Mucosal Macrophages and Tertiary Lymphoid Structures in IBD

炎症性肠病（IBD），包括克罗恩病（CD）和溃疡性结肠炎（UC），在世界范围内的发病率和患病率正在增加，尽管有靶向生物制剂的发展，但对于大量患者来说，IBD的治疗选择仍然有限。炎性肠病（IBD）的发病机制是由复杂的细胞因子网络控制的免疫、基质和上皮细胞之间的致病通讯机制模型。下一个关键步骤是建立这种异常免疫反应的时空组织。三级淋巴样结构（TLS）是在CD和UC患者肠道炎性病变周围发现的异位无序淋巴样聚集物，可能是对持续破坏肠道黏膜的病原体的反应。TLS被认为是IBD的病理标志，然而，它们的确切细胞组成和对肠道免疫的机制贡献以及IBD的发病机制在很大程度上是未知的。本提案的总体目标是揭示驱动TLS形成的机制，并阐明它们在IBD相关结肠炎小鼠模型中的功能。单个核吞噬细胞（MNPs）包括树突状细胞（DC）和巨噬细胞(M)亚群，是TLS的重要组成部分。在沙门氏菌结肠炎模型中，我们确定了粘膜驻留（CX3CR1hi） Ms的一个亚群，其功能是作为抗原呈递细胞驱动TLS形成和TLS中沙门氏菌特异性T细胞依赖的IgA反应。我们发现TLS通过限制病原菌的全身传播在沙门氏菌结肠炎中发挥保护作用，但在IBD慢性炎症条件下，TLS可能获得促炎作用。最近对人类IBD的单细胞转录分析表明，TLS功能的这种转换可能是通过促进TLS相关的致病性T细胞分化和促炎IgG而不是IgA反应来实现的。我们的总体假设是IBD发病的一个关键步骤是CX3CR1hi Ms的失调，而这种失调的Ms通过驱动产生t细胞依赖性IgG而不是IgA的致病性TLS的发展来促进IBD。我们将在三个具体目标中检验我们的假设。目的1将确定抗原呈递和CX3CR1hi Ms激活B细胞在致病性TLS发展中的作用；和Aim 2将建立CX3CR1hi Ms中TNF信号在调节TLS功能中的作用。如果成功，该研究将为IBD的发病机制提供新的见解，并确定IBD中与TLS相关的潜在生物标志物和治疗靶点（例如CX3CR1hi m衍生介质）。

The incidence and prevalence of inflammatory bowel disease (IBD), which includes Crohn’s disease (CD) and ulcerative colitis (UC), are increasing worldwide, and the treatment options for IBD are still limited for a large number of patients despite the development of targeted biologics. A mechanistic model of pathogenic communication among immune, stromal and epithelial cells controlled by elaborate cytokine networks that underlies pathogenesis of inflammatory bowel disease (IBD) has been proposed. The next critical step is to establish the spatiotemporal organization of this abnormal immune response. Tertiary lymphoid structures (TLS) are ectopic disorganized lymphoid aggregates found around intestinal inflammatory lesions in patients with CD and UC, possibly in response to persisting pathobionts that breach intestinal mucosa. TLS are recognized as a pathologic hallmark in IBD, however, their precise cellular composition and mechanistic contribution to intestinal immunity and pathogenesis of IBD are largely unknown. The overall goal of this proposal is to unravel the mechanisms that drive TLS formation and elucidate their function in mouse models of colitis relevant to IBD Mononuclear phagocytes (MNPs) that comprise dendritic cell (DC) and macrophage (M) subsets are an important constituent of TLS. In a model of Salmonella colitis, we identified a subset of mucosa-resident (CX3CR1hi) Ms that functions as an antigen-presenting cell driving TLS formation and a Salmonella-specific T cell-dependent IgA response in TLS. We found that TLS play a protective role in Salmonella colitis by restricting systemic pathogen dissemination, but under conditions of chronic inflammation observed in IBD, TLS are likely to acquire a proinflammatory role. Such conversion of TLS function may occur via promotion of TLS-associated pathogenic T cell differentiation and proinflammatory IgG instead of IgA responses as suggested by recent single cell transcriptional analyses of human IBD. Our overall hypothesis is that a key step in the pathogenesis of IBD is dysregulation of CX3CR1hi Ms, and that such dysregulated Ms promote IBD by driving the development of pathogenic TLS that produce T-cell dependent IgG instead of IgA. We will test our hypothesis in three specific aims. Aim 1 will determine the role of antigen-presentation and B cell activation by CX3CR1hi Ms in the development of pathogenic TLS; and Aim 2 will establish the role of TNF signaling in CX3CR1hi Ms in the regulation of TLS function. If successful, the study will provide novel insight into the pathogenesis of IBD and identify potential biomarkers and therapeutic targets (e.g., CX3CR1hi M-derived mediators) associated with TLS in IBD.