A type of immune cell that has granules (small particles) with enzymes that are released during infections, allergic reactions, and asthma. Neutrophils, eosinophils, and basophils are PMNs. A PMN is a type of white blood cell. Also called granular leukocyte, granulocyte, and polymorphonuclear leukocyte.

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Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.