抗体选择压作用下H9N2亚型禽流感病毒NA基因的变异

Influence of Antibody-Mediated Immune Pressure on Neuraminidase Gene Mutations of Avian Influenza Virus H9N2

将LG1株H9N2亚型禽流感病毒在带有抗LG1株母源抗体的鸡胚中分4个独立系列连续传40代后,有3个系列从10～20代起在NA基因的#99位发生了可稳定遗传的碱基"G"到"A"的突变,并使氨基酸由蛋氨酸变为异亮氨酸;有2个系列从20～30代起在#473位发生了可稳定遗传的由"A"到"G"的碱基突变,导致相应的氨基酸由天冬酰胺变为丝氨酸,另一个传代系列在50代时也发生了同样的突变。在无抗体的鸡胚上的2个独立对照系列同样传了80代,在这2个位点没有发生突变,表明这2个突变与抗体的选择压相关。在抗LG1母源抗体阳性鸡胚的连续40代传代过程中,NA基因在有抗体组的四个传代系列碱基的非同义突变(NS)与同义突变(S)比为4.6(32/7),而在无抗体组NS/S比为2.0(16/8)。有抗体组NS/S值显著高于无抗体组,也显示出抗体的选择压作用。

LG1 strain of avian influenza virus H9N2 was passaged continuously for 40 generations in chicken embryos with anti-LG1 maternal antibodies in 4 parallel experiments,of which 3 experiments had a stable mutation of ＂G＂ to ＂A＂ at #99 of the neuraminidase gene（NA）from the 20th passage resulting in a change of Met to Ile and 2 had a stable mutation of ＂A＂ to ＂G＂ at #473 of the NA gene from the 30th passage resulting in a change of Asn to Ser which occurred in the 50th passage of another experiment.Eighty continuous passages in chicken embryos without antibody did not have the same mutation,indicating that the mutations of the 2 positions were associated with selective pressure of antibodies.Analysis of the ratios of nonsynonium（NS） vs synonium（S） mutations of nucleic acids demonstrated that NS/S of 4 parallel experiments with antibodies was 4.6（32/7） compared with 2.0（16/8） of the 2 experiments without antibodies and this significant difference implied the selective pressure of antibodies.