AutoAbs to nuclear and other self-antigens deposit in and damage kidneys or bind to and deplete blood cells in SLE (8–10); IgG reacting with type II collagen, citrullinated proteins, and Ig itself (rheumatoid factor) destroys peripheral joints in RA (11); IgG bound to neutrophil myeloperoxidase and proteinase3 triggers small blood vessel injury in ANCA vasculitis (12, 13); and antibodies to nuclear antigens and cell membrane receptors facilitate skin and organ fibrosis in SSC (14–16). Here, MPO is linked to systemic lupus erythematosus.