[Sequence analysis of the HA1 regions of hemagglutinin genes of influenza viruses (H3N2) isolated from children in Beijing from 1998 - 2004].
OBJECTIVE
To characterize the HA1 regions of hemagglutinin gene of influenza viruses (H3N2) isolated from children in Beijing from 1998 - 2004.


METHODS
The HA1 regions of hemagglutinin gene were amplified by RT-PCR from the viruses isolated and identified as A3 (H3N2) from clinical samples collected from infants and children during the peak seasons of influenza between 1998 and 2004. PCR products were sequenced or cloned into T-A vector and were analyzed after being sequenced.


RESULTS
The HA1 regions of hemagglutinin genes amplified from those isolates were 987 bp in length, encoding a protein of 329 amino acids in length. The identities of nucleotides and amino acids among these H3N2 isolates in Beijing and vaccines strains from 1998 - 2004 were 95.5% - 100.0% and 93.0% - 100.0%, respectively. The homology of the HA1 regions were related to the date of virus isolation, meaning the homology was higher among those strains isolated in nearer dates than others. Seven potential N-linked glycosylation sites in the HA1 regions located at amino acid positions 8, 22, 38, 63, 126, 165 and 285 were conserved in all the viruses analyzed. Two sites at 122 and 133 were inserted in those virus isolated after 1997, and another site at 144 appeared in those isolated after 1999. More amino acid substitutions located in the five putative antigenic sites or receptor binding sites were found more in the isolates than the isolates from previous year. Phylogenetic analysis showed new branches appeared continuously during 1998 - 2004. The strains isolated during winter in 2004 belonged to different branches, suggesting the appearance of new variants.


CONCLUSIONS
Amino acid substitutions continuously occurred in the HA1 regions of hemagglutinin genes in influenza virus (H3N2) isolated from children in Beijing from 1998 - 2004, which might have resulted in antigenic drift and led to the appearance of new variants.
Zhu
Ru-nan
RN
Laboratory of Virology, Beijing Municipal Laboratory of Infection and Immunity, Capital Institute of Pediatrics, Beijing 100020, China.
Qian
Yuan
Y
Wang
Fang
F
Deng
Jie
J
Zhao
Lin-qing
LQ
Liu
Cheng-gui
CG
D019943:Amino Acid Substitution; D002681:China; D004279:DNA, Viral / Q000032:analysis; D005784:Gene Amplification; D006388:Hemagglutinins / Q000235:genetics*; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics*; D007251:Influenza, Human / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
D004279:DNA, Viral; D006388:Hemagglutinins