Department of Regional Cooperation for Infectious Diseases, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.
Cell Mol Immunol. 2011 Jul;8(4):305-14. doi: 10.1038/cmi.2011.8. Epub 2011 Apr 4.
Inflammatory stimuli, such as a microbes or lipopolysaccharides, induce a rapid release of neutrophils from the bone marrow and promote neutrophil migration into inflamed sites to promote host defense. However, an excess accumulation and retention of neutrophils in inflamed tissue can cause severe tissue injuries in the later stages of inflammation. Recent studies have reported that both CXCL12 levels in injured lungs and its receptor, CXCR4, on accumulated neutrophils in injured lungs, increased; furthermore, these studies showed that the CXCL12/CXCR4 signaling pathway participated in neutrophil accumulation in the later stages of lipopolysaccharide (LPS)-induced lung injury. However, the mechanisms underlying this increase in surface CXCR4 expression in neutrophils remain unclear. In this study, we found that surface CXCR4 expression increased in extravascular, but not intravascular, neutrophils in the lungs of LPS-induced lung injury model mice. Furthermore, ex vivo studies revealed that CXCL12 acted not only as a chemoattractant, but also as a suppressor of cell death for the lung neutrophils expressing CXCR4. Sulfatide, one of the native ligands for L-selectin, induced the increase of surface CXCR4 expression on isolated circulating neutrophils, suggesting that the activation of L-selectin may be involved in the increase in surface CXCR4. Our findings show that surface CXCR4 levels on neutrophils increase after extravasation into injured lungs, possibly through the activation of L-selectin. The CXCL12/CXCR4 signaling pathway plays an important role in the modulation of neutrophil activity during acute lung injury, not only by promoting chemotaxis but also by suppressing cell death.
炎症刺激物,如微生物或脂多糖,可诱导中性粒细胞从骨髓中快速释放,并促进中性粒细胞迁移到炎症部位,从而促进宿主防御。然而,在炎症的后期阶段,中性粒细胞在炎症组织中的过度积累和滞留会导致严重的组织损伤。最近的研究报告称,受损肺部中的 CXCL12 水平及其受体 CXCR4 在受损肺部中积累的中性粒细胞增加;此外,这些研究表明,CXCL12/CXCR4 信号通路参与了脂多糖 (LPS) 诱导的肺损伤后期中性粒细胞的积累。然而,中性粒细胞表面 CXCR4 表达增加的机制尚不清楚。在这项研究中,我们发现 LPS 诱导的肺损伤模型小鼠肺部的血管外而非血管内中性粒细胞表面 CXCR4 表达增加。此外,离体研究表明,CXCL12 不仅作为趋化因子,而且作为表达 CXCR4 的肺中性粒细胞的细胞死亡抑制剂发挥作用。唾液酸苷脂是 L-选择素的天然配体之一,可诱导分离的循环中性粒细胞表面 CXCR4 表达增加,表明 L-选择素的激活可能参与了表面 CXCR4 的增加。我们的研究结果表明,中性粒细胞在渗出到受损肺部后表面 CXCR4 水平增加,可能通过 L-选择素的激活。CXCL12/CXCR4 信号通路在急性肺损伤中对中性粒细胞活性的调节中发挥重要作用,不仅通过促进趋化作用,而且通过抑制细胞死亡。