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

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: IgG(4) (52/58, 90%) was the most prevalent IgG subclass in patients with acquired TTP, followed by IgG(1) (52%), IgG(2) (50%), and IgG(3) (33%). IgG(4) was found either alone (17/52) or with other IgG subclasses (35/52). IgG(4) was not detected in 10% of the patients. There was an inverse correlation between the frequency and abundance of IgG(4) and IgG(1) antibodies (P < 0.01). Patients with high IgG(4) levels and undetectable IgG(1) are more prone to relapse than patients with low IgG(4) levels and detectable IgG(1). Conclusions: All IgG subclasses of anti-ADAMTS13 antibodies were detected in patients with acquired TTP, with IgG(4), followed by IgG(1), antibodies dominating the anti-ADAMTS13 immune response. Levels of IgG(4) could be useful for the identification of patients at risk of disease recurrence.