Brisson C, Azorsa D O, Jennings L K, Moog S, Cazenave J P, Lanza F
URA 1459 CNRS, Institut Pasteur de Lyon, France.
Histochem J. 1997 Feb;29(2):153-65. doi: 10.1023/a:1026437522882.
CD9 is a 24-kDa membrane glycoprotein expressed on the surface of human platelets and potentially involved in cellular activation and adhesion functions. This protein belongs to a recently delineated family of cell-surface antigens that span the membrane four times, called tetraspans, and found mainly in leucocytes and tumour cells. As a first approach to clarify the function of CD9, we used immunoelectron microscopy to determine the localization of this antigen in human platelets, and compared its distribution with that of the GPIIb-IIIa integrin, the platelet receptor for fibrinogen. Monoclonal antibodies against CD9 (MAb7) and GPIIb-IIIa (HP1-1D) coupled to colloidal gold of different sizes (5 and 15 nm) were incubated with intact platelets in suspension or on ultrathin sections of platelets embedded in LR white. CD9 was found in association with GPIIb-IIIa on the inner face of alpha-granule membranes. These two antigens also colocalized on pseudopods of activated platelets and in contact regions between adjacent platelets. CD63, another member of the tetraspan family, was absent from alpha-granules but was associated with lysosomal structures. Flow cytometric analysis of platelet CD9 with a series of monoclonal antibodies revealed an increased expression upon thrombin stimulation, confirming the presence of an intracellular granular pool. The observation that CD9 and GPIIb-IIIa are stored in the same intracellular structures and migrate to the same activation zones after platelet stimulation lends support to previous suggestions of a close association between CD9 and GPIIb-IIIa in human platelets and of a possible involvement of CD9 in adhesive functions of platelets.
CD9是一种24 kDa的膜糖蛋白，表达于人类血小板表面，可能参与细胞活化和黏附功能。该蛋白属于最近划定的一类细胞表面抗原家族，这类抗原跨膜四次，称为四跨膜蛋白，主要存在于白细胞和肿瘤细胞中。作为阐明CD9功能的第一步，我们使用免疫电子显微镜来确定该抗原在人类血小板中的定位，并将其分布与纤维蛋白原的血小板受体GPIIb-IIIa整合素的分布进行比较。将针对CD9（单克隆抗体7）和GPIIb-IIIa（HP1-1D）的单克隆抗体与不同大小（5和15纳米）的胶体金偶联，与悬浮液中的完整血小板或包埋在LR白色树脂中的血小板超薄切片一起孵育。发现CD9与α颗粒膜内表面的GPIIb-IIIa相关联。这两种抗原也共定位于活化血小板的伪足以及相邻血小板之间的接触区域。四跨膜蛋白家族的另一个成员CD63不存在于α颗粒中，但与溶酶体结构相关。用一系列单克隆抗体对血小板CD9进行流式细胞术分析显示，凝血酶刺激后表达增加，证实存在细胞内颗粒池。CD9和GPIIb-IIIa储存在相同的细胞内结构中，并且在血小板刺激后迁移到相同的活化区域，这一观察结果支持了之前关于人类血小板中CD9和GPIIb-IIIa密切关联以及CD9可能参与血小板黏附功能的推测。
