Inhibitory autoantibodies against ADAMTS-13 in patients with thrombotic thrombocytopenic purpura bind ADAMTS-13 protease and may accelerate its clearance in vivo.
BACKGROUND
Many patients with acquired thrombotic thrombocytopenic purpura (TTP) harbor autoantibodies that may bind and/or inhibit ADAMTS-13 proteolytic activity and accelerate its clearance in vivo.


METHODS
To test this hypothesis, we determined ADAMTS-13 activity and antigen levels in parallel plasma samples from patients clinically diagnosed with TTP. Collagen binding, GST-VWF73 and FRETS-VWF73 assays were used to determine ADAMTS-13 activity and to detect inhibitory autoantibodies. Enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation plus Western blotting (IP/WB) were used to detect total anti-ADAMTS-13 IgG (inhibitory and non-inhibitory).


RESULTS
Among 40 patients with TTP (21 idiopathic and 19 non-idiopathic), inhibitory autoantibodies were detected (by FRETS-VWF73) in 52% of idiopathic and 0% of non-idiopathic TTP patients. In contrast, non-inhibitory IgG autoantibodies were detected in 29% of idiopathic and 50% of non-idiopathic TTP patients. The concentration of inhibitory IgG autoantibody in idiopathic TTP patients was significantly higher than that of non-inhibitory IgG in either idiopathic or non-idiopathic TTP patients. Idiopathic TTP patients demonstrated significantly reduced ADAMTS-13 activity compared with non-idiopathic patients, but only slightly lower ADAMTS-13 antigen levels. Interestingly, patients with inhibitory autoantibodies exhibited significantly lower ADAMTS-13 antigen levels than those with only non-inhibitory IgG autoantibodies or no autoantibody. Serial plasma exchanges increased levels of ADAMTS-13 activity and antigen concurrently in patients with inhibitory autoantibodies.


CONCLUSIONS
The identification of severe ADAMTS-13 deficiency and autoantibodies or inhibitors appears to be assay-dependent; the inhibitory IgG autoantibodies, in addition to binding and inhibiting ADAMTS-13 proteolytic activity, may accelerate ADAMTS-13 clearance in vivo.
Shelat
S G
SG
Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, PA 19104, USA.
Smith
P
P
Ai
J
J
Zheng
X L
XL
D051722:ADAM Proteins / Q000737:chemistry* / Q000276:immunology; D000071120:ADAMTS13 Protein; D000328:Adult; D001323:Autoantibodies / Q000737:chemistry*; D001327:Autoimmune Diseases / Q000097:blood; D002648:Child; D004797:Enzyme-Linked Immunosorbent Assay; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry; D008875:Middle Aged; D011485:Protein Binding; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood* / Q000196:embryology*; D013927:Thrombosis / Q000473:pathology; D019699:Thrombospondins / Q000737:chemistry; D014841:von Willebrand Factor / Q000096:biosynthesis
D001323:Autoantibodies; D007074:Immunoglobulin G; D019699:Thrombospondins; D014841:von Willebrand Factor; D005982:Glutathione Transferase; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human