication and spread of otherwise cytopathic viruses. These strategies either favor the clearance of virus in the absence of appreciable neuronal loss or promote the establishment of noncytolytic persistent infections. This review discusses some of these strategies, with an emphasis on how such survival techniques lessen the potential for CNS neuropathology. (+info)
Effect of multiple freeze-thaw cycles on detection of measles, mumps, and rubella virus antibodies.
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We investigated the effect of multiple freeze-thaw cycles on mumps, measles, and rubella virus serum antibody levels with whole-virus immunoglobulin G enzyme-linked immunoassays. Fresh serum samples from nine healthy adult volunteers were divided into six sets of five aliquots each. Samples were taken through a total of 10 freeze-thaw cycles and stored at 4 degrees C until assayed. Each assay measurement was done in replicates of five, and the mean value was reported. After completing 10 freeze-thaw cycles, we found no clinically or statistically significant effect on measured antibody levels and found no discernible detrimental effect on the ability to measure these antibodies by enzyme-linked immunoassays. (+info)