azurophil

Azurophil is a term used in hematology to describe structures or cells that stain with azure dyes. It is most commonly applied to azurophilic granules found in neutrophils, known as primary granules, and, by extension, to the neutrophil lineage when emphasizing these granules.

Azurophilic (primary) granules are large, dense cytoplasmic organelles formed early in granulopoiesis, during the promyelocyte stage. Their contents include enzymes and antimicrobial proteins such as myeloperoxidase, defensins, lysozyme, and various acid hydrolases. These granules are released during degranulation and contribute to the microbicidal capacity of neutrophils, including activity within phagosomes and in extracellular traps.

In ordinary light microscopy, azurophilic granules stain dark blue to purple with routine Wright-Giemsa staining, giving neutrophils a characteristic dense cytoplasmic appearance. They are distinguished from smaller, secondary (specific) granules that appear later in development and have a somewhat different chemical composition and staining profile.

Clinical and research notes emphasize that azurophils are a feature of neutrophil lineage and play a key role in innate immunity. While the term has historical usage and may appear in older literature to describe granules or cells that strongly stain with azure dyes, contemporary descriptions usually frame azurophils within the context of neutrophil biology and granulocyte maturation.