Cloning and expression of antigenic sites of hemagglutinin of Influenza A virus

Influenza A viruses are a respiratory pathogen that cause annual epidemics as well as many well-known pandemics such as Russian flu (1889), Spanish flu (1918), Asian Flu (1957) and the recent Mexico swine flu (2009). The viral envelope, the hemagglutinin (HA), in particular HA1, confers the antigenic sites, receptor binding sites and induces immune response. HA1 of the H1 influenza consists of 4 distinct antigenic sites, namely Sa, Sb, Ca and Cb. This study aims to express truncated forms of HA1 of the H1 influenza, which could be used to determine the most neutralising domains of HA. Three constructs containing different antigenic sites of HA termed, F1, F2 and F3, were cloned and expressed on Chinese Hamster Ovary (CHO) cells. Cells expressing higher antigenic determinants were selected by limiting dilution and/or Fluorescence-activated Cell Sorting (FACS). Initial experiments testing the H1 fragments against pre and post vaccination H1 human sera show little reactivity of the transfectants with the sera. The reason of loss of reactivity among recombinant H1 antigenic sites could be because of the antigenic sites being conformational rather than linear epitopes. However, the parent HA1 also shows minimum reactivity. Higher circulating H3 subtype of Influenza A in Australia and antigenic drift may influence the overall reactivity of the transfectants. Future studies discovering fragments reactivity against various human influenza sera should be carried out to examine fragment characteristics. Additional fragments of different epitopes from other influenza subtypes could also be examined and compared.