a Biotechnology Division , Korea Atomic Energy Research Institute , Jeongeup , Republic of Korea.
b Department of Biological Sciences , Chonbuk National University , Jeonju , Republic of Korea.
Virulence. 2017 Aug 18;8(6):875-890. doi: 10.1080/21505594.2016.1278334. Epub 2017 Jan 6.
The pneumococcal capsule is indispensable for pathogenesis in systemic infections; however, many pneumococcal diseases, including conjunctivitis, otitis media, and some systemic infections in immunocompromised patients, are caused by nonencapsulated Streptococcus pneumoniae (NESp). Null capsule clade 1 (NCC1), found in group 2 NESp, expresses pneumococcal surface protein K (PspK) and is becoming prevalent among pneumococcal organisms owing to the widespread use of pneumococcal conjugate vaccines. Despite its clinical importance, the molecular mechanisms underlying the prevalence of NCC1 have not been fully elucidated. Here, we investigated the role of the R3 domain of PspK in the epithelial cell adherence of NCC1. We found that the R3 domain of PspK mediated NCC1 adherence via its direct interaction with the epithelial surface protein annexin A2. Additionally, neutralization with purified recombinant PspK-R3 or rabbit anti-UD:R3 IgG inhibited binding of NESp to lung epithelial cells in vitro. Immunization with the 'repeat' domain of PspK-R3 or PspK-UD:R3 effectively elicited mucosal and systemic immune responses against PspK-R3 and provided protection against nasopharyngeal, lung, and middle ear colonization of NESp in mice. Additionally, we found that rabbit anti-UD:R3 IgG bound to PspC-R1 of the encapsulated TIGR4 strain and that UD:R3 immunization provided protection against nasopharyngeal and lung colonization of TIGR4 and deaths by TIGR4 and D39 in mice. Further studies using 68 pneumococcal clinical isolates showed that 79% of clinical isolates showed cross-reactivity to rabbit anti-UD:R3 IgG. About 87% of serotypes in the 13-valent pneumococcal conjugate vaccine (PCV) and 68% of non-vaccine serotypes were positive for cross-reactivity with rabbit anti-UD:R3 IgG. Thus, the R3 domain of PspK may be an effective vaccine candidate for both NESp and encapsulated Sp.
肺炎球菌荚膜对于全身感染的发病机制是不可或缺的;然而，许多肺炎球菌疾病，包括结膜炎、中耳炎和一些免疫功能低下患者的全身感染，是由无荚膜肺炎链球菌（NESp）引起的。在组 2 NESp 中发现的无荚膜 clade 1（NCC1）表达肺炎球菌表面蛋白 K（PspK），由于肺炎球菌结合疫苗的广泛使用，它在肺炎球菌生物中变得越来越普遍。尽管它具有重要的临床意义，但 NCC1 流行的分子机制尚未完全阐明。在这里，我们研究了 PspK 的 R3 结构域在 NCC1 上皮细胞黏附中的作用。我们发现，PspK 的 R3 结构域通过其与上皮表面蛋白 annexin A2 的直接相互作用介导 NCC1 的黏附。此外，用纯化的重组 PspK-R3 或兔抗 UD:R3 IgG 中和可抑制 NESp 在体外与肺上皮细胞的结合。用 PspK-R3 的“重复”结构域或 PspK-UD:R3 免疫有效地诱导了针对 PspK-R3 的黏膜和全身免疫反应，并为小鼠提供了针对 NESp 的鼻咽、肺和中耳定植的保护。此外，我们发现兔抗 UD:R3 IgG 与囊封 TIGR4 株的 PspC-R1 结合，UD:R3 免疫为小鼠提供了对 TIGR4 和 D39 的鼻咽和肺部定植以及死亡的保护。使用 68 株肺炎球菌临床分离株进行的进一步研究表明，79%的临床分离株对兔抗 UD:R3 IgG 表现出交叉反应。13 价肺炎球菌结合疫苗（PCV）中的 68%的血清型和非疫苗血清型对兔抗 UD:R3 IgG 均呈阳性交叉反应。因此，PspK 的 R3 结构域可能是 NESp 和囊封 Sp 的有效候选疫苗。
