Monocyte

a leukocyte, part of the human body's immune system that protects against blood-borne pathogens and moves quickly (aproximately 8–12 hours) to sites of infection in the tissues

Description
Monocytes are usually identified in stained smears by their large bi-lobed nucleus. A relatively large mononuclear leukocyte (16–22 &micro;m in diameter), that normally constitutes 3–7% of the leukocytes of the circulating blood, and is usually found in lymph nodes, spleen, bone marrow, and loose connective tissue. When treated with the usual dyes, monocytes manifest an abundant pale blue or blue-gray cytoplasm that contains numerous, fine, dust-like, red-blue granules; vacuoles are frequently present; the nucleus is usually indented, or slightly folded, and has a stringy chromatin structure that seems more condensed where the delicate strands are in contact. See also monocytoid cell, endothelial leukocyte