Definition: a polymorphonuclear leukocyte characterized by the presence of numerous large, coarse, metachromatic granules (dark purple or blue-black when treated with Wright or similar stains) that usually fill the cytoplasm and may almost mask the nucleus; these leukocytes are unique in that they do not usually occur in increased numbers as the result of infectious disease, and their phagocytic qualities are probably not significant; the granules, which contain numerous primary mediators, including heparin and histamine, may degranulate in response to hypersensitivity reactions and can be of significance in general inflammation; leukocytes can also synthesize and release, ab ovo, secondary mediators from arachidonic acid precursors in their membranes.
See Also: mast cell
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