[Cytokines and antibodies in experimental infection of wild and laboratory rodents (rodentia) with tick-borne encephalitis virus].

Persistence modeling was performed by means of infection of the wild rodents: northern red-backed vole Myodes rutilus (Pallas, 1779) and striped field mouse Apodemus agrarius (Pallas, 1771), as well as of laboratory mice with the tick-borne encephalitis virus (TBEV) in tick suspensions with subsequent detection of the TBEV, hemagglutination inhibition and virus-neutralizing antibodies, as well as expression of cytokine genes during 4 months. Detection rate of the TBEV RNA and antigen E remained high during the whole period of observations; however, virus pathogenic for laboratory suckling mice was isolated mainly during a period of 8 days post infection. At the late stages of the persistent infection (1-4 months) the TBEV RNA detection rate in northern red-backed voles and laboratory mice remained high, whereas in striped field mice it significantly declined (p < 0.001). The viral loads were significantly higher (p < 0.001) in the wild rodents compared to the laboratory mice. Average frequencies of Th2 cytokine gene expression were similar for M. rutilus (50.0 ± 8.5%) and A. agrarius (50.0 ± 9.6%) during the whole period, but Th1 cytokine mRNA detection rate after transcription activation in 2 days post infection and subsequent return to the original values were different (22.2 ± 5.0% and 38.1 ± 7.6%, respectively (p > 0.05)). Meanwhile, a part of animals with interleukin 1ß mRNA was significantly higher among A. agrarius than among M. rutilus (p < 0.05), which might cause low levels of spontaneous TBEV infection of field mice compared to red voles. Hemagglutination inhibition and virus-neutralizing antibodies were revealed in wild rodents in 30 days post infection and remained at detectable levels during 4 months. Thus, the TBEV persistence in small rodents was accompanied by the detection of the pathogenic virus in the early period, the viral RNA and antigen E during 4 months with high viral loads in wild animals exceeding the values in laboratory mice. Changes in the proinflammatory cytokine gene expression frequencies and the TBEV-specific antibodies pointed at immunomodulation as the possible mechanism of the TBEV persistence.

Evaluation of immune response and protective effect of four vaccines against the tick-borne encephalitis virus.

Among three main subtypes of the tick-borne encephalitis virus (TBEV), the Siberian subtype is currently dominant in a majority of the endemic regions of Russia. However, inactivated vaccines are based on TBEV strains of the heterologous Far Eastern or the European subtypes isolated 40-77 years ago. To analyze the efficacy of the available vaccines against currently prevailing TBEV isolates of the Siberian subtype, mice were immunized subcutaneously three times (one group per each vaccine). The expression of seven cytokine genes was determined using RT-PCR. Sera were studied using homologous and heterologous ELISA, hemagglutination inhibition (HI) and neutralization tests with TBEV strains of the Far Eastern, Siberian and European subtypes. Cross-protective efficacy of the vaccines was evaluated with the TBEV strain 2689 of Siberian subtype isolated from an ixodid tick from the Novosibirsk, South-Western Siberia, Russia in 2010. The cytokine gene expression profile indicates a predominantly Th2 response due to exogenous antigen presentation. Titers for homologous combinations of vaccine strain and strain in ELISA, HI and neutralization tests exceeded those for heterologous antigen-antibody pairs. Despite antibody detection by means of ELISA, HI and neutralization tests, the mouse protection afforded by the vaccines differed significantly. Complete protection of mice challenged with 100 LD50 virus of the Siberian subtype was induced by the vaccine "Encevir" ("Microgen", Tomsk, Russia). The minimal immunization doze (MID50) of "Encevir" protecting 50% of the mice was less than 0.0016 ml. Partial protective effect of vaccines produced in Moscow, Russia and Austria revealed MID50 within recommended intervals (0.001-0.017 ml). However, the MID50 for the vaccine "Encepur" (Novartis, Germany) 0.04 ml exceeded acceptable limits with total loss of mice immunized with vaccine diluted 32, 100 and 320 fold. These results suggest regular evaluation of TBEV vaccines in regions where heterologous virus subtypes prevail.

[Detection of the nuclear polyhedrosis virus DNA in samples from eggs and caterpillars at different stages of the gypsy moth Lymantria dispar (L.) population dynamics].

