Investigation of the inhibitory activity of extracts, fractions and secondary metabolites of <i>Silene</i> spp. (<i>Caryophyllaceae</i>) and <i>Serratula cupuliformis</i> (<i>Asteraceae</i>) on the replication of SARS-CoV-2 coronavirus

Aim. In vitro analysis of the inhibitory activity of extracts, fractions and secondary metabolites of plants of the genus Silene [Caryophylaceae] and Serratula cupuliformis [Asteraceae) on the replication of SARS-CoV-2.

Material and Methods. Silene spp. and Serratula cupuliformis of the Siberian Botanical Garden of National Research Tomsk State University were used. Ethanol extracts and butanol fractions of Silene spp. were prepared. The flavonoid shaftoside and the ecdysteroid 20-hydroxyecdysone from Lychnis chalcedonica were isolated. Analysis of BAS was carried out by the HPLC method. In vitro analysis of the inhibitory activity of extracts on SARS-CoV-2 replication was performed in Vero cell culture by direct inactivation [neutralization) of virions. Comparison samples were dry ethanol extracts of chaga [Inonotus obliquus, Basidiomycota), spices of cloves [Syzygium aromaticum, Myrtaceae) and root of licorice [Glycyrrhiza glabra L., Fabaceae).

Results. The inhibitory activity of ethanol extracts and butanol fractions of Silene spp., as well as individual compounds [shaftozide and 20-E) was revealed in the range of 50% effective concentrations [EC50) when dissolved in water from 339.85±83.92 pg/ml to 1.59±0.39 pg/ml and when dissolved in DMSO from 119.34±26.34 pg/ml to 2.22±0.57 pg/ml, respectively. The butanol fraction of Serratula cupuliformis was active with EC50=21.74±4.80 and 27.42±6.05 pg/mL. These results for some samples of Silene spp. and Serratula cupuliformis are comparable to the EC50 values of the comparators.

Conclusion. The results obtained suggest the presence of biologically active substances in the herbal preparations studied that act destructively on virions of SARS-CoV-2 and affect one of the main stages of its "life" cycle - on the attachment to receptors of sensitive cells.

Inhibitory activity of aqueous extracts of tea compositions, individual ingredients for their preparation and some plants against replication of Herpes simplex virus type 2 <i>in vitro</i>

Aim. In vitro analysis of the inhibitory activity of aqueous extracts of tea compositions, plant raw materials and as well as plants from different families against replication of Herpes simplex virus type 2.

Material and Methods. The viral strain MS of HSV‐2 was passivated on Vero cell culture. Antiviral (inhibitory) activity of aqueous extracts was studied in vitro according to the classical scheme of neutralization (inactivation) of the virus.

Results. For comparison we used control samples of aqueous extracts of Chaga mushroom (Inonotus obliquus) and grass of Alchemilla vulgaris L. with EC50 equal to 21.36±3.92 and 39.67±8.75 µg/ml (for dry raw materials) versus 103  PFU/ml HSV‐2. As a result the prevailing activity (from 15.25±3.92 to 1.71±0.54 µg/ml) was identified for extracts of tea compositions based on black and green tea, as well as individual ingredients for their composition – black tea, leaves of Mentha piperita L.,  flowers  of  Lavandula  angustifolia  Mill. and  clove  spices  (Syzygium aromaticum L.). Extracts obtained from plants that are not part of tea compositions of interest are fermented leaves of Epilobium angustifolium L. (Onagraceae) and grass of two species Euphorbia (E. pilosa L. and E. esula  L.,  Euphorbiaceae)  with  inhibitory  activity  at  concentrations  of 10.675±1.96; 2.29±0.57 and 1.71±0.54 µg/ml, respectively.

Conclusion. The results presented can become the basis for the search for individual biologically active substances of plant origin that inhibit HSV‐2 replication as well as for the development of effective medicines in the form of tea beverages and/or formulations for topical use to reduce relapses of chronic herpes.

Development of a Purified Viral Preparation for Studies of COVID-19 (SARS-CoV-2) Biology

Different methods for producing bulk quantities of concentrated and purified SARS-CoV-2 for the use as antigens and for the research into COVID-19 biology were tested.

