IBV S1基因和IL-2基因双顺反子DNA疫苗的免疫原性研究

为了研制更加有效的IBV DNA疫苗,将IBV的S1基因和禽白介素2(IL-2)基因插入双顺反子表达载体pIRES-EGFP/DsRed中,构建能分别或同时表达S1基因和IL-2基因的pIRES-S1、pIRES-IL2、pIRES-S1/IL-2质粒。通过脂质体转染Vero细胞,利用RT-PCR及间接免疫荧光检测表达。将构建的质粒用脂质体包裹后,通过腿部肌肉多点注射免疫7日龄雏鸡,二免后两周用IBV肾型强毒进行攻毒。结果表明,pIRES-S1/IL-2在体外能够诱导Vero细胞表达S1蛋白和IL-2;pIRES-S1/IL-2和pIRES-S1 pIRES-IL2免疫雏鸡后均能促进外周血T淋巴细胞亚群数量和血清中特异性抗体水平的增加,能明显增强IBV DNA疫苗对同型强毒的攻击保护,但pIRES-S1/IL-2免疫组要优于pIRES-S1 pIRES-IL2混合免疫组及其它对照组,差异显著或极显著。以上结果表明禽IL-2能同时加强DNA疫苗的细胞免疫和体液免疫应答;但抗原基因和IL-2共表达DNA疫苗的免疫效果明显要优于混合注射的DNA疫苗。

Potent immune responses elicited by a bicistronic IBV DNA vaccine expressing S1 and IL-2 gene

Candidate IBV vaccines should elicit cellular responses as well as humoral responses. S1 gene of avian infectious bronchitis virus and interleukin-2 (IL-2) gene from chicken were inserted into the bicistronic pIRES-EGFP/DsRed plasmid. The pIRES-S1, pIRES-IL2 and pIRES-S1/IL-2 plasmid expressing or co-expressing S1 and IL-2 gene were constructed. Plasmids were transfected into the Vero cells by lipofectamine, and the expressed products were detected by RT-PCR and indirect immunofluorescence assay. The 7-day-old chickens were immunized intramuscularly with plasmids encapsulated by liposome and boosted three weeks later. Two weeks after boosting, chickens were challenged by virulent IBV strain. The results showed that coadministration of a plasmid expressing IL-2 with the S1 DNA vaccine led to only a marginal increase in humoral and T cell responses. However, immunization with the bicistronic plasmid pIRES-S1/IL-2 that co-expressing S1 and IL-2 under control of a single promoter led to a dramatic augmentation of humoral and T cell responses. The protective efficacy could be significantly enhanced after injection with plasmids pIRES-S1/IL-2 or pIRES-S1 pIRES-IL2. These results demonstrate that bicistronic DNA vaccine containing IL-2 elicit remarkably immune responses and suggest that optimal humoral and cellular responses priming requires the precise temporal and spatial codelivery of Ag and IL-2.