| 研究実績の概要 |
The commonly attributed function to intestinal IgA is that of immune exclusion. In this viewpoint, secreted IgA binds to pathogens preventing their attachment to the epithelial cells, inhibiting their invasion into the host tissues. We demonstrated that IgA have additional function, regulating the gut bacterial communities. We aimed at understanding the mechanisms involved in IgA regulation of microbiota. Thus, we analyzed genetically modified mice lacking arms of adaptive immunity, such as Cd3e-/- mice. We observed that fecal bacteria from Cd3e-/- mice were highly coated by IgA comparing with WT animals. This was unexpected because the frequency of IgA-secreting plasma cells was significantly lower in Cd3e-/- mice than in WT mice. Single bacteria visualization using imaging flow cytometry showed that the IgA heavily binds on all bacterial surface in Cd3e-/- mice, while the coating appeared to be more localized or specific for bacteria of WT mice. Importantly, the heavy coating with IgA observed in Cd3e-/- mice correlates with decreased bacterial diversity in the intestine. These experiments revealed that T cell dependent, antigen-specific IgA is required to keep and maintain the targeted bacteria within the gut lumen, while the non-selected IgA like those observed in Cd3e-/- mice might contribute to elimination of such heavily coated bacteria from the gut lumen. To understand the mechanisms how gut IgA modulate retention versus elimination of the commensals, we plan to further analyze the properties of T cell-dependent or independent IgAs and their in vivo functions.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
After a lag period due to departure of the postdoctoral fellow that was supposed to conduct the proposed research, a new postdoc was hired to continue and expand the project. Although young and relatively new to the field, the progress he made since June 2017 is impressive. All the experiments so far indicated that in addition to T cell dependent diversification and selection of IgA there must be different layers of regulatory mechanisms responsible for retention or elimination of bacteria in the gut. We found that IgA enhances bacterial interaction and regulate gut homeostasis via mucus associated functional factors (manuscript under revision). Although Fab -dependent interactions are clearly involved in regulating bacterial community in the gut, we begin to evaluate the Fab-independent mechanisms for IgA function. These are clearly underappreciated so far, but nevertheless important if we remind ourselves that secretory IgA is a complex glycoprotein.
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| 今後の研究の推進方策 |
Our results so far support the hypothesis that IgA glycosylation might be an important molecular determinant to regulate composition and function of gut microbiota. Our working hypothesis is that the distinct function of T-dependent and T-independent IgA on gut microbiota might be due not only to AID-induced IgA diversification and selection but also to the glycans of secretory IgA. To address this issue, we are currently setting up lectin-ELISA to measure the amount of glycans on secretory IgA. The ELISA plates are coated with various lectins, which recognize specific pattern of glycan structures. Fecal IgA of WT and Cd3e-/- mice will be applied to the lectin-coated plates to measure the amounts of specific glycans on secretory IgA in the gut. We will screen for the quality and quantity of glycans on gut IgA, and address whether T cells are involved the regulation of IgA-glycans. We will also address the possibility that gut microbiota might modify the IgA-glycans by using fecal pellets collected from germ free and gnotobiotic animals we designed in this project. If the glycosylation patters will be distinct among fecal IgA of various animal models, we will analyze whether the glycans are modulating binding pattern of IgA with the gut microbiota. Such analyses will hopefully reveal the mechanisms and function of IgA-glycans for the maintenance of gut microbiota on mucus environment, which have a potential to shed light on a novel aspect of IgA biology in the gut.
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