We analysed the genetic content of reassortants between parent viruses differing in their ability to form filaments. The results suggest that primarily HA, M, and NP genes are involved in the control of the filament forming ability. A lower buoyant density of the filamentous forms as compared to spherical particles allowed us to obtain a sufficiently pure population of filaments. A difference in the UV-inactivation kinetics between filaments and spherical virions suggests that the infectious filamentous forms are probably represented by multigenomic particles or partial heterozygotes.

Summary. The effects of monoclonal antibody (MAb) C179 recognizing a conformational epitope in the middle of the hemagglutinine (HA) stem region were examined in a mouse model in the experiments of prevention and treatment of lethal bronchopneumonia caused by influenza A virus of H5 subtype. To model the lethal infection, avian nonpathogenic strain A/mallard duck/Pennsylvania/ 10218/84 (H5N2) was adapted to mice. This resulted in highly pathogenic pneumovirulent mouse-adapted (MA) variant, which was characterized. Three amino acid changes were found in the HA1 subunit of HA of MA virus. One of these was located inside the region of the conformational epitope recognized by MAb C179. However, this substitution was not significant for the recognition of HA and virus neutralization by MAb C179 in vitro and in vivo. Intraperitoneal administration of two different concentrations of MAb C179 one day before or two days after the virus challenge significantly decreased mortality rate. These results suggest that MAb C179 is efficient not only in the prevention and treatment of H1 and H2 influenza virus bronchopneumonia, as was reported previously, but also of H5-induced bronchopneumonia as well, and demonstrate in vivo the existence of a common neutralizing epitope in the HAs of these three subtypes.*

High-frequency reassortment of gene segments is characteristic for influenza viruses, and it is considered to be of significance for the origin of pandemic influenza. In order to analyze whether the segregation of genes in the reassortants is random, or it deviates from the random pattern, we inoculated embryonated chicken eggs simultaneously with two influenza viruses, A/WSN/33 (H1N1) and A/Duck/ Czechoslovakia/56 (H4N6), at a high multiplicity of infection. The virus yield was used for plaque cloning, and the genetic content of plaque isolates was determined by analysis of the mobility of virus-induced proteins in polyacrylamide gel (for NP and NS genes), partial sequencing (for M gene) and polymerase chain reaction analysis with strain-specific primers for the other genes. Out of 37 isolates, 27 were reassortants. The majority of the reassortants contained the HA gene of A/WSN/33 (H1N1) virus and the NP gene of A/Duck/Czechoslovakia/56 (H4N6) virus. The data demonstrate the previously unrecognized phenomenon of segment-specific deviation from the random distribution of parent genes in the reassortants. The results are discussed in connection with the problem of differential competition between influenza A virus gene segments in mixed infection and random versus non-random reassortment of gene segments under non-selective conditions.

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Influenza viruses are characterized by a high degree of antigenic variability, which causes the annual emergence of flu epidemics and irregularly timed pandemics caused by viruses with new antigenic and biological traits. Novel approaches to vaccination can help circumvent this problem. One of these new methods incorporates genetic vaccines based on adenoviral vectors. Recombinant adenoviral vectors which contain hemagglutinin–encoding genes from avian H5N1 and H5N2 (Ad–HA5–1 and Ad–HA5–2) influenza viruses were obtained using the AdEasy Adenoviral Vector System (Stratagene). Laboratory mice received a double intranasal vaccination with Ad–HA5–1 and Ad–HA5–2. This study demonstrates that immunization with recombinant adenoviruses bearing the Н 5 influenza virus hemagglutinin gene induces a immune response which protects immunized mice from a lethal dose of the H5 influenza virus. Moreover, it also protects the host from a lethal dose of the H1 virus, which belongs to the same clade as H5, but does not confer protection from the subtype H3 influenza virus, which belongs to a different clade.