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Immunology Glossary

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Acquired Immune Deficiency Syndrome (AIDS)
disease caused by infection with the human immunodeficiency virus (HIV); involves a gradual destruction of the CD4 T-cell population and increasing susceptibility to infection
acquired immunity
the state of resistance to infection that is produced by the adaptive immune response; aka adaptive immunity
acute-phase protein
plasma proteins made by the liver whose synthesis is rapidly increased in response to infection; includes mannose-binding lectin (MBL), C-reactive protein (CRP), and fibrinogen
acute-phase response
a response of innate immunity that occurs soon after the start of an infection and involves the synthesis of acute-phase proteins by the liver and their secretion into the blood
adaptive immune response
the response antigen-specific B and T lymphocytes to antigen, including the development of immunological memory; aka acquired immunity
adjuvant
substance used to enhance the adaptive immune response to any antigen; to exert its effect it must be mixed with the antigen before injection or vaccination
afferent lymphatic vessels
vessels that bring lymph drainage from connective tissue into a lymph node en route to the blood
affinity
a measure of the strength with which one molecule binds to another via a single binding site
affinity maturation
the increase in affinity of the antigen-binding site of antibodies for the antigen that occurs during the course of an adaptive immune response
agglutination
the clumping together of particles, usually caused by antibody or some other multivalent binding molecule interacting with antigens on the surfaces of adjacent particles; such particles are said to be agglutinated; when the particles are red blood cells, the phenomenon is hemagglutination; when they are white blood cells it is call leukoagglutination
allergen
an antigen that elicits hypersensitivity or allergic reactions; usually innocuous proteins that do not inherently threaten the integrity of the body
allergy
a state of hypersensitivity to a normally innocuous environmental antigen; results from the interaction between the antigen and antibodies or T cells produced by earlier exposure to the same antigen
Tumor Necrosis Factor-alpha (TNFa)
a cytokine produced by macrophages and T cells that has several functions in the immune response and is the prototype of the TNF family of cytokines; functions as cell-associated or secreted proteins that interact with receptors of the tumor necrosis factor receptor (TNFR) family
Type I interferon
cytokines (interferons-alpha and -beta) produced by virus-infected cells that interfere with viral replication by the infected cell, and also signal neighboring uninfected cells to prepare for infection
V domain
the amino-terminal domain of immunoglobulin and T-cell receptor polypeptide chains; paired ones make up the antigen-binding site; aka variable domain
V gene segment
DNA sequence in the immunoglobulin or T-cell receptor genes that encodes the first 95 or so amino acids of the V domain; there are multiple different ones in the germline genome; to produce a complete exon encoding a V domain, one must be arranged to join up with a J or rearranged DJ gene segment; aka variable gene segment
V region
the extracellular amino-terminal region of an immunoglobulin heavy or light chain or a T-cell receptor that contains variable amino acid sequences that are different between every clone of a lymphocyte and that are responsible for specificity for antigen; antigen-binding variable sequences are localized to hypervariable segments; aka variable region
vaccination
the deliberate induction of protective immunity to a pathogen by the administration of killed or non-pathogenic forms of the pathogen, or its antigens, to induce an immune response
vaccine
any preparation made from a pathogen that is used for vaccination and provides protective immunity against infection with the pathogen
variable domain
the amino-terminal domain of immunoglobulin and T-cell receptor polypeptide chains; paired ones make up the antigen-binding site; aka V domain
variable gene segment
DNA sequence in the immunoglobulin or T-cell receptor genes that encodes the first 95 or so amino acids of the V domain; there are multiple ones in the germline genome; to produce a complete exon encoding a V domain, one must be arranged to join up with a J or a rearranged DJ gene segment; aka V gene segment
variable region
the extracellular amino-terminal region of an immunoglobulin heavy or light chain or a T-cell receptor that contains variable amino acid sequences that are different between every clone of a lymphocyte and that are responsible for specificity for antigen; the antigen-binding variable sequences are localized to hypervariable segments; aka V region
