Bethesda Assay for Detecting Inhibitory Anti-ADAMTS13 Antibodies in Immune-Mediated Thrombotic Thrombocytopenic Purpura.

Chiara Vendramin,Marie Scully,John-Paul Westwood,Mari Thomas

doi:10.1055/s-0038-1672187

Chiara Vendramin, Marie Scully + Show 2 more

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https://doi.org/10.1055/s-0038-1672187

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Abstract

A diagnosis of thrombotic thrombocytopenic purpura (TTP) is confirmed by a severe deficiency (<10%) of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity. Autoantibodies to ADAMTS13 can be detected with a simplified enzyme-linked immunosorbent assay (ELISA). An alternative methodology is a Bethesda assay, which has never been formally assessed in TTP. This study aimed to investigate the inhibitory anti-ADAMTS13 antibody assay and determine if the Bethesda assay is advantageous compared with the ELISA, measuring total immunoglobulin G (IgG) antibodies to ADAMTS 13. The Bethesda method determines the neutralizing activity of anti-ADAMTS13 antibodies in pooled normal plasma. We selected six immune-mediated TTP (iTTP) patients with ADAMTS13 activity levels <10% and strong ADAMTS13 inhibitors by 50:50 mixing studies and analyzed anti-ADAMTS13 antibodies using the Bethesda and ELISA assays. ADAMTS13 activity was stable at room temperature, while a time-dependent decrease in activity was detected in assay conditions of 37°C. Adding 5 mM Ca 2+ to citrated plasma prevented loss of ADAMTS13 activity with time. There was time dependence to the antibody-mediated inactivation, after 2-hour incubation. Two of the iTTP patients had no detectable ADAMTS13 antibodies by the Bethesda assay, but had high titer of anti-ADAMTS13 antibodies and low ADAMTS13 antigen levels. The Bethesda assay can only detect anti-ADAMTS13 antibodies that functionally inhibit ADAMTS13. The anti-ADAMTS13 IgG ELISA instead allows the rapid identification of total IgG autoantibodies, detecting both inhibitory and noninhibitory antibodies.

Highlights

Thrombotic thrombocytopenic purpura (TTP) is a critical lifethreating disorder
Stability of ADAMTS13 Activity in Human Plasma A time-dependent decrease of ADAMTS13 activity in pooled normal plasma (PNP) reference plasma was observed at 37°C after 60 minutes, while ADAMTS13 proved stable at room temperature (►Fig. 1A)
We hypothesized that the time-dependent decrease of ADAMTS13 activity in PNP reference plasma observed at 37°C could have been caused by proteolytic degradation; we incubated samples for 5 to 10 minutes, respectively, with 300 mg/L dabigatran, or 1 mM Pefabloc, or 1 g/L tranexamic acid, before the following incubation step at 37°C

Summary

Introduction

Thrombotic thrombocytopenic purpura (TTP) is a critical lifethreating disorder. It is a thrombotic microangiopathy clinically characterized by microangiopathic hemolytic anemia and thrombocytopenia, and involves capillary and small vessel platelet aggregates. A diagnosis of TTP is confirmed by a severe deficiency (

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