Department of Pathology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
J Immunol. 2013 Sep 15;191(6):3254-63. doi: 10.4049/jimmunol.1300722. Epub 2013 Aug 7.
Intact Streptococcus pneumoniae expressing type 14 capsular polysaccharide (PPS14) and type III S. agalactiae containing a PPS14 core capsule identical to PPS14 exhibit noncovalent associations of PPS14 and bacterial protein, in contrast to soluble covalent conjugates of these respective Ags. Both bacteria and conjugates induce murine PPS14-specific IgG responses dependent on CD4⁺ T cells. Further, secondary immunization with conjugate and S. agalactiae, although not S. pneumoniae, results in a boosted response. However, in contrast to conjugate, PPS14-specific IgG responses to bacteria lack affinity maturation use the 44.1-idiotype and are dependent on marginal zone B cells. To better understand the mechanism underlying this dichotomy, we developed a minimal model of intact bacteria in which PPS14 and pneumococcal surface protein A (PspA) were stably attached to 1 μm (bacteria-sized) latex beads, but not directly linked to each other, in contrast to PPS14-PspA conjugate. Beads coated simultaneously with PPS14+[PspA], similar to conjugate, induced in mice boosted PPS14-specific IgG secondary responses, dependent on T cells and ICOS-dependent costimulation, and in which priming could be achieved with PspA alone. In contrast to conjugate, but similar to intact bacteria, the primary PPS14-specific IgG response to beads coated simultaneously with PPS14+[PspA] peaked rapidly, with the secondary response highly enriched for the 44.1-idiotype and lacking affinity maturation. These results demonstrate that noncovalent association in a particle, of polysaccharide and protein, recapitulates essential immunologic characteristics of intact bacteria that are distinct from soluble covalent conjugates of these respective Ags.
表达 14 型荚膜多糖 (PPS14) 的完整肺炎链球菌和含有与 PPS14 相同核心荚膜的 3 型无乳链球菌与可溶性共价缀合的相应抗原不同,表现出 PPS14 与细菌蛋白的非共价关联。两种细菌和缀合物都诱导依赖 CD4⁺T 细胞的小鼠 PPS14 特异性 IgG 反应。此外,与肺炎球菌相比,用缀合物和无乳链球菌进行二次免疫会增强反应。然而,与缀合物不同,对细菌的 PPS14 特异性 IgG 反应缺乏亲和力成熟,使用 44.1-独特型,并且依赖边缘区 B 细胞。为了更好地理解这种二分法的机制,我们开发了一个完整细菌的最小模型,其中 PPS14 和肺炎球菌表面蛋白 A (PspA) 稳定地附着在 1 μm(细菌大小)的乳胶珠上,但彼此之间没有直接连接,与 PPS14-PspA 缀合物相反。同时用 PPS14+[PspA]包被的珠子在小鼠中诱导增强的 PPS14 特异性 IgG 二次反应,依赖于 T 细胞和 ICOS 依赖性共刺激,并且可以仅用 PspA 进行启动。与缀合物相反,但与完整细菌相似,同时用 PPS14+[PspA]包被的珠子的原发性 PPS14 特异性 IgG 反应迅速达到峰值,二次反应高度富集 44.1-独特型,缺乏亲和力成熟。这些结果表明,多糖和蛋白质在颗粒中的非共价关联再现了完整细菌的基本免疫学特征,与这些相应抗原的可溶性共价缀合物明显不同。