viruses
submicroscopic pathogens composed of a nucleic acid genome enclosed in a protein coat; they replicate only in a living cell because they do not possess all the metabolic machinery required for independent life; a viral particle is called a virion
alternative pathway of complement activation
one of three pathways of complement activation; triggered by the presence of infection but does not involve antibody
anaphylactic shock
IgE-mediated allergic reaction to systemically adminstered antigen that causes circulatory collapse and suffocation due to tracheal swelling; aka systemic anaphylaxis
antibody
a type of glycoprotein molecule, also called immunoglobulin (Ig), produced by B lymphocytes, that binds antigens, often with a high degree of specificity and affinity; the basic structural unit is composed of 2 identical heavy chains and 2 identical light chains; amino-terminal variable regions of the heavy and light chains form the antigen binding sites, whereas the carboxy-terminal constant regions of the heavy chains functionally interact with other molecules in the immune system; in an individual there are millions of different ones, each with an unique binding site; secreted ones perform the various effector functions, including neutralizing antigens, activating complement, and promoting phagocytosis and destruction of microbes; membrane-bound immunoglobulin can be found on naive B lymphocytes
antigen
originally defined as any molecule that binds specifically to an antibody, the term now also refers to any molecule that can bind specifically to an antibody or T-cell receptor; those that bind to antibodies include all classes of molecules; TCR's only bind peptide fragments of proteins complexed and MHC molecules
antigen-binding site
the site on an immunoglobulin or T-cell receptor molecule that binds specific antigen
antigen presentation
the display of antigen as peptide fragments bound to MHC molecules on the surface of cells; this is the form in which antigen is recognized by most T cells
antigen-presenting cells
cells that express either MHC Class I and/or MHC Class II molecules and thus display complexes of MHC molecule and peptide antigen on their surfaces
antigen processing
the intracellular degradation of proteins into peptides that bind to MHC molecules for presentation to T cells
antigen receptor
for a B cell, this is its cell-surface immunoglobulin; for a T cell it is a rather similar molecule called the T-cell receptor; each individual lymphocyte bears receptors of a single antigen specificity
antigenic drift
a process by which point mutations in influenza virus genes cause differences in the structure of viral surface antigens; causes year-to-year antigenic differences in strains of influenza virus
T-cell priming
the activation of mature naive T cells by antigen presented to them by professional antigen-presenting cells
T-cell receptor
the highly variable antigen receptor of T lymphocytes; on most T cells it is composed of a variable alpha chain and beta chain and is known as the alpha:beta T-cell receptor; on a minority of T cells, the variable chains are gamma and delta chains, and this receptor is known as the gamma:delta T-cell receptor; both types of receptor are present at the cell surface in association with the complex of invariant CD3 chains and ? chains, which have a signaling function
T lymphocyte
lymphocytes that develop in the thymus and are responsible for cell-mediated immunity; their cell-surface antigen receptor is called the T-cell receptor; aka T cells
target cell
any cell that is acted on directly by effector T cells, effector cells, or molecules; for example, virus-infected cells are the targets of cytotoxic T cells, which kill them, and naive B cells are the targets of effector CD4 T cells, which help to stimulate them to produce antibodies
TH1 cells
a subset of CD4 T cells that are characterized by the cytokines they produce; involved mainly in activating macrophages; also called inflammatory T cells
TH2 cells
a subset of CD4 T cells that are characterized by the cytokines they produce; involved mainly in stimulating B cells to produce antibody; also called helper T cells
thymocyte
a precursor of a mature T lymphocyte present in the thymus
thymus
a lymphoepithelial organ in the upper part of the middle of the chest, just behind the breastbone; the site of T-cell development
tolerance
when the immune system of a person does not or cannot respond to an antigen; in such cases the individual is said to be tolerant of the antigen
toll-like receptors
receptors of the innate immune system that recognize frequently encountered structures called molecular patterns produced by microorganisms and that facilitate innate immune responses against the microorganism; found on phagocytes
