ADAMTS-13 plasma level determination uncovers antigen absence in acquired thrombotic thrombocytopenic purpura and ethnic differences.
BACKGROUND
The recently discovered plasma enzyme ADAMTS-13 cleaves the A2-domain of von Willebrand factor (VWF). A defective cleaving protease results in unusually large VWF multimers, which cause thrombotic thrombocytopenic purpura (TTP).


OBJECTIVE
Analysis of the ADAMTS-13 antigen levels in TTP patients compared with normal donors.


METHODS
An antigen ELISA test was built, based on high affinity anti-ADAMTS-13 monoclonal antibodies, which were generated using genetic immunization.


RESULTS
Specificity of the ADAMTS-13 antigen test was confirmed, as (i) plasma from a patient with acquired TTP but presenting without inhibitor did not contain antigen and (ii) the binding of recombinant ADAMTS-13 was inhibited by increasing amounts of normal plasma. The assay is sensitive as it can detect antigen levels as low as 1.6% of normal. The concentration in normal pooled human plasma was determined (1.03 +/- 0.15 microg mL(-1)) and arbitrarily set to 1 U mL(-1). The antigen levels in congenital TTP samples (34 +/- 21 mU mL(-1), n = 2), as well as in samples from patients with acquired TTP (231 +/- 287 mU mL(-1), n = 11), were clearly reduced when compared with normal Caucasian donors (951 +/- 206 mU mL(-1), n = 16). Remarkably, normal Chinese donors have a significantly lower antigen titer (601 +/- 129 mU mL(-1), n = 15), when compared with normal Caucasians.


CONCLUSIONS
Our results show that acquired TTP patients suffer mainly from ADAMTS-13 antigen depletion, thereby indicating the importance of ADAMTS-13 antigen determination in diagnosis and patient follow-up.
Feys
H B
HB
Laboratory for Thrombosis Research, IRC, K.U. Leuven Campus Kortrijk, E. Sabbelaan 53, 8500 Kortrijk, Belgium.
Liu
F
F
Dong
N
N
Pareyn
I
I
Vauterin
S
S
Vandeputte
N
N
Noppe
W
W
Ruan
C
C
Deckmyn
H
H
Vanhoorelbeke
K
K
D051722:ADAM Proteins / Q000097:blood*; D000071120:ADAMTS13 Protein; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D000941:Antigens / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D005006:Ethnicity; D006801:Humans; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood / Q000208:ethnology / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000941:Antigens; D001323:Autoantibodies; D017931:DNA Primers; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human