Attenuation of a reactivated cardiovirulent coxsackievirus B3: The 5'-nontranslated region does not contain major attenuation determinants

Vaccines against Group B Coxsackieviruses and Their Importance

The group B coxsackieviruses (CVBs) exist in six serotypes (CVB1 to CVB6). Disease associations have been reported for most serotypes, and multiple serotypes can cause similar diseases. For example, CVB1, CVB3, and CVB5 are generally implicated in the causation of myocarditis, whereas CVB1 and CVB4 could accelerate the development of type 1 diabetes (T1D). Yet, no vaccines against these viruses are currently available. In this review, we have analyzed the attributes of experimentally tested vaccines and discussed their merits and demerits or limitations, as well as their impact in preventing infections, most importantly myocarditis and T1D.

The introduction of mutations in the wild type coxsackievirus B3 (CVB3) IRES RNA leads to different levels of in vitro reduced replicative and translation efficiencies

Coxsackievirus B3 (CVB3) is a principal causative agent of viral myocarditis, meningitis and pancreatitis. There is no vaccine available for clinical use. It has been demonstrated that the primary molecular determinant of virulence phenotype is located in the 5' UTR of the viral genome. Translation initiation of CVB3 RNA is directed by the IRES element situated in the 5'UTR. In the present study, we analyse the effects of single point mutations introduced in different positions in the domain V of the IRES RNA of CVB3 wild type. We characterize in vitro virus replicative capacitiy and translation efficiency and we test in vivo virulence of different CVB3 mutants produced by the introduction of different mutations in the domain V of IRES by site-directed mutagenesis to abolish its structure. Our results demonstrate that all RNA mutants display different levels of decreased replication and translation initiation efficiency in vitro. The translation defect was correlated with significant reduced viral titer of mutant particles in comparison with the wild type. When inoculated in mice, mutant viruses were checked for inflammation and necrosis.In vitro and in vivo Findings strongly suggest that the most attenuated mutant strain could be considered a candidate for live-attenuated CVB3 vaccine.

Development of Group B Coxsackievirus as an Oncolytic Virus: Opportunities and Challenges

Oncolytic viruses have emerged as a promising strategy for cancer therapy due to their dual ability to selectively infect and lyse tumor cells and to induce systemic anti-tumor immunity. Among various candidate viruses, coxsackievirus group B (CVBs) have attracted increasing attention in recent years. CVBs are a group of small, non-enveloped, single-stranded, positive-sense RNA viruses, belonging to species human Enterovirus B in the genus Enterovirus of the family Picornaviridae. Preclinical studies have demonstrated potent anti-tumor activities for CVBs, particularly type 3, against multiple cancer types, including lung, breast, and colorectal cancer. Various approaches have been proposed or applied to enhance the safety and specificity of CVBs towards tumor cells and to further increase their anti-tumor efficacy. This review summarizes current knowledge and strategies for developing CVBs as oncolytic viruses for cancer virotherapy. The challenges arising from these studies and future prospects are also discussed in this review.

Molecular analysis of the role of IRES stem-loop V in replicative capacities and translation efficiencies of Coxsackievirus B3 mutants

Coxsackievirus B3 (CVB3) is a principal viral cause of acute myocarditis in humans and has been implicated in the pathogenesis of dilated cardiomyopathy. The natural genetic determinants of cardiovirulence for CVB3 have not been identified, although using strains engineered in the laboratory, it has been demonstrated elsewhere that, for several wild-type CB3 strains, the primary molecular determinant of cardiovirulence phenotype localizes to the 5' nontranslated region (5'NTR) and capsid. Stable RNA tetraloop motifs are found frequently in biologically active RNAs. These motifs carry out a wide variety of functions in RNA folding, in RNA-RNA and RNA-protein interactions. A great deal of knowledge about the structures and functions of tetraloop motifs has accumulated largely due to intensive theoretical, biochemical, and biophysical studies on one most frequently occurring family of tetraloop sequences, namely, the GNRA sequence, especially the GNAA sequence conserved in all enteroviruses. Here in this study, through construction of CVB3 chimeric mutants, the predicted stem loop (SL) V within the 5'NTR has been identified as important in determining viral cardiovirulence. Replication assays in HeLa cell monolayers revealed that wild-type CVB3 virus and two of the six mutants constructed here grow efficiently, whereas other mutant viruses replicate poorly. Furthermore, the in vitro translation products from these mutants and wild-type CVB3, demonstrated that the two mutants who replicate efficiently, translated at relatively equivalent amount than the wild-type. However, other mutants demonstrated a low efficiency in their production of protein when translated in a Rabbit Reticulocytes Lysats.

Association between toll-like receptor 8 expression and adverse clinical outcomes in patients with enterovirus-associated dilated cardiomyopathy

BACKGROUND

In recent reports, human toll-like receptor (TLR) 8 mediates the antiviral response by recognizing single-stranded RNA. The inflammatory response against enteroviral (EV) RNA replication may play an important role in dilated cardiomyopathy (DCM). The purpose of this study was to determine whether TLR8 was expressed with EV replication in patients with enterovirus-associated DCM.

METHODS

Reverse transcriptase-polymerase chain reaction analysis was performed to screen the detection of myocardial EV RNA in 198 consecutive patients with DCM. Seventy-two EV RNA-positive patients with DCM and 20 control samples constituted the study population of the present study. Levels of TLR8 and myeloid differentiation factor (MyD) 88 adaptor protein mRNA and EV RNA (plus- and minus-strand RNAs) were measured by real-time RT-PCR. Immunohistochemistry was performed to identify the cellular source of these molecules.

