Agranulocytes - Monocytes

1. Agranulocytes have unsegmented nuclei and are described as mononuclear leukocytes. They lack specific granules, but may contain azurophilic granules (0.05-0.25 um in diameter). a. Lymphocytes constitute a diverse class of cells; they have similar morphologic characteristics but a variety of highly specific functions. They normally account for 20-25% of the white blood cells in adult blood, with a considerable range of normal variation (20-45%). They respond to invasion of the body by foreign substances and organisms and assist in their inactivation. Unlike other leukocytes, lymphocytes never become phagocytic. The 2 major functional classes of lymphocytes are T cells and B cells. Lymphocytes in the blood are predominantly (about 80%) T cells.

b. Monocytes are often confused with large lymphocytes. They are large and constitute only 3-8% of the white blood cells in healthy adults. Monocytes are found only in the blood, but they remain in circulation for less than a week before migrating through capillary walls to enter other tissues or to become incorporated in the lining of sinuses. Once outside the bloodstream, they become phagocytic and apparently do not recirculate. The mononuclear phagocyte system consists of monocyte-derived phagocytic cells distributed throughout the body. Examples include the Kupffer cells of the liver and some of the macrophages of connective tissues.