The nuclear polyhedrosis virus (NPV) DNA was detected in samples from eggs and caterpillars of the gypsy moth collected in natural populations of the Western Siberia and Ural by means of PCR with primers corresponding to the polyhedrin gene. According to censuring data, the gypsy moth populations of Western Siberia were at the depression stage. The NPV DNA detection frequencies in eggs (8.6 +/- 4.8% - 13.6 +/- 5.2%) and caterpillars (21.0 +/- 6.3% - 22.2 +/- 6.7%) were not significantly differed. In the Urals, collection of the insects was performed in their gradation focus at the phase of maximal abundance. The DNA detection rate in eggs (11.4 +/- 5.0%) was confidently (p < 0.001) lower than in caterpillars (59.8 +/- 5.6%). Consequently, variations of the NPV infection prevalence during ontogenesis of Lymantria dispar (L.) was associated with the gradation cycle of the insect population dynamics.

[Changes in the reproduction of tick-borne encephalitis virus in cell cultures].

The currently used tick-borne encephalitis virus vaccines are based on the inactivation of tick-borne encephalitis virus (TBEV) of Far Eastern or West European genetic types from the primary cultures of chick embryo fibroblasts. Since the WHO recommends that vaccines should be designed using continuous cell cultures rather than chick embryos as a substrate, this investigation has compared the infection of continuous monolayer SPEV, Vero E6, and vaccine line Vero (B) cell cultures with TBEV strains of the Siberian and Far Eastern genetic types dominating in the endemic regions of Russia. After cell infection with Far Eastern (Sofyin and 205 strains) or Siberian (Aina, 2530, 2689, and 2703 strains) TBEV genetic types, the viable TBEV titers reached 2.8 Ig CPD50 for Vero (B) cells, 5.5 Ig CPD50 for Vero E6 cells, and up to 9 Ig CPD50 for SPEV cells. The quantitative scores of TBEV E antigen in enzyme immunoassay (EIA) and genome equivalents by reverse-transcription polymerase chain reaction (PCR), followed by real-time PCR, permitted one to estimate as high as 108 virions in 1 ml of culture fluid, which corresponded to those of the microscopic observations of CPD for SPEV cells and substantially exceeded the values for Vero E6 cells, and for Vero (B) cells in particular. The data of TBEV strain titration, EIA, and realtime reverse-transcription PCR suggest that the Russian vaccine Vero (B) cell line defined as meeting the WHO requirements, as well as Vero E6 cells may be used to design tick-borne encephalitis vaccine.

[Phenotypic and genetic characterization of nuclear polyhedrosis virus isolated from gypsy moth (Lymantria dispar L.) larvae from the natural populations of Western Siberia].

Six nuclear polyhedrosis virus (NPV) isolates have been isolated from dead larvae of gypsy moth in Western Siberia. Heterogeneity of virulence and reproduction activity was revealed for the NPV isolated by bioassay with Lymantria dispar L. larvae. The findings may suggest phenotypic variation of the NPV isolates. No correlation was found between virulence and reproductive activity with the only exception--the isolate Karassuk with a high virulence and a high reproductive activity. Nucleotide sequences of PCR products with primers specific to the polyhedrin gene were determined for NPV isolated Karassuk and Tatarskyi with the maximum and minimal virulence, respectively. Alignment of the nucleotide sequences demonstrated a high homology of the study polyhedrin gene fragment between NPV Western-Siberian isolates and NPV strains from the USA with two point mutations. The mutations were identical for the NPV isolated from Russia but were different from the known structures of the polyhedrin gene of the American strains. The only one from two found mutations resulted in amino acid substitution in polyhedrin protein. Consequently, the structure of both polyhedrin and encoded protein did not influence on the NPV virulence and reproductive activity.

[The effect of fodder on the susceptibility of gypsy moth (Lymantria dispar L.) to nuclear polyhedrosis virus].

Gypsy moth (Lymantria dispar L.) growing on different feeding substrates was shown to affect their susceptibility to nuclear polyhedrosis virus (NPV). The insects feeding on birch leaves had the lowest sensitivity to NPV than those on willow leaves, but the insects growing on pine needles showed the highest susceptibility. The sensitivity of the gypsy moths on willow leaves was higher than that of the gypsy moths on birch leaves and lower than that of those on pine needles. At the same time, it did not differ from that of the caterpillars on artificial feeding. The virus polyhedrons formed in the caterpillars on birch or willow leaves were more than those on another fodder.

