But the whole level of serum titer in combined vaccine group was higher than others . igg was extracted by salting out with ammonium sulfate and purified by ion exchange chromatography with deae cellulose 对分离到的血清用饱和硫酸铵盐析法提取igg ,并用deae纤维素离子交换层析法对提取的igg进行纯化。