[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.