Clark W F, Tevaarwerk G J, Reid B D, Hall S, Caveney A, Parbtani A, Kreeft J
Department of Medicine, Victoria Hospital, London, Ontario, Canada.
Thromb Haemost. 1987 Jun 3;57(3):298-301.
We have described the calcium dependence of the IgG Fc receptor (Fc-R) on human platelets by analyzing the direct binding of radiolabelled Fc fragments, monomers and dimers of IgG. Specific binding to platelets was undetectable at 37 degrees C in a calcium-free preparation but readily detected when calcium was restored. Scatchard analysis of the binding data for the calcium-restored platelets permitted calculation of the available Fc-R and the Ka of binding for the different IgG ligands. The mean Ka of binding for 12 normal subjects varied from 10(7) to 10(8) L/M, with an equal receptor number measured by Fc fragments and dimers of IgG, but a lesser amount for monomeric IgG. There was no apparent difference in Fc-R number for platelets from 6 normal male versus 6 normal female subjects. At 4 degrees C binding was detectable for dimers and polymers of IgG in a calcium-free preparation and this was markedly increased with recalcification. Thus, our data are consistent with an Fc receptor population on human platelets whose avidity for binding is significantly enhanced in a calcium-restored medium.
我们通过分析放射性标记的IgG Fc片段、单体和二聚体的直接结合情况，描述了人血小板上IgG Fc受体（Fc-R）对钙的依赖性。在无钙制剂中，37℃时未检测到与血小板的特异性结合，但恢复钙后则易于检测到。对恢复钙后的血小板结合数据进行Scatchard分析，可计算出不同IgG配体的可用Fc-R和结合的解离常数（Ka）。12名正常受试者的平均结合Ka在10⁷至10⁸L/M之间，通过Fc片段和IgG二聚体测得的受体数量相等，但单体IgG的受体数量较少。6名正常男性与6名正常女性受试者的血小板Fc-R数量没有明显差异。在4℃时，无钙制剂中可检测到IgG二聚体和聚合物的结合，重新添加钙后结合显著增加。因此，我们的数据与人类血小板上的Fc受体群体一致，其在恢复钙的培养基中结合亲和力显著增强。
