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White blood cell
The blood contains erythrocytes (red blood cells), leukocytes (white blood
cells), platelets and blood plasma.
White blood cells help to defend the body against infectious disease and
foreign materials as part of the immune system. There are normally between
4x109 and 11x109 white blood cells in a litre of healthy adult blood.
White blood cells are also called leukocytes or immune cells. As well as in
the blood, white cells are also found in large numbers in the lymphatic
system, the spleen, and in other body tissues.
A type of cancer in which white blood cells multiply out of control is
called leukemia, of which there are several types.
There are many types of white blood cell:
There are three types of granulocytes: neutrophils, basophils and
eosinophils, named according to their staining properties.
* Neutrophils, so-called because they stain neutral, contain multilobed
nuclei, normally 2-5 lobes. They are the primary cell of the acute
inflammatory response, and act by phagocytosing foreign material and
pathogens. Neutrophils are like the 'vacuum cleaners' of the immune
system, engulfing and destroying pathogens, or tissue debris after
* Eosinophils, so-called because they stain brick-red with the more
acidic stain, known as eosin. These cells have a role in the allergic
response, and in defending against parasites such as worms.
* Basophils, so-called because they stain dark-blue with the more basic
stain. These cells are the least common circulating white blood cell,
and their purpose is not that clear. Though it is thought that these
cells become tissue mast cells.
Other White Cells
* Lymphocytes, much more common in the lymphatic system, and including
the so-called "killer T-cells" The blood has three types of
lymphocytes: B cells, T cells and natural killer cells. B cells make
antibodies that bind to pathogens to enable their destruction. CD4+
(helper) T cells co-ordinate the immune response (they are what become
defective in an HIV infection). CD8+ (cytotoxic) T cells and natural
killer cells are able to kill cells of the body that are infected by a
* Monocytes share the 'vacuum cleaner' function of neutrophils, but are
much longer lived as they have an additional role. Monocytes, and their
tissue counterpart macrophages, present pieces of pathogens to T cells
so that they may be recognised again and killed, or so that an antibody
response may be mounted.
Other Tissue Cells
* Histiocytes, found in the lymphatic system and other body tissues, but
not normally in blood:
o Dendritic cells
* Mast cells