N-Heterocyclic borneol derivatives as inhibitors of Marburg virus glycoprotein-mediated VSIV pseudotype entry

There is currently no approved antiviral therapy for treatment of Marburg virus disease (MVD). Although filovirus infection outbreaks are quite rare, the high mortality rates in such outbreaks make the development of anti-filoviral drugs an important goal of medical chemistry and virology. Here, we performed screening of a large library of natural derivatives for their virus entry inhibition activity using pseudotype systems. The bornyl ester derivatives containing saturated N-heterocycles exhibited the highest antiviral activity. It is supposed that compounds with specific inhibitory activity toward MarV-GP-dependent virus entry will inhibit the rVSIV-ΔG-MarV-GP pseudotype much more efficiently than the control rVSIV-ΔG-G pseudotype. At the same time, the compounds similarly inhibiting both pseudotypes will likely affect rVSIV capsid replication or the cellular mechanisms common to the entry of both viruses. Borneol itself is not active against both pseudotypes and is nontoxic, whereas its derivatives have varying toxicity and antiviral activity. Among low-toxic borneol derivatives, six compounds turned out to be relatively specific inhibitors of MarV-GP-mediated infection (SC > 10). Of them, compound 6 containing a methylpiperidine moiety exhibited the highest virus-specific activity. Notably, the virus-specific activity of this compound is twice as high as that of the reference.

A vesicular stomatitis pseudovirus expressing the surface glycoproteins of influenza A virus

Pseudotyped viruses bearing the glycoprotein(s) of a donor virus over the nucleocapsid core of a surrogate virus are widely used as safe substitutes for infectious virus in virology studies. Retroviral particles pseudotyped with influenza A virus glycoproteins have been used recently for the study of influenza hemagglutinin and neuraminidase-dependent processes. Here, we report the development of vesicular-stomatitis-virus-based pseudotypes bearing the glycoproteins of influenza A virus. We show that pseudotypes bearing the hemagglutinin and neuraminidase of H5N1 influenza A virus mimic the wild-type virus in neutralization assays and sensitivity to entry inhibitors. We demonstrate the requirement of NA for the infectivity of pseudotypes and show that viruses obtained with different NA proteins are significantly different in their transduction activities. Inhibition studies with oseltamivir carboxylate show that neuraminidase activity is required for pseudovirus production, but not for the infection of target cells with H5N1-VSV pseudovirus. The HA-NA-VSV pseudoviruses have high transduction titers and better stability than the previously reported retroviral pseudotypes and can replace live influenza virus in the development of neutralization assays, screening of potential antivirals, and the study of different HA/NA reassortants.

[Study of the functional role of mutation in the guinea pig-adapted Ebola virus genome on a Drosophila melanogaster model]

Ebola virus virulence in guinea pigs, which appears through virus adaptation to this animal host, correlates with substitutions in the gene encoding vp24 protein. In particular, the substitution His-->Tyr186 was found when obtaining strain 8 ms. An attempt was made to clarify the functional role of this substitution in a transgenic fruit fly model. Using the drosophila transformation technique provided transgenic strains that contained genomic insertions of wild-type Ebola virus vp24 gene and the mutant gene with the His-->Tyr substitution at the above position. Thus, the drosophila strains carrying the sequences encoding for the vp24 proteins of Ebola virus Zaire and 8 ms in pUAST vector were obtained. This makes it possible to study the expression of transgenic constructs in various D. melanogaster organs and tissues.

[Antigenic differences in wild-type and guinea pig-adapted Ebola virus strains]

The splenocytes isolated from the mice immunized with wild-type or guinea pig-adapted Ebola virus strains were used to obtain hybridoma collections. Investigation of the monoclonal antibodies (mAb) obtained to one of the strains to another revealed antigenic interstrain differences in nucleoprotein and VP40. It is interesting that the differences were found in the hydridoma collection obtained against the wild-type strain. The mAbs produced by hydridomas to the adapted strain were found to equally well the antigens of both strains.

[Evaluation of Ebola virus reproduction in adult ICR white mice]

The investigators studied the ability of adult ICR mice (a laboratory model that was most approximated to the wildtype populations of mice) to maintain Ebola virus (EV) reproduction in the organism. The adult ICR mice inoculated with EV during 23 passages were shown to maintain viral reproduction in the liver. The elevated levels of platelets and the early generation of fibrin and fibrinogen degradation products suggested there were hemostatic changes that did not, however, progress to severe coagulopathy. The animals were in appearance apparently, other than adynamia observed on days 5-7. Thus, the susceptibility of the adult ICR mice to EV is characterized by their ability to maintain virus reproduction in the liver without evident signs of the infection. This pattern of susceptibility in the mice shows a possible role of this rodent species in the transmissive cycle of EV.

