Protective immunity against group Astreptococcus infection following immunization with fibronectin-binding proteins

背景资料。A组化脓性链球菌表面相关纤维连接蛋白(FN)结合蛋白在细菌侵袭上皮细胞中起重要作用。本研究的目的是检测FN结合蛋白FbAA和FbaB的功能结构域和保护性抗原性。为了研究FbaA或FbaB的功能结构域及其在化脓性链球菌上的定位，采用免疫荧光显微镜、配基印迹和Biaccore分析了一系列重组GST截短型FbAA或FbaB蛋白。用截短的蛋白免疫小鼠，确定对化脓性链球菌感染有保护作用的免疫原域。配基印迹和Biacore分析表明，含有富含脯氨酸重复结构域(RD)的FBAA片段具有FN结合活性，而N-末端和C-末端没有。免疫荧光显微镜观察结果显示，N-末端和RD暴露在外部区域，表明RD是活体上的FN结合元件。在N末端和RD免疫的小鼠中能有效地诱导产生特异性抗体，并在体外表现出对化脓性链球菌的杀菌活性。与GST免疫组相比，FBAA免疫的小鼠在感染表达FBAA的M1和M49菌株后存活时间显著延长。此外，表达FbaB的M3株攻击后，FbaB免疫的小鼠的存活时间也比对照组延长。Fn结合蛋白FbAa和FbaB是化脓性链球菌感染的潜在候选疫苗。

Background. Surface-associated fibronectin (Fn) -binding proteins of group A Streptococcus pyogenes play important roles in the bacterial invasion of epithelial cells. The aim of this study was to examine the functional domain and protective antigenicity of the Fn-binding proteins FbaA and FbaB.Methods. To investigate the functional domain of FbaA or FbaB and their localization on S. pyogenes, a series of recombinant GST-truncated FbaA or FbaB proteins were employed for immunofluorescent microscopy, ligand blot, and Biacore analyses. Mice were immunized with the truncated proteins to determine the immunogenic domains that contribute to protection against S. pyogenes infection.Results. Ligand blot and Biacore analyses revealed that the FbaA fragments harboring a proline-rich repeat domain (RD), but not the N- and C-terminal regions, possessed Fn-binding activity. Immunofluorescent microscopy findings showed that the N-terminus and RD were exposed to external regions, suggesting that the RD serves as an Fn-binding element on live organisms. Specific antibodies were efficiently induced in N-terminus- and RD-immunized mice and demonstrated bactericidal activity against S. pyogenes in vitro. FbaA-immunized mice survived significantly longer as compared to the GST-immunized group following infection with M1 and M49 strains expressing FbaA. In addition, FbaB-immunized mice also survived longer than control mice after challenge with M3 strain expressing FbaB.Conclusion. The Fn-binding proteins, FbaA and FbaB, are potential vaccine candidates for S. pyogenes infection.