ABSTRACT
Objective This study is aimed at determining whether anti-von Willebrand factor (VWF) autoantibodies are present in the plasma of idiopathic thrombotic thrombocytopenic purpura (TTP) patients with normal ADAMTS13 activity and undetectable anti-ADAMTS13 antibodies,and at examining whether murine monoclonal antibodies (mAbs) against human VWF decrease the susceptibility of VWF to ADAMTS13 in vitro.Methods Anti-VWF autoantibodies and ultralarge VWF (UL-VWF) multimers were measured in plasma samples of 53 adult patients with idiopathic TTP by enzyme-linked immunosorbent assay and sodium dodecylsulphate-agarose gel electrophoresis,respectively.Moreover,the effects of eight murine mAbs to different human VWF domains on VWF cleavage by ADAMTS13 were evaluated under fluid shear stress and static/denaturing conditions,respectively.Results Anti-VWF antibodies and UL-VWF multimers were detected in two TTP patients with normal ADAMTS13 activity and undetectable anti-ADAMTS13antibodies.The SZ34,an anti-VWF mAb,inhibited VWF proteolysis mediated by ADAMTS13 under flow,but not static conditions.Conclusion Anti-VWF antibody may be one of the causes of idiopathic TTP with normal ADAMTS13 activity and undetectable anti-ADAMTS13 antibodies.
ABSTRACT
This study was to acquire recombinant protein of von Willebrand factor cleaving protease (ADAMTS13, a disintegrin and metalloprotease with a thromboSpondin type 1 motifs 13), for further studies on its biological function in thrombosis and hemostasis. We transfected the Hela cells with the plasmid pSecTag-ADAMTS13 by lipofectamine. A positive cell cloning was selected by hygromycin-B. The recombinant protein was purified with Ni-NTA agarose column by gradient imidazole. The purity and immune activity of purified products were identified with SDS-PAGE and Western blotting respectively. We also measured the enzymatic activity of recombinant protein (rADAMTS13) by GST-His two-site ELISA assay. The results showed that we successfully constructed Hela cells ADAMTS2-4 which expressed high level of rADAMTS13. We received about 5.8 mg recombinant protein in culture supernantants per liter purified with Ni-NTA column. The protein formed a main lane at the position of 190 kDa with SDS-PAGE and reacted with polyclonal antibody against ADAMTS13 by Western blotting. The amount of rADAMTS13 activity was 6.4 U/mL, according to the normal plasma defined as 1 U/mL. In conclusion, rADAMTS13 protein had high purity, immune activity and good enzymatic activity, which could establish the experimental foundation for further research on biological function and mechanism of this unique metalloprotease.