Vertical transmission of tick-borne encephalitis virus between generations of adapted reservoir small rodents.

Vertical transmission of tick-borne encephalitis virus (TBEV) between generations of the small rodents-red voles Myodes rutilus Pallas (previously known as Clethrionomys rutilus Pallas) was shown for naturally infected reservoir hosts and after experimental infection with different sublethal doses of the viral strains. For wild red voles and for their progeny born in 240-280 days after experimental infection of their parents the TBEV was detected in up to 90% of samples by RT-PCR, ELISA and bioassays. Small amounts of the TBEV RNA found in embryos, placenta and blood cells could serve as evidence of prenatal transmission. Postnatal transfer of the virus might occur through the rodent milk. Analysis of the TBEV E gene nucleotide sequences of RT-PCR products revealed missense mutations resulting in amino acid substitution K280Q in newborn red vole in comparison with its parent female. Taken together, the data confirmed the TBEV vertical transmission among generations of its adapted mammal reservoir hosts. The virus transfer might occur before, during and/or after birth of the small rodents with high frequencies. In the wild it could provide the TBEV long-term persistence in mammal hosts without an (any) involvement of arthropod vectors thus selecting dangerous mammal-adapted variants.

[Interrelations between Ixodes persulcatus ticks and the tick-borne encephalitis virus of the red vole (Clethrionomys rutilis) in western Siberia]. / Vzaimootnosheniia kleshchei Ixodes persulcatus i virusa kleshchevogo éntsefalita s krasnoi polevkoi (Clethrionomys rutilus) v zapadnoi ibiri.

We present the data of 12-year survey (1989-2001) of the red vole population in southeastern West Siberia, including estimation of host relative numbers, abundance of immature taiga ticks, and percentage of animals with antigemagglutitnins against tick-borne encephalitis (TBE) virus. We discuss the role of demographic groups of voles as tick's hosts and their participation in the maintenance of TBE causative agent population. The estimation of spontaneous TBE infection rate in summer as well as in winter and early spring seasons, which have been made using a set of molecular-biological, serological and virological methods, demonstrates that a high proportion of red voles maintain non-pathogenic TBE causative agent over a long time, presumably, in the form of persistent infection.

Tick-borne encephalitis virus NS1 glycoprotein during acute and persistent infection of cells.

Tick-borne encephalitis virus (TBEV) was propagated in porcine embryo kidney (PS) cells until 48 h whereas human kidney (RH) cells maintained the virus persistence during at least 2 months. One of possible reasons of flavivirus chronic infection might be abnormal NS1 gene expression. Immunoblotting with monoclonal antibodies (MAbs) revealed the similarity of the intracellular and secreted NS1 nonstructural glycoprotein size and linear antigenic determinants in both the infected cell lines. However, according to the competitive binding of MAbs with the TBEV NS1 extracellular glycoprotein, its contiguous epitopes differed for acute or persistent infection. To map the TBEV NS1 glycoprotein antigenic determinants its recombinant analogues were used. All the studied MAbs could bind with the full-length NS1 recombinant protein. Deletion of the TBEV NS1 gene internal region resulted in defective NS1d1 protein without the region between 269 and 333 a.a. Lack of NS1d1 binding with 20B4 MAb and diminished binding with 22H8 and 17C3 MAbs permitted to map their antigenic determinants within or nearby deleted region, respectively. Interaction of other MAbs with the NS1 and NS1d1 recombinant proteins did not differ, suggesting that their epitopes were located in the region of N-terminal 268 a.a. or C-terminal 19 a.a. of the TBEV NS1 protein. The second NS1d2 truncated protein contained the first N-terminal 33 a.a. of the TBEV NS1 protein and was able to bind with 29G9 MAb. Taken together the data stand for the differences in the N-terminal structure of the TBEV NS1 multimers secreted from the acute and persistent infected cells whereas the intracellular and secreted monomer processing was the same. The modified NS1 protein oligomers in the RH cellular line might slow virus replication and could result in the TBEV persistence.

[Expression of the NS1 gene of tick-borne encephalitis virus in gram-negative bacteria from the mouse nasopharynx]. / Ekspressiia gena NS1 virusa kleshchevogo éntsefalita v gramotritsatel'nykh bakteriiakh--obitateliakh nosoglotki myshei.

