Genetic diversity and rapid evolution of poliovirus in human hosts.
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Biological Evolution↗
Biomedical subjects
T Hovi
Publications and source records attributed to T Hovi.
Genetic variation in vivo and proposed functional domains of the 5' noncoding region of poliovirus RNA.
Poliovirus has a single-stranded RNA genome of about 7,440 nucleotides (nt) with an unusually long 750-nt noncoding region in the 5' end (5'NCR). Several regulatory functions have been assigned to the 5'NCR. We sequenced the 5'NCRs of 33 wild-type 3 poliovirus strains to study the range and distribution of naturally occurring sequence variations. In this regard, the 5'NCR can be divided into a conserved part (nt 1 to 650) and a hypervariable part (nt 651 to 750). In the conserved part, altogether 234 unevenly distributed nucleotide positions (36%) showed variation. When these positions were plotted against the predicted secondary-structure models, it was found that the existence of most of the proposed stem-loop structures was supported by extensive structure-conserving substitutions in the stems. Regions with conserved sequences, as well as mutational hot spots, were observed. The hypervariable part of the 5'NCR varied up to 56% between the strains studied. The A + U percentage was significantly higher than in the conserved part. The number of AUG codons varied between 5 and 15 in the conserved part of the 5'NCR, while none was found in the hypervariable part. These results provide information that can be used in site-directed mutagenesis and other approaches targeted to reveal the functional domains of the 5'NCR.
Base Sequence↗
Serology versus clinical signs or symptoms and main laboratory findings in the diagnosis of exanthema subitum (roseola infantum).
Twenty-five patients with clinical exanthema subitum (roseola infantum) were enrolled into a study, where acute-phase and convalescent sera were examined for antibodies to human herpesvirus 6 (HHV-6), several other viruses, and other microbes. In addition, an acute-phase fecal specimen was examined for viruses by electron microscopy. Confirmative or suggestive serologic evidence for recent HHV-6 infection was obtained in 23 (92%) cases. Conversion to HHV-6 was found in 19 (76%), a diagnostic (greater than or equal to 4-fold) titer rise in 2, a twofold titer rise in 1, and a stable relatively high titer in 1 of the patients; only 2 (8%) individuals remained negative. The other microbial assays produced only two slight mycoplasma antibody rises and one rotavirus identification in the fecal specimen. It is concluded that if the clinical diagnosis of exanthema subitum is deemed doubtful, HHV-6 infection is verifiable in about 75% of the cases by serology.
Antibodies, Viral↗
[Can the Finnish immunization program be improved?].
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Child↗
Antigenic regions of poliovirus type 3/Sabin capsid proteins recognized by human sera in the peptide scanning technique.
We used the peptide scanning technique to identify regions of poliovirus type 3/Sabin capsid proteins that bind antibodies from human immune sera. Several reactive regions were seen in VP1, VP2, and VP3 while peptides resembling VP4 did not bind antibodies. Peptides derived from sequences of the previously known antigenic sites 1 and 3 were recognized to a moderate degree. Peptides imitating the four loops in the closed ends of the beta barrels or the alpha helical CD insertions of VP1, VP2 or VP3, whether exposed in the crystal structure or not, all represented major reactivity in the scans. In VP1 several additional reactive regions were found in the amino terminal quarter of the protein, which is buried in the crystal structure, and in a partially exposed region close to but separated from the carboxy terminus. In VP2 the nonexposed peak activities clustered in a bridge-like structure spanning from the outer to the inner surface of the capsid shell. Likewise, most of the novel antigenic regions of VP3 clustered in an internal location and partially composed of beta sheets with a conserved amino acid sequence. Whether any of the novel antigenic sites is capable of inducing neutralizing antibodies is not known.
Antibodies, Viral↗
Virus-induced interferon production in human leukocytes: a low responder to one virus can be a high responder to another virus.
