Lymphocyte
Encyclopedia
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 cell
s (NK cells). Small lymphocytes consist of T cell
s and B cell
s.
The three major types of lymphocyte are T cell
s, B cell
s and natural killer
(NK) cells.
and play a major role in defending the host from both tumor
s and viral
ly infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a surface molecule called MHC (major histocompatibility complex
) class I
. NK cells are activated in response to a family of cytokines called interferon
s. Activated NK cells release cytotoxic (cell-killing) granules
which then destroy the altered cells. They were named "natural killer cells" because of the initial notion that they do not require prior activation in order to kill cells which are missing MHC class I.
cells) and B cells (bursa
-derived cells) are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity
whereas B cells are primarily responsible for humoral immunity
(relating to antibodies
). The function of T cells and B cells is to recognize specific “non-self” antigens, during a process known as antigen presentation
. Once they have identified an invader, the cells generate specific responses that are tailored to maximally eliminate specific pathogen
s or pathogen infected cells. B cells respond to pathogens by producing large quantities of antibodies
which then neutralize foreign objects like bacteria
and viruses. In response to pathogens some T cells, called T helper cell
s, produce cytokine
s that direct the immune response while other T cells, called cytotoxic T cell
s, produce toxic granules
that contain powerful enzymes which induce the death of pathogen infected cells. Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong and rapid response if the pathogen is detected again.
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Mammalian stem cell
s differentiate
into several kinds of blood cell within the bone marrow
. This process is called haematopoiesis
. All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion. The formation of lymphocytes is known as lymphopoiesis
. B cells mature into B lymphocytes in the bone marrow, while T cells migrate to and mature in a distinct organ, called the thymus
. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen
and lymph nodes) where they survey for invading pathogen
s and/or tumor cells.
The lymphocytes involved in adaptive immunity (i.e. B and T cells) differentiate further after exposure to an antigen
; they form effector and memory lymphocytes. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (cytotoxic T cell
s) or by signaling to other cells of the immune system (helper T cells). Memory cell
s remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure.
They live weeks to several years to a whole lifetime, which is very long compared to other leukocytes.
Microscopically, in a Wright's stain
ed peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no eosinophilic
cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is approximately the size of a red blood cell (about 7 micrometres in diameter). Some lymphocytes show a clear perinuclear zone (or halo) around the nucleus or could exhibit a small clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope
. The ribosomes are involved in protein synthesis allowing the generation of large quantities of cytokine
s and immunoglobulins by these cells.
It is impossible to distinguish between T cells and B cells in a peripheral blood smear. Normally, flow cytometry
testing is used for specific lymphocyte population counts. This can be used to specifically determine the percentage of lymphocytes that contain a particular combination of specific cell surface proteins, such as immunoglobulins or cluster of differentiation
(CD) markers or that produce particular proteins (for example, cytokine
s using intracellular cytokine staining (ICCS)). In order to study the function of a lymphocyte by virtue of the proteins it generates, other scientific techniques like the ELISPOT
or secretion assay
techniques can be used.
In the circulatory system
they move from lymph node
to lymph node. This contrasts with macrophages, which are rather stationary in the nodes.
A general increase in the number of lymphocytes is known as lymphocytosis
whereas a decrease is lymphocytopenia
.
s are found through an abnormally raised lymphocyte count in an otherwise normal person).
One basis for low T cell lymphocytes occurs when the human immunodeficiency virus (HIV) infects and destroys T cells (specifically, the CD4
+ subgroup of T lymphocytes). Without the key defense that these T cells provide, the body becomes susceptible to opportunistic infection
s that otherwise would not affect healthy people. The extent of HIV progression is typically determined by measuring the percentage of CD4+ T cells in the patient's blood. The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood
.
ALC is <950 × 106 cells/μL and less likely if the ALC is >1,700 × 106 cells/μL".
and colorectal cancer
, lymphocytes can migrate into and attack the tumor. This can sometimes lead to regression of the primary tumor.
White blood cell
White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease 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 known as a...
in the vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
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...