Bacteria were isolated from the nasopharynx of BALB/c mice and electroporated with pUR290(NS1)2 containing two copies of tick-borne encephalitis virus (TBEV) strain Sofjin NS1 under the control of the lac promoter. The plasmid persisted in transformants for at least ten passages. The NS1 gene expression was detected in Gram-negative enterobacteria via immunoblotting with monoclonal antibodies against TBEV nonstructural glycoprotein NS1. Recombinant NS1 was detected in bacterial cells and in the culture medium. Intranasal immunization with recombinant bacteria activated production of antibodies against NS1 in serum of BALB/c mice. The humoral immune response to NS1 failed to protect immunized mice from a TBEV challenge.

[Monoclonal antibody study of antigens E and NS1 of Western Siberian tick borne encephalitis virus strains]. / Issledovanie s pomoshch'iu monoklonal'nykh antitel antigenov E i NS1 shtammov virusa kleshchevogo éntsefalita Zapadnoi Sibiri.

Antigenic structure of tick-borne encephalitis virus proteins was studied by ELISA with monoclonal antibodies (MAb) to E and NS1 glycoproteins of strain Sofyin. Envelope proteins appeared to be conservative which corresponded to previously determined nucleotide sequences of E gene fragments and deduced primary structures of the corresponding E protein. Five of six studied MAb to NS1 nonstructural glycoprotein of strain Sofyin reacted with this protein of all studied strains. The only exception was MAb 17C3 which discriminates West Siberian strains from Far Eastern strain Sofyin.

[Involvement of the common shrew, Sorex araneus (Insectivora, Soricidae), in circulation of the tick-borne encephalitis virus in south-western Siberia]. / Uchastie obyknovennoi burozubki Sorex araneus (Insectivora, Sorcidae) v tsirkuliatsii virusa kleshchevogo entsefalita na iuge zapadnoi Sibiri.

We presented the data on the abundance of immature instars of the taiga tick Ixodes persulcatus Schuize on the common shrews Sorex araneus L. in natural foci of tick-borne encephalitis in the south of Western Siberia. Basing on the results of virological and serological studies we demonstrated a low effectiveness of this host species as a donor of disease agent strains, which are predominant in the territory under study, for ticks feeding on shrews. The analysis of samples taken from the young shrews in winter and spring using reverse RNA transcription with polymerase chain reaction and ELISA revealed occurRence of subvirion components of the tick-borne encephalitis (RNA and capsid protein E) ether in brain, liver or spleen in 90 percent of shrews (n = 42). Neither hemagglutination antigen nor infectious virus have been detected. We discussed a possible epizootic role of the maintenance of non-infectious tick-borne encephalitis virus in overwintering animals.

[Genetic analysis of tick-borne encephalitis virus strains from West Siberia]. / Geneticheski'i analiz shtammov virusa kleshchevogo éntsefalita Zapadno'i Sibiri.

Tick-borne encephalitis (TBE) virus strains were isolated in West Siberia in the forest-steppe region near the Ob river in 1981-1992. Hybridization of genome RNA of 46 TBE strains with [32P]cDNA of TBE Sofyin strain revealed essential differences in the genomes of West-Siberian and Far-Eastern Sofyin strains of TBE virus. Nucleotide sequences of 6 TBE strains (1348-1503 n.) have been determined. A 89-98% homology of Siberian TBE strains has been shown, while the similarity of the respective fragment of E gene for West Siberian and Sofyin strains was no more than 81%. No significant changes in E gene of TBE strains have been detected over a 12-year period.

Tick-borne encephalitis virus strains of Western Siberia.

Tick-borne encephalitis virus (TBEV) strains were isolated from ticks in Western Siberia for 12 years. Molecular hybridization of the 46 viral RNA with the TBEV cDNA and oligonucleotide probes revealed differences between the Siberian and Far Eastern strains. A comparison of the viral E gene fragment nucleotide sequence showed 89-98% homology between Siberian TBEV strains, whereas their similarity with strains from other populations was less than 83%. However, the viral E and NS1 glycoprotein antigenic structures appeared to be conservative because of the degenerate genetic code. This was shown by enzyme-linked immunosorbent assay with the corresponding monoclonal antibodies (MAb). The single exception was the MAb 17C3 against nonstructural glycoprotein NS1, which could distinguish Siberian from Far Eastern strains. Moreover, the neurovirulence differed between strains from the two natural populations. Lower neuroinvasiveness of the Siberian strains in comparison with Far Eastern Sofyin strain might be caused by both E and NS1 glycoprotein mutations.

