White blood cell
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{{redirect|White Blood Cells|the album by The White Stripes|White Blood Cells (album)}}
[[Image:SEM blood cells.jpg|thumb|right| A [[scanning electron microscope]] image of normal circulating human blood. In addition to the irregularly shaped leukocytes, both red blood cells and many small disc-shaped [[platelets]] are visible.]]
'''White blood cells''', or '''leukocytes''', are [[cell (biology)|cells]] of the [[immune system]] defending the body against both [[infectious disease]] and foreign materials. Several different and diverse types of leukocytes exist, but they are all produced and derived from a [[multipotent]] cell in the [[bone marrow]] known as a [[hematopoietic stem cell]]. Leukocytes are found throughout the body, including the [[blood]] and [[lymphatic system]].<ref>{{cite book
| last = Maton
| first = die
| authorlink =
| coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
| title = Human Biology and Health
| publisher = Prentice Hall
| date = 1000008
| location = Englewood Cliffs, New Jersey, USA
| pages =
| url =
| doi =
| id =
| isbn = 0-13-981176-1}}</ref>
The number of leukocytes in the blood is often an indicator of disease. There are normally between 4×10<sup>9</sup> and 11×10<sup>9</sup> white blood cells in a [[litre]] of blood, making up approximately 1% of blood in a healthy adult.<ref name="alberts_table">{{Cite web|url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&rid=mboc4.table.4143|title=Leukocyte functions and percentage breakdown|accessdate=2007-04-14|publisher=NCBI Bookshelf|year=2005|author=Alberts, Bruce|work=Molecular Biology of the Cell}}</ref> In conditions such as [[leukemia]], the number of leukocytes is higher than normal, and in [[leukopenia]], this number is much lower. The physical properties of leukocytes, such as volume, conductivity, and granularity, may change due to activation, the presence of immature cells, or the presence of malignant leukocytes in leukemia.
==Etymology==
The name "White blood cell" derives from the fact that after [[centrifugation]] of a blood sample, the white cells are found in the ''[[Buffy coat]]'', a thin layer of nucleated cells between the sedimented red blood cells and the [[blood plasma]], which is typically white in color. The scientific term ''leukocyte'' directly reflects this description, derived from [[Greek language|Greek]] ''leukos'' - white, and ''kytos'' - cell. Blood plasma may sometimes be green if there are large amounts of neutrophils in the sample, due to the [[heme]]-containing enzyme [[myeloperoxidase]] that they produce.
==Types==
There are several different types of white blood cells. They all have many things in common, but are all different. One primary technique to classify them is to look for the presence of [[Granule (cell biology)|granules]], which allows the differentiation of cells into the categories [[granulocyte]]s and [[agranulocyte]]s:
* '''Granulocytes (polymorphonuclear leucocytes):''' leukocytes characterised by the presence of differently staining [[Granule (cell biology)|granules]] in their cytoplasm when viewed under light microscopy. These granules are [[Lipid membrane|membrane-bound]] enzymes which primarily act in the digestion of [[endocytosis|endocytosed]] particles. There are three types of granulocytes: [[neutrophil]]s, [[basophil]]s, and [[eosinophil]]s, which are named according to their staining properties.
* '''Agranulocytes (mononuclear leucocytes):''' leukocytes characterized by the apparent absence of [[Granule (cell biology)|granules]] in their [[cytoplasm]]. Although the name implies a lack of granules these cells do contain non-specific [[azurophilic granules]], which are lysosomes<ref>{{Cite book
|last = Gartner
|first = Leslie P.
|last2=Hiatt
|first2=James L.
|year=2007
|pages=p. 225
|title=Color Textbook of Histology
|edition=3rd
|publication-place = Philadelphia, PA
|place= ,China
|publisher=SAUNDERS Elsevier
|isbn=978-1-4160-2945-8}}</ref>. The cells include [[lymphocyte]]s, [[monocyte]]s, and [[macrophage]]s.
