Petrini M, Allegrini A, Ambrogi F, Valentini P, Sabbatini A, Arnaud P, Galbraith R M
Unit¿a di Ematologia, Clinica Medica 1, University of Pisa, Italy.
J Endocrinol Invest. 1995 Sep;18(8):630-7. doi: 10.1007/BF03349781.
The presence of Gc (vitamin D binding protein) has been consistently demonstrated on the membrane of B lymphocytes. This protein appears to be spatially associated with surface immunoglobulins. The origin of this surface protein has not yet been determined and the purpose of the present paper was to investigate if Gc may bind to human lymphocytes after immunoglobulin (Ig) capping. For this purpose the presence of Gc on B lymphocytes was examined by three different approaches. First, when cells were examined by immunofluorescence and quantified by flow cytometry, membrane Ig capping was followed by a dramatic decrease in positivity for Gc when compared to native cells. In addition, incubation of capped cells with purified Gc was followed by a significant increase in fluorescence, indicating that this protein had been able to bind again. Second, analysis of solubilized lymphocytes by Western blotting showed that native lymphocytes and capped cells incubated with purified Gc contained a large quantity of a 56kDa protein which was immunoreactive with anti Gc antibodies. This protein band was much weaker on blots from capped cells not treated with Gc. Third, radiobinding assays indicated that, following capping, cells were able to bind Gc in saturable fashion. These results suggest that membrane Gc could play a role in the entry of vitamin D metabolites into lymphocytes.
已持续证实在B淋巴细胞的细胞膜上存在Gc（维生素D结合蛋白）。这种蛋白质似乎在空间上与表面免疫球蛋白相关。这种表面蛋白的来源尚未确定，本文的目的是研究免疫球蛋白（Ig）帽化后Gc是否能与人类淋巴细胞结合。为此，通过三种不同方法检测了B淋巴细胞上Gc的存在情况。首先，当通过免疫荧光检查细胞并用流式细胞术进行定量时，与天然细胞相比，膜Ig帽化后Gc的阳性率显著下降。此外，用纯化的Gc孵育帽化细胞后，荧光显著增加，表明该蛋白能够再次结合。其次，通过蛋白质印迹法对溶解的淋巴细胞进行分析表明，天然淋巴细胞和用纯化的Gc孵育的帽化细胞含有大量与抗Gc抗体发生免疫反应的56kDa蛋白。在未用Gc处理的帽化细胞的印迹上，这条蛋白带要弱得多。第三，放射性结合分析表明，帽化后细胞能够以饱和方式结合Gc。这些结果表明膜Gc可能在维生素D代谢产物进入淋巴细胞的过程中起作用。
