White blood cell
Overview
 
White blood cells, or leukocytes (also spelled "leucocytes", leuco- Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 "white"), are cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 of the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 involved in defending the body against both infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

 and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

 known as a hematopoietic stem cell. They live for about 3 to 4 days in the average human body.
Encyclopedia
White blood cells, or leukocytes (also spelled "leucocytes", leuco- Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 "white"), are cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 of the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 involved in defending the body against both infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

 and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

 known as a hematopoietic stem cell. They live for about 3 to 4 days in the average human body. Leukocytes are found throughout the body, including the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 and lymphatic system
Lymphatic system
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...

.

The number of leukocytes in the blood is often an indicator of disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

. There are normally between 4×109 and 1.1×1010 white blood cells in a litre
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

 of blood, and ranging from 7 and 21 micrometres in diameter, they make up approximately 1% of blood in a healthy adult. An increase in the number of leukocytes over the upper limits is called leukocytosis
Leukocytosis
Leukocytosis is a raised white blood cell count above the normal range in the blood. It is frequently a sign of an inflammatory response, most commonly the result of infection, and is observed in certain parasitic infections...

, and a decrease below the lower limit is called leukopenia
Leukopenia
Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....

. The physical properties of leukocytes, such as volume, conductivity, and granularity
Granularity
Granularity is the extent to which a system is broken down into small parts, either the system itself or its description or observation. It is the "extent to which a larger entity is subdivided...

, may change due to activation, the presence of immature cells, or the presence of malignant leukocytes in leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...

.

Etymology

The name "white blood cell" derives from the fact that after centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...

 of a blood sample, the white cells are found in the buffy coat
Buffy coat
The buffy coat is the fraction of an anticoagulated blood sample after density gradient centrifugation that contains most of the white blood cells and platelets.-Description:...

, a thin, typically white layer of nucleated cells between the sedimented red blood cells and the blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

. The scientific term leukocyte directly reflects this description, derived from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 λευκό (white), and κύτταρο (cell). Blood plasma may sometimes be green if there are large amounts of neutrophils
Neutrophil granulocyte
Neutrophil granulocytes are the most abundant type of white blood cells in mammals and form an essential part of the innate immune system. They are generally referred to as either neutrophils or polymorphonuclear neutrophils , and are subdivided into segmented neutrophils and banded neutrophils...

 in the sample, due to the heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

-containing enzyme myeloperoxidase
Myeloperoxidase
Myeloperoxidase is a peroxidase enzyme that in humans is encoded by the MPO gene. Myeloperoxidase is most abundantly expressed in neutrophil granulocytes . It is a lysosomal protein stored in azurophilic granules of the neutrophil...

 that they produce.

Types

There are several different types of white blood cells. They all have many things in common, but are all distinct in form and function. A major distinguishing feature of some leukocytes is the presence of granules
Granule (cell biology)
In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

; white blood cells are often characterized as granulocyte
Granulocyte
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...

s or agranulocyte
Agranulocyte
Agranulocytes are a category of white blood cells characterised by the absence of granules in their cytoplasm.There are two types of agranulocytes:* Lymphocytes* Monocytes....

s:
  • Granulocytes (polymorphonuclear leukocytes): leukocytes characterised by the presence of differently staining granules
    Granule (cell biology)
    In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

     in their cytoplasm when viewed under light microscopy. These granules are membrane-bound enzymes which primarily act in the digestion of endocytosed
    Endocytosis
    Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...

     particles. There are three types of granulocytes: neutrophil
    Neutrophil granulocyte
    Neutrophil granulocytes are the most abundant type of white blood cells in mammals and form an essential part of the innate immune system. They are generally referred to as either neutrophils or polymorphonuclear neutrophils , and are subdivided into segmented neutrophils and banded neutrophils...

    s, basophil
    Basophil granulocyte
    Basophil granulocytes, sometimes referred to as basophils, are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating white blood cells....

    s, and eosinophil
    Eosinophil granulocyte
    Eosinophil granulocytes, usually called eosinophils or eosinophiles , are white blood cells that are one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells, they also control mechanisms associated with...

    s, which are named according to their staining properties.
  • Agranulocytes (mononuclear leukocytes): leukocytes characterized by the apparent absence of granules
    Granule (cell biology)
    In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

     in their cytoplasm
    Cytoplasm
    The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

    . Although the name implies a lack of granules these cells do contain non-specific azurophilic granules, which are lysosome
    Lysosome
    thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...

    s. The cells include lymphocyte
    Lymphocyte
    A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

    s, monocyte
    Monocyte
    Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...

    s, and macrophage
    Macrophage
    Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

    s.

