leucocyte (white blood cell) A colourless cell with a nucleus, found in blood and lymph. Leucocytes are formed in lymph nodes and red bone marrow and are capable of amoeboid movement. They can produce antibodies and move through the walls of vessels to migrate to the sites of injuries, where they surround and isolate dead tissue, foreign bodies, and bacteria. There are two major types: those without granules in the cytoplasm, such as lymphocytes and monocytes (see agranulocyte), and those with granular cytoplasm (granulocytes), which include basophils, eosinophils, and neutrophils.

leucocyte (white blood cell) Colourless structure containing a nucleus and cytoplasm. There are two types of leucocytes – lymphocytes and phagocytes. Normal blood contains 5000–10,000 leucocytes per cu mm. Excessive numbers of leucocytes are seen in such diseases as leukaemia. See also antibody; immune system

leucocyte A white blood cell, present in invertebrate and vertebrate animals. There are three types: lymphocytes, amoeboid, non-phagocytic cells that produce or convey antibodies; monocytes, phagocytic cells that ingest invading organisms, sometimes entering tissue to do so; and polymorphs (polymorphonuclear leucocytes, or granulocytes), also phagocytic cells, with granular cytoplasm and lobed nuclei.

leucocyte (white blood cell, WBC) (loo-kŏ-syt) n. any blood cell that contains a nucleus. In health there are three major subdivisions: granulocytes, lymphocytes, and monocytes, which are involved in protecting the body against foreign substances and in antibody production. In disease, a variety of other types may appear in the blood.