Brittain H A, Eckman J R, Swerlick R A, Howard R J, Wick T M
School of Chemical Engineering, Georgia Institute of Technology, Atlanta 30332-0100.
Blood. 1993 Apr 15;81(8):2137-43.
Adherence of erythrocytes to vascular endothelium likely contributes to the pathophysiology of episodic vascular occlusion in patients with sickle cell disease (SCD). In addition, coagulation activation has been reported in sickle patients during complications such as pain episodes. To test the hypothesis that platelet activation contributes to sickle erythrocyte binding, we investigated whether factors released from activated sickle platelets promote adherence of sickle erythrocytes to human microvascular endothelial cells (MEC) under flow conditions. Activated sickle platelet supernatant (ASPS) promoted high levels of sickle erythrocyte adherence to MEC (55.4 +/- 3.9 erythrocytes/mm2) but only moderate adherence of normal erythrocytes to MEC (14.1 +/- 0.7 erythrocytes/mm2). When MEC were incubated with an antibody (OKM5) against CD36 (a thrombospondin [TSP] receptor), platelet supernatant mediated sickle erythrocyte adherence was inhibited 86%, suggesting that TSP participated in the adherence. To further define the role of TSP in adherence, additional studies using purified TSP were performed. At a concentration of 0.2 micrograms/mL TSP in serum-free media (SFM), sickle erythrocyte adherence to MEC was 33.9 +/- 2.7 erythrocytes/mm2 and sixfold greater than either sickle erythrocyte adherence in the absence of TSP or normal erythrocyte adherence in the presence of TSP. Doubling the concentration of TSP to 0.4 micrograms/mL proportionally increased adherence of sickle erythrocytes. Incubation of MEC with OKM5 or anti-alpha v monoclonal antibodies inhibited TSP-mediated sickle erythrocyte adherence more than 95%. These data suggest that activated platelet release factors, including alpha-granule TSP, which promote receptor-mediated sickle erythrocyte adherence to microvascular endothelium. Such factors released during in vivo platelet activation could contribute to vaso-occlusive complications by promoting erythrocyte adherence and microvascular occlusion.
红细胞与血管内皮的黏附可能在镰状细胞病（SCD）患者发作性血管闭塞的病理生理过程中起作用。此外，在镰状细胞病患者的并发症（如疼痛发作）期间，已有凝血激活的报道。为了验证血小板激活导致镰状红细胞黏附的假说，我们研究了激活的镰状血小板释放的因子在流动条件下是否能促进镰状红细胞与人微血管内皮细胞（MEC）的黏附。激活的镰状血小板上清液（ASPS）可促进高水平的镰状红细胞与MEC的黏附（55.4±3.9个红细胞/mm2），但仅能促进正常红细胞与MEC的中度黏附（14.1±0.7个红细胞/mm2）。当MEC与抗CD36（血小板反应蛋白[TSP]受体）抗体（OKM5）孵育时，血小板上清液介导的镰状红细胞黏附被抑制86%，提示TSP参与了黏附过程。为了进一步明确TSP在黏附中的作用，我们使用纯化的TSP进行了更多研究。在无血清培养基（SFM）中，TSP浓度为0.2μg/mL时，镰状红细胞与MEC的黏附为33.9±2.7个红细胞/mm2，比无TSP时镰状红细胞的黏附或有TSP时正常红细胞的黏附高6倍。将TSP浓度加倍至0.4μg/mL可使镰状红细胞的黏附成比例增加。用OKM5或抗αv单克隆抗体孵育MEC可使TSP介导的镰状红细胞黏附抑制超过95%。这些数据表明，激活的血小板释放包括α-颗粒TSP在内的因子，这些因子促进受体介导的镰状红细胞与微血管内皮的黏附。体内血小板激活过程中释放的此类因子可能通过促进红细胞黏附和微血管闭塞而导致血管闭塞性并发症。
