The Molecular Basis for Antigenic Drift of Human A/H2N2 Influenza Viruses.

Influenza A/H2N2 viruses caused a pandemic in 1957 and continued to circulate in humans until 1968. The antigenic evolution of A/H2N2 viruses over time and the amino acid substitutions responsible for this antigenic evolution are not known. Here, the antigenic diversity of a representative set of human A/H2N2 viruses isolated between 1957 and 1968 was characterized. The antigenic change of influenza A/H2N2 viruses during the 12 years that this virus circulated was modest. Two amino acid substitutions, T128D and N139K, located in the head domain of the H2 hemagglutinin (HA) molecule, were identified as important determinants of antigenic change during A/H2N2 virus evolution. The rate of A/H2N2 virus antigenic evolution during the 12-year period after introduction in humans was half that of A/H3N2 viruses, despite similar rates of genetic change.IMPORTANCE While influenza A viruses of subtype H2N2 were at the origin of the Asian influenza pandemic, little is known about the antigenic changes that occurred during the twelve years of circulation in humans, the role of preexisting immunity, and the evolutionary rates of the virus. In this study, the antigenic map derived from hemagglutination inhibition (HI) titers of cell-cultured virus isolates and ferret postinfection sera displayed a directional evolution of viruses away from earlier isolates. Furthermore, individual mutations in close proximity to the receptor-binding site of the HA molecule determined the antigenic reactivity, confirming that individual amino acid substitutions in A/H2N2 viruses can confer major antigenic changes. This study adds to our understanding of virus evolution with respect to antigenic variability, rates of virus evolution, and potential escape mutants of A/H2N2.

Assessment of the virulence for chickens of Newcastle Disease virus with an engineered multi-basic cleavage site in the fusion protein and disrupted V protein gene.

Newcastle Disease virus (NDV) has shown promise as an oncolytic virus for treatment of a wide range of tumours. NDV with a multi-basic cleavage site (MBCS) in the fusion (F) protein (NDV F3aa) has increased oncolytic efficacy in several tumour models, but also increased virulence in chickens compared to non-virulent NDV F0, raising potential environmental safety issues. Previously, we generated a variant of NDV F3aa with a disrupted V protein gene and a substitution of phenylalanine to serine at position 117 of the F protein (NDV F3aa-S-STOPV). Compared to NDV F3aa this virus had decreased virulence in embryonated chicken eggs. In this study, the virulence of the virus was evaluated upon inoculation of six-week-old chickens through a natural infection route and by determination of the intracerebral pathogenicity index (ICPI). Based on these data NDV F3aa-S-STOPV classified as a non-virulent virus. Although NDV F3aa was classified as a virulent virus based on the ICPI, the virus was also less pathogenic than NDV F0 upon inoculation of six-week-old chickens. These data indicate that NDV with a MBCS is not necessarily pathogenic in chickens. In addition, these data show that F3aa-S-STOPV is safe to use in viro-immunotherapies without posing a threat for chickens upon accidental exposure.

[A/H13 and A/H16 influenza viruses: different lines of one precursors].

Analysis of the data of annual (1980-2005) monitorings of influenza A viruses in the North Caspian Sea basin and the Volga river delta, as well as the primary hemagglutinin structure of isolates of different years revealed the circulation of A/H13 and A/H16 viruses among gulls since 1976. Phylogenetic analysis revealed 3 significantly different evolutionary lines: an American line, a European line, and a line comprising the isolates from America and Eurasia. The H13N6 and H16N3 viruses isolated in Russia replicated in the respiratory and intestinal tracts of ducks and induced the production of antibodies; the H16N3 viruses induced the antibodies neutralizing viruses of subtype H16 only. The use of glycoconjugate polymers showed that the receptor phenotype of the study H16 viruses differed from that of the H13 viruses in its capacity to bind to 3'SL with a higher affinity than alphaNANA. The comparative phylogenetic analysis suggests the existence of the common precursor of H13 and H16 viruses and their further evolution in relation to environmental conditions, including their adaptation to a new host.