Granulocyte: A type of white blood cell that is filled with microscopic granules, little sacs containing enzymes that digest microorganisms. Granulocytes are part of the innate immune system, and they have somewhat nonspecific, broad-based activity. They do not respond exclusively to specific antigens, as do B-cells and T-cells. Neutrophils, eosinophils, and basophils are all types of granulocytes, and their names are derived from the staining features of their granules in the laboratory, a naming scheme that dates back to a time when certain structures could be identified in cells by histochemistry, but the functions of these intracellular structures were still not known.
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