[Development of a method for rapid detection of Ebola virus antibodies and antigen]

Despite the wide spectrum of reliable methods for identifying Ebola virus, their performance requires highly-skilled personnel, specialized laboratories, complicated equipment, and much time. Therefore, there is a need for a method that allows a physician or a medical attendant to identify the causative agent in field or bedside tests without special equipment as soon as possible. The immunoassay involving nitrocellulose membrane immuno-filtration, by using a fixed antigen (antibodies) or their immunosols, is a tried-and-true method. The time of the analysis is 7-15 min.

[Molecular mechanisms of Ebola virus reproduction]

The review presents recent data on the molecular mechanisms of the stages of an Ebola virus replication cycle, on the interaction of viral and cellular components at each stage, as well as on the mechanisms responsible for he realization of viral genetic information in the infected cell.

[The properties of Ebola virus proteins]

The paper describes the structure and functions of Ebola virus properties. It also presents information on the role of structural (NP, VP40, VP35, GP, VP30, VP24, and L) and secreted (sGP, delta-peptide, GP1, GP(1,2delta), ssGP) proteins in the viral replication cycle and in the pathogenesis of Ebola hemorrhagic fever.

[Hematological and immunological parameters during Ebola virus passages in guinea-pigs]

The trend in hematological and immunological parameters during Ebola virus passages in guinea-pigs indicated that pathophysiological changes occurred just during the second passage and further became stronger. The increase of some parameters and their correlation with the occurrence of fatal outcomes allowed the authors to reveal the most significant changes as increased juvenile platelets, whole blood virus appearance, higher echinocytes, a rise in the pro mil of blast cells and megakaryocytes in the bone marrow, and decreased neutrophilic phagocytic activity. Viral acquisition of the properties of lethality to guinea-pigs depends on the fine mechanisms responsible for viral interaction with host cells, which may lead to viral genetic changes during passages.

[Human recombinant antibodies to Ebola virus: preparation and characteristics]

Human recombinant antibodies against a purified Ebola virus (EV) lysate were selected from a combinatorial library of scFv-antibodies using the phage display technique. Nine unique antibodies were identified after sequencing the Vh- and Vl-genes encoding the selected antibodies. Solid-phase enzyme immunoassay (EIA) indicated that these antibodies were able to bind both inactivated and native EV. Immunoblotting showed that 6 antibodies identified nucleoprotein (NP), one antibody did VP24 and another antibody did VP40. One of the selected antibodies reacted with two EP proteins: VP24 and VP40. Solid-phase EIA demonstrated cross-reactivity with Marburg virus (MAR) and defined VP24 MAR as a target protein for the antibody.

[Strain differences related to Ebola virus reproduction in peritoneal macrophages and in aorta explants of guinea pigs]

Reproduction of the Ebola strains (ES) virus causing lethality in guinea pigs as well as in peritoneal macrophages and aorta explants of animals was investigated in vitro and in vivo; besides, production of interferon-gamma (IFN-gamma) and of tumor necrosis factor-alpha (TNF-alpha) by macrophages and endotheliocytes of guinea pigs was also studied. The interplay "macrophage--ES" by the example of 2 models of susceptibility to ES demonstrates that the ES lethality is not unambiguously related only with a level of virus reproduction in macrophages. The interplay "endotheliocyte--ES" is indicative of that the ES lethality is inversely dependent on a level of production of the IFN-gamma and of TNF-alpha by endotheliocytes. In general, the Eboly fever lethality is not conditioned only by the ability or inability of ES to reproduce in macrophages and endotheliocytes; it also depends on a variety of pathogenetic factors, one of which could be the cytotoxic action of immune complexes shaping in the process of infection progression.

