Center for Immunobiology and Vaccine Development, Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA.
J Immunol. 2013 Sep 15;191(6):3287-96. doi: 10.4049/jimmunol.1301153. Epub 2013 Aug 7.
Ig-binding proteins are employed by a variety of organisms to evade the immune system. To our knowledge, we now report for the first time that meningococcal strains from several capsular groups exhibit Ig-binding activity that is dependent on human serum factors. A protein mediating Ig binding was identified as T and B cell-stimulating protein B (TspB) by immunoprecipitation and by mass spectroscopic analysis of tryptic peptides. Recombinant TspB and derivatives verified Ig binding, with a preference for human IgG2 Fc, and localized the IgG-binding region to a highly conserved subdomain of TspB. Antiserum produced in mice against the conserved subdomain detected the presence of TspB on the cell surface by flow cytometry when bacteria were grown in the presence of human serum. By fluorescence microscopy, we observed formation of an extracellular matrix having characteristics of a biofilm containing TspB, human IgG, DNA, and large aggregates of bacteria. TspB is encoded by gene ORF6 in prophage DNA, which others have shown is associated with invasive meningococcal strains. Knocking out ORF6 genes eliminated IgG binding and formation of large bacterial aggregates in biofilm. Reintroduction of a wild-type ORF6 gene by phage transduction restored the phenotype. The results show that TspB mediated IgG binding and aggregate/biofilm formation triggered by factors in human serum. As has been observed for other Ig-binding proteins, the activities mediated by TspB may provide protection against immune responses, which is in accordance with the association of prophage DNA carrying ORF6 with invasive meningococcal strains.
免疫球蛋白结合蛋白被多种生物体用来逃避免疫系统。据我们所知，我们现在首次报告，来自几个荚膜群的脑膜炎奈瑟菌菌株表现出依赖人血清因子的免疫球蛋白结合活性。通过免疫沉淀和胰蛋白酶肽的质谱分析，鉴定出一种介导免疫球蛋白结合的蛋白为 T 和 B 细胞刺激蛋白 B（TspB）。重组 TspB 和衍生物验证了免疫球蛋白结合，对人 IgG2 Fc 具有偏好性，并将 IgG 结合区域定位到 TspB 的一个高度保守亚结构域。用针对保守亚结构域的抗血清通过流式细胞术检测到，当细菌在人血清存在的情况下生长时，TspB 存在于细胞表面。通过荧光显微镜观察到含有 TspB、人 IgG、DNA 和大量细菌聚集物的生物膜的形成。TspB 由噬菌体 DNA 中的 ORF6 基因编码，其他人已经表明它与侵袭性脑膜炎奈瑟菌菌株有关。敲除 ORF6 基因消除了 IgG 结合和生物膜中大型细菌聚集物的形成。通过噬菌体转导重新引入野生型 ORF6 基因恢复了表型。结果表明，TspB 介导了 IgG 结合和由人血清中的因子触发的聚集/生物膜形成。正如其他免疫球蛋白结合蛋白所观察到的，TspB 介导的活性可能提供对免疫反应的保护，这与携带 ORF6 的噬菌体 DNA 与侵袭性脑膜炎奈瑟菌菌株的关联是一致的。
