Integrin-Alpha IIb Identifies Murine Lymph Node Lymphatic Endothelial Cells Responsive to RANKL

Microenvironment and activation signals likely imprint heterogeneity in the lymphatic endothelial cell (LEC) population. Particularly LECs of secondary lymphoid organs are exposed to different cell types and immune stimuli. However, our understanding of the nature of LEC activation signals and their cell source within the secondary lymphoid organ in the steady state remains incomplete. Here we show that integrin alpha 2b (ITGA2b), known to be carried by platelets, megakaryocytes and hematopoietic progenitors, is expressed by a lymph node subset of LECs, residing in medullary, cortical and subcapsular sinuses. In the subcapsular sinus, the floor but not the ceiling layer expresses the integrin, being excluded from ACKR4+ LECs but overlapping with MAdCAM-1 expression. ITGA2b expression increases in response to immunization, raising the possibility that heterogeneous ITGA2b levels reflect variation in exposure to activation signals. We show that alterations of the level of receptor activator of NF-κB ligand (RANKL), by overexpression, neutralization or deletion from stromal marginal reticular cells, affected the proportion of ITGA2b+ LECs. Lymph node LECs but not peripheral LECs express RANK. In addition, we found that lymphotoxin-β receptor signaling likewise regulated the proportion of ITGA2b+ LECs. These findings demonstrate that stromal reticular cells activate LECs via RANKL and support the action of hematopoietic cell-derived lymphotoxin.

微环境与激活信号或可塑造淋巴内皮细胞（lymphatic endothelial cell, LEC）群体的异质性。次级淋巴器官的淋巴内皮细胞尤其会接触不同细胞类型与免疫刺激。然而，我们对于稳态下次级淋巴器官中淋巴内皮细胞激活信号的本质及其细胞来源的认知仍不全面。本研究发现，已知由血小板、巨核细胞及造血祖细胞携带的整合素α2b（integrin alpha 2b, ITGA2b），可在淋巴结的部分淋巴内皮细胞亚群中表达，这些细胞分布于髓质、皮质及被膜下窦。在被膜下窦中，该整合素仅表达于窦底层而非顶层，且不表达于ACKR4阳性淋巴内皮细胞，但与MAdCAM-1的表达存在共定位。免疫接种可上调ITGA2b的表达水平，这提示ITGA2b表达的异质性或可反映细胞接触激活信号程度的差异。本研究证实，通过过表达、中和或敲除基质边缘网状细胞中的核因子κB受体激活剂配体（receptor activator of NF-κB ligand, RANKL）以改变其表达水平，可影响ITGA2b阳性淋巴内皮细胞的比例。淋巴结来源的淋巴内皮细胞可表达核因子κB受体激活剂（receptor activator of NF-κB, RANK），而外周淋巴内皮细胞则不表达该受体。此外，本研究还发现淋巴毒素β受体信号通路同样可调控ITGA2b阳性淋巴内皮细胞的比例。上述研究结果表明，基质网状细胞可通过RANKL激活淋巴内皮细胞，并证实了造血细胞来源的淋巴毒素的调控作用。