[Dynamics of complement hemolytic activity in experimental Ebola infection]

The dynamic hemolytic activity of complements (HAC) was investigated in blood of guinea pigs in lethal and non-lethal Ebola infection. The increasing HAC dynamic activity in the animal blood was found to correlate with the infection lethal course. HAC as observed in animals with lethal infection was sweepingly increasing after they, were infected with Ebola virus, and yet after 15 hours from the infection time the complement activity parameters topped 2-fold the basic values in 100% of guinea pigs. They began to be dropping by the end of day 1, their decrease reached, when the incubation time was over (days 3-4 after infection) the basic value, after which they continued to go down to the zero value in 2-3 days before the lethal outcome. The described phenomenon, like the phenomenon of accelerated death, was even more pronounced, when the animals were infected after a single immunization by activated Ebola virus. In case, guinea pigs were infected by a non-lethal Ebola virus strain, the compliment synthesis was observed to be activated only at the end of the incubation period; the process was accompanied with a gradual raise and with a plateau-type or wave-type increase of the complement during the treatment time--it was equally accompanied with normalizing activity parameters during recovery. The detected specificity could be important in prognosticating a disease outcome. A reliable correlation was demonstrated between the complement hemolytic activity and the level of circulating immune complexes in blood of experimental animals, which can be traced both in lethal and non-lethal infection.

[Functional activity of peritoneal macrophages in experimental Ebola fever]

The phagocytic activity of peritoneal macrophages (a representative of mononuclear phagocytes) as well as the TNF-alpha were studied in animals with different susceptibility to Ebola virus (EV). The results denote the following: 1. Phagocytosis activation by peritoneal macrophages after EV is introduced into the body correlates directly with a susceptibility degree of an animal to EV. 2. The EV content in peritoneal lavage is inversely dependent on a phagocytic activity of peritoneal macrophages. The TNF-alpha activity increases, in blood serum of body susceptible to EV, 500-fold versus the unsusceptible body. Therefore, production of endogenous TNF-alpha can be interpreted as the development of body's immune protection but not as a reason for the development of vascular shock. Presumably, the nonspecific immunity factors condition the EV susceptibility.

Inactivation of Ebola virus with a surfactant nanoemulsion

Hemorrhagic fever caused by Ebola virus (EBO) is a highly contagious infection. This necessitates that the contaminated instruments, clothes, and hospital premises must be completely disinfected. Nanoemulsions are a new form of disinfectant composed of detergents and vegetable oil suspended in water. The antiviral activity of nanoemulsion ATB has been investigated against EBO. The nanoemulsion was tested against two preparations of EBO (strain Zaire) obtained from Vero cell culture fluid (EBO-zc) and from blood of infected monkeys (EBO-zb). The nanoemulsion ATB was virucidal against both preparations of EBO, inactivating the purified virus within 20 min even when diluted 1:100 with the growth medium. Inactivation of the virus in tissue preparations was also complete, but required 1:10 dilutions with media or higher. After treatment with ATB (10 and 1% concentrations), no EBO was apparent even after two passages in Vero cell culture. These data indicate that the nanoemulsion is an effective disinfectant for EBO. Because of the excellent biocompatibility of nanoemulsions, studies are planned to determine whether the nanoemulsion-killed virus is suitable for developing a vaccine against EBO.

Elaboration of laboratory strains of Ebola virus and study of pathophysiological reactions of animals inoculated with these strains

Selective passages in animals and cell cultures were used to produce a set of Ebola virus (EBO) laboratory strains with changed virulence for some animal genera. Comparative study of the genomes of wild-type EBO and selected variants formed the basis for studying the molecular causes of EBO virulence. Investigation of pathophysiological reactions of the animals inoculated with these strains allowed some key factors in Ebola fever pathogenesis to be determined.

[Analysis of antigenic determinant profiles of the Ebola virus VP35 protein N-terminal region using its short recombinant fragments]

cDNA of fragments of gene VP35 of the Ebola virus (EV) were expressed in vector pQE30 for the purpose of isolation of recombinant fragments of protein VP35. Five short affinity-purified fragments of the EV VP35 protein were analyzed, by using the methods of IEA and immunoblotting, with polyclonal antiviral sera (PAS) against EV and with hybrid monoclonal antibodies (Mabs) IC6 and 6F7 specific to EV VP35 protein. All fragments of protein VP35 with an intact N-terminal region and removed C-terminal region were found to interact effectively with PAS and with Mabs IC6 and 6F7. Rec86N, the smallest of the above fragments, comprised the initial 86 amino acid residues of the VP35 N-terminal region. A removal of 36 amino acid residues from the N-terminal region of Rec310N, the largest recombinant fragment, resulted in a loss of interaction with Mabs IC6 and 6F7, while the interaction with polyclonal antibodies remained intact. The obtained results show that the initial 86 amino acid residues of the N-terminal region of EV VP35 are of the key importance in forming the antigenic structure of VP35 and that they contain multiple B-cell epitopes. Finally, the initial 36 amino acids of VP35 predetermine the shaping-up of two antigenic determinants for Mabs IC6 and 6F7.

