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IgG subclass distribution of anti‐ADAMTS13 antibodies in patients with acquired thrombotic thrombocytopenic purpura

Summary.  Background: ADAMTS13‐neutralizing IgG autoantibodies are the major cause of acquired thrombotic thrombocytopenic purpura (TTP). Objective: To analyze the IgG subclass distribution of anti‐ADAMTS13 antibodies and a potential relationship between subclass distribution and disease prognosis. Methodology: An enzyme‐linked immunosorbent assay‐based method was used to quantify the relative amounts of IgG subclasses of anti‐ADAMTS13 antibodies in acquired TTP plasma. Results: IgG4 (52/58, 90%) was the most prevalent IgG subclass in patients with acquired TTP, followed by IgG1 (52%), IgG2 (50%), and IgG3 (33%). IgG4 was found either alone (17/52) or with other IgG subclasses (35/52). IgG4 was not detected in 10% of the patients. There was an inverse correlation between the frequency and abundance of IgG4 and IgG1 antibodies (P < 0.01). Patients with high IgG4 levels and undetectable IgG1 are more prone to relapse than patients with low IgG4 levels and detectable IgG1. Conclusions: All IgG subclasses of anti‐ADAMTS13 antibodies were detected in patients with acquired TTP, with IgG4, followed by IgG1, antibodies dominating the anti‐ADAMTS13 immune response. Levels of IgG4 could be useful for the identification of patients at risk of disease recurrence.