Chemokine CXCL17 and Mucosal Immunosurveillance

描述（申请人提供）：CXCL17是一种新发现的趋化因子，在肺、胃、小肠等粘膜组织中组成性表达。这些器官通过食物摄入和呼吸不断暴露于各种各样的病原体，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）。这些细胞作为免疫哨兵发挥着关键作用，是专业的抗原呈递细胞，也是T细胞功能的关键调节因子。目前还不清楚CXCL17是如何介导其体内功能的。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，并结合糖胺聚糖（GAGs）。这两种二硫化物都是受体激活所必需的，GAG结合对白细胞的定向迁移至关重要。最值得注意的是，序列分析显示CXCL17只含有4个保守半胱氨酸中的3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

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.