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.