The antigenic property of the H5N1 avian influenza viruses isolated in central China

Abstract

Background: Three influenza pandemics outbroke in the last century accompanied the viral antigen shift and drift, resulting in the change of antigenic property and the low cross protective ability of the existed antibody to the newly emerged pandemic virus, and eventually the death of millions of people. The antigenic characterizations of the viruses isolated in central China in 2004 and 2006-2007 were investigated in the present study.

Results: Hemagglutinin inhibition assay and neutralization assay displayed differential antigenic characteristics of the viruses isolated in central China in two periods (2004 and 2006-2007). HA genes of the viruses mainly located in two branches in phylogeny analysis. 53 mutations of the deduced amino acids of the HA genes were divided into 4 patterns. Mutations in pattern 2 and 3 showed the main difference between viruses isolated in 2004 and 2006-2007. Meanwhile, most amino acids in pattern 2 and 3 located in the globular head of the HA protein, and some of the mutations evenly distributed at the epitope sites.

Conclusions: The study demonstrated that a major antigenic drift had occurred in the viruses isolated in central China. And monitoring the antigenic property should be the priority in preventing the potential pandemic of H5N1 avian influenza virus.

Figure 1

Reactivity of the Mabs to the HA protein of virus dw/04. Due to the different Mabs were used to perform the western blot, the six reactions were performed separately and the image was resembled together. Same HA protein loading and exposure time were used in the western blot assay.

Figure 2

Phylogenetic analysis of HA gene of the 10 viruses. The phylogenetic tree was build with the program MEGA 4.1. Clades of H5N1 virus were classified according to nomenclature recommended by WHO evolution working group. The viruses used in present study were labeled by red spot.

Figure 3

Mutated sites in the crystal structure of HA protein. The crystal model is HA protein of A/Vietnam/1203/2005, built by the program PyMOL program (V1.4). A is the intact model of HA protein displayed the mutated amino acids in the five antigenic epitope sites. B is the detail profile of the five antigenic epitope sites A, B, C, D and E. The mutated amino acid sites in the 10 avian influenza viruses HA proteins located in the five epitopes were labeled. Amino acids labeled with green were pattern 1 mutation; amino acids labeled with red were pattern 2 mutation; amino acids labeled with blue were pattern 3 mutation; amino acids labeled with orange were pattern 4 mutation (table 2).