Berger G, Caen J P, Berndt M C, Cramer E M
INSERM U.348, Paris, France.
Blood. 1993 Nov 15;82(10):3034-44.
CD36 (glycoprotein [GP] IV) is a membrane GP of 88 kD found on monocytes, endothelial cells, and platelets. It may serve as a receptor for collagen and is also able to bind thrombospondin (TSP), because a monoclonal antibody to CD36 inhibits TSP binding to thrombin-stimulated platelets. In the following study, we investigated the subcellular distribution of CD36 within normal resting platelets, thrombin-stimulated platelets, and in cultured megakaryocytes (MK) by an immunogold staining technique and electron microscopy. We used an affinity-purified monospecific polyclonal antibody showing a single major band of precipitation at 88 kD via immunoblot analysis. In normal platelets, ultrastructural observation detected immunolabeling for CD36, homogeneously distributed along the platelet plasma membrane and in the luminal side of the open canalicular system (OCS). Moreover, some labeling was found around the alpha-granules along the inner face of their limiting membrane. An average of 70% of granules were labeled. The granule-associated pool of CD36 was estimated at approximately 25% of the total cell content. To exclude the possibility of a cross-reaction with GPIIb-IIIa, platelets from a patient with type I Glanzmann's thrombasthenia (which completely lack GPIIb-IIIa) were studied and showed a similar subcellular distribution of CD36, including alpha-granule membrane labeling. In activated platelets, CD36 was shown to be redistributed to the OCS and pseudopods of the plasma membrane. Platelets from a patient with the Gray platelet syndrome expressed CD36 on their plasma membrane, and some immunolabeling was also found within small abnormal alpha-granules. In cultured MK, CD36 immunolabeling was detected in the Golgi saccules, associated vesicles, immature alpha-granules, and demarcation membranes. In conclusion, this study shows the existence of a significant intragranular pool of CD36 in platelets that may play a critical role in the surface expression of alpha-granule TSP during platelet activation.
CD36（糖蛋白[GP]IV）是一种88kD的膜糖蛋白，存在于单核细胞、内皮细胞和血小板上。它可能作为胶原蛋白的受体，也能够结合血小板反应蛋白（TSP），因为针对CD36的单克隆抗体可抑制TSP与凝血酶刺激的血小板结合。在以下研究中，我们通过免疫金染色技术和电子显微镜研究了CD36在正常静息血小板、凝血酶刺激的血小板以及培养的巨核细胞（MK）中的亚细胞分布。我们使用了一种亲和纯化的单特异性多克隆抗体，通过免疫印迹分析显示在88kD处有一条单一的主要沉淀带。在正常血小板中，超微结构观察检测到CD36的免疫标记，其均匀分布在血小板质膜以及开放管道系统（OCS）的腔面。此外，在α颗粒周围其限制膜的内表面发现了一些标记。平均70%的颗粒被标记。与颗粒相关的CD36池估计约占细胞总含量的25%。为排除与GPIIb-IIIa交叉反应的可能性，对一名I型Glanzmann血小板无力症患者（完全缺乏GPIIb-IIIa）的血小板进行了研究，结果显示CD36的亚细胞分布相似，包括α颗粒膜标记。在活化血小板中，CD36被证明重新分布到质膜的OCS和伪足。患有灰色血小板综合征患者的血小板在其质膜上表达CD36，并且在小的异常α颗粒内也发现了一些免疫标记。在培养的MK中，在高尔基体囊泡、相关小泡、未成熟α颗粒和分界膜中检测到CD36免疫标记。总之，本研究表明血小板中存在大量的颗粒内CD36池，这可能在血小板活化过程中α颗粒TSP的表面表达中起关键作用。
