Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida, United States of America.
Department of Medicine, College of Medicine, University of Florida, Gainesville, Florida, United States of America.
PLoS Pathog. 2021 May 6;17(5):e1009465. doi: 10.1371/journal.ppat.1009465. eCollection 2021 May.
Salmonella Typhimurium is a causative agent of nontyphoidal salmonellosis, for which there is a lack of a clinically approved vaccine in humans. As an intracellular pathogen, Salmonella impacts many cellular pathways. However, the intercellular communication mechanism facilitated by host-derived small extracellular vesicles (EVs), such as exosomes, is an overlooked aspect of the host responses to this infection. We used a comprehensive proteome-based network analysis of exosomes derived from Salmonella-infected macrophages to identify host molecules that are trafficked via these EVs. This analysis predicted that the host-derived small EVs generated during macrophage infection stimulate macrophages and promote activation of T helper 1 (Th1) cells. We identified that exosomes generated during infection contain Salmonella proteins, including unique antigens previously shown to stimulate protective immune responses against Salmonella in murine studies. Furthermore, we showed that host EVs formed upon infection stimulate a mucosal immune response against Salmonella infection when delivered intranasally to BALB/c mice, a route of antigen administration known to initiate mucosal immunity. Specifically, the administration of these vesicles to animals stimulated the production of anti-Salmonella IgG antibodies, such as anti-OmpA antibodies. Exosomes also stimulated antigen-specific cell-mediated immunity. In particular, splenic mononuclear cells isolated from mice administered with exosomes derived from Salmonella-infected antigen-presenting cells increased CD4+ T cells secreting Th1-type cytokines in response to Salmonella antigens. These results demonstrate that small EVs, formed during infection, contribute to Th1 cell bias in the anti-Salmonella responses. Collectively, this study helps to unravel the role of host-derived small EVs as vehicles transmitting antigens to induce Th1-type immunity against Gram-negative bacteria. Understanding the EV-mediated defense mechanisms will allow the development of future approaches to combat bacterial infections.
鼠伤寒沙门氏菌是一种非伤寒沙门氏菌病的病原体，目前人类缺乏临床批准的疫苗。作为一种细胞内病原体，沙门氏菌影响许多细胞途径。然而，宿主来源的小细胞外囊泡（EVs），如外泌体，介导的细胞间通讯机制是宿主对这种感染反应的一个被忽视的方面。我们使用基于蛋白质组的全面网络分析方法，研究了来自沙门氏菌感染的巨噬细胞衍生的外泌体，以鉴定通过这些 EV 转运的宿主分子。该分析预测，在巨噬细胞感染期间产生的宿主源性小 EV 会刺激巨噬细胞，并促进 T 辅助 1（Th1）细胞的激活。我们发现，感染期间产生的外泌体包含沙门氏菌蛋白，包括以前在小鼠研究中被证明能刺激针对沙门氏菌的保护性免疫反应的独特抗原。此外，我们表明，当通过鼻腔内递送至 BALB/c 小鼠时，感染时形成的宿主 EV 会刺激针对沙门氏菌感染的粘膜免疫反应，这种抗原给药途径已知能引发粘膜免疫。具体来说，将这些囊泡给予动物会刺激针对沙门氏菌的 IgG 抗体的产生，如针对 OmpA 抗体的产生。外泌体还刺激抗原特异性细胞介导的免疫。特别是，从用来自沙门氏菌感染的抗原呈递细胞衍生的外泌体处理的动物中分离的脾单核细胞在响应沙门氏菌抗原时增加了分泌 Th1 型细胞因子的 CD4+T 细胞。这些结果表明，在感染过程中形成的小 EV 有助于沙门氏菌反应中的 Th1 细胞偏向。总的来说，这项研究有助于揭示宿主来源的小 EV 作为传递抗原的载体，诱导针对革兰氏阴性菌的 Th1 型免疫的作用。了解 EV 介导的防御机制将允许开发对抗细菌感染的未来方法。
