Granulocytes, or polymorphonuclear leukocytes, are a subgroup of white blood cells characterized by the presence of cytoplasmic granules. Granulocytes are formed in the bone marrow and can be classified as basophils, esinophils, and neutrophils. The cell types are named by their distinct staining characteristics using hematoxylin and eosin (H&E) histological preparations. Granules in basophils stain dark blue, eosinophilic components stain bright red, and neutrophilic components stain a neutral pink.