White blood cell

White blood cell

White blood cell
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.
Details
Latin leucocytus
Identifiers
Code TH H2.00.04.1.02001
Anatomical terminology

White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in fighting the body against both infectious disease and foreign invaders. All leukocytes are 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.[1]

Five[2] different and diverse types of leukocytes exist. These types are distinguished by their physical and functional characteristics. Monocytes and neutrophils are phagocytic.

The number of leukocytes in the blood is often an indicator of disease. The normal white cell count is usually between 4 and 11 x 109/L. In the USA this is usually expressed as 4000-11,000 white blood cells per microliter of blood.[3] They make up approximately 1% of the total blood volume in a healthy adult.[4] An increase in the number of leukocytes over the upper limits is called leukocytosis, and a decrease below the lower limit is called leukopenia.

Contents

  • Etymology 1
  • Types 2
    • Overview 2.1
    • Neutrophil 2.2
    • Eosinophil 2.3
    • Basophil 2.4
    • Lymphocyte 2.5
    • Monocyte 2.6
  • Fixed leukocytes 3
  • Disorders 4
    • Leukopenias 4.1
      • Neutropenia 4.1.1
      • Lymphocytopenia 4.1.2
    • Proliferative disorders 4.2
      • Neutrophilia 4.2.1
      • Eosinophilia 4.2.2
  • Counting and reference ranges 5
  • See also 6
  • References 7
  • External links 8

Etymology

The name "white blood cell" derives from the physical appearance of a blood sample after centrifugation. White cells are found in the buff, a thin, typically white layer of nucleated cells between the sedimented red blood cells and the blood plasma. The scientific term leukocyte directly reflects its description. It is derived from the Greek word leuko- meaning "white" and kytos meaning "hollow vessel", with -cyte translated as "cell" in modern use. Buffy coat 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

3D rendering of various types of white blood cells

All white blood cells are nucleated but are otherwise distinct in form and function. White cells are best classified into two major lineages: the myeloid leukocytes and the lymphocytes.[5]

The white cells of the myeloid lineage include neutrophils, monocytes, eosinophils and basophils.

Lymphocytes include T cells, B cells and natural killer cells.

Overview

Type Microscopic appearance Diagram Approx. %
in adults
See also:
Blood values
Diameter (μm)[6] Main targets[4] Nucleus[4] Granules[4] Lifetime[6]
Neutrophil 62% 10–12 Multilobed Fine, faintly pink (H&E stain) 6 hours–few days
(days in spleen and other tissue)
Eosinophil 2.3% 10–12 Bi-lobed Full of pink-orange (H&E stain) 8–12 days (circulate for 4–5 hours)
Basophil 0.4% 12–15 Bi-lobed or tri-lobed Large blue A few hours to a few days
Lymphocyte 30% Small lymphocytes 7–8 Large lymphocytes 12–15 Deeply staining, eccentric NK-cells and cytotoxic (CD8+) T-cells Years for memory cells, weeks for all else.
Monocyte 5.3% 12–15[7] Monocytes migrate from the bloodstream to other tissues and differentiate into tissue resident macrophages, Kupffer cells in the liver. Kidney shaped None Hours to days

Neutrophil

Neutrophil engulfing anthrax bacteria.

Neutrophils are the most abundant white blood cell, constituting 60-70% of the circulating leukocytes. They defend against bacterial or fungal infection. They 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, in the technical sense, PMN refers to all granulocytes. They have a multi-lobed nucleus, which consists of three to five lobes connected by slender strands.[8] This gives the neutrophils the appearance of having multiple nuclei, hence the name polymorphonuclear leukocyte. The cytoplasm may look transparent because of fine granules that are pale lilac when stained. Neutrophils are 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.[9] Neutrophils are the most common cell type seen in the early stages of acute inflammation. They make up 60-70% of total leukocyte count in human blood.[4] The life span of a circulating human neutrophil is about 5.4 days.[10]