RESULTS

Toll-like receptor 8 and MyD88 mRNA levels were higher in patients with DCM than in controls (P < .001). Immunostainings of TLR8, MyD88, and EV protein showed localization of these proteins in cardiac myocytes in patients with DCM. After a mean follow-up of 426 days, clinical outcomes (development of heart failure n = 11, cardiac death n = 3) were associated with increased levels of TLR8 and MyD88 (P < .05). Multivariate analysis showed that TLR8 (relative risk 3.2, 95% CI 1.6-6.2) was a strong predictor of heart failure and cardiac death after adjustment for baseline characteristics.

CONCLUSION

Toll-like receptor 8 and MyD88 expressions may be involved in the immune response to EV replication in enterovirus-associated DCM. In addition, TLR8 may provide important prognostic information in patients with enterovirus-associated DCM.

Detection of Coxsackievirus B3 RNA in mouse myocarditis by nested polymerase chain reaction

BACKGROUND

A majority of cases of viral myocarditis are associated with group B Coxsackieviruses (CVB) and the persistence of these viruses in the myocardium is associated with the progression of acute myocarditis to chronic dilated cardiomyopathy. A highly sensitive nested polymerase chain reaction (NPCR) is required to study the mechanisms of viral persistence in the myocardium.

OBJECTIVES

To develop an enterovirus group-specific NPCR system, to compare it to the reverse-transcription PCR (RT-PCR) plus Southern hybridisation and to investigate the dynamics of viral RNA in a murine model of myocarditis induced by CVB3.

STUDY DESIGN

Primers corresponding to the conserved sequences in the 5'-nontranslated region of enteroviruses were designed to ensure a broad specificity. The specificity of PCR products was confirmed by Southern hybridisation. The sensitivity of RT-PCR or NPCR was assessed using reconstructed infected muscle samples. The myocardial samples of the SWR murine model of CVB3-myocarditis were collected from day 1 to 30 after infection. The presence of viral RNA was detected by the RT-PCR or NPCR and infectious virus was isolated by cell culture.

RESULTS

Both RT-PCR and NPCR could detect all 11 representative enteroviruses. The NPCR could detect as few as 0.01 plaque forming unit of virus, 100 times more sensitive than the RT-PCR. Virus was isolated from the myocardium in acute phase, but was no longer recoverable after 9 days. Viral RNA was detected by the NPCR technique throughout the studied period.

CONCLUSIONS

An enterovirus group-specific NPCR system was developed and was much more sensitive than the RT-PCR technique. It can replace the Southern hybridisation of RT-PCR products. The presence of viral RNA in the myocardium after acute phase indicates a possibility of CVB3 shifting to persistent infection in the SWR mice.

Toll-like receptor 4 is expressed with enteroviral replication in myocardium from patients with dilated cardiomyopathy

Expressions of innate immune response proteins, most notably proinflammatory cytokines, against enteroviral (EV) infection have been documented in the heart of human dilated cardiomyopathy (DCM). Toll-like receptor 4 (TLR4) activates signaling pathways leading to the expression of proinflammatory cytokines implicated the etiology of DCM. We sought to determine whether EV replication activates TLR4-dependent immune response in myocardium obtained from patients with DCM. Endomyocardial biopsy tissues were obtained from 56 patients with DCM and 10 controls. Levels of plus- and minus-strand EV RNA and TLR4 mRNA were measured by real-time RT-PCR. Immunohistochemical analysis was performed to identify the cellular source of EV capsid protein VP1 and TLR4. Both plus- and minus-strand EV RNA were detected in 19 DCM patients (34%). Neither strand of EV RNA was detected in controls. TLR4 mRNA levels were higher in DCM patients than in controls (P<0.001). A positive correlation was found between TLR4 levels and each strand type of EV RNA in EV RNA-positive patients (plus-strand vs TLR4: r=0.69, P<0.001; minus-strand vs TLR4: r=0.65, P=0.002). VP1/TLR4 double staining showed extensive colocalization of VP1 and TLR4 proteins in cytoplasm of cardiac myocytes in myocardium obtained from DCM patients. EV RNA-positive patients showed lower systolic function and larger ventricular volume compared with EV RNA-negative patients left ventricular ejection fraction (LVEF): P=0.002; left ventricular end-systolic diameter (LVESD): P=0.004). The DCM subgroup with high TLR4 levels showed lower LVEF and larger LVESD than the subgroup with TLR4 levels (both P<0.001). This study suggests that myocardial expression of TLR4 associates with EV replication in human DCM. EV RNA and TLR4 mRNA levels may correlate with LV dysfunction in DCM. The expression of TLR4 against EV replication may be involved in the pathogenesis of DCM.

Biological significance of a human enterovirus B-specific RNA element in the 3' nontranslated region

The secondary structures predicted for the enteroviral 3' nontranslated region (3'NTR) all seem to indicate a conformation consisting of two (X and Y) hairpin structures. The higher-order RNA structure of the 3'NTR appears to exist as an intramolecular kissing interaction between the loops of these two hairpin structures. The enterovirus B-like subgroup possesses an additional stem-loop structure, domain Z, which is not present in the poliovirus-like enteroviruses. It has been suggested that the Z domain originated from a burst of short sequence repetitions (E. V. Pilipenko, S. V. Maslova, A. N. Sinyakov, and V. I. Agol, Nucleic Acids Res. 20:1739-1745, 1992). However, no functional features have yet been ascribed to this enterovirus B-like-specific RNA element in the 3'NTR. In this study, we tested the functional characteristics and biological significance of domain Z. A mutant of the cardiovirulent coxsackievirus group B3 strain Nancy which completely lacked the Z domain and which therefore acquired enterovirus C-like secondary structures exhibited a wild-type growth phenotype, as determined by single-cycle growth analysis with BGM cells. This result proves that the Z domain is virtually dispensable for viral growth in tissue cultures. Partial distortion of the Z domain structure resulted in a disabled virus with reduced growth kinetics, probably due to alternative conformations of the overall structure of the domain. Infection of mice showed that the recombinant coxsackievirus group B3 mutant which completely lacked the Z domain was less virulent. Pancreatic tissues from mice infected with wild-type virus and recombinant virus were equally affected. However, the heart tissue from mice infected with the recombinant virus showed only slight signs of myocarditis. These results suggest that the enterovirus B-like-specific Z domain plays a role in coxsackievirus-induced pathogenesis.

