Reactivity of human convalescent sera with influenza virus hemagglutinin protein mutants at antigenic site A.

How the antibodies of individual convalescent human sera bind to each amino acid residue at the antigenic sites of hemagglutinin (HA) of influenza viruses, and how the antigenic drift strains of influenza viruses are selected by human sera, is not well understood. In our previous study, it was found by a binding assay with a chimeric HA between A/Kamata/14/91 (Ka/91) and A/Aichi/2/68 that convalescent human sera, following Ka/91 like (H3N2) virus infection, bind to antigenic site A of Ka/91 HA. Here using chimeric HAs possessing single amino acid substitutions at site A, it was determined how those human sera recognize each amino acid residue at antigenic site A.

Possibility of mutation prediction of influenza hemagglutinin by combination of hemadsorption experiment and quantum chemical calculation for antibody binding.

We have performed a quantum-chemical MP2/6-31G* calculation for the hemagglutinin (HA) antigen-antibody system of the H3N2 influenza virus with the fragment molecular orbital method, which provides one of the world's largest ab initio electron-correlated calculations for biomolecular systems. On the basis of the calculated interfragment interaction energies (IFIEs) representing the molecular interactions between the amino acid residues in the antigen-antibody complex, we have identified those residues in the antigenic region E of HA protein that are significantly recognized by the Fab fragment of antibody with strongly attractive interactions. Combining these IFIE results with those of hemadsorption experiments by which the mutation-prohibited sites are specified has enabled us to explain most of the historical mutation data (five of six residues), which would thus provide a promising method for predicting the HA residues that have a high probability of forthcoming mutation.

Effects of single-point amino acid substitutions on the structure and function neuraminidase proteins in influenza A virus.

In order to clarify the effect of amino acid substitutions on the structure and function of the neuraminidase (NA) protein of influenza A virus, we introduced single-point amino acid substitutions into the NA protein of the A/Tokyo/3/67 (H2N2) strain using PCR-based random mutation. The rate of tolerant random one amino acid substitutions in the NA protein was 47%. Rates of tolerant substitutions for the stalk and for the surface and inner portion of the head region of the NA protein were 79, 54, and 19%, respectively.

Protective effect of nasal immunization of influenza virus hemagglutinin with recombinant cholera toxin B subunit as a mucosal adjuvant in mice.

To develop an efficient nasal influenza vaccine, influenza A and B virus HA with rCTB as a mucosal adjuvant were administered to mice intranasally. Serum anti-HA IgG and IgA antibody responses for both HA vaccines were significantly increased in the presence of rCTB. Higher HI and neutralizing antibody titers and higher mucosal IgA antibody responses in the respiratory tract were detected when rCTB was added than without rCTB.

Comparison of epitope structures of H3HAs through protein modeling of influenza A virus hemagglutinin: mechanism for selection of antigenic variants in the presence of a monoclonal antibody.

Starting with nine plaques of influenza A/Kamata/14/91(H3N2) virus, we selected mutants in the presence of monoclonal antibody 203 (mAb203). In total, amino acid substitutions were found at nine positions (77, 80, 131, 135, 141, 142, 143, 144 and 146), which localized in the antigenic site A of the hemagglutinin (HA). The escape mutants differed in the extent to which they had lost binding to mAb203.

[Accumulation of amino acid substitutions promotes irreversible structural changes in the hemagglutinin of human influenza AH3 virus during evolution].

During protein evolution the amino acid substitutions accumulate with time. However, the effect of accumulation of the amino acid substitutions to structural changes has not been estimated well. We will propose that the discordance of amino acid substitution on the HA protein of influenza A virus is useful for the assessment of structural changes during evolution.

Accumulation of amino acid substitutions promotes irreversible structural changes in the hemagglutinin of human influenza AH3 virus during evolution.

In order to clarify the effect of an accumulation of amino acid substitutions on the hemadsorption character of the influenza AH3 virus hemagglutinin (HA) protein, we introduced single-point amino acid changes into the HA1 domain of the HA proteins of influenza viruses isolated in 1968 (A/Aichi/2/68) and 1997 (A/Sydney/5/97) by using PCR-based random mutation or site-directed mutagenesis. These substitutions were classified as positive or negative according to their effects on the hemadsorption activity. The rate of positive substitutions was about 50% for both strains.

Seroprevalence of noroviruses in swine.

Noroviruses (NVs) are important human pathogens that cause acute gastroenteritis. Genetically related animal enteric NVs have also been described, but there is no evidence of interspecies transmission of NVs. In this study we characterized antibody prevalence among domestic pigs by using recombinant capsid antigens of two human NVs (Norwalk and Hawaii) and one swine NV (SW918) that is genetically related to GII human NVs.

Isolation of influenza A H1N2 viruses from an outbreak in Yokohama City during the 2001-2002 influenza season in Japan.

Emergence of Influenza A H1N2 viruses was documented worldwide during the 2001-2002 influenza season. In Japan, H1N2 viruses were isolated from two students of a junior high school in an influenza outbreak in Yokohama City, February 2001. Genetic and antigenic analyses demonstrated that the H1N2 viruses isolated in Japan shared common features with those isolated in other countries.

Viruses detected in the caecum contents of healthy pigs representing a new genetic cluster in genogroup II of the genus "Norwalk-like viruses".

Viruses of the genus 'Norwalk-like viruses' (NLVs) detected in humans have been genetically classified into two major genetic groups, genogroups I and II (GI and GII), which together are made up of at least 14 genetic subgroups. However, a comparable classification of NLVs in other species remains to be carried out. We sequenced a 2-kb region from within the RNA polymerase gene to the 3' end of open reading frame 2 (ORF2) of two NLV strains previously detected in the caecum contents of healthy pigs.