[A comparison of the immune response induced by DNA or by an inactivated vaccine against tick-borne encephalitis]. / Sravnenie immunnogo otveta, indutsirovannogo DNK ili inaktivirovannoi vaktsinoi protiv kleshchevogo éntsefalita.

BALB/c mice were immunized with recombinant plasmid DNA pSVK3-ENS1 and pcDNAI-NS3 containing, respectively, genes E-NS1 and NS3 of tick-borne encephalitis (TBE) virus. Antibodies to TBE virus proteins were detected in the blood sera of the immunized animals by the method of the enzyme immunoassay. Though the titers of virus-specific antibodies in the sera of mice immunized with protein vaccines exceeded those registered after immunization with DNA vaccines, essential protective immunity was observed after the use of both vaccines.

[Structural changes in the gypsy moth (Ocneria dispar L.) hemogram in polyhedrosis]. / Strukturnye izmeneniia v gemogramme neparnogo shelkopriada (Ocneria dispar L.) pri poliédroze.c

Structural changes in hemogram of Gypsy moth larvae from a population in the phase of quantity increase are studied morphometrically and cytochemically. The counts of granulocytes and prohemocytes are increased, as are the counts of hemocytes possessing phenol oxidase activity and hemocytes reducing nitroblue tetrazolium. Atypical virus morphogenesis is observed.

Tick-borne encephalitis virus NS3 gene expression does not protect mice from homologous viral challenge.

Tick-borne encephalitis virus (TBEV) NS3 gene has been subcloned into the expression vector pcDNAI and expressed in eukaryotic cells. Immunization of mice with the recombinant plasmid pcDNAI-NS3 induced antibodies against NS3 protein but did not protect from viral challenge.

[Isolation of a complex of tick-borne encephalitis viral proteins by affinity chromatography using monoclonal antibodies to proteins NS5 and NS3]. / Vydelenie kompleksa belkov virusa kleshchevogo éntsefalita metodom affinnoi khromatografii s ispol'zovaniem monoklonal'nykh antitel k belkam NS5 i NS3.

Affinity chromatography of lysates of continuous porcine embryo cells infected with tick-borne encephalitis (TBE) virus on sepharose with immobilized monoclonal antibodies to TBE virus proteins NS5 and NS3 results in isolation of a stable protein complex. This complex contains viral proteins NS5, NS3, p49, and, probably, two more cell proteins. This complex is not detected at the early stage of infection, and 24 h after infection its structure does not depend on the specificity of immobilized monoclonal antibodies used in affinity chromatography and on the time elapsed after the infection. Immunoprecipitates of infected cells phosphorylated TBE virus protein NS5 in vitro, but possessed no RNA-polymerase activity. Elution of the complex with buffers with pH 3.5 or 11.1 or with 2M urea failed to purify the active replicase. The complex of viral and cellular proteins isolated by affinity chromatography on different immunoadsorbents did not possess RNA-polymerase activity because of inactivation or absence of additional subunit(s).

[Secretion of tick-borne encephalitis virus glycoproteins E and NS1 heterocomplex in the late stage of infection]. / Sekretsiia geterokompleksa glikoproteinov E i NS1 virusa kleshchevogo éntsefalita na pozdnei stadii infektsii.

The heterocomplex of glycoproteins E and NS1 of tick-borne encephalitis (TBE) virus was isolated from culture fluid of continuous SPEV (porcine embryo kidney) cells by affinity chromatography on CL4B sepharose with immobilized monoclonal antibodies to TBE virus protein NS1. Comparison of the TBE E-NS1 heterocomplex from culture fluid and cells showed the predominance of secreted extracellular form. A similar TBE virus heterocomplex E-NS1 was revealed in the blood sera of patients with TBE but not in their lymphocytes. Extracellular localization of the E-NS1 complex at the late stage of infection rules out its hypothesized participation in the replication of TBE virus. Virtual absence of the heterocomplex and presence of proteins E and NS1 in high concentrations in the cells makes the nonspecific aggregation of these proteins impossible. Evidently, the extracellular heterocomplex E-NS1 may react with virusspecific antibodies or with cytotoxic T lymphocytes.