Kunkel E J, Chomas J E, Ley K
Department of Biomedical Engineering, University of Virginia School of Medicine, Charlottesville 22908, USA.
Circ Res. 1998;82(1):30-8. doi: 10.1161/01.res.82.1.30.
Leukocyte accumulation during inflammation depends on the concerted action of selectin and integrin adhesion molecules, which promote capture, rolling, and arrest of these cells on activated endothelium. In addition to interacting with endothelial cells, leukocytes can also adhere to already adherent leukocytes through an L-selectin-dependent mechanism. Initiation of adhesion through this mechanism has been called nucleation and leads to characteristic geometric patterns (ie, clusters and strings) of adherent leukocytes in flow chambers. We have used intravital microscopy of tumor necrosis factor-alpha (TNF-alpha)-treated mouse cremaster muscles to quantitatively investigate the potential role of leukocyte-leukocyte adhesion in initiating and maintaining the leukocyte clusters that are commonly observed in inflamed venules. Our data show that in TNF-alpha-treated venules with diameters between 23 and 108 microm, leukocyte adhesion occurs in clusters that are 19 to 50 microm long and 8 to 44 microm wide. They are almost entirely made up of slow-rolling leukocytes. Of all leukocytes recruited into a cluster (100%), the majority enter the cluster rolling along the endothelium and sharply reduce their velocity in the absence (59%) or presence (15%) of other leukocytes in proximity (one cell diameter). Some of the rolling leukocytes (17%) pass through the cluster without reducing their velocity. Recruitment of leukocytes from the free flow regime into a cluster is a rare event and accounts for only 7 (1.2%) of 476 leukocytes arriving in the cluster. However, of the leukocytes captured from the free flow, 6 initiated contact with a slow-rolling leukocyte rather than making direct contact with the endothelium. Our data show that leukocyte-leukocyte interactions can occur in vivo but are not important for cluster formation. This is confirmed by the observation of normal cluster formation in L-selectin-deficient mice, in which leukocyte-leukocyte interactions under flow are abolished. We conclude that leukocyte-mediated nucleation contributes little to leukocyte recruitment during inflammation in vivo. Cluster formation appears to be dominated by areas of endothelium with a higher expression of E-selectin, because cluster formation is greatly reduced in E-selectin-deficient mice.
炎症过程中的白细胞聚集依赖于选择素和整合素黏附分子的协同作用，这些分子促进白细胞在活化内皮细胞上的捕获、滚动和黏附。除了与内皮细胞相互作用外，白细胞还可通过L-选择素依赖机制黏附于已黏附的白细胞。通过这种机制启动的黏附被称为成核作用，并导致流动小室内黏附白细胞出现特征性的几何图案（即簇状和串状）。我们利用肿瘤坏死因子-α（TNF-α）处理的小鼠提睾肌活体显微镜技术，定量研究白细胞-白细胞黏附在启动和维持炎症小静脉中常见的白细胞簇方面的潜在作用。我们的数据显示，在直径为23至108微米的TNF-α处理的小静脉中，白细胞黏附以簇状形式发生，这些簇长19至50微米，宽8至44微米。它们几乎完全由缓慢滚动的白细胞组成。在招募到一个簇中的所有白细胞（100%）中，大多数沿着内皮滚动进入簇中，并且在附近没有其他白细胞（一个细胞直径范围内）时，速度急剧降低（59%），或者在有其他白细胞时，速度也急剧降低（15%）。一些滚动的白细胞（17%）不降低速度就穿过簇。从自由流动状态招募白细胞进入簇是一个罕见事件，在到达簇的476个白细胞中仅占7个（1.2%）。然而，从自由流动中捕获的白细胞中，有6个是与缓慢滚动的白细胞开始接触，而不是直接与内皮接触。我们的数据表明，白细胞-白细胞相互作用可在体内发生，但对簇的形成并不重要。这一点在L-选择素缺陷小鼠中正常簇形成的观察中得到证实，在这种小鼠中，流动状态下的白细胞-白细胞相互作用被消除。我们得出结论，白细胞介导的成核作用在体内炎症过程中对白细胞招募的贡献很小。簇的形成似乎以内皮细胞上E-选择素表达较高的区域为主导，因为在E-选择素缺陷小鼠中，簇的形成大大减少。
