Distribution of Viral RNA in Mouse Tissues during Acute Phase of Coxsackievirus B5 Infection

Investigating the virulence of coxsackievirus B6 strains and antiviral treatments in a neonatal murine model

Coxsackievirus B6 (CVB6), a member of the human enterovirus family, is associated with severe diseases such as myocarditis in children. However, to date, only a limited number of CVB6 strains have been identified, and their characterization in animal models has been lacking. To address this gap, in this study, a neonatal murine model of CVB6 infection was established to compare the replication and virulence of three infectious-clone-derived CVB6 strains in vivo. The results showed that following challenge with a lethal dose of CVB6 strains, the neonatal mice rapidly exhibited a series of clinical signs, such as weight loss, limb paralysis, and death. For the two high-virulence CVB6 strains, histological examination revealed myocyte necrosis in skeletal and cardiac muscle, and immunohistochemistry confirmed the expression of CVB6 viral protein in these tissues. Real-time PCR assay also revealed higher viral loads in the skeletal and cardiac muscle than in other tissues at different time points post infection. Furthermore, the protective effect of passive immunization with antisera and a neutralizing monoclonal antibody against CVB6 infection was evaluated in the neonatal mouse model. This study should provide insights into the pathogenesis of CVB6 and facilitate further research in the development of vaccines and antivirals against CVBs.

A neonatal mouse model of central nervous system infections caused by Coxsackievirus B5

As one of the key members of the coxsackievirus B group, coxsackievirus B5 (CV-B5) can cause many central nervous system diseases, such as viral encephalitis, aseptic meningitis, and acute flaccid paralysis. Notably, epidemiological data indicate that outbreaks of CV-B5-associated central nervous system (CNS) diseases have been reported worldwide throughout history. In this study, which was conducted to promote CV-B5 vaccine and anti-virus drug research, a 3-day-old BALB/c mouse model was established using a CV-B5 clinical isolate (CV-B5/JS417) as the challenge strain. Mice challenged with CV-B5/JS417 exhibited a series of neural clinical symptoms and death with necrosis of neuronal cells in the cerebral cortex and the entire spinal cord, hindlimb muscles, and cardiomyocytes. The viral load of each tissue at various post-challenge time points suggested that CV-B5 replicated in the small intestine and was subsequently transmitted to various organs via viremia; the virus potentially entered the brain through the spinal axons, causing neuronal cell necrosis. In addition, this mouse model was used to evaluate the protective effect of a CV-B5 vaccine. The results indicated that both the inactivated CV-B5 vaccine and anti-CVB5 serum significantly protected mice from a lethal infection of CV-B5/JS417 by producing neutralizing antibodies. In summary, the first CV-B5 neonatal mouse model has been established and can sustain CNS infections in a manner similar to that observed in humans. This model will be a useful tool for studies on pathogenesis, vaccines, and anti-viral drug evaluations.

Enteroviruses as causative agents in type 1 diabetes: loose ends or lost cause?

Considerable evidence implies that an enteroviral infection may accelerate or precipitate type 1 diabetes (T1D) in some individuals. However, causality is not proven. We present and critically assess evidence suggesting that islet β cells can become infected with enterovirus, and argue that this may result in one of several consequences. Occasionally, a fully lytic infection may arise and this culminates in fulminant diabetes. Alternatively, an atypical persistent infection develops which can be either benign or promote islet autoimmunity. We propose a model in which the 'strength' of the β cell response to the establishment of a persistent enteroviral infection determines the final disease outcome.

Arsenic trioxide influences viral replication in target organs of coxsackievirus B3-infected mice

New antiviral agents are urgently needed. Based on in vitro studies, arsenic trioxide (As₂O₃) seems to affect viral replication, although this has been studied only marginally in vivo. In this study the replication of coxsackievirus B3 (CVB3) was studied in Balb/c mice administered 1 mg As₂O₃/kg bw once daily during 7 days of infection and in Vero cells exposed for 3 or 5 days to 0.4, 2 or 4 μM As₂O₃. Viral RNA was measured by reverse transcription PCR (RT-PCR) (in vitro and in vivo) and arsenic concentration was measured by inductively coupled plasma-mass spectrometry (ICP-MS) (in vivo). In vivo, As₂O₃ decreased viral RNA in the brain on days 3 (by 81%; p < 0.05) and 7 (by 97%; p < 0.01) and in the pancreas on day 7 (by 75%; p < 0.05), two of the target organs of this infection. The results were confirmed in vitro, where As₂O₃ dose-dependently reduced viral RNA, with the effect being more pronounced in the surrounding culture medium than inside the infected cells, indicating an impaired virion release. Thus, As₂O₃ reduced CVB3 replication both in vitro and in vivo, indicating that As₂O₃ is a viable option in the pursuit of new therapeutic agents against viral infections.