We measured the amounts of interferon (IFN) induced by four wild-type strains and two attenuated vaccine strains of poliovirus, testing each virus in 12-58 separate batches of human peripheral blood leukocytes. There were big and consistent differences in the mean amounts of IFN formed by leukocytes from different donors in response to all these polioviruses. Almost invariably, the wild-type polioviruses gave rise to more IFN than the corresponding attenuated strains, but overall, the amounts induced by one strain of poliovirus were proportional to those induced by another. There were indications of similar correlations with six different influenza viruses and with three strains of herpes simplex virus. In contrast, there was no correlation between the IFN yields induced with a poliovirus, three other enteroviruses, and various other viruses. These results suggest that the leukocytes from a given individual have a capacity to form IFN in vitro that is determined both by the genetic make-up of that individual and the particular virus concerned. If the same phenomenon applies to IFN production by cells in vivo, it may have a role in pathogenesis of viral infections.
Enterovirus↗
Generation of virus genetic lineages during an outbreak of poliomyelitis.
Wild poliovirus type 3 isolates collected during the Finnish outbreak (1984 to 1985) in different geographical locations were compared by partial RNA sequencing. The entire 5' non-coding end and a discontinuous part of the capsid coding region were sequenced from 15 isolates. Combining the present sequence data with previously published data and analysing these by the maximum parsimony method showed that the epidemic strains had diverged in cocirculating lineages. Genetic comparison of strains isolated from a single person often revealed a branched structure in the phylogenetic tree indicating high potential for diversification. The extent of variation generated under immunological pressure during an infection lasting for weeks in one person was high as compared with the observed geographical variation.
Antigens, Viral↗
RGD-dependent entry of coxsackievirus A9 into host cells and its bypass after cleavage of VP1 protein by intestinal proteases.
The recently reported nucleotide sequence of coxsackievirus A9 (CAV-9) showed that unlike other enteroviruses, CAV-9 has an insertion of about 17 amino acids at the C-terminal end of VP1 (K. H. Chang, P. Auvinen, T. Hyypiä, and G. Stanway, J. Gen. Virol. 70:3269-3280, 1989). This sequence includes the RGD (arginine-glycine-aspartic acid) motif which is known to be important in certain protein-protein interactions. We studied the inhibitory effect of RGD-containing peptides in the attachment of CAV-9 to African green monkey kidney cells. A peptide corresponding to the RRGDM sequence derived from the inserted segment of CAV-9 was found to block virus attachment effectively, and the inhibition was dose dependent. Substitution of glutamic acid for the homologous aspartic acid completely abolished the inhibitory effect, indicating great specificity of the action. During replication in the gut, all enteroviruses are exposed to host proteolytic enzymes. Exposure of CAV-9 to purified trypsin or human intestinal fluid resulted in selective cleavage of the VP1 capsid protein. Intact and trypsin-cleaved VP1 proteins gave identical N-terminal sequences, indicating that cleavage of VP1 takes place near the C terminus. Attachment of proteolytically cleaved infectious CAV-9 to green monkey kidney cells was not prevented by RGD-containing peptides, indicating that cleaved CAV-9 is able to bypass RGD-dependent entry. The altered receptor specificity of proteolytically cleaved viruses may have important consequences in the pathogenesis of enteric infections.
Amino Acid Sequence↗
Covariance of lowered capacity to induce interferon in human leukocytes and temperature sensitivity of type 3 poliovirus.
Attenuated poliovirus strains induce less interferon-alpha (IFN-alpha) in human leukocyte cultures than their parental wild-type strains or other neurovirulent strains. We have used a set of type 3 Leon/Sabin recombinant poliovirus strains to show that production of IFN in this system is closely associated with the genomic region that codes for capsid protein VP3; a mutation in this gene also causes the temperature sensitivity of the attenuated Sabin 3 strain and is partly responsible for the loss of neurovirulence of this vaccine strain. Sixteen independent poliovirus isolates, derived from the Sabin 3 virus but showing in vitro and in vivo markers of neurovirulence, were also tested. These gave IFN yields equivalent to or higher than those obtained with the neurovirulent Leon type 3 poliovirus. The relatively low IFN yields with the Sabin 3 virus seem not to be a direct consequence of its temperature sensitivity, but the two properties coincide with all the type 3 poliovirus strains tested.
Capsid↗
Remaining problems before eradication of poliomyelitis can be accomplished.
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Animals↗
Cytomegalovirus is frequently isolated in bronchoalveolar lavage fluid of bone marrow transplant recipients without pneumonia.