[In vitro synthesis of immunoglobulins caused by an inactivated Ebola virus]

An in vitro model Ebola infection was used to study the humoral response of human mononuclear cells to stimulation by purified inactivated Ebola virus antigen. Inactivated Ebola virus was cocultivated with human mononuclear cells in the presence or absence of B-cell mitogen LPS E. coli: B5. An increase in the rate of synthesis of immunoglobulins (both IgG and, to a less extent, other classes) was observed. The Ebola virus proteins were suggested to exert no suppression effect on B-cells. The IgM/IgG synthesis was evaluated by EIA in supernatants after 7 days of cultivation. It was concluded that Ebola fever is accompanied by active humoral immune response, which provides a promising basis for further search of the methods of treatment of this disease.

[Titration of Ebola and Marburg viruses by plaque formation under semi liquid agar]

The method of titration of Ebola and Marburg viruses using plaque formation under semifluid agar cover is considered. Advantages of this method over conventional method of titration of these viruses with the use of hard agar cover are discussed.

[Effect of Ebola virus antigen on proliferative response of human lymphocytes in vitro: imbalance in production of tumor necrosis factor alpha and interleukin-1]

An in vitro model infection caused by Ebola virus (EV) showed a high production of tumor necrosis factor-alpha by human peripheral lymphocytes concurrently with a simultaneous reduction in the synthesis of interleukin-1 in response EV antigen stimulation. This may be an important factor in that VE suppresses the body's immunological resistance, which in turn causes unterferon deficiency and suppresses the formation of T helper cells.

Study of the pathogenesis of Ebola fever in laboratory animals with different sensitivity to this virus

Pathophysiological parameters were compared in animals with different sensitivity to Ebola virus infected with this virus. Analysis of the results showed the differences in immune reactions underlying the difference between Ebola-sensitive and Ebola-resistant animals. No neutrophil activation in response to Ebola virus injection was noted in Ebola-sensitive animal. Phagocytic activity of neutrophils in these animals inversely correlated with animal sensitivity to Ebola virus. Animal susceptibility to Ebola virus directly correlated with the decrease in the number of circulating T and B cells. We conclude that the immune system plays the key role in animal susceptibility and resistance to Ebola virus.

[Antigenic structure of Ebola virus VP35 protein]

Antigenic structure of Ebola virus (EV) (strain Mayinga) nucleocapsid protein VP35 was analyzed using monoclonal antibodies to EV VP35 and polyclonal antibodies to EV. EV protein VP35 was shown to have antigenic sites inducing the production of antibodies in animals. For better characterization of protein VP35 antigenic structure. EV gene encoding the full-length VP35 was cloned in vector pQE31 as a recombinant fusion protein (rec.VP35). The antigenic and immunogenic properties of rec.VP35 and EV VP35 were compared by ELISA and Western blot analysis with polyclonal and monoclonal antibodies. Antibodies of positive sera and VP35 MAbs cross reacted with the analyzed antigens. The topography of epitopes on EV VP35 and rec.VP35 was studied using MAbs and polyclonal antibodies to rec.VP35 in a competitive antibody binding assay. Two epitopes of one site were identified on these proteins. These epitopes are present on infectious virion protein VP35 and are stable during physicochemical exposures.

Molecular characterization of guinea pig-adapted variants of Ebola virus

Serial passage of initially nonlethal Ebola virus (EBOV) in outbred guinea pigs resulted in the selection of variants with high pathogenicity. Nucleotide sequence analysis of the complete genome of the guinea pig-adapted variant 8mc revealed that it differed from wild-type virus by eight mutations. No mutations were identified in nontranscribed regions, including leader, trailer, and intragenic sequences. Among noncoding regions the only base change was found in the VP30 gene. Two silent base changes were found in the open reading frame (ORF) encoding NP protein. Nucleotide changes resulting in single-amino-acid exchanges were identified in both NP and L genes. Three other mutations found in VP24 caused amino acid substitutions, which are responsible for larger structural changes of this protein, as indicated by an alteration in electrophoretic mobility. A highly pathogenic EBOV variant K5 from another passaging series showed an amino acid substitution at nearly the same location in the VP24 gene, suggesting the importance of this protein in the adaptation process. In addition, sequence variability of the GP gene was found when plaque-purified clones of EBOV-8mc were analyzed. Three of five viral clones showed insertion of one uridine residue at the GP gene-editing site, which led to a significant change in the expression of virus glycoproteins. This observation suggests that the editing site is a hot spot for insertion and deletion of nucleotides, not only at the level of transcription but also of genome replication. Irrespective of the number of uridine residues at the editing site, all plaque-purified clones of EBOV variant 8mc resembled each other in their pathogenicity for guinea pigs, indicating either the absence or only supportive role of mutations in the GP gene on the adaptation process.

