ADAMTS13 and thrombotic thrombocytopenic purpura: Regarding the increase of the inhibitory potential of anti-ADAMTS13 antibodies parallel to the switch to IgG4-dominance prior to a relapse, this finding suggests that, because of the stronger inhibitory capacity of autoantibodies, lower IgG concentrations may be sufficient to cause severe ADAMTS13 deficiency resulting in increased risk of a TTP episode.