Microbiome and Early Development of Mucosal Immune System

在小鼠和人类中，肺内炎症反应的调节和调节性T细胞(Treg)之间的联系已经被很好地建立起来，越来越多的证据表明，微生物群在整个小肠的Treg细胞的诱导中发挥着重要作用。我在小牛犊身上的研究表明，肠道的微生物定植始于出生时，这种定植与粘膜免疫系统的广泛发育变化有关。然而，目前尚不清楚这种早期的微生物定植是否与牛肠道中Tregs的诱导有关。此外，目前尚不清楚在牛肠道中诱导的Tregs是否可以定位于肺，并在调节定植于上呼吸道(URT)的细菌病原体入侵肺部后的炎症反应中发挥作用。我的研究计划将重点放在微生物群在新生小牛小肠中诱导Tregs的作用上。我们将确定整个新生小牛肠道内Treg种群的特征，并将它们的发育与区域微生物组分析相关联，以确定共生细菌的存在是否与Treg发育显著相关。这些分析将侧重于所有潜在肠道Treg亚群的详细表型和功能特征，并确定对微生物组反应的特定群体。第二个目标是确定新生小牛在肠道内暴露于URT中的共生菌是否也能诱导肠道抗原特异性Tregs。我们将分析Treg对两种细菌，曼海姆溶血杆菌(Mh)和多杀性巴氏杆菌(Pm)的反应，这两种细菌都是城市轨道交通和主要牛呼吸道病原体中的共生细菌。我们的初步数据表明，在生命的第一周口服这些细菌可以减少牛肺的炎症反应。因此，我们将确定用这两种细菌口服免疫新生小牛是否会增加肺内抗原特异性Tregs的丰度，并分析这些Tregs抑制炎症反应的机制。Mh和Pm的实验性呼吸道挑战也将用于确定抑制的肺部炎症是否与增强细菌清除和控制肺部病理有关。这些研究将对了解肠道和URT中共生细菌之间的关系以及新生儿接触这些细菌如何影响免疫反应的发展具有广泛的意义。此外，如果肠道暴露于URT共生菌导致Tregs归巢到肺，这将揭示一种新的口服疫苗策略，当URT共生菌入侵肺部时，用于控制呼吸道疾病。这一信息将对疫苗开发具有广泛的意义，因为已知URT共生细菌是人类和许多家养物种中的机会性入侵者。

A connection between the regulation of inflammatory responses in the lung and regulatory T cells (Tregs) is well established for mice and humans and there is increasing evidence that the microbiome plays an important role in the induction of Treg cells throughout the small intestine. My research in young calves demonstrated microbial colonization of the intestine begins during birth and this colonization is associated with extensive developmental changes in the mucosal immune system. It is not known, however, whether this early microbial colonization is associated with an induction of Tregs in the bovine intestine. Further, it is not known whether Tregs induced in the bovine intestine can home to the lung and play a role in regulating inflammatory responses following pulmonary invasion by bacterial pathogens that colonize the upper respiratory tract (URT). My research program will focus on the role of the microbiome in the induction of Tregs in the small intestine of newborn calves. We will characterize Treg populations throughout the intestine of newborn calves and correlate their development with regional microbiome analyses to determine if the presence of commensal bacteria is significantly associated with Treg development. These analyses will focus on a detailed phenotypic and functional characterization of all potential enteric Treg subpopulations and identify specific populations responding to the microbiome. A second objective is to determine whether enteric exposure of newborn calves to commensal bacteria that reside in the URT can also induce enteric antigen-specific Tregs. We will analyze Treg responses to two bacteria, Mannheimia haemolytica (Mh) and Pasteurella multocida (Pm) that are both commensals in the URT and major bovine respiratory pathogens. Our preliminary data indicate oral ingestion of these bacteria during the first week of life reduces inflammatory responses in the bovine lung. Therefore, we will determine if oral immunization of newborn calves with these two bacteria increases the abundance of antigen-specific Tregs in the lung and analyze the mechanisms by which these Tregs suppress inflammatory responses. Experimental respiratory challenges with Mh and Pm will also be used to determine if suppressed lung inflammation is associated with enhanced bacterial clearance and control of lung pathology. These studies will be of broad significance in understanding relationships between commensal bacteria in both the intestine and URT and how neonatal exposure to these bacteria influences development of immune responses. Further, if enteric exposure to URT commensal bacteria induces Tregs homing to the lung this will reveal a novel oral vaccine strategy for the control of respiratory disease when URT commensal bacteria invade the lung. This information will be of broad significance for vaccine development since URT commensal bacteria are known to be opportunistic invaders of the lung in humans and many domestic species.