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Encephalomyocarditis virus was photoinactivated by a dilution of 1:30,000 neutral red and 70 minutes exposure to light. A dye inactivation of the EMC virus is possible without destruction of its antigenicity. The EMC virus vaccine induced a good immunity response in mice; we did not find any infectious virus.
Encephalomyocarditis (EMC) virus RNA contains a covalently bound sequence of polyriboadenylic acid (poly(A). This was determined by two-dimensional gel electrophoresis of complete T1 and pancreatic RNase digests of formamidesucrose gradient-purified RNA and subsequent analysis of the product by alkaline hydrolysis. The size of the EMC virus genomic poly(A) sequence was estimated by formamide-polyacrylamide gel electrophoresis of the RNase-resistant product, or by [3H-]poly(U) hybridization to freshly purified virion RNA, to be, on average, 40 nucleotides in length. The evidence obtained from [3H-]isoniazid labelling and other experiments would indicate that the poly(A) sequence is located at the 3'-terminus of EMC virus RNA.
Deproteinized encephalomyocarditis [32P]RNA, after digestion with a mixture of RNases A, T1 and T2, yields mononucleotides and a labelled compound, which is positively charged at pH 3.5. This product can be digested with pronase and has a close electrophoretic mobility to a protein with a molecular weight of 7000-8000. Covalently bound nucleotide-peptides were isolated from this compound after treatment with RNases and pronase. It was shown that the 5'-terminal uridylic acid is covalently linked with peptides. The phosphodiester bond between uridylic acid and peptides is discussed.
Replication of encephalomyocarditis virus and its cytopathic effects were studied in myelinated cultures of dorsal root ganglia obtained from newborn mice. Six hours after infection virus progeny was detected in the culture. At 24 h the virus titer reached 2 times 10(6) PFU per culture and remained at this level until 48 h. The first cytopathic alterations began at 24 h and consisted of rounding of Schwann and satellites cells and their detachment from neurons. Later, bead-like swellings of the myelin appeared along the axons followed by splitting and degeneration of lamellae. The cytopathic effect in the neurons started 29 h after infection, reaching complete neuronolysis at 48 h. Virus particles, scattered or arranged in crystal-like aggregates, were first seen in the cytoplasm of glial cells and then in neurons and axons.
Encephalomyocarditis virus in aerosols is inactivated rapidly at relative humidities below 50%. In glycerol-water mixtures a similar decrease of infectivity occurs when the glycerol concentration exceeds 78% (wt/wt), corresponding to a relative humidity of 50%. The decay in aerosols does not involve oxygen or surface-dependent factors. Variation of temperature shows the inactivation to be a low-energy process with an activation enthalpy of 15 kcal per mol. The damage could be ascribed to dehydration of the virion, presumably proceeding to removal of structurally essential water molecules. This might trigger irreversible changes in the protein coat, resulting in disintegration of the virion.
The M variant of encephalomyocarditis virus is very closely related serologically to five other strains of encephalomyocarditis virus. Despite the serological relationship, these five viruses differ markedly from the M variant in their tissue tropisms and only the M variant infects beta cells of the pancreas, producing diabetes.
Poly(A)-containing encephalomyocarditis virus RNA functions as an excellent template for cDNA synthesis in vitro with an RNA-dependent DNA polymerase in the presence of an oligothymidylate primer. Under appropriate conditions, discrete transcripts of increasing chain length were obtained, suitable for sequence analysis. A limited cDNA fragment of 36 nucleotides, primer (dT)10 included, was synthesized when dGTP was omitted from the reaction mixture and its primary structure was elucidated using direct DNA-sequencing methods. The complement corresponds to the 3' end of encephalomyocarditis RNA. The hexanucleotide (5'-3')(A-A-U-A-A-A) found in this sequence is also present in all 3' non-coding regions of poly(A)-containing eukaryotic mRNAs studied until now, in nearly identical positions relative to the poly(A) tail. The possible biological significance of this structural homology is discussed.
In poliomyelitis and encephalomyocarditis virus RNAs the relative frequencies of several short oligonucleotide sequences differ substantially from those expected on a random basis. The frequencies of CpGp-containing sequences are low, and the frequency of GpUpApGp is considerably lower than that of GpApUpGp. The relationship of these findings to those obtained from host cell RNAs is descussed.
Translation of encephalomyocarditis virus RNA in a cell-free system from uninfected Krebs ascites cells results in the synthesis of a major polypeptide product with a molecular weight of approximately 112,000. In contrast, when the viral RNA is translated in a cell-free system from virus-infected cells, this polypeptide is absent and the largest polypeptide produced has a molecular weight of about 100,000. This latter polypeptide comigrates on sodium dodecyl sulfate-gels with in vivo virus capsid precursor A, and the two have identical patterns of CNBr-generated peptides. A polypeptide having a molecular weight of 12,500 is also a major translation product in the system from infected cells (but not from uninfected cells). This polypeptide appears to be generated by cleavage of the NH-2-terminal portion of the viral RNA-dependent polypeptides by a proteolytic activity present in the infected cell-free system. This proteolytic activity copurifies with the 23,000-molecular weight viral capsid protein gamma, found in infected cells, through chromatography on DEAE-cellulose and cellulose phosphate. This suggests that gamma is itself a proteolytic enzyme involved in maturation of the viral capsid precursor.
