Elner S G, Elner V M, Pavilack M A, Todd R F, Mayo-Bond L, Franklin W A, Strieter R M, Kunkel S L, Huber A R
Department of Ophthalmology, University of Michigan, Ann Arbor.
Lab Invest. 1992 Feb;66(2):200-11.
As part of the blood-retina barrier, the neuroectodermally-derived retinal pigment epithelial (RPE) monolayer is strategically positioned to interact with circulating leukocytes and regulate their access to the retina. We, therefore, studied whether human RPE cells express intercellular adhesion molecule-1 (ICAM-1), a specialized cell surface glycoprotein that binds the leukocyte function antigen-1 receptor present on all leukocytes. Using specific monoclonal antibody to ICAM-1, immunohistochemical staining of freshly-isolated primary and fourth passaged human RPE cells resulted in delicate reaction product that increased dramatically upon exposure to human recombinant (r) interferon-gamma (rIFN-gamma), interleukin-1-beta (rIL-1 beta), or tumor necrosis factor-alpha (rTNF-alpha). Fluorescence-activated cell sorting analysis demonstrated 2-fold increases in constitutive RPE ICAM-1 expression within 6 hours of exposure to physiologic concentrations of rIFN-gamma, rIL-1 beta, or rTNF-alpha. In standardized leukocyte adherence assays, cultured RPE cells showed avid binding of neutrophils that increased significantly after stimulation with rIFN-gamma, rIL-1 beta, or rTNF-alpha (p less than 0.001). In parallel assays, monoclonal antibody to either ICAM-1 on RPE cells, or subunits of leukocyte function antigen-1 receptors on leukocytes significantly blocked leukocyte binding to unstimulated (p less than 0.001) or rIFN-gamma-stimulated RPE cells (p less than 0.001). To demonstrate RPE ICAM-1 expression in intact human tissue, fresh uveoretinal explants were exposed to rIFN-gamma, rIL-1 beta, or rTNF-alpha and stained using mAb to ICAM-1. Tissue sections of cytokine-stimulated explants revealed dramatic increases in RPE ICAM-1 immunoreactivity over the low levels observed in unstimulated uveoretinal tissue. Our results indicate that: (a) ICAM-1 is expressed at low levels on unstimulated RPE cells, (b) RPE ICAM-1 may be augmented by inflammatory cytokines, and (c) RPE ICAM-1 is a functional receptor mediating leukocyte binding. ICAM-1 on RPE cells at the blood-retina barrier may regulate leukocytic infiltration in ocular diseases in which leukocytes are important pathogenetically and may be important to the generation of ocular immune responses.
作为血视网膜屏障的一部分，神经外胚层来源的视网膜色素上皮（RPE）单层细胞处于关键位置，可与循环中的白细胞相互作用，并调节它们进入视网膜。因此，我们研究了人类RPE细胞是否表达细胞间黏附分子-1（ICAM-1），这是一种特殊的细胞表面糖蛋白，可与所有白细胞上存在的白细胞功能抗原-1受体结合。使用针对ICAM-1的特异性单克隆抗体，对新鲜分离的原代和传代四次的人类RPE细胞进行免疫组织化学染色，结果显示出微弱的反应产物，在暴露于人类重组（r）干扰素-γ（rIFN-γ）、白细胞介素-1-β（rIL-1β）或肿瘤坏死因子-α（rTNF-α）后，反应产物显著增加。荧光激活细胞分选分析表明，在暴露于生理浓度的rIFN-γ、rIL-1β或rTNF-α后6小时内，RPE细胞组成性ICAM-1表达增加了2倍。在标准化的白细胞黏附试验中，培养的RPE细胞显示出对中性粒细胞的强烈结合，在用rIFN-γ、rIL-1β或rTNF-α刺激后，这种结合显著增加（p<0.001）。在平行试验中，针对RPE细胞上的ICAM-1或白细胞上白细胞功能抗原-1受体亚单位的单克隆抗体，可显著阻断白细胞与未刺激（p<0.001）或rIFN-γ刺激的RPE细胞的结合（p<0.001）。为了证明完整人类组织中RPE细胞ICAM-1的表达，将新鲜的葡萄膜视网膜外植体暴露于rIFN-γ、rIL-1β或rTNF-α，并用抗ICAM-1单克隆抗体进行染色。细胞因子刺激的外植体组织切片显示，RPE细胞ICAM-1免疫反应性较未刺激的葡萄膜视网膜组织中观察到的低水平有显著增加。我们的结果表明：（a）未刺激的RPE细胞上低水平表达ICAM-1；（b）RPE细胞ICAM-1可能会被炎性细胞因子增强；（c）RPE细胞ICAM-1是介导白细胞结合的功能性受体。血视网膜屏障处RPE细胞上的ICAM-1可能在白细胞在发病机制中起重要作用的眼部疾病中调节白细胞浸润，并且可能对眼部免疫反应的产生很重要。
