人体肠道微生物是保证宿主免疫系统正常发育成熟的基础。现在已知不同种类的肠道细菌对宿主T细胞亚群的免疫刺激作用不尽相同。未培养的分节丝状菌（Segmented filamentous bacteria, SFB）是目前唯一被证实能在小鼠回肠内引起Th17细胞分化发育的细菌。2012年我们首次报道了该菌在人体内只分布在0-36个月婴幼儿体内。该菌无法体外分离培养加上极强的宿主定植特异性限制了对该菌的研究。本课题首先通过转录组学、代谢组学等方法开展人SFB定植和婴儿Th17细胞发育相关性的研究。再根据我们已经体外成功培养小鼠SFB的基础上，开展人SFB体外富集培养，并对人SFB全基因组测序。同时分离纯化人SFB各个细胞组份，利用人肠上皮细胞和无菌小鼠模型筛选对免疫细胞有分化调节作用的功能组份。本项目的实施对揭示肠道细菌在免疫系统发育中的作用有重大意义，为今后开发免疫调节微生态制剂提供理论参考。

Human gut microbiota has been recognized as an important factor in the development of human immune system. It has been known that T cells differentiation is depended on gut microbiota and different bacterial species determine the maturation of T-cell subgroup. Segmented filamentous bacteria (SFB), is indigenous gut bacteria commonly found in the intestine of animals but rarely seen in human adults. SFB play an important role in the development of host immune system, particularly for the development of Th17 cells. We previously documented the presence of the bacteria in the gut of young Chinese children (< 3 years old) but not in the older children (>3 years old). Moreover, SFB can not be cultivated in vitro yet and shows very strong host specificity in host colonization. In the present study we proposed to establish the relationship of the SFB colonization in infants with the development of the infants Th17 cells by means of comparison of the transcriptomics and metabolomics profiles between the SFB positive and SFB negative infants. In addition, we will set up an in vitro method to cultivate human SFB in test tubes based on the results that we obtained from successfully cultivation of mouse SFB in vitro. Meanwhile, we will isolate and screen the potential cell components from the cultivated SFB bacterial cells and test the immune-modulation effect through the cell models and germ-free mouse models. Documenting the presence of SFB in the gut of children may shed light on the interaction between SFB and the gut immune system. Probiotics are well known therapy for children with various clinical GI diseases, and have become a common therapeutic modality for children. As a consequence of our study, SFB may emerge as a new probiotic therapy for young children.