常见的变化有细胞变圆、聚集、坏死、溶解或脱落等.50%组织细胞感染量(TCID50)测定法是测定病毒能使50%的组织培养细胞发生感染的最小量.一般是将病毒悬液作10倍的系列稀释,分别接种细胞,经一定时间后观察CPE、血细胞吸附等指标,以最高稀释度能感染50%细胞的量为终点.最后用统计方法计算出50%组织细胞感染量（50%tissuecultureinfectiousdose,TCID50).蚀斑测定是一种检查和准确滴定病毒感染性的方法.将稀释的病毒悬液加入单层细胞培养瓶中.病毒吸附后,再覆盖一层融化的半固体营养琼脂,使病毒在单层细胞培养中有限扩散.结果是每一个有感染性的病毒在单层细胞中可产生一个局限性的感染灶.用活性染料(如中性红)染色,则活细胞着色,受病毒感染而破坏的细胞不着色,形成肉眼可见的蚀斑(plaque).每个蚀斑是由一个感染性病毒颗粒形成的,称作蚀斑形成单位(plaqueformingunit,PFU).病毒悬液中的感染性病毒量的滴度可用PFU／ml表示.Answer:Assumingthatthesamecellsystemisused,thatthevirusformsplaquesonthosecells,andthatnoproceduresareaddedwhichwouldinhibitplaqueformation,1mlofvirusstockwouldbeexpectedtohaveabouthalfofthenumberofplaqueformingunits(PFUs)asTCID50.Thisisonlyanestimatebutisbasedontherationalethatthelimitingdilutionwhichwouldinfect50%ofthecelllayerschallengedwouldoftenbeexpectedtoinitiallyproduceasingleplaqueinthecelllayerswhichbecomeinfected.Insomeinstances,twoormoreplaquesmightbychanceform,andthustheactualnumberofPFUsshouldbedeterminedexperimentally.Mathematically,theexpectedPFUswouldbesomewhatgreaterthanone-halftheTCID50,sincethenegativetubesintheTCID50representzeroplaqueformingunitsandthepositivetubeseachrepresentoneormoreplaqueformingunits.AmorepreciseestimateisobtainedbyapplyingthePoissondistribution.WhereP(o)istheproportionofnegativetubesandmisthemeannumberofinfectiousunitspervolume(PFU/ml),P(o)=e(-m).ForanytiterexpressedasaTCID50,P(o)=0.5.Thuse(-m)=0.5andm=-ln0.5whichis~0.7.Therefore,onecouldmultiplytheTCID50titer(perml)by0.7topredictthemeannumberofPFU/ml.Whenactuallyapplyingsuchcalculations,rememberthecalculatedmeanwillonlybevalidifthechangesinprotocolrequiredtovisualizeplaquesdonotaltertheexpressionofinfectiousvirusascomparedwithexpressionunderconditionsemployedforTCID50.Thusasaworkingestimate,onecanassumematerialwithaTCID50of1x105TCID50/mlwillproduce0.7x105PFUs/ml.