The group B coxsackieviruses and myocarditis

The six serotypes of the group B coxsackieviruses (CVB) are common human enteroviruses linked etiologically to inflammatory cardiomyopathies. This has been demonstrated by molecular detection of enteroviral RNA in human heart tissue, serologic associations with disease, and virus isolation from cases of fulminant myocarditis. The murine model of CVB-associated myocarditis has demonstrated that CVB can be attenuated through mutations at different genomic sites. Human CVB3 isolates demonstrate varying degrees of cardiovirulence in the murine model; one site of virulence determination has been mapped to domain II of the 5' non-translated region. The interplay of CVB replication and the immune response to that replication in the heart is a complex interaction determining the extent to which the virus replication is limited and the degree to which a pathogenic inflammation of cardiac muscle occurs. Studies of CVB3-induced myocarditis in murine strains lacking subsets of the immune system or genes regulating the immune response have demonstrated a pivotal role of the T cell response to the generation of myocarditis. While CVB are associated with 20-25% of cases of myocarditis or cardiomyopathy, the severity of the disease and the existence of attenuated strains shown to generate protective immunity in animal models indicates that vaccination against the CVBs would be valuable.

Nitric oxide and Coxsackievirus B3 myocarditis: differential expression of inducible nitric oxide synthase in mouse heart after infection with virulent or attenuated virus

Increased expression of inducible nitric oxide synthase (iNOS) has been found in inflammatory myocardial disease and increased production of nitric oxide (NO) has both an inhibitory effect on virus replication and a cytotoxic effect on host cells. To investigate the relationship between severity of enteroviral myocarditis and iNOS expression, a characterised murine model was infected with either cardiovirulent or an attenuated Coxsackievirus B3 and myocardial samples were collected on Day 7. The ability of these viruses to induce NOS expression was compared by measurement of iNOS enzyme activity and localisation of iNOS protein or peroxynitrite, a product of excessive NO production. In accordance with previous reports, high expression of iNOS was detected in mice infected with the cardiovirulent virus. The iNOS protein was located mainly in infiltrating macrophages in and around foci of necrotic myofibres where viral genomic RNA was detected. In contrast, the level of iNOS expression was significantly lower in mice infected with the attenuated virus. This correlates with fewer and smaller myocarditic lesions and less infiltrating cells in the heart. iNOS was not detected in mock-infected mice by the above assays. These findings suggest that one mechanism of attenuation may be associated with the reduced ability of the variant to induce NOS expression in the heart. This also confirms a cytotoxic role for NO in the pathogenesis of Coxsackievirus B3-induced myocarditis.

Characterization of enterovirus isolates from patients with heart muscle disease in a selenium-deficient area of China

An association of enterovirus infection with endemic cardiomyopathy (Keshan disease [KD]) and outbreaks of myocarditis in selenium-deficient rural areas of southwestern China has been established. Enteroviruses have been isolated from patients with KD or during outbreaks of myocarditis in last two decades. Six of these isolates grew readily in cell lines (Vero or HEp-2) and were investigated by a novel molecular typing method apart from serotyping and pathogenicity. A neutralization assay identified two isolates from KD as coxsackievirus serotype B2 (CVB2) and two isolates from myocarditis as coxsackievirus serotype B6 (CVB6) but failed to type the remaining two isolates, also from myocarditis. Direct nucleotide sequencing of reverse transcription-PCR products amplified from the 5' nontranslated region (5'NTR) of these viruses confirmed that they belong to a phylogenetic cluster consisting of coxsackie B-like viruses, including some echovirus serotypes. Sequence analysis of the coding region for viral capsid protein VP1 showed that two isolates serotyped as CVB2 have the highest amino acid sequence homology with CVB2 and that the remaining four isolates, two CVB6 and the two unknown serotypes, are most closely related to the sequence of CVB6. Sequences among these isolates varied from 82.3 to 99% in the 5'NTR and from 69 to 99% in VP1, indicating no cross contamination. The pathogenicity of these viruses in adult and suckling mice was assessed. None caused pathologic changes in the hearts of adult MF-1 or SWR mice, although pancreatitis was evident. However, the four CVB6-like viruses caused death in suckling mice, similar to a virulent coxsackievirus group B3 laboratory strain. In conclusion, the sequence data confirm that coxsackievirus group B serotypes are predominant in the region in which KD is endemic and may be the etiological agents in outbreaks of myocarditis. VP1 genotyping of enteroviruses is accurate and reliable. Animal experiments indicate that isolates may differ in pathogenicity.

High prevalence of enteroviral genomic sequences in myocardium from cases of endemic cardiomyopathy (Keshan disease) in China

OBJECTIVE

To verify the aetiological involvement of enterovirus and identify the viral genomic sequences in Keshan disease.

DESIGN

Formalin fixed, paraffin embedded myocardial necropsy tissue samples were collected in Keshan disease endemic regions. Fourteen cases with a histologically confirmed diagnosis of subacute or chronic Keshan disease were studied. Control tissue included 10 samples of myocardium from cases of cerebral trauma and one from accidental acid intoxication. One sample from a case of enteroviral myocarditis was used as a positive control. The presence of viral genomic RNA was investigated using an established reverse transcription nested polymerase chain reaction (PCR) coupled with direct nucleotide sequencing. Further investigations of PCR positive samples included in situ antigen detection or hybridisation to confirm positive results.

