疟原虫全虫疫苗长效保护性下降机制初探

A preliminary study of the mechanism for reduced efficacy of and protection by a malaria vaccine

目的探讨疟疾红外期全虫疫苗免疫保护性随时间逐渐降低的机制。方法取C57BL/6及BALB/c小鼠,经尾静脉分别接种10 000或50 000约氏疟原虫(P.yoelii)17XNL子孢子,3h后给予氯喹控制红内期感染的发生。一部分小鼠于接种后30、90、180d用10 000同种疟原虫子孢子进行攻击检查保护性;另一部分在相同时间点取血,分离淋巴细胞,进行流式抗体染色,检测免疫保护性及其与肝脏淋巴细胞表型间的相互关系。结果疟原虫全虫抗原免疫后30d两种小鼠均可产生100%的免疫保护;免疫后90d,C57BL/6保护性开始下降,180d时保护性将至40%,而BALB/c小鼠保护性无明显变化。C57BL/6小鼠肝脏CD8^+T_(EM)细胞PD-1的表达在免疫后180d显著上升(t=7.369,P<0.01),BALB/c小鼠无明显变化(t=1.368,P>0.05)。C57BL/6小鼠肝脏CD8^+T_(EM)细胞PD-1的表达免疫后随时间增加而升高,其中免疫后180d较90d时上升趋势更显著(t=6.175,P<0.01)。结论在C57BL/6小鼠,疟原虫红外期全虫疫苗免疫保护性随免疫时间延长逐渐降低与肝脏CD8^+T细胞PD-1表达增高有关。

Objectives To investigate the mechanism for reduced efficacy of and protection by a malaria vaccine.Methods C57BL/6 or BALB/c mice were intravenously inoculated 3 times with 10 kor 50 kWT Plasmodium yoelii sporozoites（spz）at 4-week intervals.Three hours after injection,the mice were treated with 0.8 mg of chloroquine（CQ）for 10 consecutive days.Mice were challenged with 10 k WT spz that were injected intravenously 30,90,or 180 dafter immunization.The phenotype of hepatic lymphocytes was determined with flow cytometry. Results Both C57BL/6 and BALB/c mice had 100% protection 30 dafter immunization.However,10% of C57BL/6 mice（1/10）had detectable blood stage parasitemia 90 dafter immunization,and 60% of C57BL/6 mice（6/10）had parasitemia 180 dafter immunization.All of the BALB/c mice had 100% protection 180 dafter immunization.Phenotypic analysis of lymphocytes indicated that PD-1 expression on CD8-＋T cells increased significantly in C57BL/6 mice 90 dafter immunization but not in BALB/c mice.Moreover,the level of PD-1 expression in mice 180 dafter immunization was significantly higher than that in mice 90 dafter immunization（t=6.175,P〈0.01）. Conclusion The reduced efficacy of and protection by malaria vaccine was correlated with a high level of PD-1 expression on CD8-＋T cells.