B Cells and Antibody Play Critical Roles in the Immediate De(4)

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RNAintissueswasassessedindependentlybyreal-time u-(i)Viremia.Inwild-typemice,viremiawasdetectedatday2orogenicRT-PCRusingprimersthatcorrespondedtoacon-aftersubcutaneousinfectionbutrapidlydecreasedtoalevelservednucleotidesequenceintheWNVenvelopegene(27).belowdetectionbyday6.In MTmice,acomparablelevelofThesensitivityoftheRT-PCRassaywasgreaterthanthatofinfectiousvirus( 102PFU/ml)wasmeasuredinseraatday2theplaqueassay,asWNVRNAthatcorrespondedto1to5butthiswasfollowedbyPFU(or 100to500copiesofviralRNA)pergramwas4asustainedincreasethroughday8untillevelsexceeded10PFU/ml(Fig.3A).Parallelresultsreliablydetected(datanotshown).

wereobservedwhenviralRNAlevelsweremeasured,withDistributionofWNVintissuesofwild-typeandB-cell- de cientmice.Thelevelsofinfectiousvirusand/orviralRNAmice500-foldwithinhigher4dayslevelsofinfectionofWNVRNA(Fig.3D).beingThus,detectedBcellsin MTandweredeterminedfromsera,peripheralorgans(spleenandantibodyappeartobeessentialforcontainingthelevelsofliver),andtheCNS(braincortexandinferiorandsuperiorWNVinserum.

spinalcord)ofwild-type(days2,4,6,8,10,and12)and MT(ii)Lymphnodes.ThelevelsofWNVRNAinthedraining(day2,4,6,and8)miceafterinfectionwith106PFUperpoplitealandinguinallymphnodesweresimilarbetweenwild-mouse(Fig.3).Because MTmicerapidlysuccumbedtoin-typeand MTmiceearlyinthecourseofinfection.ViralRNAfection,datafromthelasttwotimepoints(days10and12)wasdetectedatday2afterinfectionandremainedelevatedwerenotcollected.Severalobservationswerenoted.throughoutthecourseofinfection.However,byday8

after

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