[Monoclonal antibodies to Ebola virus: isolation, characteristics, and study of cross reactivity with Marburg virus]

Thirteen hybridoma strains producing monoclonal antibodies (Mabs) to Ebola virus were prepared by fusion of NS-O mouse myeloma cells with splenocytes of BALB/c mice immunized with purified and inactivated Ebola virus (Mayinga strain). Mabs directed against viral proteins were selected and tested by ELISA. Protein specificity of 13 Mabs was determined by immunoblotting with SDS-PAGE proteins of Ebola virus. Of these, 11 hybridoma Mabs reacted with 116 kDa protein (NP) and 2 with Ebola virus VP35. Antigenic cross-reactivity between Ebola and Marburg viruses was examined in ELISA and immunoblotting with polyclonal and monoclonal antibodies. In ELISA, polyclonal antibodies of immune sera to Ebola or Marburg viruses reacted with heterologous filoviruses, and two anti-NP Ebola antibodies (Mabs 7E1 and 6G8) cross-reacted with both viruses. Target proteins for cross-reactivity, Ebola NP (116 kDa) and Marburg NP (96 kDa), and VP35 of both filoviruses were detected by immunoblotting with polyclonal and monoclonal antibodies (6G8) to Ebola virus.

[Assay for level of Marburg virus in blood and isolates from experimentally infected animals]

Measurements of concentrations of Marburg virus in guinea pig saliva, urine, and feces showed that as early as by the end of incubation period the virus concentrations in the feces and saliva were 2.3-3.3 lg LD50. In the blood the content of the virus was high and increased by the end of the disease, while the concentrations in the urine, saliva, and feces were virtually the same throughout the disease.

Immune and pathophysiological processes in baboons experimentally infected with Ebola virus adapted to guinea pigs

The dynamics of pathophysiological and immunological parameters monitored in monkeys Papio hamadryas infected with the guinea pig-adapted Ebola virus strain demonstrated that this viral strain preserved its virulence for monkeys and caused the disease with characteristic features similar to those caused by non-adapted Ebola virus. However, certain previously unknown patterns have been observed: (1) prolongation of the febrile period by two days; (2) extended period was characterized by stability of serum biochemical parameters; (3) marked vacuolization of the neutrophil cytoplasm; (4) appearance of juvenile lymphocytes on day 3 and by the end of the disease; and (5) a considerable increase in the spontaneous mononuclear proliferation (along with a decrease in the mitogen-induced proliferation) during the terminal stage of infection. The severity of pathological coagulation was found to correlate with the activity of serum cytokines IFN-alpha and TNF-alpha: their activities increased about 250- and 100-fold, respectively. There was significant alteration in the activity of natural killer cells, that dropped by the time of animal death.

[Effect of an infections dose of the Ebola virus on survivability and immunologic indicators in guinea pigs]

Analysis of the time course of immunological parameters in intact guinea pigs and animals immunized with inactivated Ebola virus (EV) inoculated with high and low doses of EV strain lethal for guinea pigs showed that high doses induced a higher resistance of the lymphocytic component of immunity than low doses, but activation of the neutrophil phagocytosis was far less expressed after high doses than after low ones. This indicates a qualitative effect of the infective dose of EV on the development of immunological reactions in animals, which modifies the ratio between the lymphocytic and neutrophilic components of immunity.

