Francisella tularensis is a tier 1 select agent responsible for tularemia in humans and a wide variety of animal species. Extensive research into understanding the virulence factors of the bacterium has been ongoing to develop an efficacious vaccine. At least two such virulence factors are described as capsules of F. tularensis: the O-antigen capsule and the capsule-like complex (CLC). These two separate entities aid in avoiding host immune defenses but have not been clearly differentiated. These components are distinct and differ in composition and genetic basis. The O-antigen capsule consists of a polysaccharide nearly identical to the lipopolysaccharide (LPS) O antigen, whereas the CLC is a heterogeneous complex of glycoproteins, proteins, and possibly outer membrane vesicles and tubes (OMV/Ts). In this review, the current understanding of these two capsules is summarized, and the historical references to "capsules" of F. tularensis are clarified. A significant amount of research has been invested into the composition of each capsule and the genes involved in synthesis of the polysaccharide portion of each capsule. Areas of future research include further exploration into the molecular regulation and pathways responsible for expression of each capsule and further elucidating the role that each capsule plays in virulence.

中文翻译：

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图拉弗朗西斯菌多糖：真正的胶囊是什么？

图拉弗朗西斯菌（Francisella tularensis）是负责人类和多种动物图拉菌血症的一级选择剂。为了理解有效的疫苗，正在进行广泛的研究以了解细菌的毒性因子。至少两种这样的毒力因子被描述为土拉弗朗西斯菌的胶囊：O-抗原胶囊和胶囊样复合物（CLC）。这两个独立的实体有助于避免宿主的免疫防御，但尚未明确区分。这些成分是不同的，并且在组成和遗传基础上也不同。O抗原胶囊由几乎与脂多糖（LPS）O抗原相同的多糖组成，而CLC是糖蛋白，蛋白质以及可能的外膜囊泡和管（OMV / Ts）的异质复合物。在这篇评论中 总结了对这两种胶囊的当前理解，并阐明了对图莱特氏菌“胶囊”的历史参考。已经对每个胶囊的组成和与每个胶囊的多糖部分合成有关的基因进行了大量研究。未来的研究领域包括进一步探索负责每个胶囊表达的分子调控和途径，并进一步阐明每个胶囊在毒力中的作用。