Epitope mapping of ADAMTS13 autoantibodies in acquired thrombotic thrombocytopenic purpura

can lead to thrombotic thrombocytopenic purpura (TTP), a disease associated with the widespread formation of platelet-rich thrombi in many organs. Autoantibodies that inactivate ADAMTS13 are the most frequent cause of acquired TTP. Little is known about epitope specificity and reac-tivity of anti-ADAMTS13 antibodies. In this study, a series of ADAMTS13 do-mains were expressed in Escherichia coli, and the reactivity of purified recombinant fragments with anti-ADAMTS13 auto-antibodies from 25 patients with severe ADAMTS13 deficiency was evaluated in vitro. All TTP plasmas contained antibod-ies directed against the cysteine-rich spacer (cys-rich/spacer) domain of ADAMTS13. In the plasma of 3 patients, antibodies were detected that reacted exclusively with the cys-rich/spacer domain, underscoring the importance of this region for functional activity of ADAMTS13. In 64 % of the plas-mas, antibodies reacted with the 2 CUB domains, and in 56 % they reacted with the isolated first thrombospondin type 1 (TSP-1) repeat and with the compound fragment consisting of the catalytic, the disintegrin-like, and the TSP1-1 domain. Less frequently, in 28 % of the plasmas, antibodies reacted with the TSP1 repeats 2 to 8. Unexpectedly, antibodies reacted with the propeptide region in 20 % of the plasmas. In conclusion, this study shows that even though anti-ADAMTS13 autoan-tibodies react with multiple domains of the protease, the cys-rich/spacer domain is consistently involved in antibody reac-tivity. (Blood. 2004;103:4514-4519) © 2004 by The American Society of Hematolog