Key Points Fibrinogen is a specific trigger for cytolytic eosinophil degranulation. Eosinophils adhere to and degrade fibrinogen substrates in a CD11b-dependent manner. Fibrinogen-interacting eosinophils are more metabolically active than collagen. In inflamed human tissues, we often find intact eosinophilic granules, but not eosinophils themselves. Eosinophils, tissue-dwelling granulocytes with several homeostatic roles, have a surprising association with fibrinogen and tissue remodeling. Fibrinogen is a complex glycoprotein with regulatory roles in hemostasis, tumor development, wound healing, and atherogenesis. Despite its significance, the functional link between eosinophils and fibrinogen is not understood. We tested IL-5–primed mouse bone marrow–derived and human blood–sorted eosinophil activity against FITC-linked fibrinogen substrates. The interactions between these scaffolds and adhering eosinophils were quantified using three-dimensional laser spectral, confocal, and transmission electron microscopy. Eosinophils were labeled with major basic protein (MBP) Ab to visualize granules and assessed by flow cytometry. Both mouse and human eosinophils showed firm adhesion and degraded up to 27 ± 3.1% of the substrate area. This co-occurred with active MBP-positive granule release and the expression of integrin CD11b. Mass spectrometry analysis of fibrinogen proteolytic reactions detected the presence of eosinophil peroxidase, MBP, and fibrin α-, β-, and γ-chains. Eosinophil activity was adhesion dependent, as a blocking Ab against CD11b significantly reduced adhesion, degranulation, and fibrinogenolysis. Although adhered, eosinophils exhibited no proteolytic activity on collagen matrices. Cytolytic degranulation was defined by loss of membrane integrity, cell death, and presence of cell-free granules. From transmission electron microscopy images, we observed only fibrinogen-exposed eosinophils undergoing this process. To our knowledge, this is the first report to show that fibrinogen is a specific trigger for cytolytic eosinophil degranulation with implications in human disease.

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纤维蛋白原是细胞溶解嗜酸性粒细胞脱粒的特定触发因素

关键点 纤维蛋白原是细胞溶解嗜酸性粒细胞脱粒的特定触发因素。嗜酸性粒细胞以 CD11b 依赖性方式粘附并降解纤维蛋白原底物。与纤维蛋白原相互作用的嗜酸性粒细胞比胶原蛋白更具代谢活性。在发炎的人体组织中，我们经常发现完整的嗜酸性粒细胞，而不是嗜酸性粒细胞本身。嗜酸性粒细胞是具有多种稳态作用的组织内粒细胞，与纤维蛋白原和组织重塑有着惊人的关联。纤维蛋白原是一种复杂的糖蛋白，在止血、肿瘤发展、伤口愈合和动脉粥样硬化形成中具有调节作用。尽管具有重要意义，但嗜酸性粒细胞和纤维蛋白原之间的功能联系尚不清楚。我们测试了 IL-5 引发的小鼠骨髓来源和人血分选的嗜酸性粒细胞对 FITC 连接的纤维蛋白原底物的活性。使用三维激光光谱、共聚焦和透射电子显微镜对这些支架和粘附的嗜酸性粒细胞之间的相互作用进行量化。嗜酸性粒细胞用主要碱性蛋白 (MBP) Ab 标记以显示颗粒并通过流式细胞术进行评估。小鼠和人类嗜酸性粒细胞均表现出牢固的粘附性，并且降解了多达 27 ± 3.1% 的底物面积。这与活跃的 MBP 阳性颗粒释放和整合素 CD11b 的表达同时发生。纤维蛋白原蛋白水解反应的质谱分析检测到嗜酸性粒细胞过氧化物酶、MBP 和纤维蛋白 α-、β-和 γ-链的存在。嗜酸性粒细胞活性依赖于粘附，因为针对 CD11b 的阻断抗体显着降低了粘附、脱粒和纤维蛋白原溶解。虽然坚持，嗜酸性粒细胞对胶原基质没有蛋白水解活性。细胞溶解脱粒定义为膜完整性丧失、细胞死亡和无细胞颗粒的存在。从透射电子显微镜图像中，我们仅观察到暴露于纤维蛋白原的嗜酸性粒细胞正在经历这一过程。据我们所知，这是第一份表明纤维蛋白原是细胞溶解性嗜酸性粒细胞脱粒的特定触发因素的报告，对人类疾病有影响。