蛇毒Botrocetinで発現されるvon Willebrand因子活性に関する研究 ： Ⅱ.von Willebrand病各病型におけるBotrocetin cofactor活性測定の検討

Abstract

Recently I have established an assay for the snake venom coaggulutinin activity of platelets (botrocetin cofactor : Bcof) that is specifically dependent on the amount of plasma von Willebrand factor (vWF), and suggested that this assay can be used as an alternative diagnostic method for von Willebrand disease (vWD). In this study, I have measured Bcof in a total of 50 plasmas from patients with hemophilia A and 45 plasmas from those with vWD. Next, vWF in patient plasmas with vWD was indirectly radiolabeled by [¹²⁵Ⅰ] anti-vWF monoclonal antibody designated as 2.2.9 to evaluate botrocetin-mediated binding ability to platelet glycoprotein Ⅰb (GPⅠb). The result of this assay was compared with that of the previous assay using antibiotic ristocetin, which also mediates the interaction between vWF and GPⅠb. In hemophilia A, Bcof was significantly higher (152.5±108%) than normal and showed a good correlation to vWF antigen (vWF : Ag) or ristocetin cofactor (Rcof) (vWF : Ag/Bcof r= 0.93, Rcof/Bcof r=0.92). In vWD patients, the levels of Bcof were significantly lower than normal, usually less than 47%. In 23 cases of Type Ⅰ vWD, Bcof ranged from below 5% to 47%. In vWD patients with Type ⅡA (8 cases), ⅡC (3 cases) and ⅡF (1 case), Bcof levels were moderately decreased, ranging from below 5% to 30% but higher than Rcof. In Type ⅡB (3 cases), ⅡD (2 cases) and ⅡE (2 cases), Bcof showed a parallel decrease (24%-40%) with Rcof. Indirectly radiolabeled vWF in all patient plasmas except for Type ⅡB showed more decreased binding than normal, in good accord with Bcof. In Type ⅡB, both the ristocetin and botrocetin mediated vWF binding abilitity were enhanced (120-140%). In Types ⅡA, ⅡC and ⅡF, botrocetin-mediated binding ability was distributed from 30% to 60%, whereas ristocetin-mediated binding abilities stayed within 5%-10%.