RNA viruses cause a multitude of human diseases, including several pandemic events in the past century. Upon viral invasion, the innate immune system responds rapidly and plays a key role in activating the adaptive immune system. In the innate immune system, the interactions between pathogen-associated molecular patterns and host pattern recognition receptors activate multiple signaling pathways in immune cells and induce the production of pro-inflammatory cytokines and interferons to elicit antiviral responses. Macrophages, dendritic cells, and natural killer cells are the principal innate immune components that exert antiviral activities. In this review, the current understanding of innate immunity contributing to the restriction of RNA viral infections was briefly summarized. Besides the main role of immune cells in combating viral infection, the intercellular transfer of pathogen and host-derived materials and their epigenetic and metabolic interactions associated with innate immunity was discussed. This knowledge provides an enhanced understanding of the innate immune response to RNA viral infections in general and aids in the preparation for the existing and next emerging viral infections.
Humans ; Immunity, Innate ; Interferons ; RNA ; RNA Viruses ; Virus Diseases

Turnip yellow mosaic virus (TYMV) is a spherical plant virus that has a single 6.3 kb positive strand RNA genome. Information for TYMV replication is limited, except that the 3'-terminal sequence and 5'-untranslated region are required for genome replication. When a foreign sequence was inserted at the position upstream of the coat protein (CP) open reading frame (ORF), replication of the recombinant TYMV was comparable to wild type, as long as an RNAi suppressor was provided. In contrast, when the foreign sequence was inserted between the CP ORF and the 3'-terminal tRNA-like structure, replication of the recombinant virus was not detected. This result suggests that the CP ORF contains an essential replication element which should be appropriately spaced with respect to the 3'-end. Analysis of TYMV constructs containing a part or a full additional CP ORF indicates that the 3' quarter of the CP ORF is required for TYMV replication.
Animals ; Brassica napus ; Ecthyma, Contagious ; Genome ; Open Reading Frames ; Plant Viruses ; RNA ; Tymovirus ; Viruses

We have previously observed that a sequence in coat protein (CP) ORF of Turnip yellow mosaic virus (TYMV) is required for efficient replication of the virus. The sequence was predicted to take a stem-loop structure, thus termed SL2. While examining various SL2 mutants, we observed that all the modifications resulting in extension of translation beyond the CP ORF significantly suppressed subgenomic RNA accumulation. The genomic RNA level, in contrast, was not affected. Introduction of an in-frame stop codon in the CP ORF of these constructs restored the level of subgenomic RNA. Overall, the results suggest that the read-through makes the subgenomic RNA unstable.
Animals ; Brassica napus ; Codon, Terminator ; Ecthyma, Contagious ; RNA ; Tymovirus ; Viruses

Hantaviruses are negative-strand RNA viruses that contain three segmented (L/M/S) genome and belong to the genus hantavirus of the family Bunyaviridae. Due to such an unique structure of segmented RNA genome, hantaviruses have a possibility to produce reassortants that containing genomic sets mixed with different segments originated from both parental viruses during the genetic interaction. To investigate whether this phenomenon occurs in vitro, Hantaan (HTN) and Seoul (SEO) viruses were co-infected into Vero-E6 cells and virulent Maaji (MAA) virus was superinfected into avirulent Prospect Hill (PH) virus-infected Vero-E6 cells, respectively. To select only reassortants among progeny viruses, well separated plaque clones were analyzed by multiplex RT-PCR. The putative reassortant viruses detected by 1st multiplex RT-PCR were plaque-purified three times and confirmed by 2nd multiplex RT-PCR. Only 3 reassortants like HTN/HTN/SEO, SEO/HTN/HTN and SEO/HTN/SEO and only 2 reassortants like PH/MAA/MAA, MAA/MAA/PH as designated in order of L/M/S of genomic segments have been identified so far. These results indicate that genetic reassortment can be induced by mixed-infection of two more distantly related serotypes of hantavirus. Interestingly, reassortant SEO/HTN/SEO containing HTN viral M RNA segment is isolated more frequently. This implies that preferential selection of M genome segments occurred when RNA genomes were packaged into virion and also the process of packaging of RNA segments into virion is not random phenomenon. These reassortants would be helpful to know whether genetic reassortment is dependent on genetic distance between hantaviruses and which viral RNA segment plays an important role in coding for virulence marker. Therefore, genetic reassortment can be useful genetic tool to understand genetical, and biological function of hantavirus.
Bunyaviridae ; Clinical Coding ; Clone Cells ; Genome ; Hantavirus* ; Humans ; Parents ; Product Packaging ; Reassortant Viruses ; RNA ; RNA Viruses ; RNA, Viral ; Seoul ; Virion ; Virulence

