ADAMTS13 and thrombotic thrombocytopenic purpura: A recent study showed that while IgG switching to IgG4 subclass is a protective mechanism in IgG4-mediated autoimmune diseases with anti-ADAMTS13 autoantibodies (TTP; thrombotic thrombocytopenic purpura), this is not relevant for Pemphigus foliaceus (PF) in which anti-Dsg1 (desmoglein-1) IgG4 subclass exacerbates the pathogenicity in anti-Dsg1 autoantibodies (210).