.
Under the microscope
Optical microscope
The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the...
, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include 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 (NK cells). Small lymphocytes consist of 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 and 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.
Types
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, 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 and natural killer
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...
(NK) cells.
Natural killer cells
NK cells are a part of the innate immune systemInnate immune system
The innate immune system, also known as non-specific immune system and secondary line of defence, comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner...
and play a major role in defending the host from both 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...
s and viral
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
ly infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a surface molecule called MHC (major histocompatibility complex
Major histocompatibility complex
Major histocompatibility complex is a cell surface molecule encoded by a large gene family in all vertebrates. MHC molecules mediate interactions of leukocytes, also called white blood cells , which are immune cells, with other leukocytes or body cells...
) class I
MHC class I
MHC class I molecules are one of two primary classes of major histocompatibility complex molecules and are found on every nucleated cell of the body...
. NK cells are activated in response to a family of cytokines called interferon
Interferon
Interferons are proteins made and released by host cells in response to the presence of pathogens—such as viruses, bacteria, or parasites—or tumor cells. They allow communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors.IFNs belong to...
s. Activated NK cells release cytotoxic (cell-killing) 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:...
which then destroy the altered cells. They were named "natural killer cells" because of the initial notion that they do not require prior activation in order to kill cells which are missing MHC class I.
T cells and B cells
T cells (thymusThymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
cells) and B cells (bursa
Bursa of Fabricius
In birds, the bursa of Fabricius is the site of hematopoiesis, a specialized organ that, as first demonstrated by Bruce Glick and later by Max Cooper and Robert Good, is necessary for B cell development in birds...
-derived cells) are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity
Cell-mediated immunity
Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells , antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen...
whereas B cells are primarily responsible for humoral immunity
Humoral immunity
The Humoral Immune Response is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage . B Cells transform into plasma cells which secrete antibodies...
(relating to 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...
). The function of T cells and B cells is to recognize specific “non-self” antigens, during a process known as antigen presentation
Antigen presentation
Antigen presentation is a process in the body's immune system by which macrophages, dendritic cells and other cell types capture antigens and then enable their recognition by T-cells....
. Once they have identified an invader, the cells generate specific responses that are tailored to maximally eliminate specific 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 or pathogen infected cells. B cells respond to pathogens by producing large quantities of 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...
which then neutralize foreign objects like 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...
and viruses. In response to pathogens some T cells, called T helper cell
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...
s, produce cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s that direct the immune response while other T cells, called 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, produce toxic 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:...
that contain powerful enzymes which induce the death of pathogen infected cells. Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong and rapid response if the pathogen is detected again.
Development
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
s differentiate
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
into several kinds of blood cell within 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...
. This process is called haematopoiesis
Haematopoiesis
Haematopoiesis is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells...
. All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion. The formation of lymphocytes is known as lymphopoiesis
Lymphopoiesis
Lymphopoiesis refers to the generation of lymphocytes, one of the five different types of white blood cells , and is also more formally called lymphoid hematopoiesis.-The name Lymphopoiesis:...
. B cells mature into B lymphocytes in the bone marrow, while T cells migrate to and mature in a distinct organ, called the thymus
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the 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 lymph nodes) where they survey for invading 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/or tumor cells.
The lymphocytes involved in adaptive immunity (i.e. B and T cells) differentiate further after exposure to an 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...
; they form effector and memory lymphocytes. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (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) or by signaling to other cells of the immune system (helper T cells). Memory cell
Memory cell
Memory cell may refer to:* Memory cell, a building block of computer data storage*Memory B cell, an antibody producing cell*Memory T cell, an infection fighting cell...
s remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure.
They live weeks to several years to a whole lifetime, which is very long compared to other leukocytes.
