Tyagi S, Nicholson-Weller A, Barbashov S F, Tas S W, Klickstein L B
Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA.
Arthritis Rheum. 2000 Oct;43(10):2248-59. doi: 10.1002/1529-0131(200010)43:10<2248::AID-ANR12>3.0.CO;2-S.
To investigate the role of intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins in the production of superoxide (O2-) by C1q-stimulated human polymorphonuclear leukocytes (PMN).
PMN were pretreated with F(ab')2 fragments of monoclonal antibodies (mAb) that blocked or did not block beta2 integrin-mediated adhesion. The cells were added to wells coated with C1q, and the production of O2- was monitored kinetically as a color change due to reduction of cytochrome c. In some experiments, C1q was co-immobilized with purified ICAM-1.
Blocking mAb to the shared beta2 integrin subunit, CD18, completely inhibited the O2- response triggered by immobilized C1q, while blocking mAb to the alpha subunits of the beta2 integrins each partially blocked the O2- response. PMN treated with C1q were found to activate the beta2 integrins lymphocyte function-associated antigen 1 and CR3 for binding to ICAM-1. Co-immobilization of ICAM-1 with C1q cooperatively triggered O2- production by PMN.
beta2 integrin binding to an ICAM provided an essential costimulatory signal for O2-production triggered by C1q in PMN. Our findings suggest a model for PMN activation in which 2 stimuli are required for O2- production: a first signal that also activates PMN beta2 integrins, followed by a second, beta2 integrin-mediated signal, which occurs physiologically upon PMN binding to ICAM-1. The requirement for this dual signal for PMN generation of O2- would serve as a regulatory mechanism to limit the production of O2- to a tissue environment where C1q, or some other stimulus, is colocalized with stromal cells bearing up-regulated ICAM-1. This mechanism may explain why all tissues can express ICAM-1 and may explain in part why inhibitors of tumor necrosis factor alpha, a major physiologic stimulus of ICAM-1 up-regulation, are potent antiinflammatory agents.
研究细胞间黏附分子1（ICAM-1）和β2整合素在C1q刺激的人多形核白细胞（PMN）产生超氧化物（O2-）中的作用。
用阻断或不阻断β2整合素介导黏附的单克隆抗体（mAb）的F(ab')2片段预处理PMN。将细胞加入包被有C1q的孔中，由于细胞色素c的还原导致颜色变化，动态监测O2-的产生。在一些实验中，将C1q与纯化的ICAM-1共固定。
针对共同的β2整合素亚基CD18的阻断性mAb完全抑制了固定化C1q触发的O2-反应，而针对β2整合素α亚基的阻断性mAb各自部分阻断了O2-反应。发现用C1q处理的PMN可激活β2整合素淋巴细胞功能相关抗原1和CR3以结合ICAM-1。ICAM-1与C1q共固定可协同触发PMN产生O2-。
β2整合素与ICAM的结合为C1q在PMN中触发的O2-产生提供了重要的共刺激信号。我们的研究结果提示了一种PMN激活模型，其中O2-产生需要两种刺激：第一种信号也激活PMNβ2整合素，随后是第二种由β2整合素介导的信号，该信号在PMN与ICAM-1结合时生理性发生。PMN产生O2-需要这种双重信号将作为一种调节机制，将O2-的产生限制在C1q或其他一些刺激与上调ICAM-1的基质细胞共定位的组织环境中。这种机制可以解释为什么所有组织都能表达ICAM-1，也可以部分解释为什么肿瘤坏死因子α（ICAM-1上调的主要生理刺激物）的抑制剂是有效的抗炎剂。
