Lozano M L, Rivera J, Gónzález-Conejero R, Moraleda J M, Vicente V
Unit of Hematology and Hemotherapy, School of Medicine, Hospital General Universitario, Regional Center for Blood Donation, Murcia, Spain.
Transfusion. 1997 Apr;37(4):368-75. doi: 10.1046/j.1537-2995.1997.37497265336.x.
The storage of platelet concentrates (PCs) induces a reduction in the platelet surface expression of glycoprotein (GP) Ib alpha. The location of the platelets' high-affinity binding site for thrombin has been postulated as being located on GPIb alpha. This study attempts to determine whether loss or alteration of GPIb alpha during storage of PCs is related to impairment in the reactivity of platelets to thrombin.
In this study, platelet surface expression of GPIb alpha was monitored by means of flow cytometry, throughout standard storage of PCs for up to 10 days. Two thrombin-induced platelet responses, the binding of radiolabeled fibrinogen and the platelet surface expression of P-selectin, were evaluated. Thrombin-binding assays were also performed to assess the number of thrombin receptors in platelets.
The surface expression of the GPIb/IX complex declines during storage of PCs. The thrombin-induced maximal binding of fibrinogen in platelets stored for 3, 7, and 10 days was 77 +/- 7 percent, 60 +/- 20 percent, and 34 +/- 25 percent, respectively, of that found in fresh platelets. Moreover, the concentration of thrombin needed for 50 percent of platelets to express the CD62 antigen P-selectin at the surface increased from 0.05 U per mL in fresh platelets to 0.11, 0.56, and 1.2 U per mL in platelets stored for 3, 7, and 10 days, respectively. Thrombin-binding experiments demonstrated a significant reduction in the number of high-affinity binding sites throughout storage of PCs (55 +/- 21 sites/platelet in 10-day-stored platelets vs. 73 +/- 25 in fresh platelets). A significant correlation was also observed between the number of high-affinity thrombin-binding sites and surface expression of GPIb alpha. Selective blockage of the thrombin-binding site on GPIb alpha with monoclonal antibody LJ-Ib10 also inhibited the response of fresh platelets to thrombin, up to a level equivalent to that found in 3-day-stored platelets.
The loss of the GPIb alpha-located high-affinity thrombin-binding site may impair the ability of platelets to become activated by thrombin as storage time increases.
血小板浓缩物（PCs）的储存会导致糖蛋白（GP）Ibα在血小板表面的表达减少。血小板上凝血酶高亲和力结合位点的位置被推测位于GPIbα上。本研究旨在确定PCs储存过程中GPIbα的丢失或改变是否与血小板对凝血酶反应性的损害有关。
在本研究中，通过流式细胞术监测PCs在长达10天的标准储存过程中GPIbα在血小板表面的表达。评估了两种凝血酶诱导的血小板反应，即放射性标记纤维蛋白原的结合以及P-选择素在血小板表面的表达。还进行了凝血酶结合试验以评估血小板中凝血酶受体的数量。
在PCs储存期间，GPIb/IX复合物的表面表达下降。储存3天、7天和10天的血小板中，凝血酶诱导的纤维蛋白原最大结合量分别为新鲜血小板中该结合量的77±7%、60±20%和34±25%。此外，50%的血小板在表面表达CD62抗原P-选择素所需的凝血酶浓度从新鲜血小板中的0.05 U/mL分别增加到储存3天、7天和10天的血小板中的0.11 U/mL、0.56 U/mL和1.2 U/mL。凝血酶结合实验表明，在PCs的整个储存过程中，高亲和力结合位点的数量显著减少（储存10天的血小板中为55±21个位点/血小板，而新鲜血小板中为73±25个）。在高亲和力凝血酶结合位点的数量与GPIbα的表面表达之间也观察到显著相关性。用单克隆抗体LJ-Ib10选择性阻断GPIbα上的凝血酶结合位点也抑制了新鲜血小板对凝血酶的反应，抑制程度高达与储存3天的血小板相当的水平。
随着储存时间的增加，位于GPIbα上的高亲和力凝血酶结合位点的丢失可能会损害血小板被凝血酶激活的能力。