Characteristics
Wright's stain
Wright's stain is a histologic stain that facilitates the differentiation of blood cell types. It is used primarily to stain peripheral blood smears and bone marrow aspirates which are examined under a light microscope...
ed peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no eosinophilic
Eosinophilic
Eosinophilic refers to the staining of certain tissues, cells, or organelles after they have been washed with eosin, a dye.Eosin is an acidic dye; thus, the structure being stained is basic....
cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is approximately the size of a red blood cell (about 7 micrometres in diameter). Some lymphocytes show a clear perinuclear zone (or halo) around the nucleus or could exhibit a small clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...
. The ribosomes are involved in protein synthesis allowing the generation of large quantities of cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s and immunoglobulins by these cells.
It is impossible to distinguish between T cells and B cells in a peripheral blood smear. Normally, flow cytometry
Flow cytometry
Flow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
testing is used for specific lymphocyte population counts. This can be used to specifically determine the percentage of lymphocytes that contain a particular combination of specific cell surface proteins, such as immunoglobulins or cluster of differentiation
Cluster of differentiation
The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on white blood cells, providing targets for immunophenotyping of cells...
(CD) markers or that produce particular proteins (for example, cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s using intracellular cytokine staining (ICCS)). In order to study the function of a lymphocyte by virtue of the proteins it generates, other scientific techniques like the ELISPOT
ELISPOT
The Enzyme-linked immunosorbent spot assay is a common method for monitoring immune responses in humans and animals. It was developed by Cecil Czerkinsky in 1983....
or secretion assay
Secretion assay
Secretion assay is a process used in cell biology to identify cells that are secreting a particular protein . It was first developed by Manz et al. in 1995....
techniques can be used.
| CLASS | FUNCTION | PROPORTION | PHENOTYPIC MARKER(S) |
| NK cells | Lysis of virally infected cells and tumour cells | 7% (2-13%) | CD16 CD16 CD16 is a low affinity Fc receptor.It is a cluster of differentiation found on the surface of natural killer cells, neutrophil polymorphonuclear leukocytes, monocytes and macrophages... CD56 but not CD3 CD3 CD3 or CD-3 may be:* CD3 , an antigen, cluster of differentiation protein , part of the T cell receptor complex on a mature T lymphocyte* Ford CD3 platform* MediaMax CD-3, copy protection scheme* MiniCD, a 3-inch CD... |
| Helper T cells | Release cytokines and growth factors that regulate other immune cells | 46% (28-59%) | TCR T cell receptor The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is responsible for recognizing antigens bound to major histocompatibility complex molecules... αβ, CD3 CD3 CD3 or CD-3 may be:* CD3 , an antigen, cluster of differentiation protein , part of the T cell receptor complex on a mature T lymphocyte* Ford CD3 platform* MediaMax CD-3, copy protection scheme* MiniCD, a 3-inch CD... and 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... |
| Cytotoxic T cells 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... |
Lysis of virally infected cells, tumour cells and allografts | 19% (13-32%) | TCR T cell receptor The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is responsible for recognizing antigens bound to major histocompatibility complex molecules... αβ, CD3 CD3 CD3 or CD-3 may be:* CD3 , an antigen, cluster of differentiation protein , part of the T cell receptor complex on a mature T lymphocyte* Ford CD3 platform* MediaMax CD-3, copy protection scheme* MiniCD, a 3-inch CD... and 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... |
| γδ T cells | Immunoregulation and cytotoxicity | TCR T cell receptor The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is responsible for recognizing antigens bound to major histocompatibility complex molecules... γδ and CD3 CD3 CD3 or CD-3 may be:* CD3 , an antigen, cluster of differentiation protein , part of the T cell receptor complex on a mature T lymphocyte* Ford CD3 platform* MediaMax CD-3, copy protection scheme* MiniCD, a 3-inch CD... |
|
| B cells 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... |
Secretion of antibodies | 23% (18-47%) | MHC class II MHC class II MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells .... , CD19 CD19 B-lymphocyte antigen CD19 also known as CD19 , is a protein that in humans is encoded by the CD19 gene.- Function :... and CD21 |
In the circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
they move from lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
to lymph node. This contrasts with macrophages, which are rather stationary in the nodes.
