[Sequence and phylogenetic analysis of the haemagglutinin genes of H9N2 avian influenza viruses isolated in central China during 1998-2008].

The purpose of this study is to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of avian influenza virus(AIV). Haemagglutinin (HA) genes from, 6 of 25 avian influenza viruses (AIVs) H9N2 strains with different pathogenicity isolated in central China during last 10 years were amplified by reverse transcriptase PCR (RT-PCR), completely sequenced and phylogenetically analyzed. The purpose of this study was to explore the effects of the HA sequence variation on the pathogenicity and antigenicity of AIV. The results showed that all 6 representative H9N2 isolates belong to low pathogenic AIVs, since none of the amino acid sequences at the cleavage site of the HA of the isolates possessed the basic motif required for highly pathogenic viruses (R-X-R/K-R). There were eight potential glycosylation sites in HA of the isolates, except that 3# and 12# had an extra one. The higher pathogenicity of 3# and 12# was probably due to the extra glycosylation site (145aa-147aa) in HA1, which might alter the conformational structure of HA resulting in the mutation or deletion of the binding sites of anti-HA antibody, and has effects on receptor binding sites thus changed the antigenicity of the virus. Our results suggested that attention should be paid to the transmission and natural evolution of H9N2 AIV in order to control AIV H9N2.