Leucocyte Health Dictionary

See HLA SYSTEM.... human leucocyte antigen (hla)

The scienti?c name for white blood cells. Leucocytes contain no HAEMOGLOBIN so are colourless, and have a well-formed NUCLEUS. Healthy people have around 8,000 leucocytes per cubic millimetre of blood. There are three main classes of white cells: granulocytes, lymphocytes and monocytes.

Granulocytes Also known as polymorphonuclear leucocytes (‘polys’), these normally constitute 70 per cent of the white blood cells. They are divided into three groups according to the staining reactions of these granules: neutrophils, which stain with neutral dyes and constitute 65–70 per cent of all the white blood cells; eosinophils, which stain with acid dyes (e.g. eosin) and constitute 3–4 per cent of the total white blood cells; and basophils, which stain with basic dyes (e.g. methylene blue) and constitute about 0·5 per cent of the total white blood cells.

Lymphocytes constitute 25–30 per cent of the white blood cells. They have a clear, non-granular cytoplasm and a relatively large nucleus which is only slightly indented. They are divided into two groups: small lymphocytes, which are slightly larger than erythrocytes (about 8 micrometres in diameter); and large lymphocytes, which are about 12 micrometres in diameter.

Monocytes Motile phagocytic cells that circulate in the blood and migrate into the tissues, where they develop into various forms of MACROPHAGE such as tissue macrophages and KUPFFER CELLS.

Site of origin The granulocytes are formed in the red BONE MARROW. The lymphocytes are formed predominantly in LYMPHOID TISSUE. There is some controversy as to the site of origin of monocytes: some say they arise from lymphocytes, whilst others contend that they are derived from histiocytes – i.e. the RETICULO-ENDOTHELIAL SYSTEM.

Function The leucocytes constitute one of the most important of the defence mechanisms against infection. This applies particularly to the neutrophil leucocytes (see LEUCOCYTOSIS). (See also ABSCESS; BLOOD – Composition; INFLAMMATION; PHAGOCYTOSIS; WOUNDS.)... leucocytes

(differential blood count) a determination of the proportions of the different kinds of white cells (leucocytes) present in a sample of blood. Usually 100 white cells are counted and classified under the microscope or by electronic apparatus, so that the results can readily be expressed as percentages of the total number of leucocytes and the absolute numbers per litre of blood. The information often aids diagnosis of disease.... differential leucocyte count

see HLA system.... human leucocyte antigen system