Inverse correlation between the presence of angiotensin-converting enzyme 2 autoantibodies and activity in vasculopathy patients. The relative (%) activity of serum angiotensin-converting enzyme (ACE) 2 compared with the reference value and ELISA score of the same sera were plotted in (a) 26 healthy subjects, (b) 16 patients without vasculopathy, and (c) 18 vasculopathy patients, respectively, and Pearson correlation coefficients were calculated. The relative ACE2 activities were determined based on a reference serum (mixed sera from healthy subjects). (d) Western blot analysis to detect ACE2 protein in serum. Immunoprecipitation followed by immunoblotting was performed on sera of healthy subjects (H1 to H3) and vasculopathy patients (P1 to P5). ACE2 was detected as a major band about 90 kDa in size (see also Additional file 3).