Chemokine CXCL17 and Mucosal Immunosurveillance

描述(申请人提供)：CXCL17是一种新近发现的趋化因子，在肺、胃和小肠等粘膜组织中有结构性表达。这些器官通过食物摄入和呼吸持续暴露在各种各样的病原体中，因此必须保持高度警惕，以建立快速有效的免疫反应。CXCL17可能在这一过程中发挥重要作用，因为它选择性地招募未成熟的树突状细胞(DC)。这些细胞扮演着免疫哨兵的关键角色，是专业的抗原提呈细胞，也是T细胞功能的关键调节细胞。目前，CXCL17在体内的作用机制尚不清楚。趋化因子的特征是它们采用相同的三维结构，具有四个保守的半胱氨酸，形成两个二硫键，并与糖胺多聚糖(GAG)结合。这两种二硫化物都是受体激活所必需的，而GAG结合是白细胞定向迁移的关键。最值得注意的是，序列分析表明，CXCL17只有四个保守的半胱氨酸中的三个，因此可能不采用典型的趋化因子结构；它也有明显的不同 正电荷残基的分布，表明了一种新的Gag结合机制。CXCL17的另一个不同寻常的特点是，它只有在高浓度下才有活性，并且在比大多数趋化因子(？M比NM)高出100-1000倍的浓度时显示最佳活性。由于结构决定功能，我们假设在稳态条件下，CXCL17介导的未成熟DC从血管系统到组织的募集在粘膜免疫监控中发挥着重要而非多余的作用。我们此次R21捐赠的具体目的是：目的1.用趋化实验鉴定CXCL17介导的DC亚型(S)在小鼠肺内的募集，以及人DC亚型(S)在体外的募集。目的2.确定CXCL17溶液的结构，并用核磁共振波谱表征其与GAG的结合；以及目的3.系统地删除CXCL17的N-端残基，以确定CXCL17是否可以转化为更有效的激动剂。 公共卫生相关性：肺和胃等器官通过食物摄取和呼吸持续暴露于各种病原体，因此必须保持高度警惕，以确保有效和快速的免疫反应，在这个过程中，被称为树突状细胞(DC)的专门免疫细胞发挥哨兵作用。我们认为CXCL17这一新发现的趋化因子在DC功能的调节中起着重要作用，并进一步提出CXCL17在结构上是独特的，其结构特性与其调节DC功能的能力密切相关。我们计划进行的结构和功能研究 CXCL17的特性应该为人类的免疫监测过程提供关键的见解。

DESCRIPTION (provided by applicant): CXCL17, a recently discovered chemokine, is constitutively expressed in mucosal tissues such as lung, stomach, and the small intestines. These organs are continuously exposed to a wide variety of pathogens via food intake and breathing, and so must be on high alert to mount a rapid and efficient immune response. CXCL17 could play an important role in this process, as it selectively recruits immature dendritic cells (DCs). These cells play a key role as immunological sentinels, and are professional antigen-presenting cells, and key regulators of T cell functions. Currently nothing is known about how CXCL17 mediates its in vivo functions. Characteristic features of chemokines are that they adopt the same three-dimensional structure, have four conserved cysteines that form two disulfide bonds, and bind glycosaminoglycans (GAGs). Both the disulfides are essential for receptor activation, and GAG binding is critical for directed migration of leukocytes. Most remarkably, sequence analysis reveals that CXCL17, has only three of the four conserved cysteines, and so may not adopt the typical chemokine structure; it also has a distinctly different distribution of positively charged residues, suggesting a novel GAG-binding mechanism. Another unusual feature of CXCL17 is that it is active only at high concentrations, and shows optimal activity at 100-1000x higher concentrations than is normally observed for most chemokines (?M vs. nM). As structure dictates function, we hypothesize that CXCL17-mediated recruitment of immature DCs from the vasculature to the tissues under steady-state conditions plays an important and non-redundant role in mucosal immunosurveillance. Our Specific Aims for this R21 grant are to: Aim 1. Characterize CXCL17-mediated recruitment of DC subtype(s) in vivo in a mouse lung, and recruitment of human DC subtype(s) in vitro using chemotaxis assays. Aim 2. Determine the CXCL17 solution structure and characterize its binding with GAG using NMR spectroscopy; and Aim 3. Determine whether CXCL17 can be converted to a more potent agonist by systematically deleting its N-terminal residues. PUBLIC HEALTH RELEVANCE: Organs such as the lung and stomach are continuously exposed to a wide variety of pathogens via food intake and breathing, and so must be on high alert for an efficient and quick immune response, a process during which specialized immune cells called dendritic cells (DCs) function as sentinels. We propose that CXCL17, a newly discovered chemokine, plays an important role in regulating DC function, and we further propose that CXCL17 is structurally unique, and that its structural properties are intimately linked to its ability to regulate DC function. Our planned studies on the structural and functional characterization of CXCL17 should provide critical insights into the immunosurveillance process in humans.