罗非鱼无乳链球菌PLGA微球口服疫苗免疫效果的研究

The immune effect of PLGA microparticles containing GBS on Nile tilapia

目的探讨用聚乳酸-羟基乙酸[poly(D,L-lactic-co-glycolic)acid,PLGA]包裹无乳链球菌制备的口服疫苗对罗非鱼的免疫保护效果。方法复乳溶剂挥发法制备包裹无乳链球菌全菌和破碎后上清的PLGA微球,通过口服给予方式免疫尼罗罗非鱼,以注射灭活全菌疫苗为阳性对照,免疫后第7、14、21、28天测定受免鱼血清的白细胞吞噬百分比与吞噬指数、血清中的溶菌酶与超氧化物歧化酶活性以及抗体水平。人工攻毒实验比较罗非鱼无乳链球菌PLGA微球的免疫保护作用。结果实验组鱼的白细胞吞噬百分比、吞噬指数、溶菌酶和超氧化物歧化酶均显著高于阴性对照组,低于阳性对照组;抗体水平也有类似结果,但第14天后阳性对照组鱼的抗体水平开始下降,而实验组鱼则仍维持在较高水平。攻毒实验显示全菌和破碎后的上清微球疫苗相对免疫保护率(RPS)分别为57.63%和34.40%,阳性对照组为94.53%。结论本研究制备的罗非鱼无乳链球菌PLGA微球口服疫苗能够增强罗非鱼对无乳链球菌的免疫反应,并可通过缓释作用使机体维持较高的抗体水平,可为罗非鱼提供一定的免疫保护,但其RPS低于全菌灭活注射疫苗。

To investigate the immune effects of PLGA-capsulated group B Streptococcus agalactiae（GSB） as an oral vaccine,Nile tilapias（Oreochromis niloticus） were intragastrically immunized with PLGA microparticles containing GBS whole cell and supernatant after ultrasonication,which were assigned as test groups. Positive control was treated with formalin-killed GSB intraperitoneally. Negative controls include untreated group and the group treated with microparticles containing PBS. The percentage of phagocytes（PP）,phagocytic index（PI）,lysozymeactivities,superoxide dismutase（SOD） activities and antibody level（OD450 nm） were detected each week. Four weeks after immunization,tilapias were challenged by artificial infection with Streptococcus agalactiae and relative percent survivals（RPS） were calculated. Data showed that the PP,PI,lysozyme activities,SOD activities of the test groups were higher than those in negative controls,and lower than those in positive control. Antibody level in test groups was lower than that in positive controls,but remained at high level after booster compared to the continuous decrease in positive control. The RPS of GBS whole cell and supernatant after ultrasonication groups were 57.63%and 34.40% respectively,while RPS of positive control group was 94.53%. Taken together,PLGA microparticles（as adjuvants） encapsulated GBS provides effective protection for Nile tilapia against GBS infection,and they can increase the time of immune protection by sustained release,but with lower RPS compared to killed GSB.