Mechanisms regulating leukocyte rolling mediated by selectin ligand PSGL-1

白细胞通过一个多步骤的过程从血液迁移到非淋巴组织，该过程涉及细胞滚动、停滞和移行。P-选择素糖蛋白配体-1(P-选择素糖蛋白配体-1)是白细胞上表达的P-选择素的主要配体，其作为滚动受体的作用已被阐明，但调节PSGL-1介导的滚动以及从滚动到停止的机制尚不清楚。在本研究项目中，我们阐明了PSGL-1介导的两种机制，它们可以调节从滚动到停止的转变。第一种机制是PSGL-1介导的刺激LFA-1依赖的细胞黏附。我们发现，抗体介导的PSGL-1在Th1细胞上的交联会增强LFA-1依赖的细胞与ICAM-1的结合。PSGL-1交联剂与Th1刺激趋化因子CXCL10(IP-10)或CCLS(RANTES)联合刺激，对LFA-1介导的Th1细胞黏附和LFA-1在细胞表面的再分布均有明显的促进作用。此外，在流动条件下，PSGL-1介导的P-选择素滚动增强了Th1细胞在ICAM-1上的聚集。这些结果支持PSGL-1介导的滚动相互作用诱导细胞内信号导致整合素激活，促进Th1细胞停滞和随后迁移到靶组织的观点。第二种机制是PSGL-1与趋化因子的相互作用。我们证明了人PSGL-1与CCL27(CTACK)相互作用，并且硫酸化酪氨酸在CCL27-PSGL-1相互作用中起着关键作用。在功能上，PSGL-1降低了表达CCL27受体CCR10的L1.2细胞的趋化能力。PSGL-1对趋化因子介导的反应的调节可能会影响白细胞迁移过程中从滚动到趋化因子介导的停滞的转变。

Leukocytes migrate from the blood into non-lymphoid tissues through a multi-step process that involves cell rolling, arrest, and transmigration. Although the role of P-selectin glycoprotein ligand-1 (PSGL-1), a major ligand for P-selectin expressed on leukocytes, as a rolling receptor has been clarified, the mechanisms regulating the PSGL-1-mediated rolling and the transition from rolling to arrest are not well understood. In this research project, we clarified two PSGL-1-mediated mechanisms that can regulate the transition form rolling to arrest. The first mechanism is the PSGL-1-mediated stimulation of LFA-1-dependent cell adhesion. We showed that antibody-mediated cross-linking of the PSGL-1 on Th1 cells enhances LFA-1-dependent cell binding to ICAM-1. Combined stimulation by PSGL-1 cross-linking and the Th1-stimulating chemokine CXCL10 (IP-10) or CCLS (RANTES) showed a more-than additive effect on LFA-1-mediated Th1 cell adhesion as well as on LFA-1 redistribution on the cell surface. Moreover, PSGL-1-mediated rolling on P-selectin enhanced the Th1 cell accumulation on ICAM-1 under flow conditions. These results support the idea that PSGL-1-mediated rolling interactions induce intracellular signals leading to integrin activation, facilitating Th1-cell arrest and subsequent migration into target tissues. The second mechanism is the interaction of PSGL-1 with chemokines. We showed that human PSGL-1 interacts with CCL27 (CTACK), and that sulfated tyrosines play a critical role in the CCL27-PSGL-1 interaction. Functionally, PSGL-1 reduced the chemotaxis of L1.2 cells expressing CCR10, the receptor for CCL27. Regulation of chemokine-mediated responses by PSGL-1 may affect the transition from rolling to chemokine-mediated arrest during leukocyte migration.