Inhibition of angiotensin-converting enzyme 2 activity by IgG purified from patient serum. (a) Purified IgG from the sera of healthy volunteers (H1 to H3) and patients with vasculopathy (P1, P5, and P6) was detected by SDS-PAGE and Coomassie Brilliant Blue staining. The molecular weights of the heavy (50 kDa) and light (25 kDa) chains of IgG are shown. (b) The inhibition of angiotensin-converting enzyme (ACE) 2 activity by 5 μg purified IgG was examined in triplicate assays. As a control, ACE2 activity in standard rACE2 was measured in the absence of IgG. As shown, ACE2 activity was significantly reduced when the recombinant enzyme was co-incubated with IgG from the patients. P < 0.01. RFU, relative fluorescence unit.