Eosinophil

Eosinophils compose about 2-4% of the WBC total. This count fluctuates throughout the day, seasonally, and during menstruation. It rises in response to allergies, parasitic infections, collagen diseases, and disease of the spleen and central nervous system. They are rare in the blood, but numerous in the mucous membranes of the respiratory, digestive, and lower urinary tracts.[8]

They primarily deal with parasitic infections. 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. They secrete chemicals that destroy these large parasites, such as hook worms and tapeworms, that are too big for any one WBC to phagocytize. In general, their nucleus is bi-lobed. The lobes are connected by a thin strand.[8] The cytoplasm is full of granules that assume a characteristic pink-orange color with eosin staining.

Basophil

Basophils are chiefly responsible for allergic and antigen response by releasing the chemical histamine causing vasodilation. Because they are the rarest of the white blood cells (less than 0.5% of the total count) and share physicochemical properties with other blood cells, they are difficult to study.[11] They can be recognized by several coarse, dark violet granules, giving them a blue hue. The nucleus is bi- or tri-lobed, but it is hard to see because of the number of coarse granules that hide it.

They excrete two chemicals that aid in the body's defenses: histamine and heparin. Histamine is responsible for widening blood vessels and increase the flow of blood to an injured tissue. It also makes blood vessels more permeable so neutrophils and clotting proteins can get into connective tissue more easily. Heparin is an anticoagulant that inhibits blood clotting and promotes the movement of white blood cells into an area. They can also release chemical signals that attract eosinophils and neutrophils to an infection site.[8]

Lymphocyte

Lymphocytes are much more common in the lymphatic system than in blood. Lymphocytes are distinguished by having a deeply staining nucleus that may be eccentric in location, and a relatively small amount of cytoplasm. Lymphocytes include:

Monocyte

Monocytes share the "vacuum cleaner" (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.

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.

Disorders

There are two major categories of white blood cell disorders: proliferative and leukopenias.[12] In the proliferative disorders there is an increase in the number of white blood cells. This increase is commonly reactive (ex. due to infection) but may also be cancerous. In leukopenias there is a decrease in the number of white blood cells. Both proliferative disease and leukopenias are quantitative disorders of white blood cells. Qualitative disorders of white blood cells are another category. These are disorders in which the number of white blood cells is normal but the cells do not function normally.[13]

Leukopenias

A range of disorders can cause decreases in white blood cells. This type of white blood cell decreased is usually the neutrophil. In this case the decrease may be called neutropenia or granulocytopenia. Less commonly, a decrease in lymphocytes (called lymphocytopenia or lymphopenia) may be seen.[12]

Neutropenia

Neutropenia can be acquired or intrinsic.[14] A decrease in levels of neutrophils on lab tests is due to either decreased production of neutrophils or increased removal from the blood.[12] The following list of causes is not complete.

Symptoms of neutropenia are associated with the underlying cause of the decrease in neutrophils. For example, the most common cause of acquired neutropenia is drug-induced, so an individual may have symptoms of medication overdose or toxicity. Treatment is also aimed at the underlying cause of the neutropenia.[15] One severe consequence of neutropenia is that it can increase the risk of infection.[13]

Lymphocytopenia

Defined as total lymphocyte count below 1.0x109/L, the cells most commonly affected are CD4+ T cells. Like neutropenia, lymphocytopenia may be acquired or intrinsic and there are many causes.[13] This is not a complete list.

Like neutropenia, symptoms and treatment of lymphocytopenia are directed at the underlying cause of the change in cell counts.

Proliferative disorders

An increase in the number of white blood cells in circulation is called leukocytosis.[12] This increase is most commonly caused by inflammation.[12] There are four major causes: increase of production in bone marrow, increased release from storage in bone marrow, decreased attachment to veins and arteries, decreased uptake by tissues.[12] Leukocytosis may affect one or more cell lines and can be neutrophilic, eosinophilic, basophilic, monocytosis, or lymphocytosis.

