Granular leukocytes are a type of white blood cell that contain tiny sacs filled with enzymes designed to break down microorganisms. Also known as granulocytes, they belong to the innate immune system and possess a broad, non-specific activity, unlike B-cells and T-cells that target specific antigens. Granulocytes include neutrophils, eosinophils, and basophils, each named according to how their granules stain in laboratory tests. Neutrophils have granules that show "neutral" staining, eosinophils contain granules that easily stain with the acid dye eosin, and basophils have granules that take up basic dyes. This method of classification dates back to a time when cellular structures were identified through histochemistry, even though their functions were not fully understood. Despite this, classifying granulocytes as neutrophils, eosinophils, and basophils remains both prevalent and practical today.
