MPO and vasculitis: As S. aureus infections can precede the development of MPO-AAV20–22, they are related to an overlapping form of vasculitis (PR3-AAV)14,29 and nasal colonization of S. aureus has been found in people with MPO-AAV19 we identified a S. aureus-derived peptide with sequence homology to human MPO441–451 by protein BLAST.