DataSheet_1_Pericyte derived chemokines amplify neutrophil recruitment across the cerebrovascular endothelial barrier.csv

Excessive neutrophil extravasation can drive immunopathology, exemplified in pyogenic meningitis caused by Streptococcus pneumoniae infection. Insufficient knowledge of the mechanisms that amplify neutrophil extravasation has limited innovation in therapeutic targeting of neutrophil mediated pathology. Attention has focussed on neutrophil interactions with endothelia, but data from mouse models also point to a role for the underlying pericyte layer, as well as perivascular macrophages, the only other cell type found within the perivascular space in the cerebral microvasculature. We tested the hypothesis that human brain vascular pericytes (HBVP) contribute to neutrophil extravasation in a transwell model of the cerebral post-capillary venule. We show that pericytes augment endothelial barrier formation. In response to inflammatory cues, they significantly enhance neutrophil transmigration across the endothelial barrier, without increasing the permeability to small molecules. In our model, neither pericytes nor endothelia responded directly to bacterial stimulation. Instead, we show that paracrine signalling by multiple cytokines from monocyte derived macrophages drives transcriptional upregulation of multiple neutrophil chemokines by pericytes. Pericyte mediated amplification of neutrophil transmigration was independent of transcriptional responses by endothelia, but could be mediated by direct chemokine translocation across the endothelial barrier. Our data support a model in which microbial sensing by perivascular macrophages generates an inflammatory cascade where pericytes serve to amplify production of neutrophil chemokines that are translocated across the endothelial barrier to act directly on circulating neutrophils. In view of the striking redundancy in inflammatory cytokines that stimulate pericytes and in the neutrophil chemokines they produce, we propose that the mechanism of chemokine translocation may offer the most effective therapeutic target to reduce neutrophil mediated pathology in pyogenic meningitis.

中性粒细胞（neutrophil）过度外渗可诱发免疫病理损伤，以肺炎链球菌（Streptococcus pneumoniae）感染引发的化脓性脑膜炎为例。目前学界对放大中性粒细胞外渗的具体机制认知不足，这限制了以中性粒细胞介导的病理过程为靶点的治疗创新研发。既往研究多聚焦于中性粒细胞与内皮细胞（endothelia）的相互作用，但小鼠模型的数据亦提示，位于内皮下方的周细胞（pericyte）层，以及脑微血管血管周围间隙中唯一的另一类细胞——血管周围巨噬细胞（perivascular macrophages），同样参与了这一过程。本研究针对“人脑血管周细胞（human brain vascular pericytes, HBVP）可在脑毛细血管后静脉的Transwell模型中促进中性粒细胞外渗”这一假说展开验证。研究结果显示，周细胞可增强内皮屏障的完整性。在炎症信号刺激下，周细胞可显著促进中性粒细胞跨内皮屏障迁移，且不会提升小分子物质的通透性。在本研究的模型中，周细胞与内皮细胞均无法直接响应细菌刺激。相反，本研究发现，单核细胞衍生巨噬细胞分泌的多种细胞因子通过旁分泌信号通路，可诱导周细胞上调多种中性粒细胞趋化因子（chemokines）的转录水平。周细胞介导的中性粒细胞迁移增强效应不依赖于内皮细胞的转录应答，但可通过趋化因子直接跨内皮屏障转运来实现。本研究数据支持如下模型：血管周围巨噬细胞通过感知微生物信号引发炎症级联反应，周细胞在此过程中可放大中性粒细胞趋化因子的产生，这类趋化因子经跨内皮屏障转运后，可直接作用于循环中的中性粒细胞。鉴于激活周细胞的炎症细胞因子以及周细胞产生的中性粒细胞趋化因子均存在显著的功能冗余，本研究提出，趋化因子跨内皮屏障转运的机制，或许是降低化脓性脑膜炎中中性粒细胞介导的病理损伤的最有效治疗靶点。