===Overview table===
{|class="wikitable"
! Type !! Microscopic Appearance !! Diagram !! Approx. %<br/>in adults<ref name="isbn0-443-01657-7">{{cite book |author=Daniels, Victor G.; Wheater, Paul R.; Burkitt, H. George |title=Functional histology: a text and colour atlas |publisher=Churchill Livingstone |location=Edinburgh |year=1979 |pages= |isbn=0-443-01657-7 |oclc= |doi=}}</ref><br><sup> See also:<br/>[[Blood_values#Hematology|Blood values]] !! Diameter ([[micrometre|μm]])<ref name="isbn0-443-01657-7"/> !! Main targets<ref name="alberts table">{{Cite web|url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&rid=mboc4.table.4143|title=Leukocyte functions and percentage breakdown|accessdate=2007-04-14|publisher=NCBI Bookshelf|year=2005|author=Alberts, Bruce|work=Molecular Biology of the Cell}}</ref> !! Nucleus<ref name="alberts table"/> !! Granules<ref name="alberts table"/> !! Lifetime<ref name="isbn0-443-01657-7"/>
|-
! [[Neutrophil]]
| [[Image:pBNeutrophil.jpg|75px]] || [[Image:Neutrophil.png|75px]] || 40-75% || 10-12 ||
*[[bacteria]]
*[[fungi]]
| [[multilobed]] || fine, faintly pink || 6 hours-few days<br/>(days in [[spleen]] and other tissue)
|-
| [[Eosinophil]] || [[Image:Eosinophil.jpg|75px]] || [[Image:Eosinophil2.png|75px]] || 1-6% || 10-12 ||
*[[parasites]]
*in [[allergic]] reactions
| [[bi-lobed]] || full of pink-orange (when stained) || 8-12 days (circulate for 4-5 hours)
|-
| [[Basophil granulocyte|Basophil]] || [[Image:PBBasophil.jpg|75px]] || [[Image:Basophil.png|75px]] || <1% || 9-10 ||
*in [[allergic]] reactions
|bi- or tri-lobed || large blue || ?
|-
| [[Lymphocyte]] || [[Image:Lymphocyte2.jpg|75px]] || [[Image:Lymphocyte.png|75px]] || 20-45% || 7-8 ||
* [[B cell]]s: various [[pathogens]]
* [[T cell]]s:
**[[CD4|CD4+]] ([[helper T cell|helper]]): intracellular bacteria.
**[[CD8|CD8+]] [[cytotoxic T cell|cytotoxic]] T cells: [[virus (biology)|virus]]-infected and [[tumor]] cells.
**[[gamma/delta T cells|γδ T cell]]s:
* [[Natural killer cell]]s: [[virus (biology)|virus]]-infected and [[tumor]] cells.
| deeply staining, eccentric || only NK-cells <ref name=T4> Semester 4 medical lectures at Uppsala University 2008 by Leif Jansson</ref> || weeks to years
|-
| [[Monocyte]] || [[Image:pBMonozyt.jpg|75px]] || [[Image:Monocyte.png|75px]] || 2-6% ||rowspan=2| 14-17 ||rowspan=2| various || kidney shaped ||rowspan=2| none || hours-days
|-
| [[Macrophage]] || [[Image:Macrophage.jpg|75px]] || [[Image:Macrophage.png|75px]] || N/A || || months-years
|}
===Neutrophil===
{{Main|Neutrophil}}
Neutrophils defend against [[bacterial]] or [[fungal]] infection and other very small inflammatory processes that are usually first responders to microbial infection; their activity and death in large numbers forms [[pus]]. They are also known as polymorphonuclear leukocytes. They have a multilobed nucleus which may appear like multiple nuclei, hence the name polymorphonuclear leukocyte. The cytoplasm may look transparent because of fine granules that are faintly pink in color. Neutrophils are very active in phagocytosing bacteria and are present in large amount in the pus of wounds. These cells are not able to renew their lysosomes used in digesting microbes and die after having phagocytosed a few pathogens {{Fact|date=May 2008}}.
===Eosinophil===
{{Main|Eosinophil}}
Eosinophils primarily deal with [[parasitic]] infections and an increase in them may indicate such. Eosinophils are also the predominant inflammatory cells in allergic reactions. The most important causes of eosinophilia include allergies such as asthma, hay fever, and hives; and also parasitic infections. Generally their nucleus is bi-lobed. The cytoplasm is full of granules which assume a characteristic pink-orange color with eosin stain.
