Role of Immunity and the Microbiota in Enteropathogenic E. coli Eradication

摘要 病原体引起的肠道和腹泻疾病是全世界儿童死亡的重要原因。 据估计，这些疾病每年在全球5岁以下儿童中造成近100万人死亡， 在这一年龄段中居死因第二位。这在很大程度上是因为他们对 新生儿和幼儿以肠道感染为主。在健康的成人肠道中，微生物区系提供 “殖民抵抗”，形成一道屏障，抵御入侵的病原体。增加的易感性 感染通常被归因于免疫系统的不成熟；然而，其他因素可能 发挥重要作用，因为新生儿对不同刺激的免疫反应有很大差异。 我们实验室最近的研究表明，新生小鼠的微生物区系在介导 对沙门氏菌和轮状柠檬酸杆菌的定植抗性，这种细菌通过以下方式模拟感染 致肠性大肠杆菌(EPEC)，全球最常见的由细菌引起的腹泻死亡原因。匮乏 定植抗性的产生是由于新生儿微生物区系中缺乏梭状芽胞杆菌所致。我们也 发现感染后诱导的IgG，而不是IgA，识别表面轮状芽胞杆菌毒力因子和 肠腔内结合的致病细菌导致它们被中性粒细胞调理和吞噬， 而表型上无毒的病原体仍然留在肠腔内，并被 微生物区系。因此，免疫系统和微生物区系在轮状芽孢杆菌中起着协同和重要的作用。 根除。在这项提案中，我们提出了三个具体目标：(1)确定梭状芽胞杆菌 物种在肠道中调节对肠道病原体的抑制；(Ii)了解促进 保护性梭状芽孢杆菌在新生儿肠道的定植和(Iii)确定 针对轮状芽胞杆菌毒力因子的肠道免疫球蛋白可保护新生儿免受感染。建议进行的研究 有可能对人类健康，特别是对婴儿和儿童的健康产生重大影响。

ABSTRACT Enteric and diarrheal diseases caused by pathogens are important causes of childhood death worldwide. These diseases are estimated to cause near 1 million deaths per year in children under 5 years old worldwide, ranking second as the cause of death in this age group. This is largely due to their increased susceptibility of neonates and young children to enteric infections. In the healthy adult gut, the microbiota provides “colonization resistance”, forming a barrier against invading pathogens. The increased susceptibility to infections has been generally ascribed to immaturity of the immune system; however, additional factors may play an important role because immune responses to different stimuli are highly variable among neonates. Recent studies in our laboratory showed that the microbiota of neonatal mice is impaired in mediating colonization resistance against Salmonella and Citrobacter rodentium, a bacterium that models infection by enteropathogenic E. coli (EPEC), the most common cause of diarrheal deaths by bacteria worldwide. The lack of colonization resistance was caused by the absence of Clostridiales in the neonatal microbiota. We also found that IgG, but not IgA, induced after infection recognized surface C. rodentium virulence factors and bound virulent bacteria within the intestinal lumen leading to their opsonization and engulfment by neutrophils, while phenotypically avirulent pathogens remained in the intestinal lumen and are out-competed by the microbiota. Thus, the immune system and the microbiota play cooperative and essential roles in C. rodentium eradication. In this proposal, we proposed three specific Aims (i) to identify mechanisms by which Clostridia species mediate inhibition of enteric pathogen in the gut; (ii) understand the mechanisms that promote the colonization of protective Clostridiales in the neonatal intestine and (iii) determine the mechanism by which intestinal IgG against C. rodentium virulence factors protects neonates from infection. The proposed studies have the potential for a major impact on human health and in particular on that of infants and children.