Monocyte

From Freepedia

A monocyte is a leukocyte, part of the human body's immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. It is one of the 5 major types of white blood cell, based on the appearance of white blood cells in stained smears as viewed under a light microscope. Monocytes are 12 to 20 micrometers in diameter. On a Wright's stained peripheral blood smear they appear larger than red blood cells and have a bluish-grey cytoplasm with a large cytoplasm to nucleus ratio. Monocytes are typically identified by flow cytometry by surface expression of the protein CD14, a receptor for bacterial endotoxin that gives rise to septicaemia.

Monocytes are produced by the bone marrow from haematopoietic stem cell precursors, circulate in the blood stream for about one to three days and then typically move into tissues throughout the body. In the tissues monocytes mature into different types of macrophages at different anatomical locations.

Monocytes are responsible for phagocytosis, or digestion, of foreign substances in the body. Monocytes can perform phagocytosis using intermediary (opsonising) protiens such as antibodies or complement that coat the pathogen, as well as by binding to the microbe directly via pathogen-recognition receptors. Monocytes are also capable of killing infected host cells via antibody, termed antibody-mediated cellular cytotoxicity. Vacuolization may be present in a cell that has recently phagocytized foreign matter.

Monocytes which migrate from the blood stream to other tissues are called macrophages. Macrophages are responsible for protecting tissues from foreign substances but are also the predominant cells involved in atherosclerosis.

A monocyte count is part of a complete blood cell count and is expressed as a ratio of monocytes to the total number of white blood cells counted.

Cardiovascular system - Blood

Red blood cells - White blood cells - Platelets - Blood plasma

White blood cells

Granulocytes (Neutrophil granulocytes, Eosinophil granulocytes, Basophil granulocytes) - Lymphocytes - Monocytes

Coagulation