Human enteric viruses are one of the major causes of acute gastroenteritis outbreaks. A rapid and precise detection of virus is critical for prompt diagnosis. For this purpose, nucleic acid-based techniques such as reverse transcription (RT)-PCR have been developed. Although RT-PCR is a rapid, specific and sensitive method to detect virus, many steps or reactions are required, especially when various types of viruses are targeted. In this study, we developed a quick and effective method to detect human enteric viruses with a few reactions. Our candidate viruses were as follows: one DNA virus (adenovirus: AdV) and seven RNA viruses including poliovirus (PV), coxsackievirus A (CoxA) and B (CoxB), human rotavirus (HRV), hepatitis A virus (HAV), norovirus (NorV), and astrovirus (AstV). With this amount of samples, theoretically, a total of fifteen biomolecular reactions have to be performed, which include seven RT reactions and eight subsequent PCR with specific primers in each case. Specific primers, enterovirus universal primers, and random primers were applied independently to compare the outcomes of RT and PCR steps in each viral sample. We found that random 9-mer is ideal for the RT reactions of RNA viruses with negligible differences in sensitivity and specificity of viral detection except HRV. Hence, HRV cDNA generated by HRV-specific primer and AdV DNA were amplified in a single tube by duplex PCR. The cDNAs generated by RT using random 9-mers were divided into two reaction tubes without losing sensitivity: one duplex PCR detects enteroviruses (PV, CoxA, CoxB) and HAV, the other detects NorV and AstV. In conclusion, it is possible to detect eight enteric viruses with a substantially reduced number of reactions, which are composed of five reactions, two RT and three PCR reactions.
Collodion ; Disease Outbreaks ; DNA ; DNA Viruses ; DNA, Complementary ; Enterovirus ; Gastroenteritis ; Hepatitis A virus ; Hip ; Humans ; Norovirus ; Poliovirus ; Polymerase Chain Reaction ; Reverse Transcription ; RNA Viruses ; Rotavirus ; Sensitivity and Specificity ; Viruses

In order to investigate the implication of viral replication in acute, subacute, and chronic infections of coxsackievirus B3 (CVB3), we examined the histopathological changes and plus- and minus-strand viral RNA dynamics in heart, pancreas, brain, and liver of CVB3-infected A/J mice. Mice were inoculated intraperitoneally with CVB3 and sacrificed on 1, 2, 3, 4, 7, 10, 14, 21, 30, 60, and 90 days post infection (p.i.). Plus- and minus-strand viral RNAs in the organs were quantitated and the organs were additionally evaluated histopathologically for inflammation. No inflammatory infiltrates were observed in the liver, brain, and heart. In contrast, massive lymphocyte infiltration and fat replacement were shown in the pancreas with loss of acinar cells. Both plus- and minus-strand viral RNA levels were detected by 21 days p.i. in heart, 90 days p.i. in pancreas, 4 days p.i. in liver, and 10 days p.i. in brain. The plus-strand RNA was found at least fifty fold higher than the minus-strand RNA by 4 days p.i. in heart and pancreas and by 3 days p.i. in liver. The plus- to minus-strand RNA ratio in brain was found less than 1:20. Our data indicate that viral replication was actively occurred in heart, pancreas, and liver during acute CVB3 infection, whereas viral replication was limited in brain. Furthermore, chronic persistent viral RNA was observed in pancreas. In conclusion, CVB3 at low dose of virus induces severe pancreatitis but marginal or no inflammatory changes in the heart, liver, and brain.
Acinar Cells ; Animals ; Brain ; Heart ; Inflammation ; Liver ; Lymphocytes ; Mice ; Pancreas ; Pancreatitis ; RNA ; RNA, Viral ; Viruses