Suppressive effect of Ebola virus on T cell proliferation in vitro is provided by a 125-kDa GP viral protein

Ebola virus (EV), an extremely infectious pathogen, causes severe hemorrhagic fever in humans and nonhuman primates. The disease pattern includes damage of parenchymal cells of vital organs in association with hemostatic and immune disorders. Vaccination with the inactivated virions does not provide an effective immune protection against the disease. The inadequate immune response may be directly caused by the virus, and, hence, it may presumably be crucial in the pathogenic process and prophylactic treatment of Ebola infection. The suggested immunosuppressive properties of EV were examined in this study. We have demonstrated that the whole heat-inactivated virions can dose-dependently suppress human lymphocyte mitogen-stimulated proliferation in vitro. In further analyses, we identified the viral protein responsible for the suppressive effect, and we showed that it was provided by a protein corresponding to a 125-kDa envelope glycoprotein (GP-125). The protein alone inhibited lymphocyte proliferation, whereas the other viral proteins were without significant effect on blastogenesis. To determine the immunosuppressive properties of different portions of GP-125, deletion mutants of GP were designed based on predicted localisation of antigen sites. They were expressed as recombinant proteins and studied in proliferation assays. We identified a 40-amino acid sequence at the N-terminus of GP-125 that exerted a suppressive effect on blastogenesis.

Characterization of the L gene and 5' trailer region of Ebola virus

The nucleotide sequences of the L gene and 5' trailer region of Ebola virus strain Mayinga (subtype Zaire) have been determined, thus completing the sequence of the Ebola virus genome. The putative transcription start signal of the L gene was identical to the determined 5' terminus of the L mRNA (5' GAGGAAGAUUAA) and showed a high degree of similarity to the corresponding regions of other Ebola virus genes. The 3' end of the L mRNA terminated with 5' AUUAUAAAAAA, a sequence which is distinct from the proposed transcription termination signals of other genes. The 5' trailer sequence of the Ebola virus genomic RNA consisted of 676 nt and revealed a self-complementary sequence at the extreme end which may play an important role in virus replication. The L gene contained a single ORF encoding a polypeptide of 2212 aa. The deduced amino acid sequence showed identities of about 73 and 44% to the L proteins of Ebola virus strain Maleo (subtype Sudan) and Marburg virus, respectively. Sequence comparison studies of the Ebola virus L proteins with several corresponding proteins of other non-segmented, negative-strand RNA viruses, including Marburg viruses, confirmed a close relationship between filoviruses and members of the Paramyxovirinae. The presence of several conserved linear domains commonly found within L proteins of other members of the order Mononegavirales identified this protein as the RNA-dependent RNA polymerase of Ebola virus.

Preparation and use of hyperimmune serum for prophylaxis and therapy of Ebola virus infections

To obtain hyperimmune serum appropriate for the treatment of filovirus infection, methods were developed to immunize nonsusceptible animals with live Ebola (EBO) virus preparations. Immune plasma with high ELISA and neutralization-specific antibody titers was obtained by multiple immunization of sheep and goats with preparations of live EBO virus. Goat immunoglobulin was prepared by Cohn's method and tested on guinea pigs, using an EBO virus strain that is highly pathogenic for guinea pigs. Prophylaxis with these immunoglobulins within 48 h after infection was effective in challenge experiments, with a log10 prophylaxis index as high as 1.92+/-0.52. Other studies have shown that equine anti-EBO virus immunoglobulins worked well in baboons. The goat immunoglobulins were also tested in preclinical trials on laboratory animals; after being positively evaluated, they were administered to volunteers in clinical trials for biologic safety and reactivity, and they were administered to researchers suspected of becoming infected with EBO during their experimental work. These immunoglobulins may be useful for the emergency treatment of persons accidentally infected with EBO.

[Dynamics of immunologic indicators in guinea pigs upon administering various preparations of the Ebola virus]

Immunological and hematological values are analyzed in guinea pigs infected with Ebola virus (EV) strain weakly pathogenic for these animals, inactivated EV, and EV strain adapted to guinea pigs and causing a lethal infection in them. The disease induced by lethal EV differed from that induced by other EV strains. Blastic wave in lymphoid organs in the absence of antibodies to EV detected by enzyme immunoassay, elimination of circulating immune complexes, and appearance of eosinophils in the blood of guinea pigs infected with lethal EV suggest the formation of aggressive immune complexes actively precipitating in tissues and contributing to the development of pathological process typical of Ebola infection.

[Methods for controlling colonization of air and laboratory surfaces by pathogens of certain especially dangerous viral infections]

Regular check-ups of the laboratory environment (air and working surfaces) for contamination with the objects of investigations are obligatory for laboratories working with viruses causing grave diseases, such as Ebola, Marburg, and Machupo fevers and Venezuelan equine encephalomyelitis. Methods for indication and identification of these agents have been developed and experimentally tried.