tonsils
large aggregates of lymphoid cells lying on each side of the pharynx
toxoids
toxins that have been deliberately inactivated by heat or chemical treatment so that they are no longer toxic but can still provoke a protective immune response on vaccination
antigenic shift
a process by which influenza viruses reassort their segmented genomes and change their surface antigens radically; new viruses arising by antigenic shift are the usual cause of influenza pandemics
autoimmune disease
disease in which the pathology is caused by an immune response to normal components of healthy tissue
autoimmunity
adaptive immunity specific for an antigenic component of the individual's own body
B cells
lymphocytes that are dedicated to making immunoglobulins and antibodies
B-cell receptor
the antigen receptor on B cells; each B cell is programmed to make a single type of immunoglobulin; the cell-surface form of this immunoglobulin serves as the beta-cell receptor for specific antigen; associated in the membrane with the immunoglobulin are the signal transduction molecules Igalpha and Igbeta
B lymphocytes
lymphoctyes that are dedicated to making immunoglobulins and antibodies; aka B cells
bacteria
diverse prokaryotic microorganisms that are responsible for many infectious diseases of humans and other animals
bone marrow
the tissue in the center of certain bones that is the major site of generation of all the cellular elements of blood (hematopoiesis)
carrier
foreign protein to which small non-immunogenic antigens, or haptens, can be coupled to render the hapten immunogenic; in vivo, self proteins can also serve as carriers if they are suitably modified by the hapten; this is important in allergy to drugs
CD molecules
cell surface molecules expressed on various cell types in the immune system that are designed by the "cluster of differentiation" or CD nomenclature
CD4
a cell surface glycoprotein on some T cells that recognize antigens presented by MHC Class II molecules; CD4 binds to MHC Class II molecules on the antigen-presenting cell and acts as a co-receptor to augment the T cell's response to antigen
serology
the study of the blood (serum) antibodies and their reactions with antigen; often used to refer to the diagnosis of infectious disease by detection of microbe-specific antibodies in the serum of the patient
serotypes
antigenically different strains of a bacterium or other pathogen that can be distinguished by immunological means, for example by antibody-based detection tests; also used to describe human alloantigens such as HLA and blood group antigens
serum
the cell-free fluid that remains when blood or plasma forms a clot; blood antibodies are found in this fraction
specificity
the property of antibodies and other antigen-binding molecules for selective interaction with only one or a few types of molecules or cells
spleen
organ situated adjacent to the cardiac end of the stomach; one function of this organ is to remove old or damaged red blood cells from circulation; the other is as a secondary lymphoid organ that responds to blood-borne pathogens and antigens
stem cell
the undifferentiated cell that divides continuously and gives rise to additional type of these cells and to cells of multiple different lineages; for example, all blood cells arise from a common hematopoetic type of this cell in the bone marrow
superantigen
molecules that, by binding non-specifically to MHC Class II molecules and T-cell receptors, stimulate the polyclonal activation of T cells; includes several staphylococcal enterotoxins; their importance lies in the ability to activate many T cells, resulting in the production and release large amounts of cytokines; toxic shock syndrome is mediated by this
suppressor CD4 T cells
antigen-specific CD4 T cells whose actions can suppress immune response; aka regulatory CD4 T cells
systemic anaphylaxis
a rapid-onset and potentially fatal form of IgE-mediated allergic reaction, in which antigen in the bloodstream triggers the activation of mast cells throughout the body, causing circulatory collapse and suffocation due to tracheal swelling
T cells
lymphocytes that develop in the thymus and are responsible for cell-mediated immunity; their cell-surface antigen receptor is called the T-cell receptor; aka T lymphocytes
T-cell activation
the stimulation of mature naive T cells by antigen presented to them by professional antigen-presenting cells; leads to their proliferation and differentiation into effector T cells
T-cell areas
parts of secondary lymphoid tissues where the lymphocytes are predominantly T cells
CD4 T cells
the subset of T cells that express the CD4 co-receptor and recognize peptide antigens presented by MHC Class II molecules
CD8
