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

背景。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。本研究的目的是研究fn结合蛋白FbaA和fbab的功能域和保护性抗原性。为了研究FbaA或FbaB的功能域及其在化脓性链球菌上的定位，我们使用了一系列重组gst截断的FbaA或FbaB蛋白进行免疫荧光显微镜、配体印迹和Biacore分析。用截断的蛋白免疫小鼠，以确定对化脓性葡萄球菌感染有保护作用的免疫原结构域。配体印迹和Biacore分析显示，FbaA片段含有富含脯氨酸的重复结构域（RD），而不含N端和c端区域，具有fn结合活性。免疫荧光显微镜结果显示，n端和RD暴露在外部区域，这表明RD在活生物体上是一个与fn结合的元件。在n端免疫和rd免疫小鼠体内有效诱导特异性抗体，并在体外对化脓性葡萄球菌显示出杀菌活性。与gst免疫组相比，FbaA免疫小鼠在感染表达FbaA的M1和M49菌株后存活时间明显更长。此外，用表达fbab的M3菌株攻毒后，fbab免疫小鼠的存活时间也比对照组小鼠长。fn结合蛋白FbaA和FbaB是化脓性葡萄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.