RESULTS

Nine of 14 myocardial samples from Keshan disease cases and the positive control were positive for the enteroviral RNA. All the controls were negative. Six of the PCR positive samples were investigated further by in situ enteroviral antigen or RNA detection and all were positive. DNA sequencing of six representative PCR products confirmed that they were homologous to the 5' non-translated region of enteroviral genomic RNA. Five had highest homology to coxsackievirus B genotypes and one was identical to poliovirus type 3.

CONCLUSIONS

These results support an aetiological role for enteroviral infection in Keshan disease. Nucleotide sequence data suggest that coxsackievirus B or coxsackie B like viruses are often involved in Keshan disease.

Genomic determinants of cardiovirulence in coxsackievirus B3 clinical isolates: localization to the 5' nontranslated region

Coxsackievirus B3 (CVB3) infections can cause myocarditis in humans and are implicated in the pathogenesis of dilated cardiomyopathy. The natural genetic determinants of cardiovirulence for CVB3 have not been identified, although using strains engineered in the laboratory, cardiovirulence determinants have been identified in the CVB3 5' nontranslated region (5'NTR) and capsid. The myocarditic phenotypes of two CVB3 clinical isolates were determined using an established murine model of inflammatory heart disease. The 5'NTRs and capsid proteins of the noncardiovirulent CVB3/CO strain and cardiovirulent CVB3/AS strain were examined to determine their influence on the cardiovirulence phenotype. Six intratypic chimeric viruses were constructed in which 5'NTR and capsid sequences of the infectious cDNA copy of the cardiovirulent CVB3/20 genome were replaced by homologous sequences from CVB3/CO or CVB3/AS. Chimeric strains were tested for cardiovirulence by inoculation of C3H/HeJ mice. Sections of hearts removed at 10 days postinoculation were examined for evidence of myocarditis by light microscopy and assayed for the presence of virus. Replacement of the CVB3/20 capsid coding region by that from the homologous region of CVB3/CO resulted in no change in the cardiovirulent CVB3/20 phenotype, with virus recoverable from the heart at 10 days postinoculation. However, recombinant virus containing the CVB3/CO 5'NTR alone or the 5'NTR and capsid sequences together were not myocarditic, and infectious virus was not recovered from the myocardium. Chimeric viruses containing the CVB3/AS 5'NTR alone, capsid sequence alone, or both together preserved the myocarditic phenotype. These data support the 5'NTR as the primary site in the determination of the natural cardiovirulence phenotype of CVB3.

Localization of enteroviral antigen in myocardium and other tissues from patients with heart muscle disease by an improved immunohistochemical technique

The association of enterovirus infection and heart muscle diseases has been investigated extensively by detection of viral genomic RNA using nucleic acid hybridization and the reverse transcription-polymerase chain reaction. To further understand the role of enterovirus and its persistence in these diseases, an immunohistochemical technique was optimized to investigate the expression of viral capsid proteins in situ. A monoclonal antibody (5-D8/1) against an epitope in the N-terminus of capsid protein VP1, conserved in the enterovirus genus, was employed. To enhance sensitivity, the EnVison system was used to detect antigen-antibody complex. VP1 was detected in formalin-fixed, paraffin-embedded endomyocardial biopsy or postmortem myocardial tissues and in liver, spleen, lung, kidney, and pancreas from patients with myocarditis or dilated cardiomyopathy, but not from controls. VP1 was localized in cytoplasm of myofibers, often adjacent to necrosis and infiltrate in myocarditis, and was clustered or scattered in dilated cardiomyopathy. This technique can be used for a definitive laboratory diagnosis of enterovirus-associated diseases and for studying the mechanisms of virus persistence in chronic myocardial disease.

Molecular detection of enteroviruses from an outbreak of hand, foot and mouth disease in Malaysia in 1997

Enterovirus 5'UTR sequences were detected by RT-PCR in 22 out of 47 suspected hand, foot and mouth disease (HFMD) patients during an outbreak of the disease with incidences of fatal brainstem encephalomyelitis in Malaysia in 1997. Genetic and phylogenetic analyses of the isolates 5'UTR sequences suggest the presence of predominantly enteroviruses with high sequence similarities to Echovirus 1 and Coxsackievirus A9 in the Malaysian peninsula. No fatal cases, however, were associated with these isolates. The remaining isolates, including all (4/4) isolates of the fatal cases from the Malaysian peninsula and Sarawak shared very high sequence identity with enterovirus 71MS (EV71). These findings suggest that several enteroviruses were circulating in Malaysia during the outbreak period, with only EV71 causing fatal infections.

Characterization of anti-heart antibodies in mice after infection with coxsackie B3 virus

Coxsackie virus B3 (CVB3) infection results in a marked inflammatory response and the production of autoantibodies to cardiac antigens, with cardiac myosin heavy chain documented to be the most immunogenic antigen. The present study investigated the temporal appearance of anti-heart antibodies in mice after mock infection or infection with an attenuated variant of CVB3 or wildtype CVB3 by SDS-PAGE and Western blotting. Further characterization of the autoantigens was carried out using 2D electrophoresis followed by Western blotting. Mice infected with wildtype CVB3 demonstrated high levels of IgG anti-heart antibodies, reacting predominantly with myosin heavy chain but also with numerous other myocardial proteins. Significant increases in anti-myosin heavy chain, anti-actin, and anti-tropomyosin antibodies were seen in wildtype-infected mice as early as day 7 postinfection compared to those mice that were mock infected or infected with attenuated virus. Characterization of other antigens revealed novel reactivities against myosin subfragments, heat shock proteins, and desmin and its subfragments.