===Basophil===
{{Main|Basophil granulocyte}}
Basophils are chiefly responsible for [[allergic]] and [[antigen]] response by releasing the chemical [[histamine]] causing [[inflammation]]. The nucleus is bi- or tri-lobed, but it is hard to see because of the number of coarse granules which hide it.
They are characterised by their large blue granules.
===Lymphocyte===
{{Main|Lymphocyte}}
Lymphocytes are much more common in the lymphatic system. Lymphocytes are distinguished by having a deeply staining nucleus which may be eccentric in location, and a relatively small amount of cytoplasm. The blood has three types of lymphocytes:
* [[B cell]]s: B cells make [[antibody|antibodies]] that bind to [[pathogens]] to enable their destruction. (B cells not only make [[antibody|antibodies]] that bind to [[pathogens]], but after an attack, some B cells will retain the ability to produce an antibody to serve as a 'memory' system.)
* [[T cell]]s:
**[[CD4|CD4+]] ([[helper T cell|helper]]) T cells co-ordinate the immune response and are important in the defence against intracellular bacteria. In acute HIV infection, these T cells are the main index to identify the individual's immune system activity. Research have shown (Pantaleo 1994) that CD8+ cells are also another index to identify human's immune activity.
**[[CD8|CD8+]] [[cytotoxic T cell|cytotoxic]] T cells are able to kill virus-infected and [[tumor]] cells.
**[[gamma/delta T cells|γδ T cell]]s possess an alternative T cell receptor as opposed to CD4+ and CD8+ αβ T cells and share characteristics of helper T cells, cytotoxic T cells and natural killer cells.
* [[Natural killer cell]]s: Natural killer cells are able to kill cells of the body which are displaying a signal to kill them, as they have been infected by a [[virus (biology)|virus]] or have become [[cancer]]ous.
===Monocyte===
{{Main|Monocyte}}
Monocytes share the "vacuum cleaner" ([[phagocytosis]]) function of neutrophils, but are much longer lived as they have an additional role: they present pieces of [[pathogen]]s to T cells so that the pathogens may be recognized again and killed, or so that an antibody response may be mounted. Monocytes eventually leave the bloodstream to become tissue macrophages which remove dead cell debris as well as attacking microrganisms. Neither of these can be dealt with effectively by the neutrophils. Unlike neutrophils, monocytes are able to replace their lysosomal contents and are thought to have a much longer active life. They have the kidney shaped nucleus and typically agranulated. They also possess abundant cytoplasm.
===Macrophage===
{{Main|Macrophage}}
Once monocytes move from the bloodstream out into the body tissues, they undergo changes (differentiate) allowing [[phagocytosis]] and are then known as [[macrophage]]s.
==Medications causing leukopenia==
Some medications can have an impact on the number and function of white blood cells. [[Leukopenia]] is the reduction in the number of white blood cells, which may affect the overall white cell count or one of the specific populations of white blood cells. For example, if the number of [[neutrophil]]s is low, the condition is known as [[neutropenia]]. Likewise, low [[lymphocyte]] levels are termed [[lymphopenia]]. Medications which can cause leukopenia include [[clozapine]], an [[antipsychotic]] medication with a rare adverse effect leading to the total absence of all granulocytes (neutrophils, basophils, eosinophils). Other medications include [[immunosuppression|immunosuppressive]] drugs, such as [[sirolimus]], [[mycophenolate mofetil]], [[tacrolimus]], and [[cyclosporine]]. [[Interferons]] used to treat [[multiple sclerosis]], like [[Rebif]], [[Avonex]], and [[Betaseron]], can also cause leukopenia.
==Fixed leukocytes==
Some leukocytes migrate into the tissues of the body to take up a permanent residence at that location rather than remaining in the blood. Often these cells have specific names depending upon which tissue they settle in, such as fixed macrophages in the liver which become known as [[Kupffer cell]]s. These cells still serve a role in the immune system.
* [[Histiocyte]]s
* [[Dendritic cell]]s (Although these will often migrate to local lymph nodes upon ingesting antigens)
* [[Mast cell]]s
* [[Microglia]]
==References==
{{reflist}}
==External links==
* {{MeshName|Leukocytes}}
{{Blood}}
{{Immune_system}}
[[Category:Blood tests]]
[[Category:Hematology]]
[[Category:Immunology]]
[[Category:Immune system]]
[[Category:Leukocytes| ]]
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