White blood cell: Wikis

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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 (WBCs), or leukocytes (also spelled "leucocytes"), are cells of the immune system defending the body against both infectious disease and foreign materials. Five[1] 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.[2]

The number of WBCs in the blood is often an indicator of disease. There are normally between 4×109 and 1.1×1010 white blood cells in a litre of blood, making up approximately 1% of blood in a healthy adult.[3] An increase in the number of leukocytes over the upper limits is called leukocytosis, and a decrease below the lower limit is called leukopenia. 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.

Contents

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, typically white layer of nucleated cells between the sedimented red blood cells and the blood plasma. The scientific term leukocyte directly reflects this description, derived from 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. A major distinguishing feature of some leukocytes is the presence of granules; white blood cells are often characterized as granulocytes or agranulocytes:

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Overview table

Type Microscopic Appearance Diagram Approx. %
in adults[6]
See also:
Blood values
Diameter (μm)[6] Main targets[3] Nucleus[3] Granules[3] Lifetime[6]
Neutrophil PBNeutrophil.jpg Neutrophil.png 54–62%[5] 10–12 multilobed fine, faintly pink (H&E Stain) 6 hours–few days
(days in spleen and other tissue)
Eosinophil Eosinophil.jpg Eosinophil2.png 1–6% 10–12 bi-lobed full of pink-orange (H&E Stain) 8–12 days (circulate for 4–5 hours)
Basophil PBBasophil.jpg Basophil.png <1% 12–15 bi-lobed or tri-lobed large blue a few hours to a few days
Lymphocyte Lymphocyte2.jpg Lymphocyte.png 25–33% 7–8 deeply staining, eccentric NK-cells and Cytotoxic (CD8+) T-cells [7] weeks to years
Monocyte Monocyte.png 2–10% 14–17 Monocytes migrate from the bloodstream to other tissues and differentiate into tissue resident macrophages or dendritic cells. kidney shaped none hours to days
Macrophage Macrophage.jpg Macrophage.png 21 (human)[8] Phagocytosis (engulfment and digestion) of cellular debris and pathogens, and stimulation of lymphocytes and other immune cells that respond to the pathogen. activated: days
immature: months to years
Dendritic cells Dendritic cell.JPG Dendritic Cell ZP.svg Main function is as an antigen-presenting cell (APC) that activates T lymphocytes. similar to macrophages

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 commonly referred to as polymorphonuclear (PMN) leukocytes, although technically PMN refers to all granulocytes. 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 pale lilac. 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.[citation needed] Most common cell seen in acute inflammation, come in and kill foreign substance.

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

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 characterized by their large blue granules.

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 cells: B cells make antibodies that bind to pathogens to enable their destruction. (B cells not only make 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 cells:
    • CD4+ (helper) T cells co-ordinate the immune response and are important in the defense against intracellular bacteria. In acute HIV infection, these T cells are the main index to identify the individual's immune system activity. Research has shown [9] that CD8+ cells are also another index to identify human's immune activity.
    • CD8+ cytotoxic T cells are able to kill virus-infected and tumor cells.
    • γδ T cells 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 cells: 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 or have become cancerous.

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 pathogens 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 microorganisms. 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 are typically agranulated. They also possess abundant cytoplasm.

Once monocytes move from the bloodstream out into the body tissues, they undergo changes (differentiate) allowing phagocytosis and are then known as macrophages.

Medication 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 neutrophils 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 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 cells. These cells still serve a role in the immune system.