We prospectively studied the presence of cytomegalovirus in bronchoalveolar lavage through virus isolation in 21 bone marrow transplant recipients before and after transplantation. All 14 lavage specimens collected before bone marrow transplantation were negative for cytomegalovirus. During the period from 20 to 90 days after transplantation, 12 of 24 lavage specimens (50%) from 14 patients without lung problems were positive for cytomegalovirus. Cytomegalovirus was isolated from 4 of 10 lavage specimens (40%) in 7 patients with pneumonia during the same interval. We conclude that culture for cytomegalovirus in bronchoalveolar lavage fluid is not a reliable method for establishing the virus's causative role in pneumonia soon after bone marrow transplantation. Among 14 patients in whom bronchoalveolar lavage was done at an asymptomatic stage, 6 of 9 patients with cytomegalovirus and none of 5 without cytomegalovirus in the lavage fluid later developed pneumonia. All of the patients subsequently developing pneumonia also had acute graft-versus-host disease, suggesting an immunopathologic mechanism, possibly triggered by cytomegalovirus, for cytomegalovirus-associated pneumonia.
Adult↗
Antigenic modification of polioviruses by host proteolytic enzymes.
Incubation of polioviruses with human intestinal fluid is known to result in molecular and antigenic modification of the virion surface. Studies with different inhibitors of serine proteases suggested that trypsin in the intestinal fluid is most likely responsible for the primary cleavage of VP 1. However, minor differences could be distinguished between the final cleavage products produced by purified trypsin and intestinal fluid, respectively. Other enzymes present in intestinal fluid may thus contribute to the modification of polioviruses in vivo. No evidence was obtained in favour of any biological significance of these further modifications. Another serine protease plasmin, which is generated in the body from its ubiquitous precursor plasminogen under various physiological and pathological conditions, was also shown to be able to cleave VP 1 of polioviruses and bring about the corresponding modification of antigenic site 1. This observation extends the potential pathogenetic consequences of the host enzyme-mediated proteolytic modification of polioviruses from intestinal mucosa to most other tissues.
Antigens, Viral↗
Genomic variation of herpes simplex virus type 2 isolates analysed by hybridization after electroblotting from polyacrylamide gels.
Genomic variation of herpes simplex virus type 2 (HSV-2) strains was analysed by polyacrylamide gradient gel electrophoresis and subsequent hybridization to cloned HSV-2 sequences. Two probes were used, one from the L-segment and one from the S-segment of the HSV-2 genome. The probes did not contain a-repeat sequences. Hybridization to the specific sequences in individual DNA fragments obtained by use of the frequently cleaving restriction endonuclease Alu I revealed variations in the genome not detectable by analysing the fragment size only. The use of 35S-labelled deoxynucleotide in the radioactive labelling of the probe further improved the resolution of the method.
DNA, Viral↗
Good seroresponse to enhanced-potency inactivated poliovirus vaccine in patients on chronic dialysis.
The outbreak of paralytic poliomyelitis in Finland in 1984 was halted by nationwide oral poliovirus vaccination campaign. Immunocompromised patients, including those with chronic uraemia and on continuous dialysis, were excluded from the oral vaccination group and instead were given a dose of the new enhanced-potency inactivated poliovirus vaccine before the campaign. We studied the antibody response to this vaccine in 49 patients on chronic dialysis, using conventional antigen of all three serotypes and two additional type 3 strains. It was observed that 86% (42 of 49) of patients either had a satisfactory concentration of neutralising poliovirus antibodies against all three serotypes prior to vaccination, or responded with at least a four-fold increase of antibodies. Fourteen of 21 patients originally seronegative to at least one of the five virus strains used showed a striking seroconversion. One patient remained seronegative to type 1 poliovirus while two and four other patients were left with low (less than 8) titres of type 1 and 3 antibodies respectively. The latter seven patients showed moderate or good responses to the other two serotypes. We conclude that the enhanced-potency inactivated poliovirus vaccine produces a good antibody response in uraemic patients.
Adolescent↗
Type 3 poliovirus/Finland/1984 is genetically related to common Mediterranean strains.
