MPO and immune system disorder: This function requires recruitment via chemokines to extravascular sites of infection where neutrophils rapidly contain bacterial and fungal proliferation by phagocytosis and the secretion of cytoplasmic granules packed with potent antimicrobial agents, including myeloperoxidase (MPO), lysozyme, and defensins.1 In keeping with this critical function, disorders associated with reduced neutrophil number and/or function are associated with immunodeficiency.