Turnip yellow mosaic virus (TYMV) is a spherical plant virus that has a single 6.3 kb positive strand RNA as a genome. Previously, we have made the recombinant TYMV construct containing a 0.7 kb eGFP gene or a 1.8 kb GUS gene. The genomic RNAs from these constructs were efficiently encapsidated. To examine in more detail whether size constraint exists for replication and packaging of TYMV, we have inserted into the TY-GUS an extra sequence derived from either eGFP or GUS. We also made a recombinant containing RNA1 sequence of Flock house virus. These TYMV recombinants were introduced into Nicotiana benthamiana leaves by agroinfiltration. Northern blot analysis of the viral RNAs in the agroinfiltrated leaves showed that the genomic RNA band from the recombinant TYMV became weaker as longer sequence was inserted. The result also showed that the efficiency of genomic RNA encapsidation decreased sharply when an extra sequence of 2.2 kb or more was inserted. In contrast, the recombinant subgenomic RNA containing an extra sequence of up to 3.2 kb was efficiently encapsidated. Overall, these results show that size constraint exists for replication and encapsidation of TYMV RNA.
Blotting, Northern ; Genome ; Genome Size* ; Plant Viruses ; Product Packaging* ; RNA ; RNA, Viral ; Tobacco ; Tymovirus*

Turnip yellow mosaic virus (TYMV) is a non-enveloped icosahedral virus that has a single 6.3 kb positive-strand RNA as a genome. Previously, it was observed that the recombinant construct TY-eGFP2, where an eGFP gene was inserted at the position downstream of the coat protein (CP) ORF of TYMV genome, barely replicated. The inhibition of replication was relieved by insertion of an additional copy of the 3' quarter of the CP ORF after the foreign sequence. In this study, we have examined if the 3' quarter of the CP ORF contains any replication elements. M-fold analysis predicted three stem-loop structures in this region. Analysis of the TY-eGFP2 constructs containing one or two of these stem-loop structures indicates that the secondary structure predicted in the region between nt-6139 and nt-6181, termed SL2, is essential for TYMV replication. The critical role of SL2 was confirmed by the observation that deletion of the 3' quarter of the CP ORF from the wild-type TYMV genome nearly abolished replication and that insertion of SL2 into the deletion mutant restored the replication. Mutations disrupting the stem of SL2 greatly reduced viral RNA replication, indicating that the secondary structure is essential for the enhancing activity.
Animals ; Brassica napus ; Coat Protein Complex I ; Ecthyma, Contagious ; Genome ; RNA ; RNA, Viral ; Tymovirus ; Viruses

The human immune system has evolved to fight against foreign pathogens. It plays a central role in the body's defense mechanism. However, the immune memory geared to fight off a previously recognized pathogen, tends to remember an original form of the pathogen when a variant form subsequently invades. This has been termed 'original antigenic sin'. This adverse immunological effect can alter vaccine effectiveness and sometimes cause enhanced pathogenicity or additional inflammatory responses, according to the type of pathogen and the circumstances of infection. Here we aim to give a simplified conceptual understanding of virus infection and original antigenic sin by comparing and contrasting the two examples of recurring infections such as influenza and dengue viruses in humans.
Dengue ; Dengue Virus ; Humans ; Immune System ; Influenza, Human ; Memory ; RNA Viruses* ; RNA* ; Virulence

The human immune system has evolved to fight against foreign pathogens. It plays a central role in the body's defense mechanism. However, the immune memory geared to fight off a previously recognized pathogen, tends to remember an original form of the pathogen when a variant form subsequently invades. This has been termed 'original antigenic sin'. This adverse immunological effect can alter vaccine effectiveness and sometimes cause enhanced pathogenicity or additional inflammatory responses, according to the type of pathogen and the circumstances of infection. Here we aim to give a simplified conceptual understanding of virus infection and original antigenic sin by comparing and contrasting the two examples of recurring infections such as influenza and dengue viruses in humans.
Dengue ; Dengue Virus ; Humans ; Immune System ; Influenza, Human ; Memory ; RNA Viruses* ; RNA* ; Virulence