ADAMTS13 and thrombotic thrombocytopenic purpura: A defective regulation of T-reg and tolerogenic dendritic cells may be responsible for the occurrence of anti-ADAMTS13 antibodies, in analogy with what has been shown in other autoimmune coagulation inhibitors, such as anti-FVIII antibodies.122 HIV infection may also be a risk factor for TTP, although this association has not been confirmed by all Authors.123 The inhibitors are more frequently IgG, although occasional production of IgA and IgM antibodies has been described.