a cell-surface glycoprotein on some T cells that recognizes antigens presented by MHC Class I molecules; binds to MHC Class I molecules on the antigen-presenting cell and acts as a co-receptor to augment the T-cell's response to antigen
CD8 T cells
the subset of T cells that express the CD8 co-receptor and recognize peptide antigens presented by MHC Class I molecules; aka cytotoxic CD8 T cells
cell-mediated immunity
any adaptive immune response in which antigen-specific effector T cells dominate; defined operationally as all adaptive immunity that cannot be transferred to a naive recipient with serum antibody; these immune responses include CD4+ T cell-mediated activation of macrophages that have phagocytosed microbes and CD8+ cytolytic T lymphocyte killing of infected cells; aka cellular immunity
chemokines
large group of small proteins involved in guiding white blood cells to sites where their functions are needed; have a central role in inflammatory responses
chemotaxis
movement of a cell directed by a chemical concentration gradient; the movement of lymphocytes, PMN's, monocytes, and other leukocytes into various tissues is often directed by gradients of chemokines
classical pathway of complement activation
one of three pathways of complement activation; activated by antibody bound to antigen and involves complement components C1, C4, and C2 in the generation of C3 and C5 convertases
clonal deletion
the elimination of immature lymphocytes that bind to self antigens; main mechanism that produces self-tolerance
clonal selection
the central principle of adaptive immunity; the mechanism by which adaptive immune responses derive only from individual antigen-specific lymphocytes, which are stimulated by the antigen to proliferate and differentiate into antigen-specific effector cells
common lymphoid progenitor
stem cell that gives rise to all lymphocytes and is derived from a pluripotent hematopoietic stem cell
complement
a set of plasma proteins that act in a cascade of reactions to attack extracellular forms of pathogens; as a result of this becoming activated, pathogens become coated with these components, which can either kill the pathogen directly or cause its engulfment and destruction by phagocytes; there are 3 pathways of this becoming activated and they differ in how they are initiated; the classical pathway is activated by antigen-antibody complexes, the alternative pathway by microbial surfaces, and the lectin pathway by plasma lectins that bind to microbes; each pathway consists of a cascade of proteolytic enzymes that generate inflammatory mediators and opsonins, and leads to the formation of a lytic complex that inserts into cell membranes
secondary immune response
the adaptive immune response provoked by a second exposure to an antigen; differs from the primary response by starting sooner and building more quickly; aka secondary response
secondary lymphoid tissues
the lymph nodes, spleen, and mucosa-associated lymphoid tissues; the tissues in which immune response are initiated; the more highly organized tissues such as lymph nodes and spleen are also often known as secondary lymphoid organs
secretory component
fragment of the poly-Ig receptor left attached to dimeric IgA after its transport across epithelial cells; aka secretory piece
self antigens
a term used to describe all the normal constituents of the body to which the immune system would respond were it not for the mechanisms of tolerance that destroy or inactivate self-reactive B and T cells
self MHC
a person's own MHC molecules
self peptides
peptides produced from the body's own proteins; in the absence of infection these peptides occupy the peptide-binding sites of MHC molecules on cell surfaces; in a normal functioning immune system, they do not elicit an immune response
self-renewal
the ability of a population of cells to renew itself
self-tolerance
the normal situation whereby a person's immune system does not respond to constituents of the person's body
sensitization
in connection with allergy, the first exposure to an allergen that elicits an IgE response; allergic reactions occur only in individuals who have already been sensitized
sepsis
the toxic effects of infection of the bloodstream; usually caused by Gram-negative bacteria
septic shock
shock syndrome that is frequently fatal, caused by the systemic release of the cytokine TNF-alpha after bacterial infection of the bloodstream, usually with Gram-negative bacteria
septicemia
bacterial invasion of the blood
seroconversion
the phase of an infection when antibodies against the infecting agent are first detectable in the blood
complement activation
the initiation by pathogens of a series of reactions involving the complement components of plasma, leading to the death and elimination of the pathogen
complement receptors (CR)