Viral RNA kinetics is associated with changes in trace elements in target organs of Coxsackie virus B3 infection

Trace elements are pivotal for the host defense, as well as potentially important for viral replication and virulence. Studies of sequential changes in viral replication in target organs of infection are sparse and a possible association with changes in specific trace elements is unknown. In this study Balb/c mice were infected with Coxsackie virus B3 (CVB3). Results indicated that sequential changes in viral replication (RT-PCR) were related to changes in trace element (arsenic, copper, iron, selenium and zinc) concentrations (as determined by ICP-MS) on days 3, 5 and 7 of the infection in serum, heart, lung, liver, pancreas, kidney, spleen, intestine and brain. After an initial viral peak on day 3, viral load drastically decreased in all organs, i.e. by >99% (serum), 97% (lung), 98% (liver), 60% (pancreas), 95% (kidney) and 93% (spleen), except in the heart, intestine and brain in which viral load increased after day 3. Selenium decreased in all organs except the heart while arsenic decreased in all organs except the kidney, spleen and brain. Moreover, selenium was negatively correlated to viral load in serum, liver, pancreas and intestine. To conclude, these findings give evidence that trace elements are directly involved in the replication of CVB3.

Effective transduction by self-complementary adeno-associated viruses of human dendritic cells with no alteration of their natural characteristics

BACKGROUND

Effective gene delivery techniques are required to genetically manipulate dendritic cells (DCs). We therefore investigated the feasibility of using various self-complementary recombinant adeno-associated virus (scAAV) serotypes to deliver genes to human DCs.

METHODS

Monocytes isolated from healthy volunteers were differentiated to immature DCs (iDC) by incubation with interleukin (IL)-4 and granulocyte macrophage colony-stimulating factor. The iDCs were transduced with scAAV1, 2, 3, 4, 5, 6 or 8 at various multiplicities of infection (MOIs). Transduction efficiency (TE), cell viability and functional characteristics of the transduced DCs were evaluated.

RESULTS

TE of scAAV was three-fold greater than TE of conventional recombinant adeno-associated virus with a single-stranded genome. The TEs of scAAV2, 5, and 6 were much higher than those of the other scAAVs; at 1000 MOI, the TEs were 22.2% +/- 9.5%, 27.0% +/- 8.8% and 28.4% +/- 6.0%, respectively. Exposure of iDCs to 5000 MOI of these viruses increased their TEs, leading to the transduction of nearly the entire DC population. In addition, gene transfer by scAAV did not cause any cytotoxicity. Flow cytometric analysis of scAAV-transduced DCs showed no changes in surface marker profiles. Moreover, transduced cells maintained their functional properties, as represented by active antigen uptake. These cells could efficiently differentiate into mature DCs, as shown by their release of IL-12, the substantial loss of antigen-uptake activity, and the ability of T-cell stimulation.

CONCLUSIONS

These findings strongly indicate that scAAVs, especially subtypes 2, 5 and 6, hold a promising potential as gene delivery tools in human DCs.

Primary neurons become less susceptible to coxsackievirus B5 following maturation: the correlation with the decreased level of CAR expression on cell surface

Coxsackievirus B (CVB) is one of the major pathogens of aseptic meningitis and meningioencephalitis, particularly in newborn infants. To analyze the influence of neural maturation on susceptibility to CVB infection, we prepared immature and mature neurons from 16-day-old BALB/c embryonic cortex. In contrast to immature neurons, mature neurons were less susceptible to CVB5 infection, as indicated by the decrease of cytopathic features. In mature neurons, progeny virus production was significantly hindered, and virus capsid protein VP1 synthesis and virus genome amplification were concomitantly reduced. In addition, the expression of coxsackievirus and adenovirus receptor (CAR), the major receptor of CVB5, was down-regulated in mature neurons. The antibody treatment specific to CAR significantly attenuated CVB5 susceptibility of immature neurons. These findings demonstrate that mature neurons become less susceptible to CVB by the decrease of CAR level. Thus, the data strongly support the idea that the level of virus receptor in neurons is one of the crucial determinants in the age-dependency of CVB virulence in central nervous system.

Mutation variants generated from nonvirulent coxsackievirus B3 acquire virulence phenotypes by active virus replication

OBJECTIVE

To understand coxsackievirus B3 (CVB3) virulence at the molecular level.

METHOD

A mutation library was generated from noncardiovirulent CVB3/0. Highly virulent mutation variants were recovered and characterized both phenotypically and genotypically.

RESULTS

The variants consistently caused destruction of multiple tissues together with active virus production and induced severe mortality in vivo. The extent of infectious virus generation was directly correlated with that of histopathological aberration. Genotypic analysis of the entire genome indicated that the virulent viruses encode nucleotide substitutions in the 5'-nontranslated region, which have previously been identified in other virulent CVB3s.

CONCLUSION

The present study provides evidence that particular nucleotide substitutions in the 5'-nontranslated region of nonvirulent CVB3 can lead to active virus replication, which is sufficient to induce virulence.