抗金葡菌肽聚糖模拟肽抗血清的被动保护作用

Passive immune protection of a Staphylococcus aureus peptidoglycan mimic peptide against Staphylococcus aureus infection

目的探讨针对金葡菌肽聚糖(PGN)模拟序列抗血清的被动保护作用。方法应用在线软件(http://www.ddg-pharmfac.net/mhcpred/MHCPred)和T细胞表位分析软件DNAstar对模拟PGN表位的SP31(ATWSHHLSSAGL)进行分析,改造SP31序列后合成四分枝多价抗原肽(multiple antigenic peptide,MAP)MAP-P31.1,以MAP-P31.1免疫小鼠和家兔,体外鉴定抗MAP-P31.1血清对MRSA/MSSA杀菌作用,体内观察饱和硫酸铵纯化免疫兔血清对金葡菌攻击动物的保护作用。结果将原始SP31序列改造为ATWSHHLSSAGLGGAS序列。2种抗MAP-P31.1血清均可结合PGN。用热灭活S.aureus再次加强免疫,抗血清的效价可有10倍以上升高(P<0.05)。抗MAP-P31.1血清在有补体或无补体作用下均有显著抑菌/杀菌作用(P<0.01),且显著优于抗金葡菌免疫的全菌血清及抗MAP-P31血清(P<0.001)。抗MAP-P31.1血清显著增强小鼠巨噬细胞对MRSA与MSSA的吞噬作用,过继转移后可保护小鼠抵御金葡菌致死性攻击(P<0.05),小鼠肾脏、脾脏中荷菌量显著降低(P<0.05)。结论模拟肽MAP-P31.1作为免疫原所诱导的抗血清具备了体外对MRSA的杀菌/抑制作用,但体内对MRSA的保护作用并不显著。

Peptidoglycan（PGN） is a conserved component of the cell wall of Gram-positive bacteria includingS. aureus. However, PGN, as a thymus-independent antigen, can＇t be considered as a vaccine candidate because ofits weak immunogenicity. In this study, we modified SP31 peptide（ATWSHHLSSAGLSAGG） mimicing the PGN ofS. aureus by online MHC prediction（http：//www.ddg-pharmfac.net/mhcpred/MHCPred） and DNAStar, and evaluatedits passive protective immunization in mice. The results showed that the modified MAP-P31.1 by adding a-GGAStail fulfilled a T cell epitope with a higher antigenic index and 10-fold antisera boosted by heat-killed S.aureus thanthat of the original MAP-P31. In vitro, our results also showed that anti-MAP-P31.1 sera had more potentbactericidal/bacteriostatic activity against MSSA with or without complements than that of anti-MAP-P31 andanti-S. aureus sera. Importantly, anti-MAP-P31.1 sera also had a bactericidal/bacteriostatic activity on MRSA,whereas anti-MAP.P31 sera did not. In addition, anti-MAP-P31.1 sera also increased phagocytosis activity ofmurine peritoneal macrophage against MSSA and MRSA. Finally, purified anti-MAP-P31.1 sera notably prolongedliving time and survival of mice infected with MSSA, and the bacterial loads in the spleens, livers, and kidneys weredecreased after administering anti-MAP-P31.1. Our results above showed that the modified MAP-P31.1 mimicpeptide induce an improved antibody response to MRSA in vitro, but do not confer an effective protection againstMRSA infection in vivo.