cell-surface proteins on various cell types that recognize and bind complement proteins bound to antigens (chiefly C3b); these on phagocytes facilitate the phagocytic engulfment of pathogens coated with complement; include CR1, CR2, CR3, CR4, and the receptor for C1q
conformational epitopes
epitopes on a protein antigen that are formed from several separate regions in the primary sequence of a protein brought together by protein folding; antibodies that bind these bind only to native folded proteins; aka discontinuous epitopes
constant domains
the constituent domains of the constant regions of immunoglobulin and T-cell receptor polypeptide; aka C domains
constant region
the portion of immunoglobulin (Ig) or T cell receptor (TCR) polypeptide chains that does not vary in sequence among different clones of B and T cells and is not involved in antigen binding; for immunoglobulins there are several versions of these, but within each isotope (class of antibody) the sequence will be the same; aka C region
cytokines
proteins made by cells that affect the behavior of other cells; those made by lymphocytes are often called lymphokines or interleukins (IL); bind to specific receptors on their target cells
cytotoxic CD8 T cells
the subset of T cells that express the CD8 co-receptor and recognize peptide antigen presented by MHC Class I molecules
cytotoxic T cells
T cells that can kill other cells; almost all are CD8 T cells; important in host defense against viruses and other cytosolic pathogens because they recognize and kill the infected cells
cytotoxins
proteins made by cytotoxic T cells that participate in the destruction of target cells; perforins, granzymes or fragmentins, and granulysin are examples
defensins
peptides produced in epithelia and phagocyte granules which act as broad-spectrum antibiotics that kill a wide variety of bacteria and fungi
pluripotent hematopoietic stem cell
stem cell in bone marrow that gives rise to all the cellular elements of the blood
polymorphonuclear leukocytes
white blood cells with irregularly shaped, multibodied nuclei and cytoplasmic granules; there are 3 types: neutrophils, eosinophils, and basophils; aka granulocytes
present
cells carrying cell-surface complexes of peptide antigens and MHC molecules are said to _____ these antigens to T lymphocytes
primary immune response
the adaptive immune response that follows a person's first exposure to an antigen; aka primary response
primary lymphoid tissues
anatomical sites of lymphocyte development; the bone marrow and the thymus gland
professional antigen-presenting cells
cells that can present antigen to naive T cells and activate them; this not only displays peptide antigens bound to appropriate MHC molecules but also has co-stimulatory molecules on its surface that are needed to activate the T cell; includes only dendritic cells, macrophages, and B cells
programmed cell death
apoptosis
protective immunity
the specific immunological resistance to a pathogen that follows either from specific vaccination or recovery from an infection with the pathogen
pus
thick yellowish-white fluid that is formed in infected wounds; composed of dead and dying white blood cells (principally neutrophils), tissue debris, and dead microorganisms
pyogenic bacteria
extracellular encapsulated bacteria that cause the formation of pus at sites of infection
recirculation
of lymphocytes, their continual movement from blood to secondary lymphoid tissues to lymph and back to the blood; an exception to this pattern is traffic to the spleen; lymphocytes both enter and leave the spleen in the blood
regulatory CD4 T cells
antigen specific CD4 T cells whose actions can suppress immune responses
respiratory burst
metabolic change accompanied by a transient increase in oxygen consumption that occurs in neutrophils and macrophages when they have taken up opsonized particles; leads to the generation of toxic oxygen metobolites and other anti-bacterial substances that attack the phagocytosed material
delayed-type hypersensitivity (DTH)
a form of cell-mediated immunity elicited by antigen in the skin and mediated by CD4 TH1 cells; named because the reaction appears hours to days after antigen is injected
dendritic cells
professional antigen-presenting cells with a branched, dendritic morphology; the most potent stimulators of T-cell responses; aka interdigitating reticular cells, they are derived from the bone marrow and are distinct from the follicular dendritic cell that presents antigen to B cells; immature ones take up and process antigens but cannot yet stimulate T cells; mature or activated ones are present in secondary lymphoid tissues and are able to stimulate T cells
diapedesis
the movement of white blood cells from the blood across blood vessel walls into tissues
diversity