Lymphocytes and disease
A lymphocyte count is usually part of a peripheral complete blood cell count and is expressed as percentage of lymphocytes to total white blood cells counted.A general increase in the number of lymphocytes is known as lymphocytosis
Lymphocytosis
Lymphocytosis is an increase in the number or proportion of lymphocytes in the blood, usually detected when a complete blood count is routinely obtained. Lymphocytes normally represent 20 to 40% of circulating white blood cells...
whereas a decrease is lymphocytopenia
Lymphocytopenia
Lymphocytopenia, or lymphopenia, is the condition of having an abnormally low level of lymphocytes in the blood. Lymphocytes are a white blood cell with important functions in the immune system...
.
High
An increase in lymphocyte concentration is usually a sign of a viral infection (in some rare case, leukemiaLeukemia
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...
s are found through an abnormally raised lymphocyte count in an otherwise normal person).
Low
A low normal to low absolute lymphocyte concentration is associated with increased rates of infection after surgery or trauma.One basis for low T cell lymphocytes occurs when the human immunodeficiency virus (HIV) infects and destroys T cells (specifically, the 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...
+ subgroup of T lymphocytes). Without the key defense that these T cells provide, the body becomes susceptible to opportunistic infection
Opportunistic infection
An opportunistic infection is an infection caused by pathogens, particularly opportunistic pathogens—those that take advantage of certain situations—such as bacterial, viral, fungal or protozoan infections that usually do not cause disease in a healthy host, one with a healthy immune system...
s that otherwise would not affect healthy people. The extent of HIV progression is typically determined by measuring the percentage of CD4+ T cells in the patient's blood. The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in 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....
.
Immunodeficiency
"A CD4 count of <200 × 106 cells/μL is very likely if the EDEmergency department
An emergency department , also known as accident & emergency , emergency room , emergency ward , or casualty department is a medical treatment facility specialising in acute care of patients who present without prior appointment, either by their own means or by ambulance...
ALC is <950 × 106 cells/μL and less likely if the ALC is >1,700 × 106 cells/μL".
Tumor-Infiltrating Lymphocytes
In some cancers, e.g., melanomaMelanoma
Melanoma is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye...
and colorectal cancer
Colorectal cancer
Colorectal cancer, commonly known as bowel cancer, is a cancer caused by uncontrolled cell growth , in the colon, rectum, or vermiform appendix. Colorectal cancer is clinically distinct from anal cancer, which affects the anus....
, lymphocytes can migrate into and attack the tumor. This can sometimes lead to regression of the primary tumor.
Blood content
See also
- AddressinAddressinAddressin also known as mucosal vascular addressin cell adhesion molecule 1 is a protein that in humans is encoded by the MADCAM1 gene....
- AnergyAnergyAnergy is a term in immunobiology that describes a lack of reaction by the body's defense mechanisms to foreign substances, and consists of a direct induction of peripheral lymphocyte tolerance. An individual in a state of anergy often indicates that the immune system is unable to mount a normal...
- Complete blood countComplete blood countA complete blood count , also known as full blood count or full blood exam or blood panel, is a test panel requested by a doctor or other medical professional that gives information about the cells in a patient's blood...
- CytotoxicityCytotoxicityCytotoxicity is the quality of being toxic to cells. Examples of toxic agents are a chemical substance, an immune cell or some types of venom .-Cell physiology:...
- Human leukocyte antigenHuman leukocyte antigenThe human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
- Lymphoproliferative disordersLymphoproliferative disordersLymphoproliferative disorders refer to several conditions in which lymphocytes are produced in excessive quantities. They typically occur in patients who have compromised immune systems...
- Reactive lymphocyteReactive lymphocyteReactive lymphocytes are lymphocytes that become large as a result of antigen stimulation. Typically they can be more than 30 µm in diameter with varying size and shape....
- Secretion assaySecretion assaySecretion assay is a process used in cell biology to identify cells that are secreting a particular protein . It was first developed by Manz et al. in 1995....
- TrogocytosisTrogocytosisTrogocytosis is a process whereby lymphocytes conjugated to antigen-presenting cells extract surface molecules from these cells and express them on their own surface...