Characterization of Coxsackie B virus RNA in myocardium from patients with dilated cardiomyopathy by nucleotide sequencing of reverse transcription-nested polymerase chain reaction products

This study was performed to detect and characterize the enterovirus present in myocardium of some patients with heart muscle disease by nucleotide sequencing of polymerase chain reaction (PCR) products after amplification with enterovirus group-specific primers. Enterovirus sequences have been detected previously in myocardium of patients with myocarditis or dilated cardiomyopathy and seem causal, although the particular virus serotypes involved have not been identified. In a prospective study of endomyocardial biopsy specimens from 35 consecutive patients with suspected heart muscle disease, enterovirus sequences from the 5' nontranslated region were amplified by reverse transcription-nested PCR using group-specific primers. This region contains both conserved and variable sequence motifs, characteristic of particular enterovirus serotypes. The nucleotide sequences of individual PCR products were determined by cycle sequencing and compared with all known sequences (GenBank/EMBOL), using the GCG software package. Endomyocardial biopsy specimens from 9 of 21 (42.9%) patients with a histologically confirmed diagnosis of dilated cardiomyopathy were positive for enterovirus by PCR, compared with only 1 of 14 (7.1%) patients with other myocardial pathological conditions (Fisher's exact probability=0.0275: odds ratio=9.75; 95% confidence interval=1.31-72.78). The nucleotide sequence of the PCR products differed, indicating no cross-contamination. However, computerized comparison showed that each had greatest homology with the 5' nontranslated region of Coxsackie B virus but contained up to 11% sequence variations compared with the prototype Coxsackie B3 strain Nancy. Parallel investigation of tissue from our mouse model of Coxsackievirus B3-induced myocarditis showed that nucleotide sequence changes are not introduced by reverse transcription or PCR. These data support the link between enteroviral infection and dilated heart muscle disease and suggest that Coxsackie B serotypes are the enteroviruses most frequently involved.

Nucleotide sequence of an attenuated mutant of coxsackievirus B3 compared with the cardiovirulent wildtype: assessment of candidate mutations by analysis of a revertant to cardiovirulence

BACKGROUND

Coxsackievirus B3 (CVB3) causes myocarditis in the SWR (H2q) mouse model and persistence of CVB3 in myocardium disposes to the development of dilated cardiomyopathy. An attenuated strain of CVB3 has been isolated, sequenced and several candidate mutations for attenuation identified. Derivation of a revertant to cardiovirulence allows the significance of these mutations to be assessed.

OBJECTIVES

To ascertain which candidate mutation(s) determine(s) the attenuated phenotype.

STUDY DESIGN

A revertant to cardiovirulence was isolated following passage through severe combined immunodeficient disease (SCID) mouse heart. The 5'-non-translated region (NTR) and region coding for capsid proteins were sequenced and compared to the wildtype and attenuant.

RESULTS

There are five candidates for attenuation: (1) A-G at base 580 in the 5'-NTR; (2) A-T at base 690 in the 5'-NTR; (3) CG-GC at bases 1401/2 (Thr to Ser at amino acid 151 in VP2); (4) AA-GT at bases 2691/2 (Lys to Ser at amino acid 80 in VP1); (5) A-G at base 2916 (Asp to Gly at amino acid 155 in VP1). It was shown previously that mutations at 580, 690 and 2691/2 are not important in attenuation. Additionally, there are three novel mutations in the coding region of the revertant and one in the 5'-NTR which are unlikely to be relevant for attenuation as they are not present in the attenuant. Of nucleotide changes seen at 1401/2 and 2916 in the attenuant, only 2916 reverts to the wildtype sequence and so is a strong candidate for a determinant of attenuation.

Molecular typing of enteroviruses: current status and future requirements. The European Union Concerted Action on Virus Meningitis and Encephalitis

Human enteroviruses have traditionally been typed according to neutralization serotype. This procedure is limited by the difficulty in culturing some enteroviruses, the availability of antisera for serotyping, and the cost and technical complexity of serotyping procedures. Furthermore, the impact of information derived from enterovirus serotyping is generally perceived to be low. Enteroviruses are now increasingly being detected by PCR rather than by culture. Classical typing methods will therefore no longer be possible in most instances. An alternative means of enterovirus typing, employing PCR in conjunction with molecular genetic techniques such as nucleotide sequencing or nucleic acid hybridization, would complement molecular diagnosis, may overcome some of the problems associated with serotyping, and would provide additional information regarding the epidemiology and biological properties of enteroviruses. We argue the case for developing a molecular typing system, discuss the genetic basis of such a system, review the literature describing attempts to identify or classify enteroviruses by molecular methods, and suggest ways in which the goal of molecular typing may be realized.

Characterisation of genomic RNA of Coxsackievirus B3 in murine myocarditis: reliability of direct sequencing of reverse transcription-nested polymerase chain reaction products

SWR mice develop viral myocarditis histologically similar to the human disease following inoculation with a cardiovirulent Coxsackievirus B3 (CVB3), reactivated from a sequenced cDNA clone of Nancy strain. A sequence of 215 nucleotides, or 628 nucleotides in representative cases, of the 5'non-translated region (5'NTR) of CVB3 genome was amplified from myocardial samples of the infected mice by reverse transcription-nested polymerase chain reaction (RT-NPCR). In order to verify the viral nucleotide sequence and detect the mutation frequency of the viral RNA, the nucleotide sequence of NPCR products were determined by direct sequencing in both orientations. The amplified products from mouse heart on day 1-13 post-inoculation were sequenced and, in each case, the consensus sequence was identical to the published sequence of CVB3 (Nancy strain). To evaluate further the reproducibility of these techniques, three tissue samples from the same infected mouse heart were processed independently. Sequences of their RT-NPCR products were identical to each other as well as to the published sequence. When two attenuated CVB3 mutants were amplified and sequenced, single mutations were detected. To evaluate the overall fidelity of these two combined techniques, genomic RNA of a different CVB3 Nancy strain stock, Coxsackievirus A9 or poliovirus sabin 1 was amplified and the NPCR products sequenced. Each product showed 100% homology with its published sequence. These results demonstrate that the coupled technique of the enterovirus RT-NPCR with direct sequencing of NPCR products generates accurate consensus sequence data and this technique proved to be useful in verification of enteroviral amplicons and in detection of nucleotide mutations. In addition, a low mutation frequency was found in the 5'NTR of CVB3 detected in myocardial samples of immunocompetent mice up to 13 days.

