Expression of factor VIII activity in the presertce of anti-factor VIII inhibitor antibodies

使用凝块波形分析和凝血酶生成试验研究了在存在和-FVIII抗体的情况下因子VIII（FVIII）：C的表达。使用了7种同种抗体和4种抗人FVIII的单克隆抗体。前者包含3个识别重链A2结构域的同种抗体和4个识别轻链C2结构域的同种抗体。后者包含识别A1和A2结构域的单克隆抗体，以及识别C2结构域的2个单克隆抗体。将10或20个Bethesda单位（BU）/ml用FVIII缺乏血浆稀释的抑制剂IgG与正常血浆混合。孵育后随时间取出混合物，然后测定最大凝血加速（|Min2|）和FVIII：C。此外，在凝血酶生成测定系统上测量峰高和内源性凝血酶电位（ETP）。在存在最终浓度超过5 BU/ml抑制剂的情况下，低水平的FVIII：C和|Min2|甚至在孵育120分钟后也能检测到。特别是在识别重链A2结构域的同种抗体和单克隆抗体中检测到低水平的FVIII：C。类似地，在大多数情况下，即使在20 BU/ml抑制剂的存在下，也检测到少量凝血酶产生，特别是在识别A2结构域的抗体中，而不是在识别C2的抗体中。这些结果表明，在存在高滴度抑制剂的情况下，FVIII：C的表达水平较低，并证实了定期输注FVIII浓缩物对血友病和抑制剂患者的预防作用。

The expression of factor VIII (FVIII) : C in the presence of and-FVIII antibodies was studied using clot waveform analysis and thrombin generation test. Seven kinds of alloantibodies and 4 kinds of monoclonal antibodies against human FVIII were used. The former contains 3 alloantibodies recognizing A2 domain in the heavy chain and 4 alloantibodies recognizing C2 domain in the light chain. The latter contains each monoclonal antibody recognizing A1 and A2 domain, and 2 monoclonal antibodies recognizing C2 domain. Ten or twenty Bethesda units (BU) /ml of inhibitor IgG diluted with FVIII deficient plasma were mixed with normal plasma. The mixture was removed after incubation with time, and then maximum coagulation acceleration (| Min2 |) and FVIII : C were measured by MDAII. Moreover, both Peak Height and Endogenous Thrombin Potential (ETP) were measured on thrombin generation assay system. In the presence of final concentration of over 5 BU/ml inhibitors, low levels of FVIII : C and | Min2 | were detected even after 120 min incubation. Especially, the low levels of FVIII : C were detected in the alloantibodies and monoclonal antibody recognizing A2 domain in the heavy chain. Similarly, in most cases, small amount of thrombin generation was detected even in the presence of 20 BU/ml of inhibitors, especially in the antibodies recognizing A2 domain rather than C2-recognized antibodies. These findings indicate the expression of low levels of FVIII : C in the presence of high titer inhibitor, and confirm the prophylactic effect during regular infusions of FVIII concentrates for patients with hemophilia and inhibitors.