the existence of a large number of lymphocytes with different antigenic specifications in any individual; the lymphocyte repertoire is large and diverse
draining lymph node
the lymph node to which extracellular fluid collected at a site of infection first travels
edema
abnormal accumulation of fluid in connective tissue, leading to swelling
effector cells
the cells that perform effector functions during an immune response, such as secreting cytokines (ie helper T cells), killing microbes (ie macrophages, neutrophils, and eosinophils), killing microbe-infected host cells (ie CTL's), or secreting antibodies (ie differentiated B cells); B cell effector cells would be memory cells or plasma cells; T cell effector cells would be T helper cells or cytotoxic T cells
effector mechanisms
the physiological and cellular processes used by the immune system to destroy pathogens and remove them from the body
efferent lymphatic vessel
vessel in which lymph and lymphocytes leave a lymph node en route to the blood
encapsulated bacteria
bacteria that possess thick carbohydrate coats that protect them from phagocytosis; cause extracellular infections and can be dealt with by phagocytes only if the bacteria are first coated with antibody and complement
endocytic vesicle
membrane vesicle that is pinched off from the plasma membrane and takes extracellular material into cells
endocytosis
the uptake of extracullular material into cells by endocytic vesicles that form by pinching off pieces of plasma membrane
parasites
the unicellular protozoa and multicellular worms that infect animals and humans and live within them
passive immunization
the injection of specific antibodies to provide protection against a pathogen or toxin; the administered antibodies may derive from human blood donors, immunized animals, or hybridoma cell lines
passive transfer of immunity
transfer of immunity to a non-immune individual by the injection of specific antibody, immune serum, or T cells
pathogen
an organism, most commonly a microorganism, that can cause disease
pathology
the scientific study of disease or detectable damage to tissue caused by disease
pattern recognition receptors
receptors of the innate immune system that recognize frequently encountered structures called "molecular patterns" produced by microorganisms and that facilitate innate immune responses against the microorganism; these on phagocytes include toll-like receptors
perforin
one of the proteins released by cytotoxic T cells on contact with their target cells; forms pores in the target cell membrane that contribute to cell killing
peripheral lymphoid tissues
the lymph nodes, spleen, and mucosa-associated lymphoid tissues; tissues in which immune responses are initiated; more highly organized tissues such as lymph nodes and spleen are also often known as these tissues; aka secondary lymphoid tissues
Peyer's patches
gut-associated lymphoid tissue present in the wall of the small intestine, especially the ileum
phagocyte
a cell specialized to perform phagocytosis; the principal ones in mammals are neutrophils and macrophages
phagocytosis
cellular internalization of particulate matter, such as bacteria, by means of endocytosis; cells specialized in this are known as phagocytes
phagolysosome
intracellular vesicle formed by fusion of a phagosome with a lysosome, in which the phagocytosed material is broken down by degradative lysosomal enzymes
phagosome
intracellular vesicle containing material taken up by phagocytosis
plasma cells
terminally differentiated B lymphocytes that secrete antibody
endotoxin
a component of the outer leaflet of Gram-negative bacteria, also called lipopolysaccharide, which is released from dying bacteria, which stimulates many innate immune responses including the secretion of cytokines and induction of microbial activities in macrophages and the expression of adhesion molecules for leukocytes on endothelium
endothelium
the cell layer that lines blood vessels
eosinophil
white blood cell that is one of the three types of granulocytes; contain granules that stain with eosin and whose contents are secreted when the cell is stimulated; contribute chiefly to defense against parasitic infections
epitope
the specific portion of a macromolecular antigen to which an antibody binds; in the case of a protein antigen recognized by a T cell, it is the peptide portion that binds to a major histocompatibility complex molecule for recognition by the T cell receptor; aka antigenic determinant
erythrocyte
red blood cell
extravasation
the movement of cells or fluid from within blood vessels to the surrounding tissues
F(ab')2
a proteolytic fragment of IgG that consists of the two Fab arms held together by a disulfide bond; produced by digesting IgG with pepsin
Fab fragment