Overview table

Type Microscopic Appearance Diagram Approx. %
in adults
See also:
Blood values 
Diameter (μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

)
Main targets Nucleus Granules Lifetime
Neutrophil
Neutrophil granulocyte
Neutrophil granulocytes are the most abundant type of white blood cells in mammals and form an essential part of the innate immune system. They are generally referred to as either neutrophils or polymorphonuclear neutrophils , and are subdivided into segmented neutrophils and banded neutrophils...

54–62% 10–12
  • bacteria
    Bacteria
    Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

  • fungi
multilobed  fine, faintly pink (H&E Stain) 6 hours–few days
(days in spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

 and other tissue)
Eosinophil
Eosinophil granulocyte
Eosinophil granulocytes, usually called eosinophils or eosinophiles , are white blood cells that are one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells, they also control mechanisms associated with...

 
1–6% 10–12
  • larger parasites
  • modulate allergic
    Allergy
    An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...

     inflammatory
    Inflammation
    Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

     responses
  • bi-lobed  full of pink-orange (H&E Stain) 8–12 days (circulate for 4–5 hours)
    Basophil
    Basophil granulocyte
    Basophil granulocytes, sometimes referred to as basophils, are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating white blood cells....

     
    <1% 12–15
  • release histamine
    Histamine
    Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...

     for inflammatory
    Inflammation
    Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

     responses
  • bi-lobed or tri-lobed  large blue a few hours to a few days
    Lymphocyte
    Lymphocyte
    A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

     
    28–33% 7–8
  • B cell
    B cell
    B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

    s: releases antibodies and assists activation of T cells
  • T cell
    T cell
    T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

    s:
    • Th (T helper) cells
      T helper cell
      T helper cells are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other...

      : activate and regulate T and B cells
    • CD8+
      CD8
      CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...

       cytotoxic T cell
      Cytotoxic T cell
      A cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or...

      s: virus-infected and tumor
      Tumor
      A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

       cells.
    • γδ T cells:
    • Regulatory (suppressor) T cell
      Regulatory T cell
      Regulatory T cells , sometimes known as suppressor T cells, are a specialized subpopulation of T cells which suppresses activation of the immune system and thereby maintains tolerance to self-antigens. The existence of regulatory T cells was the subject of significant controversy among...

      s: Returns the functioning of the immune system to normal operation after infection; prevents autoimmunity
      Autoimmunity
      Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...

  • Natural killer cell
    Natural killer cell
    Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...

    s: virus-infected and tumor
    Tumor
    A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

     cells.
  • deeply staining, eccentric NK-cells and Cytotoxic (CD8+) T-cells years for memory cells, weeks for all else.
    Monocyte
    Monocyte
    Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...

     
    2–10% 7.72–9.99 Monocytes migrate from the bloodstream to other tissues and differentiate into tissue resident macrophages, Kupffer cell
    Kupffer cell
    Kupffer cells, also known as Browicz-Kupffer cells and stellate macrophages, are specialized macrophages located in the liver lining the walls of the sinusoids that form part of the reticuloendothelial system .-History:The cells were first observed by Karl Wilhelm von Kupffer in 1876...

    s in the liver.
    kidney shaped none hours to days
    Macrophage
    Macrophage
    Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

     
    21 (human) Phagocytosis (engulfment and digestion) of cellular debris and pathogen
    Pathogen
    A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

    s, and stimulation of lymphocyte
    Lymphocyte
    A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

    s and other immune cells that respond to the pathogen.
    activated: days
    immature: months to years
    Dendritic cell
    Dendritic cell
    Dendritic cells are immune cells forming part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system. That is, dendritic cells function as antigen-presenting cells...

    s
    Main function is as an antigen-presenting cell
    Antigen-presenting cell
    An antigen-presenting cell or accessory cell is a cell that displays foreign antigen complexes with major histocompatibility complex on their surfaces. T-cells may recognize these complexes using their T-cell receptors...

     (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
    Pus
    Pus is a viscous exudate, typically whitish-yellow, yellow, or yellow-brown, formed at the site of inflammatory during infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection of pus within or beneath the epidermis is known as a pustule or...

    . They are commonly referred to as polymorphonuclear (PMN) leukocytes, although technically PMN refers to all granulocytes. They have a multi-lobed 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 lysosome
    Lysosome
    thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...

    s (used in digesting microbes) and die after having phagocytosed a few pathogens. Neutrophils are the most common cell type seen in the early stages of acute inflammation, and make up 60-70% of total leukocyte count in human blood. The life span of a circulating human neutrophil is about 5.4 days.