Differential recruitment of B and T cells in coxsackievirus B4-induced pancreatitis is influenced by a capsid protein

Two genetically similar variants of coxsackievirus B4, CB4-P and CB4-V, cause distinct disease syndromes in mice. A multidisciplinary approach was used to examine the events occurring in situ. The CB4-P variant induced acute pancreatitis, followed by repair of the exocrine tissues, while the CB4-V variant induced chronic pancreatitis, characterized by extensive destruction of the exocrine tissues. Since CB4-V replicated more efficiently than CB4-P in vivo, the more extensive tissue injury associated with CB4-V infection could be explained as the result of a higher level of viral replication. However, the fact that CB4-V replicated more efficiently in a mouse strain that survives infection than in a strain that succumbs to infection suggests that immune-mediated mechanisms as well as viral cytolysis may contribute to pancreatic tissue injury. To address the role of the immune system in virus-induced pancreatitis, the cell types within the inflammatory infiltrate were analyzed by flow cytometry. B cells (34 to 75%) were the most abundant, followed by T cells (10 to 30%), natural killer cells (4 to 8%), and macrophages (0 to 6%). Recruitment (and perhaps proliferation) of B and T cells to the pancreatic tissues was influenced by viral strain. Differential recruitment of T and B cells may reflect altered antigenic sites between CB4-P and CB4-V. The viral sequence that affected T- and B-cell recruitment was identified as a threonine residue at position 129 of the VP1 capsid protein.

Generation of an infectious cDNA of a highly cardiovirulent coxsackievirus B3(CVB3m) and comparison to other infectious CVB3 cDNAs

An infectious cDNA of a highly myocarditic coxsackievirus B3 (CVB3m; Nancy strain) was cloned. Sequence data revealed 43 extra non-viral nucleotides upstream of the initial 5' sequence. However, the authentic 5' end sequence was maintained during replication of viral RNA transfected into HeLa cells, suggesting the RNA synthesizing complex edits the picornaviral 5' terminus sequence. Nucleotide sequences of the 5' nontranslated region and the capsid protein gene sequence of CVB3m were compared with the published sequences of five other CVB3 Nancy strains and two main lineages were found. In comparative assays for cardiovirulence, three of four CVB3 tested were cardiovirulent in adolescent male CD-1 mice. Only one of the three available CVB3 strains was neutralized with several anti-CVB3m monoclonal antibodies, suggesting that mutations in the surface epitopes of the capsid polypeptides contribute to antigenic drift within the serotype, perhaps in part through immunoselective pressures. Thus, phenotypic diversity of CVB3 within the prototype Nancy strain is an example of RNA viruses adapting to changing environments (cells, mice and humans) through mutations and selective pressure.

Coxsackievirus-induced chronic inflammatory myopathy: virus variants distinguish between acute cytopathic effects and pathogenesis of chronic disease

Infection with the Tucson strain of coxsackievirus B1 (CVB1T) causes the development of chronic inflammatory myopathy (CIM) and hind limb weakness in susceptible strains of mice. In this study, a panel of six plaque-purified viruses exhibiting either small or large plaque phenotypes was derived from parental CVB1T and parental CVB1T that had been passaged through monkey kidney cells. All six variants caused similar acute histopathology in muscle, but three of four passaged viruses (AMP1, AMP2, and AMP3) did not induce CIM while the fourth (MP3) caused some hind limb weakness but without associated muscle inflammation. In contrast, both viruses (MP1 and MP2) isolated directly from the parental CVB1T stock were myopathic. Large plaque MP2 caused higher mortality and more rapid inhibition of host cell biosynthesis, but both MP1 and MP2 induced CIM that was comparable to that induced by parental CVB1T. Plaque size was a stable characteristic of the variants but did not correlate with their ability to induce CIM. Five of the six variants showed equivalent levels of replication in muscle, monkey kidney cells, and GB myoblasts while one, AMP3, was selectively impaired for replication. Receptor binding and virus-induced inhibition of host cell transcription and translation were not linked to myopathogenicity. Thus, most of the passaged variants are robust infectious viruses, suggesting that viral induction of CIM does not depend solely on cytopathogenicity during the acute infection.

A mutation in the puff region of VP2 attenuates the myocarditic phenotype of an infectious cDNA of the Woodruff variant of coxsackievirus B3

Coxsackievirus B3 (CVB3) infections induce myocarditis in humans and mice. Little is known about the molecular characteristics of CVB3 that activate the cellular immunity responsible for cardiac inflammation. Previous experiments have identified an antibody escape mutant (H310A1) of a myocarditic variant of CVB3 (H3) that attenuates the myocarditic potential of the virus in mice in spite of ongoing viral replication in the heart. We have cloned full-length infectious cDNA copies of the viral genome of both the wild-type myocarditic H3 variant of CVB3 and the antibody escape mutant H310A1. Progeny viruses maintained the myocarditic and attenuated myocarditic potential of the parent viruses, H3 and H310A1. The full sequence of the H3 viral cDNA is reported and compared with those of previously published CVB3 variants. Comparison of the full sequences of H3 and H310A1 viruses identified a single nonconserved mutation (A to G) in the P1 polyprotein region at nucleotide 1442 resulting in an asparagine-to-aspartate mutation in amino acid 165 of VP2. This mutation is in a region that corresponds to the puff region of VP2. Nucleotide 1442 of the H3 and H310A1 cDNA copies of the viral genome was mutated to change amino acid 165 of VP2 to aspartate and asparagine, respectively. The presence of asparagine at amino acid 165 of VP2 is associated with the myocarditic phenotype, while an aspartate at the same site reduces the myocarditic potential of the virus. In addition, high-level production of tumor necrosis factor alpha by infected BALB/c monocytes is associated with asparagine at amino acid 165 of VP2 as has been previously demonstrated for the H3 virus. These findings identify potentially important differences between the H3 variant of CVB3 and other previously published CVB3 variants. In addition, the data demonstrate that a point mutation in the puff region of VP2 can markedly alter the ability of CVB3 to induce myocarditis in mice and tumor necrosis factor alpha secretion from infected BALB/c monocytes.

