Myeloperoxidase deficiency is a disorder featuring lack in either the quantity or the function of myeloperoxidase–an iron-containing protein expressed primarily in neutrophil granules. There are two types of myeloperoxidase deficiency: primary/inherited and secondary/acquired. Lack of functional myeloperoxidase leads to less efficient killing of intracellular pathogens, particularly Candida albicans, as well as less efficient production and release of neutrophil extracellular traps (NETs) from the neutrophils to trap and kill extracellular pathogens.
The majority of myeloperoxidase-deficient individuals, however, do not display any significant tendencies towards chronic infections from most bacteria. Specific stains bind to myeloperoxidase, and individuals who display large, granulated cells without this stain through flow cytometry typically have myeloperoxidase deficiency. In this way, it's apparent when neutrophils are present in an individual but peroxidase activity is absent. Both disorders interfere with neutrophils' abilities to kill pathogens through reaction with oxidative species. However, chronic granulomatous disease leads to inadequate H<sub>2</sub>O<sub>2</sub> production, while myeloperoxidase deficiency is characterized by a lack of myeloperoxidase to interact with present H<sub>2</sub>O<sub>2</sub>. Continued antibiotic use is not recommended in myeloperoxidase-deficient patients who don't experience recurrent infections.