Medical Definition of Granular leukocyte

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Granular leukocyte: A type of white blood cell filled with microscopic granules (tiny sacs) containing enzymes that digest microorganisms.

Granular leukocytes -- they are better known as granulocytes -- are part of the innate immune system and have somewhat non specific, 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. They are named by the staining features of their granules in the laboratory:

  • Neutrophils have "neutral" subtle granules;
  • Eosinophils have prominent granules that stain readily with the acid dye eosin; and
  • Basophils have prominent granules that stain readily basic (non acidic) dyes.

This classification 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 yet fathomed. However, the classification of granulocytes into neutrophils, eosinophils and basophils is still widely used (and quite useful).

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Reviewed on 12/27/2018

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