Notes

  1. ^ LaFleur-Brooks, M. (2008). Exploring Medical Language: A Student-Directed Approach, 7th Edition. St. Louis, Missouri, USA: Mosby Elsevier. pp. 398. ISBN 978-0-323-04950-4. 
  2. ^ Maton, D., Hopkins, J., McLaughlin, Ch. W., Johnson, S., Warner, M. Q., LaHart, D., & Wright, J. D. (1000008). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. 
  3. ^ a b c d Alberts, B. (2005). "Leukocyte functions and percentage breakdown". Molecular Biology of the Cell. NCBI Bookshelf. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=leukocyte,functions&rid=mboc4.table.4143. Retrieved 2007-04-14. 
  4. ^ Gartner, L. P., & Hiatt, J. L. (2007). Color Textbook of Histology (3rd ed.). Philadelphia, PA: SAUNDERS Elsevier. pp. 225. ISBN 978-1-4160-2945-8. 
  5. ^ a b http://www.wisc-online.com/objects/index_tj.asp?objID=AP14704
  6. ^ a b c Daniels, V. G., Wheater, P. R., & Burkitt, H. G. (1979). Functional histology: A text and colour atlas. Edinburgh: Churchill Livingstone. ISBN 0-443-01657-7. 
  7. ^ Semester 4 medical lectures at Uppsala University 2008 by Leif Jansson
  8. ^ Krombach, F., Münzing, S., Allmeling, A. M., Gerlach, J. T., Behr, J., & Dörger, M. (1 September 1997). "Cell size of alveolar macrophages: an interspecies comparison". Environ. Health Perspect. 105 Suppl 5: 1261–3. doi:10.2307/3433544. ISSN 00916765. PMID 9400735. 
  9. ^ Pantaleo, G., Demarest, J. F., Soudeyns, H., et. al. (August 1994). "Major expansion of CD8+ T cells with a predominant V beta usage during the primary immune response to HIV". Nature 370 (6489): 463–7. doi:10.1038/370463a0. PMID 8047166. 

External links


Simple English

The purpose of white blood cells (also called leukocytes) is to stop a person from getting sick. Although germ-fighting is their main goal, they also remove poison, waste and hurt cells from a person's body. The different types of white blood cells are: Monocytes, Neutrophils, Eosinophils and Basophils and Lymphocytes. The number of white blood cells increases when a person is fighting infection or disease and decrease when a person is healthy. The white blood cell is very important. Without them, a person would not be able to live. With all the bacteria that get into the body daily, it is impossible to live without white blood cells.

Contents

Types of white blood cells

Lymphocytes

Lymphocytes are round white blood cells a bit bigger than a red blood cell. Their center is round and they have little cytoplasm. Part of the lymphatic system, these target specific germs or poisons using their antibodies. There are three known types of lymphocytes, called T-cells, B-cells and Natural Killer cells.

Monocytes

Monocytes are reserve cells which turn into macrophages and Dendritic cells , which work together in tissues to fight disease. Monocytes have a kidney bean shaped center and lots of cytoplasm. They may appear as macrophages in a non-round shape when they pass through tissue to eat germs, "junk" cells, and dead cells.

Granulocytes

The next three types of white blood cells are referred to as granulocytes since they all contain rough, grain-like particles that assist in attacking viruses and bacteria. Granulocytes are also called polymorphonuclear leukocytes because of the shape of the nucleus, which has three segments.

Neutrophils

Neutrophils are the most abundant type of white blood cells in mammals, 70% of leukocytes. They are an essential part of the immune system. They get to the site of an injury within minutes, and make up much of the content of pus. They have a short life-span of a couple of days.

The nucleus, which looks like a string of beads, does not take up stain strongly. Like phagocytes, they actually eat the bacteria and dead cells. They also release a bunch of proteins which work to damage the bacteria.

Basophils

Basophils are rare granulocytes, making up only 0.1 to 0.3% of leukocytes. The nucleus is hidden by granules which turn dark blue in color when stained. Basophils carry histamine and heparin, and other protein chemicals. They appear at the sites of ectoparasite infection, or allergies. Exactly how they operate is not yet clear.

Eosinophils

Eosinophils or, less commonly, acidophils, are leukocytes that are one of the immune system components which combat parasites and certain infections. Along with mast cells, they work on allergy and asthma. Eosinophils are round cells with a lobed nucleus and granules which turn red when recolored. These granules are protein chemicals that can be poured out to help destroy invaders.

Cell testing

A special test called a Differential count shows how many white blood cells there are in a person's body, and can also tell a doctor how much of each type are in there. These are used to show what a person's body is currently fighting, if it is fighting anything at all.


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