a proteolytic fragment of IgG that consists of the light chain and the amino-terminal half of the heavy chain held together by an interchain disulfide bond; called Fab because it is the Fragment with antigen-binding specificity; in the intact IgG molecule the parts corresponding to the Fab fragment are often called Fab or Fab arms
Fc fragment
a fragment of an antibody, resulting from proteolytic cleavage, that consists of the carboxy-terminal halves of the two heavy chains disulfide-bonded to each other; called Fc because it was the Fragment that was most readily crystallized in early studies of IgG antibody structure; in an intact antibody the part corresponding to the Fc fragment is called Fc, Fc region, or Fc piece
Fc receptors
cell-surface receptors for the Fc portion of some immunoglobulin isotypes; they include the Fc-gamma and Fc? receptors
Fc region
the part corresponding to the Fc fragment in an intact antibody
fever
a rise of body temperature above the normal; caused by cytokines produced in response to infection
myeloid progenitors
stem cells in the bone marrow that give rise to granulocytes, monocytes, and macrophages
naive B cell
a mature B cell that has left the bone marrow but has not yet encountered its specific antigen
naive T cell
a mature T cell that has left the thymus but not yet encountered its specific antigen
natural killer cells
large, granular, cytotoxic lymphocytes that circulate in the blood; important in innate immunity to viruses and other intracellular pathogens and also kill certain tumor cells; the cytotoxic cells in antibody-dependent cell-mediated cytotoxicity (ADCC); aka NK cells
necrosis
the death of cells by lysis that results from chemical or physical injury; leaves extensive cellular debris that must be removed by phagocytosis; neighboring tissue is also damaged by the molecules released from necrotic cells
neutralization
the mechanism by which antibodies binding to sites on pathogens prevent growth of the pathogen and/or its entry into cells; the toxicity of bacterial toxins can similarly be neutralized by bound antibody
neutrophils
phagocytic white blood cells that enter infected tissues in large numbers; contain granules that stain with neutral dyes; after entry into infected tissues, engulf and kill extracellular pathogens in large numbers; aka neutrophilic polymorphonuclear leukocytes (PMN's); type of granulocyte; most abundant white blood cell
nitric oxide
a biologic effector molecule with a broad range of activities that, in macrophages, function as a potent microbicidal agent that kills ingested organisms
NK cells
large, granular, cytotoxic lymphocytes that circulate in the blood; important in innate immunity to viruses and other intracellular pathogens and also kill certain tumor cells; the cytotoxic cells in antibody-dependent cell-mediated cytotoxicity (ADCC); aka natural killer cells
opportunistic pathogen
a microorganism that causes disease only in individuals whose immune systems are in some way compromised
opsonins
a macromolecule that becomes attached to the surface of a microbe that can be recognized by surface receptors of neutrophils and macrophages and that increases the efficiency of phagocytosis of the microbe; include antibodies and complement components that bind to pathogens and facilitate their phagocytosis by neutrophils or macrophages
opsonization
the coating of the surface of a pathogen or other particle with any molecule that makes it more readily ingested by phagocytosis; antibody and complement do this for extracellular bacteria for phagocytosis by neutrophils and macrophages because the phagocytic cells carry receptors for these molecules
framework regions
relatively invariant regions within the variable domains of immunoglobulins and T-cell receptors that provide a protein scaffold for the hypervariable regions
fungi
single-celled and multicellular eukaryotic organisms, including the yeasts and molds, that can cause a variety of diseases; immunity to them involves both humoral and cell-mediated responses
gene segments
multiple short DNA sequences in the immunoglobulin and T-cell receptor genes; can be rearranged in many different combinations to produce the vast diversity of immunoglobulin or T-cell receptor polypeptide chains
germinal center
area in secondary lymphoid tissue that is a site of intense B-cell proliferation, selection, maturation, and death; form around follicular dendritic cell networks when activated B cells migrate into lymphoid follicles
granulocytes
white blood cells with irregularly shaped, multi-lobed nuclei, and cytoplasmic granules; three types are neutrophils, eosinophils, and basophils; aka polymorphonuclear leukocytes
gut-associated lymphoid tissues
lymphoid tissues closely associated with the gastrointestinal tract, including the palatine tonsils, Peyer's patches in the intestine, and layers of intrepithelial lymphocytes; aka GALT
H chain
