Department of Microbial Infection and Immunity, The Ohio State University, Columbus, OH, USA; Department of Microbiology, The Ohio State University, The Ohio State University, Columbus, OH, USA.
Department of Microbiology, The Ohio State University, The Ohio State University, Columbus, OH, USA; Department of Biology, Washington University in St. Louis, MO 63130, USA.
Vaccine. 2020 Aug 10;38(36):5803-5813. doi: 10.1016/j.vaccine.2020.06.049. Epub 2020 Jul 17.
Listeria monocytogenes is a facultative intracellular pathogen responsible for the life-threatening disease listeriosis. The pore-forming toxin listeriolysin O (LLO) is a critical virulence factor that plays a major role in the L. monocytogenes intracellular lifecycle and is indispensable for pathogenesis. LLO is also a dominant antigen for T cells involved in sterilizing immunity and it was proposed that LLO acts as a T cell adjuvant. In this work, we generated a novel full-length LLO toxoid (LLO) in which the cholesterol-recognition motif, a threonine-leucine pair located at the tip of the LLO C-terminal domain, was substituted with two glycine residues. We showed that LLO lost its ability to bind cholesterol and to form pores. Importantly, LLO retained binding to the surface of epithelial cells and macrophages, suggesting that it could efficiently be captured by antigen-presenting cells. We then determined if LLO can be used as an antigen and adjuvant to protect mice from L. monocytogenes infection. Mice were immunized with LLO alone or together with cholera toxin or Alum as adjuvants. We found that mice immunized with LLO alone or in combination with the Th2-inducing adjuvant Alum were not protected against L. monocytogenes. On the other hand, mice immunized with LLO along with the experimental adjuvant cholera toxin, were protected against L. monocytogenes, as evidenced by a significant decrease in bacterial burden in the liver and spleen three days post-infection. This immunization regimen elicited mixed Th1, Th2, and Th17 responses, as well as the generation of LLO-neutralizing antibodies. Further, we identified T cells as being required for immunization-induced reductions in bacterial burden, whereas B cells were dispensable in our model of non-pregnant young mice. Overall, this work establishes that LLO is a promising vaccine antigen for the induction of protective immunity against L. monocytogenes by subunit vaccines containing Th1-driving adjuvants.
李斯特菌单核细胞增生李斯特菌是一种兼性细胞内病原体，可导致危及生命的李斯特菌病。穿孔毒素李斯特菌溶血素 O（LLO）是一种关键的毒力因子，在李斯特菌细胞内生命周期中发挥主要作用，是发病机制所必需的。LLO 也是参与杀菌免疫的 T 细胞的主要抗原，有人提出 LLO 作为 T 细胞佐剂发挥作用。在这项工作中，我们生成了一种新型全长 LLO 类毒素（LLO），其中胆固醇识别基序，即位于 LLO C 端结构域顶端的亮氨酸-苏氨酸对，被两个甘氨酸残基取代。我们表明 LLO 丧失了结合胆固醇和形成孔的能力。重要的是，LLO 保留了与上皮细胞和巨噬细胞表面的结合能力，表明它可以被抗原呈递细胞有效捕获。然后，我们确定 LLO 是否可以用作抗原和佐剂来保护小鼠免受李斯特菌感染。用 LLO 单独或与霍乱毒素或 Alum 作为佐剂免疫小鼠。我们发现，用 LLO 单独或与 Th2 诱导佐剂 Alum 联合免疫的小鼠不能免受李斯特菌感染的保护。另一方面，用 LLO 与实验佐剂霍乱毒素联合免疫的小鼠受到保护，这体现在感染后三天肝脏和脾脏中的细菌负荷显著降低。这种免疫方案引发了混合 Th1、Th2 和 Th17 反应，并产生了 LLO 中和抗体。此外，我们确定 T 细胞是免疫诱导减少细菌负荷所必需的，而在我们的非妊娠年轻小鼠模型中 B 细胞是可有可无的。总体而言，这项工作表明 LLO 是一种有前途的疫苗抗原，可用于诱导含有 Th1 驱动佐剂的亚单位疫苗对李斯特菌的保护性免疫。