Strains of poliovirus type 3 isolated in Finland in 1984 and 1985 (P3/Fin/84) are known to differ considerably from the type 3 vaccine strains in both nucleotide sequence and antigenic properties. In the search for the origin of the outbreak we first tested 80 type 3 strains that had been isolated elsewhere in the world during the years 1953 to 1986. An oligonucleotide probe complementary to a highly variable 17 nucleotide interval in the 5' non-coding region of the genomic RNA of P3/Fin/84 reacted with five strains. Also it was revealed that two of the latter five strains were related to the P3/Fin/84 strains in two separate genomic regions compared after partial RNA sequencing. One of them was isolated in Switzerland in 1980 and the other in Turkey in 1981. The Swiss strain was from a patient who had recently returned from a journey to various Mediterranean countries. Consequently, 16 other strains isolated in the late 1970s and early 1980s in Europe or in the Mediterranean countries were studied in detail by partial genomic sequencing and with neutralizing monoclonal antibodies. Two separate regions of the genome were compared by sequencing and corresponding dendrograms were constructed. The Switzerland and Turkey strains were found to be the strains most closely related to the viruses of the 1984 Finland epidemic. These results indicate that type 3 poliovirus strains related to P3/Fin/84 had been circulating in Mediterranean countries since the late 1970s.
Amino Acid Sequence↗
Rapid molecular evolution of wild type 3 poliovirus during infection in individual hosts.
A panel of nine neutralizing monoclonal antibodies was used to analyse the antigenic properties of 188 plaque-purified type 3 poliovirus strains from 17 faecal specimens, derived from eight people during a 2 month observation period. Most poliovirus specimens consisted of a mixture of antigenically distinct variants and the composition of the mixture was found to change between sequential specimens in many individuals, indicating antigenic evolution. Thirty-five strains representing different antigenic patterns were selected for partial sequencing of genomic RNA. Mutations leading to amino acid substitutions, as well as silent mutations, were seen at and close to the known antigenic sites. The frequency of silent mutations was used to estimate the evolutionary potential of the virus. The largest difference in silent changes between strains isolated from one person was 0.8%, which corresponds to a minimum of about 60 mutations per genome within a period of 3 weeks. The observed incidence of silent mutations between isolates from different persons was usually between 0.8 and 2%. These figures agree with the previously reported overall mutation rates of poliovirus, determined by other methods.
Amino Acid Sequence↗
Improved distribution of antigenic site specificity of poliovirus-neutralizing antibodies induced by a protease-cleaved immunogen in mice.
Previous studies showed that the distribution of antigenic site specificity of neutralizing antibodies to type 3 poliovirus obtained with the inactivated poliovirus vaccine can be deficient as compared with that obtained following poliovirus infection. This observation was shown by the relatively low capacity of sera from inactivated-poliovirus-vaccine-immunized persons to neutralize poliovirus cleaved at antigenic site 1. We investigated possibilities for improving the situation in a mouse model. Balb/c mice were immunized with intact or trypsin-cleaved type 3 poliovirus (Saukett strain). Sera from mice immunized with the intact virus readily neutralized the intact virus but neutralized the cleaved virus only rarely. In contrast, cleaved-virus-immunized mice produced antibodies that were able to neutralize the cleaved virus as well as the intact one. Mice immunized with a 100-fold-higher dose of the intact virus produced significant levels of antibodies to the cleaved virus, too. Somewhat surprisingly, mice immunized with high doses of the cleaved virus produced antibodies specific for the intact loop between beta sheets B and C of VP1 (virion protein 1), which should be cleaved in the immunogen. This was shown by a higher titer of antibodies to intact Saukett virus than to the corresponding cleaved virus, as well as to a type 1/type 3 hybrid poliovirus in which only the BC loop amino acids were derived from type 3 poliovirus. The cleavage-induced enhanced availability of antigenic determinants residing outside the BC loop was also shown by increased neutralization titers of monoclonal antibodies specific for some of these other determinants. These results indicate that by using a trypsin-cleaved type 3 poliovirus as a parenteral immunogen, it is possible to change the distribution of antigenic site specificities of neutralizing antibodies to resemble that following poliovirus infection.
Animals↗