Neutrophilia

Neutrophilia is an increase in the absolute neutrophil count in the peripheral circulation. Normal blood values vary by age.[13] Neutrophilia can be caused by a direct problem with blood cells (primary disease). It can also occur as a consequence of an underlying disease (secondary). Most cases of neutrophilia are secondary to inflammation.[15]

Primary causes[15]

Secondary causes[15]

Eosinophilia

A normal eosinophil count is considered to be less than 0.65×109/L.[13] Eosinophil counts are higher in newborns and vary with age, time (lower in the morning and higher at night), exercise, environment, and exposure to allergens.[13] Eosinophilia is never a normal lab finding. Efforts should always be made to discover the underlying cause, though the cause may not always be found.[13]

Counting and reference ranges

The complete blood cell count is a blood panel that includes the overall WBC count and various subsets such as the absolute neutrophil count. Reference ranges for blood tests specify the typical counts in healthy people.

See also

References

  1. ^
  2. ^ LaFleur-Brooks, M. (2008). Exploring Medical Language: A Student-Directed Approach (7th ed.). St. Louis, Missouri, USA: Mosby Elsevier. p. 398.  
  3. ^ "Vital and Health Statistics Series 11, No. 247 (03/2005)" (PDF). Retrieved 2014-02-02. 
  4. ^ a b c d e Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter (2002). "Leukocyte functions and percentage breakdown". Molecular Biology of the Cell (4th ed.). New York: Garland Science.  
  5. ^ Orkin, SH; Zon, LI (Feb 22, 2008). "SnapShot: hematopoiesis.". Cell 132 (4): 712.  
  6. ^ a b Daniels, V. G., Wheater, P. R., & Burkitt, H.G. (1979). Functional histology: A text and colour atlas. Edinburgh: Churchill Livingstone.  
  7. ^ Handin, Robert I.; Samuel E. Lux; Thomas P. Stossel (2003). Blood: Principles and Practice of Hematology (2nd ed.). Philadelphia: Lippincott Williams and Wilkins. p. 471.  
  8. ^ a b c d Saladin, Kenneth (2012). Anatomy and Physiology: the Unit of Form and Function (6 ed.). New York: McGraw Hill.  
  9. ^ Wheater, Paul R.; Stevens, Alan (2002). Wheater's basic histopathology: a colour atlas and text. Edinburgh: Churchill Livingstone.  
  10. ^ Pillay, J.; Den Braber, I.; Vrisekoop, N.; Kwast, L. M.; De Boer, R. J.; Borghans, J. A. M.; Tesselaar, K.; Koenderman, L. (2010). "In vivo labeling with 2H2O reveals a human neutrophil lifespan of 5.4 days". Blood 116 (4): 625–7.  
  11. ^ Falcone, Franco; Haas, Helmut; Gibbs, Bernard (15 December 2000). "The human basophil: a new appreciation of its role in immune responses.". Blood 96 (13): 4028–38.  
  12. ^ a b c d e f Vinay Kumar et al. (2010). Robbins and Cotran pathologic basis of disease. (8th ed.). Philadelphia, PA: Saunders/Elsevier.  
  13. ^ a b c d e f g Kenneth Kaushansky et al., ed. (2010). Williams hematology (8th ed.). New York: McGraw-Hill Medical.  
  14. ^ Richard A. McPherson, Matthew R. Pincus, Naif Z. Abraham Jr. et al. (ed.). Henry's clinical diagnosis and management by laboratory methods (22nd ed.). Philadelphia, PA: Elsevier/Saunders.  
  15. ^ a b c d Lee Goldman; Andrew I. Schafer (eds.). Goldman's Cecil medicine (24th ed.). Philadelphia: Elsevier/Saunders.  
  16. ^ McBride, JA; Dacie, JV; Shapley, R (Feb 1968). "The effect of splenectomy on the leucocyte count.". British journal of haematology 14 (2): 225–31.  

External links