The Variation Characterization Analysis Of Pandemic A/H1N1Influenza Virus Under Antibody Selected Pressure

There are three types of influenza viruses(A, B and C).The whole world influenzapandemics are only caused by influenza A viruses. The pandemic2009influenzaA/H1N1had swept over200countries and areas in the world, posing a serious threat topublic health security. Though the world is no longer in phase of influenza pandemic,weshould not slacken the work of surveillance and the research on pandemic A/H1N1influenza virus in the post-pandemic phase, in case that the virus will become an newpandemic strain through variation and threat human health again.The variation ofinfluenza includes antigenicity, pathogenicity, drug tolerance and transmissibility.In thestudy,we paied attention to study variation of antigenicity and pathogenicity of thepandemic2009influenza A/H1N1used mice as the mammalian animal models and toconstruct the reverse genetics system of the virus primarily.With the continuous popularity of influenza and virus vaccination,the numble ofhuman with influenza antibody has been increasing.Whether the immune pressure willpromote the antigenic variation of pandemic2009A/H1N1influenza virus to evade theimmune system defencesshould be studied. In additiona, part of the infected patients onclinic showed severe performance, sequence analysis indicated that some mutant strainsmay have a higher pathogenicity.Therefore, study on the variation characterization ofpandemic A/H1N1influenza virus under selective pressure of antibodies will help us toexplore the mechanism and tendency of the antigenical and pathogenical variation ofthis virus on molecular level to provide guidance and reference for the virus preventionand control.In this study,on the basis of analysis of the complete genome sequence of the XDstrain separated in the laboratory,its pathogenicity to the BALB/c mice wasdetected.The XD wild-type strain was serially passaged in mice immuned withinactivated A/H1N1influenza vaccine to carry out the variant strain, while the controlstrain were aquried through serial lung-to-lung passage in na ve mice. To evaluate virusvariation, antigenic relatedness(R), MLD50, rate of weight change and survival were tested as the evaluation index. The results indicated that the pathogenicity andantigenicity of pandemic A/H1N1influenza virus have changed after serial passages inmouse lung. The antigenicity under antibody pressure changed more remarkablely thanthat without antibody pressure,.R is0.35and the virus pathogenicity was enhanced by18times, but the one without antibody pressure by1000times.To study molecular basis of this virus variation, the strains with obvious antigenicityor pathogenicity change have been selected.The genome sequences were sequenced to screenamino acid sites related to antigenicity and pathogenicity,including HA-S183P、 HA-N156D、HA-D222G and HA-R223Q as antigenical sites and PB1-R296T、PA-I94V、NP-D375N、HA-N156D、HA-D222G and HA-R223Q as pathogenical sites.The pandemic A/H1N1influenza virus reverse genetics system UIXD-P18-2-E1has been constructed after the key amino acid sites were found, and the virus rUIXD-P18-2-C1has been rescued in vitro. rUIXD-P18-2-C1are the same with the parentalstrain UIXD-P18-2-E1through the evaluation of biological characteristics. Thispandemic A/H1N1influenza virus reverse genetics system will provide foundation forthe research on the molecular mechanism of variation of XD strian.