Leukocyte - definition and function

A white BLOOD cell, also referred to as a WBC. Leukocytes are the foundation of the body’s IMMUNE RESPONSE and are phagocytic-that is, they have the ability to consume other cells. They circulate in the blood and the LYMPH as well as reside in tissues throughout the body. There are three basic types of leukocytes: granulocytes, monocytes, and lymphocytes. Each type has several subtypes. The SPLEEN and lymph tissues produce monocytes and lymphocytes; the red BONE MARROW produces granulocytes.

A healthy adult has between 5,000 and 10,000 leukocytes per microliter of blood, with granulocytes accounting for about 70 percent. Increases in certain subtypes of leukocytes suggest particular health conditions. A substantial increase overall in LEUKOCYTE count may indicate a cancer of the bone marrow such as LEUKEMIA or LYMPHOMA. The ratio between erythrocytes (red blood cells) and leukocytes in the blood is also an important diagnostic indicator.

For further discussion of leukocytes within the context of blood and lymph structure and function please see the overview section “The Blood and Lymph.”

See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND FUNCTION; ERYTHROCYTE; HEMATOPOIESIS; PHAGOCYTOSIS; PLASMA; PLATELET; SIDE EFFECT; THYMUS.

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