Classification of granules in neutrophils. Peroxidase-positive (azurophilic or primary) granules are characterized by the content of MPO and may be further divided based on their content of defensins into large, defensin-rich granules and the smaller defensin-poor granules. The peroxidase-negative granules may be divided into specific (secondary) granules and gelatinase (tertiary) granules on the basis of their relative content of lactoferrin and gelatinase. All granules contain lysozyme. Secretory vesicles share some of their membrane proteins with peroxidase-negative granules, whereas others are unique to secretory vesicles. Def., defensins; Gela., gelatinase; Tert., tertiary.