leukocyte /lo̅o̅″kəsīt/ [Gk, leukos + kytos, cell] , a blood cell that participates in immunity and inflammation. Five categories of leukocytes are classified by nuclear appearance and the presence or absence of granules in the cytoplasm. Lymphocytes have no granules or a few scattered azurophilic granules. The granulocytes are monocytes, neutrophils, basophils, and eosinophils. White cells are able to pass through endothelial gap junctions by diapedesis and migrate by ameboid movements. Leukocytes measure 8 to 20 μm in diameter. Normal WBC counts vary from 4500 to 11,500 leukocytes per μL. Leukocytes function as phagocytes of bacteria, fungi, and viruses; detoxifiers of proteins that may result from allergic reactions and cellular injury; and immune system cells. Also called white blood cell, white corpuscle. Also spelled leucocyte. Compare erythrocyte, platelets. See also complete blood count, differential white blood cell count, leukocytosis, leukopenia. −leukocytic, adj.
