Pujanauski Lindsey, Colino Jesus, Flora Michael, Torres Raul M, Tuomanen Elaine, Snapper Clifford M
Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814; Department of Biological Sciences, Birla Institute of Technology and Sciences, Pilani 333031, India;
Integrated Department of Immunology, National Jewish Health and University of Colorado School of Medicine, Denver, CO 80206;
J Immunol. 2016 May 1;196(9):3677-85. doi: 10.4049/jimmunol.1502709. Epub 2016 Mar 30.
Intact, inactivated Streptococcus pneumoniae [including the unencapsulated S. pneumoniae, serotype 2 strain (R36A)] markedly inhibits the humoral immune response to coimmunized heterologous proteins, a property not observed with several other intact Gram-positive or Gram-negative bacteria. In this study, we determined the nature of this immunosuppressive property. Because phosphorylcholine (PC), a major haptenic component of teichoic acid in the S. pneumoniae cell wall, and lipoteichoic acid in the S. pneumoniae membrane were previously reported to be immunosuppressive when derived from filarial parasites, we determined whether R36A lacking PC (R36A(pc-)) was inhibitory. Indeed, although R36A(pc-) exhibited a markedly reduced level of inhibition of the IgG response to coimmunized chicken OVA (cOVA), no inhibition was observed when using several other distinct PC-expressing bacteria or a soluble, protein-PC conjugate. Further, treatment of R36A with periodate, which selectively destroys PC residues, had no effect on R36A-mediated inhibition. Because R36A(pc-) also lacks choline-binding proteins (CBPs) that require PC for cell wall attachment, and because treatment of R36A with trypsin eliminated its inhibitory activity, we incubated R36A in choline chloride, which selectively strips CBPs from its surface. R36A lacking CBPs lost most of its inhibitory property, whereas the supernatant of choline chloride-treated R36A, containing CBPs, was markedly inhibitory. Coimmunization studies using cOVA and various S. pneumoniae mutants, each genetically deficient in one of the CBPs, demonstrated that only S. pneumoniae lacking the CBP pneumococcal surface protein A lost its ability to inhibit the IgG anti-cOVA response. These results strongly suggest that PspA plays a major role in mediating the immunosuppressive property of S. pneumoniae.
完整的、灭活的肺炎链球菌[包括无荚膜的肺炎链球菌2型菌株（R36A）]能显著抑制对共同免疫的异源蛋白的体液免疫反应，这一特性在其他几种完整的革兰氏阳性或革兰氏阴性细菌中未观察到。在本研究中，我们确定了这种免疫抑制特性的本质。由于磷壁酸（PC）是肺炎链球菌细胞壁中磷壁酸的主要半抗原成分，且肺炎链球菌膜中的脂磷壁酸先前报道称源自丝虫寄生虫时具有免疫抑制作用，我们确定了缺乏PC的R36A（R36A(pc-)）是否具有抑制作用。事实上，尽管R36A(pc-)对共同免疫的鸡卵清蛋白（cOVA）的IgG反应的抑制水平显著降低，但使用其他几种不同的表达PC的细菌或可溶性蛋白-PC偶联物时未观察到抑制作用。此外，用高碘酸盐处理R36A可选择性破坏PC残基，但对R36A介导的抑制作用没有影响。由于R36A(pc-)也缺乏需要PC才能附着于细胞壁的胆碱结合蛋白（CBPs），且用胰蛋白酶处理R36A可消除其抑制活性，我们将R36A在氯化胆碱中孵育，氯化胆碱可选择性地从其表面去除CBPs。缺乏CBPs的R36A失去了大部分抑制特性，而含有CBPs的氯化胆碱处理的R36A的上清液具有显著的抑制作用。使用cOVA和各种肺炎链球菌突变体进行的共同免疫研究表明，每个突变体在基因上都缺乏一种CBPs，结果显示只有缺乏CBP肺炎球菌表面蛋白A的肺炎链球菌失去了抑制IgG抗cOVA反应的能力。这些结果强烈表明，PspA在介导肺炎链球菌的免疫抑制特性中起主要作用。
