Autoantibodies to ADAMTS13 in human immunodeficiency virus‐associated thrombotic thrombocytopenic purpura

Background and ObjectivesThrombotic thrombocytopenic purpura (TTP) is a potentially fatal thrombotic microangiopathic disorder that can result from human immunodeficiency virus (HIV) infection. The pathogenesis involves a deficiency of the von Willebrand factor (vWF) cleaving protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin motifs member 13) and the presence of anti‐ADAMTS13 autoantibodies. However, there is insufficient information regarding the epitope specificity and reactivity of these autoantibodies. This study aimed to perform epitope‐mapping analysis to provide novel insights into the specific epitopes on ADAMTS13 domains affected by autoantibodies.Materials and MethodsThe study analysed 59 frozen citrate plasma samples from HIV‐associated TTP patients in South Africa, measuring ADAMTS13 activity using Technozyme® ADAMTS13 activity test, total immunoglobulin (Ig) M and IgA antibodies levels using ELISA kit and purifying IgG antibodies using NAb™ Protein G spin columns. A synthetic ADAMTS13 peptide library was used for epitope mapping.ResultsOverall, 90% of samples showed anti‐ADAMTS13 IgG autoantibodies, with 64% of these antibodies being inhibitory, as revealed by mixing studies. Samples with ADAMTS13 antigen levels below 5% showed high anti‐ADAMTS13 IgG autoantibody titres (≥50 IU/mL), whereas those with 5%–10% levels had low autoantibody titres (<50 IU/mL).The metalloprotease, cysteine‐rich and spacer domains were 100% involved in binding anti‐ADAMTS13 IgG antibodies, with 58% of samples containing antibodies binding to the C‐terminal part of the ADAMTS13 disintegrin‐like domain, indicating different pathogenic mechanisms.ConclusionThe metalloprotease, cysteine‐rich and spacer domains are the primary targets for anti‐ADAMTS13 IgG autoantibodies in patients with HIV‐associated TTP. These findings suggest potential effects on the proteolytic activity of ADAMTS13, highlighting the complex nature of the pathogenic mechanisms involved.