Serological and molecular evidence of enterovirus infection in patients with end-stage dilated cardiomyopathy

OBJECTIVE

To study the relative diagnostic value of enterovirus-specific molecular biological and serological assays in patients with end-stage dilated cardiomyopathy, and to investigate the possible role of other cardiotropic viruses in dilated cardiomyopathy.

DESIGN

Analysis of recipient myocardial tissue and serum from patients with dilated cardiomyopathy and controls undergoing cardiac transplantation for end-stage cardiac disease.

SETTING

University virology department and transplantation unit.

METHODS

Reverse transcriptase-polymerase chain reaction and nucleotide sequence analysis of myocardial RNA and DNA; enterovirus-specific in situ hybridization; enterovirus-specific immunoglobulin M detection.

RESULTS

Enterovirus RNA was detected in myocardial tissue from only a small proportion of (five of 75) hearts. However, although enterovirus-specific immunoglobulin M responses were detected in 22 (28%) of 39 controls patients, a significantly higher prevalence was observed among patients with dilated cardiomyopathy (22 (56%) of 39 patients; P < 0.005). All enteroviruses detected in myocardium showed greatest nucleotide sequence homology with coxsackievirus type B3. Detection of enterovirus RNA in myocardium by the polymerase chain reaction and by in situ hybridisation gave comparable results. Other potentially cardiotropic virus genomes, including human cytomegalovirus, influenzaviruses, and coronaviruses were not detected in myocardium.

CONCLUSION

This study found that enterovirus-specific immunoglobulin M responses provided the strongest evidence of enterovirus involvement in patients with end-stage dilated cardiomyopathy. However, the high background prevalence of these responses limits their diagnostic value. The finding that enteroviruses detected in myocardium were coxsackievirus type B3 accords with recent findings in patients with acute myocarditis, and indicates that this serotype is the major cardiotropic human enterovirus.

Permissiveness of human embryonal fibroblasts for coxsackieviruses B3. Investigations on virus genetic markers in vitro and localization of virus receptor distribution by immunogold replica technique

In our previous paper (29) we could show, that the replication of four Coxsackie B3 virus strains in human fibroblast lines from different origin was dependent on both the virus strain and the cell line used. Although generally no cytopathic effect could be observed out of one virus strain more pathogenic virus variants could be selected able to destroy virus-sensitive as well as insensitive fibroblasts. The present study was designed to characterize these virus strains by using several in vitro genetic markers. Differences were found concerning plaque size and the temperature marker, whereas the other markers (d, DD, DEAE-D) remained constant. Furthermore, these models of persistent as well as lytic CVB3 infection were analysed by immunoelectron microscopy to study the interaction of viral ligands with cellular receptors. The qualitative and quantitative differences in adsorption of the CVB3 strains to two human fibroblast lines as well as to HeLa cells corresponded well with the virological results. They underline that even in vitro in human cell lines of different origin changes in distribution, quantity and quality of receptors were demonstrable forming the base for the various virus sensitivity.

Genetics of coxsackievirus B cardiovirulence and inflammatory heart muscle disease

Coxsackieviruses B (CVBs) are etiological agents of human inflammatory myocardial disease. The genetics of the coxsackieviral virulence phenotype in mice are now beginning to be understood with the availability of infectious cDNA copies of CVB genomes. Investigations to date with CVB3 and CVB4 have shown that sites within a non-translated region and in the capsid proteins can affect the virulence phenotype. The relative importance of these sites to expression of the phenotype remains unclear.

Coxsackievirus B3 clinical isolates and murine myocarditis

Fifteen clinical coxsackievirus B3 (CVB3) isolates were assessed for cardiopathologic capabilities in adolescent male CD-1 mice in comparison to two well characterized cardiovirulent CVB3 strains. One isolate was cardiovirulent, one minimally cardiovirulent and the remaining 13 isolates were noncardiovirulent. The two cardiovirulent isolates and one well characterized cardiovirulent strain, established higher viremic titers, in comparison to five noncardiovirulent isolates that were examined. The two cardiovirulent isolates and one well characterized cardiovirulent strain replicated to significantly higher titers than five noncardiovirulent isolates in primary cultures of murine neonatal or adolescent cardiac fibroblasts. Nucleotide sequence analysis of an area defined by nucleotides(N)300-N599 in the 5'-nontranslated region were performed on the two well characterized cardiovirulent CVB3 strains, the two cardiovirulent isolates and 12 noncardiovirulent isolates. The data detected a single discriminatory nucleotide position. An A was present at N565 in three of four cardiovirulent CVB3, whereas a U or C was present in this position in 12 of 12 noncardiovirulent CVB3. In toto, these data are compatible with the hypothesis that the type of the nucleotide at N565, a position within the internal ribosome entry site, is associated with capacity of a CVB3 for replication in vivo and in vitro and this capacity for vigorous replication is associated with cardiovirulence.

A point mutation in the VP4 coding sequence of coxsackievirus B4 influences virulence

In analyzing the molecular determinants of virulence of coxsackievirus B4, chimeric viruses were constructed from avirulent and virulent viruses. The vCB424 recombinant contained a single nucleotide substitution on an avirulent genetic background, resulting in replacement of Ser-16 of VP4 with Arg-16. Mice infected with vCB424 displayed an intermediate phenotype.

