Interactions of probiotics and gut microbes with the immune system: examining roles of food components, microbial metabolites and neurochemical mediators

肠道微生物与宿主之间的相互作用在宿主防御的许多方面都很重要，在免疫活动的编排和免疫系统发育中发挥作用。然而，许多问题仍然与肠道微生物与宿主细胞相互作用的机制有关，这对宿主防御和肠道屏障的免疫稳态很重要。肠道界面的宿主细胞不仅遇到肠道微生物，而且还遇到微生物代谢产物和各种食物成分。乳酸菌（LAB）是肠道微生物，通常在发酵食品中食用，并作为益生菌。了解乳酸菌影响免疫系统的机制，为了解益生菌作用的具体机制以及肠道微生物在更广泛范围内的作用提供了有价值的见解。发酵食品中的LAB既受到食品成分的影响，又引起食品成分的变化;这反过来又会改变食用这些食品时它们对免疫系统的影响。这项工作的一个目标是研究乳酸菌在发酵乳中如何与宿主细胞相互作用，以及这些相互作用如何受到牛奶发酵过程中产生的微生物产物的影响。膳食纤维和益生元通常在食物中消费，以获得潜在的健康益处，部分原因是它们对肠道微生物活性的影响。纤维和益生元的发酵导致微生物代谢产物的产生，包括对免疫系统具有下游影响的短链脂肪酸。这项研究的另一个目的是确定这些产品如何调节肠道微生物如LAB的作用，并改变它们对免疫系统的影响。由于几种膳食纤维和益生元的成分也可以直接激活免疫系统的细胞，有关直接和间接影响的信息有助于了解它们对宿主防御的影响。此外，目前的证据表明，纤维和益生元对免疫系统的影响在性别之间存在差异，这表明宿主因素（如雌激素）在饮食-微生物相互作用中发挥着重要作用。因此，重要的是要测试饮食成分和补充剂对女性和男性的影响差异。本研究的第三个目的是分析膳食纤维和益生元对免疫系统的直接和间接影响，并考虑到性别差异。这项研究的预期结果将是对免疫系统如何受到食物成分，LAB，微生物产品，它们之间的相互作用的影响的新见解，并更清楚地了解性别之间的影响差异。参与这项研究的学生将获得经验和知识，有助于更好地了解食品成分，益生菌和肠道微生物活性对宿主防御的结果的应用，这些都是加拿大人日常生活中饮食策略的重要元素。

Interactions between gut microbes and their hosts are now known to be important in many aspects of host defence, playing roles in choreographing immune activity and in immune system development. Nevertheless, many questions remain related to the mechanisms of gut microbes’ interactions with host cells that are important for host defence and immune homeostasis at the intestinal barrier. Host cells at the intestinal interface encounter not only gut microbes, but also products of microbial metabolism, and varied food components. Lactic acid bacteria (LAB) are gut microbes that are often consumed in fermented foods and as probiotics. Understanding the mechanisms through which LAB influence the immune system provides valuable insight into specific mechanisms of probiotic action as well as the actions of gut microbes on a broader scale. LAB in fermented foods are both influenced by, and cause changes in, food components; this in turn can alter their impact on the immune system when these foods are consumed. One objective of this work is to examine how LAB in fermented milk interact with host cells, and how these interactions are influenced by microbial products made during milk fermentation. Dietary fibres and prebiotics are often consumed in foods for their potential health benefits, mediated in part through their impact on gut microbial activity. Fermentation of fibres and prebiotics leads to microbial metabolite production, including short chain fatty acids with downstream effects on the immune system. Another objective of this research is to determine how these products modulate actions of gut microbes such as LAB and alter their impact on the immune system. Since components of several dietary fibres and prebiotics can also directly activate cells of the immune system, information about direct and indirect effects is useful for understanding their impact on host defence. In addition, current evidence indicating that effects of fibres and prebiotics on the immune system differ between sexes points to an important role for host factors such as estrogen in diet-microbe interactions. Thus, it is important to test differences in the impact of dietary components and supplements on females and males. A third objective of this research is to analyze direct and indirect effects of dietary fibres and prebiotics on the immune system, taking sex-based differences into account. Anticipated outcomes of this research will be new insight into how the immune system is affected by food components, LAB, microbial products, the interactions between them, and a clearer understanding of differences in impact between sexes. Students involved in this research will gain experience and knowledge that can contribute to better understanding of applications for food components, probiotics and the outcomes of gut microbial activity on host defence, elements important for dietary strategies in the daily lives of Canadians.