However, MPO can be found in some macrophage subpopulations including resident tissue macrophages such as Kupffer cells [9], peritoneal macrophages [10], and microglia [11], as well as in organ infiltrating macrophages in various inflammatory diseases including atherosclerosis [12], multiple sclerosis (MS) [13], and AAV [14]. Here, MPO is linked to myeloid sarcoma.