Experimental myocarditis induced by two different coxsackievirus B3 variants: aspects of pathogenesis and comparison of diagnostic methods

The ability of two coxsackievirus B3 (CBV3) variants to induce myocarditis in BALB/c mice was studied and plaque-forming assay, polymerase chain reaction (PCR), in situ hybridization, and immunohistochemistry were compared for detecting viruses and viral components in the myocardium. The virological findings were related to histopathologic and ultrastructural changes in the myocardium. CBV3-W induced severe myocarditis characterized by massive myocyte necrosis. Widely distributed myocyte damage clearly preceded modest inflammatory infiltrates in the myocardium. In contrast, CBV3-M1 induced mild myocardial injury. Both variants caused fulminant pancreatitis with nearly complete necrosis of the exocrine pancreas. CBV3 RNA was identified by PCR in the myocardium of CBV3-W-infected mice until the end of the follow-up period of 14 days. Moreover, semiquantitative results were obtained when the PCR/hybridization results were analyzed by a phosphor imaging system. Immunohistochemistry and in situ hybridization from formaldehyde-fixed, paraffin-embedded specimens were highly similar in detecting viral components during the early stages of the myocardial injury. The results indicate that: (i) direct viral damage plays an essential role in acute murine CBV3-induced myocarditis, (ii) PCR appears a useful and sensitive diagnostic method in acute myocarditis, and (iii) immunohistochemistry as a specific and relatively rapid method might be practicable also in studying the early stages of acute myocarditis from archival clinical material.

The cardiovirulent phenotype of coxsackievirus B3 is determined at a single site in the genomic 5' nontranslated region

We report the construction of chimeric coxsackievirus B3 (CVB3) strains in which sequences of an infectious cDNA copy of a noncardiovirulent CVB3 genome were replaced by the homologous sequences from a cardiovirulent CVB3 genome to identify which of 10 predicted genetic sites determine cardiovirulence. Cardiovirulent phenotype expression was consistently linked to nucleotide 234 (U in cardiovirulent CVB3 and C in avirulent CVB3) in the 5' nontranslated region. Reconstructions of the parental noncardiovirulent CVB3 genome from chimeras restored the noncardiovirulent phenotype when tested in mice. Inoculation of severe combined immunodeficient (scid) mice with the noncardiovirulent CVB3 strain resulted in massive cardiomyocyte necrosis in all animals. Sequence analysis of viral genomes isolated from twelve scid mouse hearts showed that only nucleotide position 234 was different (a C-->U transition) from that in the input parental noncardiovirulent CVB3 genome. Higher-order RNA structures predicted by two different algorithms did not demonstrate an obvious local effect caused by the C-->U change at nucleotide 234. Initial studies of parental and chimeric CVB3 replication in primary cultures of fetal murine heart fibroblasts and in adult murine cardiac myocytes demonstrated that viral RNA transcriptional efficiency is approximately 10-fold lower for noncardiovirulent CVB3 than for cardiovirulent CVB3. CVB3 did not shut off protein synthesis in murine cardiac fibroblasts, nor were levels of viral protein synthesis significantly different as a function of viral phenotype. Taken together, these data support a significant role for determination of the CVB3 cardiovirulence phenotype by nucleotide 234 in the 5' nontranslated region, possibly via a transcriptional mechanism.

A single amino acid substitution in the capsid protein VP1 of coxsackievirus B3 (CVB3) alters plaque phenotype in Vero cells but not cardiovirulence in a mouse model

We previously described a large plaque attenuant (p14V-1) derived from a cardiovirulent Coxsackievirus B3 (CVB3) and showed that there were no major determinants of either attenuation or plaque phenotype in the 5' nontranslated region (5'NTR). Part of the region encoding the last 124 amino acids of VP3 and the first 106 amino acids of VP1 of the attenuant was then sequenced and compared to the wild-type. Three nucleotide changes were found in the VP1 coding region: a silent single base change at nucleotide position 2467 (C to U) and a double-base change at position 2690-1 (AA to GT), which leads to a change from lysine to serine at amino acid position 80. This mutation maps to the begining of B-C loop of the three-dimensional structure of VP1 of CVB3, where a distinct surface projection is formed. Two infectious chimeric cDNA clones were constructed, based on a cardiovirulent cDNA construct. In one construct, the 5'NTR and the VP3-VP1 region were from p14V-1 and in the other, only the VP3-VP1 region was from this attenuant. Both chimeric viruses produced large plaques on Vero cell monolayers, similar to p14V-1 but larger than the prototypic cardiovirulent virus. In vivo experiments showed that both chimeric viruses induced myocarditis in a murine model, similar to wild-type virus. We conclude that mutation serine-80 in capsid protein VP1 of p14V-1 is a determinant of the large plaque phenotype but is not responsible for attenuation.

Rapid genomic evolution of a non-virulent coxsackievirus B3 in selenium-deficient mice results in selection of identical virulent isolates

Previous work from our laboratory demonstrated that selenium deficiency in the mouse allows a normally benign (amyocarditic) cloned and sequenced Coxackievirus to cause significant heart damage. Furthermore, Coxsackievirus recovered from the hearts of selenium-deficient mice inoculated into selenium-adequate mice still induced significant heart damage, suggesting that the amyocarditic Coxsackievirus had mutated to a virulent phenotype. Here we report that sequence analysis revealed six nucleotide changes between the virulent virus recovered from the selenium-deficient host and the avirulent input virus. These nucleotide changes are consistent with known differences in base composition between virulent and avirulent strains of Coxsackievirus. To the best of our knowledge, this is the first report of a specific nutritional deficiency driving changes in a viral genome, permitting an avirulent virus to acquire virulence due to genetic mutation.