Bacterial outer membrane vesicles, a potential vaccine candidate in interactions with host cells based

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Bacterial outer membrane vesicles, a potential vaccine candidate in interactions with host cells based Wei Cai1, Dinesh Kumar Kesavan1, Jie Wan1, Mohamed Hamed Abdelaziz1, Zhaoliang Su1,2 and Huaxi Xu1*

Abstract Both Gram-Positive and Gram-Negative bacteria can secrete outer membrane vesicles (OMVs) in their growth and metabolism process. Originally, OMVs were considered as a by-product of bacterial merisis. However, many scientists have reported the important role of OMVs in many fields recently. In this review, we briefly introduce OMVs biological functions and then summarize the findings about the OMVs interactions with host cells. At last, we will make an expectation about the prospects of the application of OMVs as vaccines. Keywords: Outer membrane vesicles, Host cells, Vaccines, Bacterium, Immunity

Background OMVs secretion is a normal phenomenon during the growth of bacteria. OMVs are spherical, bilayered, membranous nanostructures (shown in Fig. 1). OMVs productions are not consistent in size, varying from approximately 20 nm to 250 nm. The parent bacterial membrane releases them and hence they contain numerous proteins, similar to parent bacteria [1–4]. Not only that, OMVs are demonstrated in abundance in bacterial components such as DNA [5], RNA [6, 7], lipopolysaccharide (LPS) [8], enzymes [9, 10], peptidoglycan [11] and some molecules [10]. Here, we enumerate some examples about virulence factors carried by OMVs (listed in Table 1). These characteristics of OMVs endow with critical significance in pathogenesis and communication between bacteria and host cells. Recent studies have revealed that OMVs play fundamental roles in activating immune system and facilitate manifest responses against OMVs in the host [12]. Despite of the increasing findings about effects of OMVs on host, innovative strategies based on OMVs have shown great potential in clinical implications and other relevant fields as we will discuss in this review.

* Correspondence: [email protected] 1 Department of Immunology, Jiangsu University, Zhenjiang 212013, Jiangsu, China Full list of author information is available at the end of the article

Simplified introduction of OMVs biological functions and biosynthesis OMVs are not described useless as originally thought. Electron microscopy [2–4, 10] and proteomic analyses [1–4] have confirmed OMVs are heterogeneous nanostructures packaging various bioactive components. They function as mediators to transmit biological information among different bacteria and host. For example, bacterial OMVs serve as nanovesicles to deliver important biological substances, which can promote the entry of bacterial antigens or even genes. Colitogenic Bacteroides thetaiotaomicron OMVs assist bacterial antigens access host cells in a sulfatase-dependent manner [13]. Bacterial OMVs shoot short RNAs to boost the host-pathogen interaction [6, 7]. In addition, OMVs can act as a delivery system for virulence factors [14] or antibiotic resistence genes [15]. For instance, Bacteroides thetaiotaomic