The diabetogenic capacity of the M-variant of encephalomyocarditis (EMC) virus was markedly diminished after passage in mouse kidney cell cultures. One passage in mice fully restored this capacity. Virus harvested after five passages in either susceptible (SWR/J) or resistant (C57BL/6J) strains of mice was capable of producing diabetes in susceptible SWR/J mice but not in resistant C57BL/6J mice. Resistance was not overcome by inoculating mice with high concentrations of virus. Immunofluorescence studies showed that islets from strains of mice (i.e. CBA, AKR, C57BL/6J, A/J) that did not develop diabetes after infection with EMC virus, nonetheless, contained virus antigens. The percentage of cells in the islets containing virus antigens varied from 3-6% in CBA to 13-5% in A/J. In contrast 38% of the islet cells in susceptible SWR/J mice contained virus antigens. It is concluded that both the genetic background of the host and the passage history of the virus influence the development of diabetes.
Thirty temperature-sensitive mutants of encephalomyocarditis virus have been isolated and partially characterized. Fifteen of these mutants are phenotypically RNA+ thirteen are RNA-, and two are RNA +/-. Six RNA + mutants, one RNA- mutants, and one RNA +/- mutant have virions which are more thermosensitive at 56 degree C than the wild-type virions. Hela cells infected at the nonpermissive temperature with any of the RNA+ mutants produced neither infective nor noninfective viral particles. The cleavage of the precursor polypeptides in cells infected with 11 of the RNA+ mutants was defective at the nonpermissive temperature. This defect in cleavage occurred only in those precursor polypeptides leading to capsid proteins.
The M variant of encephalomyocarditis virus (EMC) infects pancreatic beta cells and causes the development of a diabetic syndrome in susceptible strains of mice. By examining four F1 crosses of susceptible and resistant strains of mice, we found that the development of diabetes after infection was inherited as a recessive trait. Analysis of the data from the F2 generation indicated that more than one gene was involved in the development of EMC-diabetes. The severity and frequency of abnormal glucose levels in EMC-infected animals was markedly influenced by environmental factors.
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Reproduction of mouse encephalomyocarditis virus (EMC) was studied in 5 continuous primate cell lines: HeLa, Fl, Detroit-6, P/7, and MIO inoculated with guanidine-dependent variant of poliomyelitis virus in the absence of guanidine. Poliomyelitis virus stimulated EMC virus reproduction in all cell lines under study. This stimulation effect was studied at length in HeLa and MIO cells. In HeLa cells, stimulation was observed at a low and moderate multiplicity of infection of EMC virus but not at a high (100 PEU/cell) multiplicity. Also, when EMC virus reproduction was stimulated, a shortening of the latent period of its multiplication cycle, an increase in the number of antigen-containing cells and the number of infectious centers were observed. In MIO cells, stimulation was found to occur both with low and high doses of EMC virus but not to be accompanied by a shortening in the latent period of EMC reproduction cycle, or any increase in the antigen-containing cells or number of infectious centers. In both cell types upon mixed infection the synthesis of virus-specific RNA's of EMC virus was enhanced. It is suggested that the stimulating effect of poliomyelitis virus is realized in HeLa and MIO cells at different stages of EMC virus reproduction.
The prevalence of encephalomyocarditis virus (EMC) antibodies among selected human populations in various regions of the world was determined by the plaque reduction neutralization method. Antibody rates among children ranged from 1.0 to 33.9%, while those among adults varied from 3.2 to 50.6%. No differences between sexes were found in the frequency of EMC infection. The pattern of age-specific antibody rates observed among the study populations suggests that EMC infection occurs primarily during childhood. There appeared to be no association between the presence of EMC antibodies and potential exposure to rats. Sera from diabetic, suspected encephalitis, and myocarditis patients were also examined for EMC neutralizing antibodies. The prevalence of antibodies among these groups was not significantly different from that of control populations in the same geographic regions. No association was demonstrated between EMC infection and these three diseases. The results of this study indicate that EMC infection in man is fairly common but that most human cases are probably asymptomatic and/or unrecognized.
Mice infected with encephalomyocarditis virus, Semliki Forest virus, influenza A2 virus, Herpesvirus hominis type 2, or murine cytomegalovirus developed a state of hyporeactivity to interferon induction. In general, the capacity of infected animals to produce interferon in response to inducers became progressively impaired during the course of infection. The severity and time of onset of hyporeactivity, however, were dependent upon the inducer and the nature of the viral infection. During viral infections associated with generalized hyporesponsiveness, a factor that could inhibit interferon production by murine cells in culture was identified in the serum. This serum hyporeactive factor may have mediated the development of hyporeactivity in vivo. Hyporeactivity of the host's interferon response was associated with progression of viral infection and may be partially responsible for the limited effectiveness of interferon inducers in the modification of viral infections, when administered after onset of symptoms.
The effect of treatment with exogenous interferon was compared with two interferon inducers, polyinosinic acid-polycytidylic acid [poly(I:C)] and [poly(I:C)]-poly-l-lysine complex (P-L-L complex), in two model encephalomyocarditis virus infections of mice. Although both inducers stimulated the production of interferon, the peak serum levels induced by P-L-L complex were five- to eightfold greater than those induced with poly(I:C). When encephalomyocarditis virus was inoculated by either the intraperitoneal or the intranasal route, interferon and both of the inducers protected mice against mortality and prolonged the mean day of death when the compounds were given prior to or immediately after viral challenge. In general, treatment with interferon was not as successful as treatment with poly(I:C) or P-L-L complex. In these infections, P-L-L complex appeared to be the most effective agent in that successful treatment resulted when drug therapy was initiated as late as 48 h after virus inoculation. An examination of the effect of treatment on the pathogenesis of the infection indicated that protection was associated with the prevention of viremia and subsequent seeding of target organs, particularly the central nervous system.