[Change in biochemical and hemostatic indicators in guinea pigs upon administering Ebola virus preparations]

The biochemical and hemostatic parameters were compared in guinea pigs after inoculation of Ebola virus strains lethal and nonlethal for them and of inactivated antigen of this virus. The time course of the main hemostatic and biochemical parameters in animals challenged with the lethal strain of Ebola virus differed much from that in other groups. This permits us to hypothesize that modification of the virus in the course of adaptation to the host results in the appearance of properties boosting the enzymatic processes and, hence, in depletion and failure of antioxidant and hemostatic defence, which aggravates the pathological process.

[Changes in certain indicators of hemostasis in rabbits upon administration of Ebola virus preparations]

Changes in some parameters of hemostasis in rabbits insusceptible to Ebola virus (EV) in various periods after reinoculations with live and inactivated virus are described. Challenge with both control protein and live and inactivated EV leads to imbalance in the hemostasis system, which is compensated for in the course of follow-up and does not result in clinically manifest disorders of blood clotting. However, the mechanisms of development of the hemostasis imbalance caused by the control protein and virus preparations were different. In the former case no fibrinogen degradation products were detected in the blood serum, whereas in the latter they appeared in the serum after each reinoculation of the virus. This indicates a peculiar effect of EV on hemostasis.

[Immunobiological properties of vp24 protein of Ebola virus expressed by recombinant vaccinia virus]

Immunological and biochemical parameters were studied in guinea pigs immunized with recombinant vaccinia virus containing full-sized gene of Ebola virus vp24 protein and then infected with virulent strain of Ebola virus. The majority of the studied parameters changed similarly in guinea pigs immunized with recombinant vaccinia virus and control guinea pigs inoculated with vaccinia virus both before and after challenge with Ebola virus. However, in animals immunized with recombinant vaccinia virus producing vp24 some biochemical parameters, the mean life span after challenge with Ebola virus, the level of antibodies to the virus, and the phagocytic activity of neutrophils indicated the development of immunological processes other than in controls, namely, the development of immune response to vp24. Although these processes did not eventually lead to the survival of animals, they prolonged the mean life span and resulted in the production of anti-Ebola antibodies, though the level thereof was low. These data demonstrate that recombinant vaccines against Ebola fever are a promising trend of research.

[Isolation and characteristics of regional cytomegalovirus strains]

Two strains of cytomegalovirus were isolated from seropositive patients. The strains were identified and characterized by virological and immunological methods and may be used for research and practical studies.

[Effect of inactivated Ebola virus on colony forming activity of human hematopoietic stem cells]

The effect of Ebola virus antigen on the growth of hemopoietic precursors was studied. Incubation of mononuclear cells with the viral antigen led to a dose-dependent decrease of erythroid colony formation but did not alter the growth of the granulocyto-macrophagal precursors. Hence, Ebola virus antigen is capable of directly affecting the hemopoietic activity of precursors in man by inhibiting the growth of erythroid colonies.

[Study of the phagocytic ability of blood polymorphonuclear leukocytes from rabbits and guinea pigs upon administering Ebola virus]

Study of the phagocytic activity of polymorphonuclear leukocytes (PMNL) of rabbits resistant to Ebola virus and guinea pigs susceptible to it, repeatedly challenged with live or inactivated Ebola virus in accordance with the immunization protocols, showed a much higher phagocytic activity in animals resistant to the virus than in those susceptible to it. Such behavior of PMNL in guinea pigs may be explained by the absence of the necessary cytokine background activating the neutrophils.

[Cloning and primary structure determination of genes coding for IE2 and PP150 proteins of human cytomegalovirus]

The epidemiological situation with cytomegalovirus infection in Siberia is still to be studied and serological diagnosis of human cytomegalovirus (HCMV) is not satisfactory. Two regions of HCMV genome (strain AD-169) have been examined for obtaining diagnostic reagents by expression cloning. Using polymerase chain reaction, fragments of gene of the immediate early protein (IE2) and of the region encoding for the entire hydrophilic part (1176 bp) of the large phospoprotein gene (pp150) have been obtained. Both fragments were cloned in bacterial vectors. Analysis of nucleotide sequence showed negligible substitutions in comparison with previously reported sequences for these genes.

[Experimental Ebola fever in Macaca mulatta]

Aerogenic infection of M. rhesus with Ebola virus causes in them a disease similar in the principal clinical and virological parameters a grave form of Ebola fever in humans, as it is described in literature. Rapid development of symptoms of total intoxication in the presence of fever, hemorrhagic diathesis, and high viremia are indicative of the infection severity in monkeys.