    Eosinophil

    Eosinophils 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. 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
    Antigen
    An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

     response by releasing the chemical histamine
    Histamine
    Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...

     causing vasodilation
    Vasodilation
    Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...

    . 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 cell
      B cell
      B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

      s: B cells make antibodies
      Antibody
      An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

       that bind to pathogens to enable their destruction. (B cells not only make antibodies
      Antibody
      An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

       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
      T cell
      T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

      s:
      • CD4+
        CD4
        CD4 is a glycoprotein expressed on the surface of T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...

         (helper) T cells having co-receptor CD4 is known as CD4+ T cells.These cells binds with the antigen having MHC II receptor on its surface. Then it presents this antigen to B cells. B cells produce antibodies to destroy antigen. Thus CD4+ T cell is also known as antigen presenting cells.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 that CD8+ cells are also another index to identify human's immune activity.
      • CD8+
        CD8
        CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...

         cytotoxic
        Cytotoxic T cell
        A cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or...

         T cells are able to kill virus-infected and tumor
        Tumor
        A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

         cells.T cells having co-receptor CD8 are known as CD8+ T cells. These cells kills damaged or cancerous cells. CD8 binds with MHC I receptor of damaged cells(carrying antigen). All nucleated cells possess MHC I on its surface.
      • 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 cell
      Natural killer cell
      Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...

      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 or have become cancer
      Cancer
      Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

      ous.

    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
    Pathogen
    A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

    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 microorganisms. Neither of these can be dealt with effectively by the neutrophils. Unlike neutrophils, monocytes are able to replace their lysosomal
    Lysosome
    thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...

     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 macrophage
    Macrophage
    Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

    s.

    Medication causing leukopenia

    Some medications can have an impact on the number and function of white blood cells. Leukopenia
    Leukopenia
    Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....

     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
    Neutropenia
    Neutropenia, from Latin prefix neutro- and Greek suffix -πενία , is a granulocyte disorder characterized by an abnormally low number of neutrophils, the most important type of white blood cell...

    . Likewise, low lymphocyte
    Lymphocyte
    A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

     levels are termed lymphopenia. Medications which can cause leukopenia include clozapine
    Clozapine
    Clozapine is an antipsychotic medication used in the treatment of schizophrenia, and is also used off-label in the treatment of bipolar disorder. Wyatt. R and Chew...

    , an antipsychotic
    Antipsychotic
    An antipsychotic is a tranquilizing psychiatric medication primarily used to manage psychosis , particularly in schizophrenia and bipolar disorder. A first generation of antipsychotics, known as typical antipsychotics, was discovered in the 1950s...

     medication with a rare adverse effect leading to the total absence of all granulocytes (neutrophils, basophils, eosinophils). Other medications include immunosuppressive
    Immunosuppression
    Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other...

     drugs, such as sirolimus
    Sirolimus
    Sirolimus , also known as rapamycin, is an immunosuppressant drug used to prevent rejection in organ transplantation; it is especially useful in kidney transplants. A macrolide, sirolimus was first discovered as a product of the bacterium Streptomyces hygroscopicus in a soil sample from Easter...

    , mycophenolate mofetil
    Mycophenolate mofetil
    Mycophenolate mofetil is an immunosuppressant and prodrug of mycophenolic acid, used extensively in transplant medicine. It is a reversible inhibitor of inosine monophosphate dehydrogenase in purine biosynthesis, which is necessary for the growth of T cells and B cells...

    , tacrolimus
    Tacrolimus
    Tacrolimus is an immunosuppressive drug that is mainly used after allogeneic organ transplant to reduce the activity of the patient's immune system and so lower the risk of organ rejection...

    , and cyclosporine. Interferons used to treat multiple sclerosis
    Multiple sclerosis
    Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...

    , 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
    Kupffer cell
    Kupffer cells, also known as Browicz-Kupffer cells and stellate macrophages, are specialized macrophages located in the liver lining the walls of the sinusoids that form part of the reticuloendothelial system .-History:The cells were first observed by Karl Wilhelm von Kupffer in 1876...

    s. These cells still serve a role in the immune system.
    • Histiocyte
      Histiocyte
      A histiocyte is a cell that is part of the mononuclear phagocyte system . The mononuclear phagocytic system is part of the organism's immune system...

      s
    • Dendritic cell
      Dendritic cell
      Dendritic cells are immune cells forming part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system. That is, dendritic cells function as antigen-presenting cells...

      s (Although these will often migrate to local lymph nodes upon ingesting antigens)
    • Mast cell
      Mast cell
      A mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin...

      s
    • Microglia
      Microglia
      Microglia are a type of glial cell that are the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system . Microglia constitute 20% of the total glial cell population within the brain...


    External links

    • http://www.hematologyatlas.com
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