尽管鸡大肠杆菌的致病力是多因素控制的，但通过肺泡毛细血管进入血循环是其发挥致病作用的关键一步。iss基因为血清抗性基因，与致病力相关，体外试验证实一株鸡致病性大肠杆菌HO2菌株的Iss融合蛋白抗血清可以降低HO2菌株在血清中的存活率。但iss基因序列差异位点与拷贝数对细菌致病力的影响以及对Iss蛋白免疫防制效果的影响仍然不明。因此拟采集数十株鸡大肠杆菌菌株，进行致病力试验、血清抗性试验、iss基因套式PCR、实时荧光定量PCR、测序及Iss蛋白间接ELISA检测，确定iss基因序列差异位点与拷贝数对Iss蛋白的表达水平、血清抗性及菌株致病力的影响；依据iss基因序列差异设计若干原核表达系统，分别分离Iss蛋白并免疫鸡只获得相应抗体，通过体外试验和动物试验分析抗Iss蛋白抗体对试验动物是否具有保护作用或交叉保护作用。为探讨iss基因对细菌致病力的影响及对Iss蛋白免疫防制效果的影响提供依据。

In order to determine the immune potential of iss gene, the virulence of avian E.coli isolates will be detected, and each isolate will be examined for the presence of iss gene by using PCR techniques.Antiserum against Iss fusion and normal serum will be both generated. The possession of Iss protein will be detected by indirect ELISA, and survival of avian E.coli isolates in normal serum will be linked with the survival of them in antiserum to analyze the immune effect of antibody on avian E.coli serum-resistance in vitro. And it will be detected that chickens immuned with Iss fusion will, or will not be protected against challenge by avian pathogenic E.coli in vivo. Influence of iss sequence on virulence of avian E.coli and immune potential of Iss protein will be determined.