Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
J Immunol. 2012 Apr 1;188(7):3223-36. doi: 10.4049/jimmunol.1101032. Epub 2012 Mar 2.
L-selectin functions as an important adhesion molecule that mediates tethering and rolling of lymphocytes by binding to high endothelial venule (HEV)-expressed ligands during recirculation. Subsequent lymphocyte arrest and transmigration require activation through binding of HEV-decorated homeostatic chemokines such as secondary lymphoid tissue chemokine (SLC; CCL21) to its counterreceptor, CCR7. Importantly, L-selectin also functions as a signaling molecule. In this study, signaling induced by ligation of L-selectin using mAb or endothelial cell-expressed ligand significantly enhanced the chemotaxis of murine T cells and B cells to SLC but not to other homeostatic chemokines. Consistent with the expression levels of L-selectin in different lymphocyte subsets, L-selectin-mediated enhancement of chemotaxis to SLC was observed for all naive lymphocytes and effector/memory CD8(+) T cells, whereas only a subpopulation of effector/memory CD4(+) T cells responded. During in vivo mesenteric lymph node migration assays, the absence of L-selectin on lymphocytes significantly attenuated both their ability to migrate out of the HEV and their chemotaxis away from the vessel wall. Notably, ligation of L-selectin and/or CCR7 did not result in increased CCR7 expression levels, internalization, or re-expression. Pharmacologic inhibitor studies showed that L-selectin-mediated enhanced chemotaxis to SLC required intact intracellular kinase function. Furthermore, treatment of lymphocytes with the spleen tyrosine kinase family inhibitor piceatannol reduced their ability to migrate across the HEV in peripheral lymph nodes. Therefore, these results suggest that "cross-talk" in the signaling pathways initiated by L-selectin and CCR7 provides a novel mechanism for functional synergy between these two molecules during lymphocyte migration.
L-选择素作为一种重要的黏附分子，在循环过程中通过与高内皮静脉（HEV）表达的配体结合，介导淋巴细胞的拴系和滚动。随后的淋巴细胞停滞和迁移需要通过结合 HEV 装饰的稳态趋化因子，如次级淋巴组织趋化因子（SLC；CCL21）与其受体 CCR7 来激活。重要的是，L-选择素也作为一种信号分子发挥作用。在这项研究中，使用 mAb 或内皮细胞表达的配体交联 L-选择素诱导的信号显著增强了小鼠 T 细胞和 B 细胞对 SLC 的趋化性，但对其他稳态趋化因子没有作用。与不同淋巴细胞亚群中 L-选择素的表达水平一致，L-选择素介导的 SLC 趋化性增强观察到所有幼稚淋巴细胞和效应记忆 CD8(+)T 细胞，但只有一部分效应记忆 CD4(+)T 细胞有反应。在体内肠系膜淋巴结迁移实验中，淋巴细胞上 L-选择素的缺失显著削弱了它们从 HEV 中迁移出和向血管壁迁移的能力。值得注意的是，L-选择素和/或 CCR7 的交联并未导致 CCR7 表达水平、内化或再表达的增加。药理学抑制剂研究表明，L-选择素介导的 SLC 趋化性增强需要完整的细胞内激酶功能。此外，用脾酪氨酸激酶家族抑制剂白藜芦醇处理淋巴细胞会降低其穿过外周淋巴结 HEV 的能力。因此，这些结果表明，L-选择素和 CCR7 启动的信号通路中的“串扰”为这两种分子在淋巴细胞迁移过程中的功能协同提供了一种新的机制。