the larger of the two component polypeptides of an immunoglobulin molecule; each has a variable domain and constant domains; the different antibody isotopes, including IgM, IgG, IgD, IgA, and IgE are distinguished by structural differences in the constant region of these; the constant region of these also mediate the distinctive effector functions on the antibody molecule; aka heavy chain
heavy chain
the larger of the two component polypeptides of an immunoglobulin molecule; each has a variable domain and constant domains; the different antibody isotopes, including IgM, IgG, IgD, IgA, and IgE are distinguished by structural differences in the constant region of these; the constant region of these also mediate the distinctive effector functions on the antibody molecule; aka H chain
helper CD4 cells
CD4 T cells are sometimes generally known as helper cells because their function is to help other cell types to perform their functions; sometimes refers to TH2 cells only, the cells that help B cells to produce antibody
hematopoiesis
the generation of the cellular elements of blood, including the red blood cells, white blood cells, and platelets; these cells all originate from pluripotent hematopoietic stem cells whose diffentiated progeny divide under the influence of various hematopoietic growth factors
herd immunity
the phenomenon whereby those people in a population who have no protective immunity against a pathogen are largely protected from infection when the majority of the population is resistant to the pathogen
memory T cells
long-lived antigen-specific T cells that are activated in secondary and subsequent immune responses to an antigen
MHC Class I molecules
the class of MHC molecules that present peptides generated in the cytosol to CD8 T cells; consist of a heterodimer of a Class I heavy chain associated with beta-2-microglobulin
MHC Class II molecules
the class of MHC molecules that present peptides generated in intracellular vesicles to CD4 T cells; consist of a heterodimer of Class II alpha and beta chains
MHC molecules
major histocompatibility complex molecules; highly polymorphic glycoproteins encoded by the major histocompatibility complex; form complexes with peptides and present peptide antigens to T cells; there are two classes--MHC Class I and MHC Class II molecules--with different roles in the immune response; also known as histocompatibility antigens because they are the main alloantigens involved in the rejection of transplanted tissues
monoclonal antibodies
antibodies produced by a single clone of B lymphocytes and that are therefore identical in structure and antigen specificity
monocytes
white blood cells with a bean-shaped nucleus; precursors of tissue macrophages
mucosa
the mucus-secreting epithelia that line the respiratory, intestinal, and urogenital tracts; conjunctiva of the eye and the mammary glands are also in this category; aka mucosal surfaces
mucosa-associated lymphoid tissue
aggregations of lymphoid cells in mucosal epithelia and in the lamina propria beneath; the main mucosa-associated lymphoid tissues are the gut-associated lymphoid tissues (GALT) and the bronchial-associated lymphoid tissues (BALT); aka MALT
mucus
slimy protective secretion produced by many internal epithelia
mutagen
any agent, such as a chemical or radiation, that can cause a mutation
mutation
an alteration in the DNA sequence of a gene
myeloid lineage
a subset of bone marrow derived cells comprising granulocytes, monocytes, and macrophage
hinge region
the region of immunoglobulin heavy chains that can assume multiple conformations, thereby imparting a flexibility in the orientation of the two antigen-binding sites; allows antibody to simultaneously bind two epitopes that are anywhere within reach of one another
histamine
a vasoactive amine stored in mast cell granules; released when antigen binds to IgE molecules on mast cells and causes dilation of local blood vessels and contraction of smooth muscle, producing some of the symptoms of immediate hypersensitivity reactions; drugs can counter its action
hives
itchy red swellings in the skin caused by IgE-mediated reactions; aka urticaria or nettle rash
HLA
human leukocyte antigen; genetic designation for the human MHC; individual loci are designated by capital letters, as in HLA-A, and alleles are designated by numbers, as in HLA-A*0201
HLA Class I molecules
the name for the human version of the MHC Class I molecules
HLA Class II molecules
the name for the human version of the MHC Class II molecules
HLA-A, HLA-B, HLA-C
the highly polymorphic human MHC Class I molecules
HLA-DP, HLA-DQ, and HLA-DR
the highly polymorphic human MHC Class II molecules; each Class II molecule is made from alpha and beta chains encoded by A and B genes, respectively; for example, the HLA-DP-alpha and HLA-DP-beta chains are encoded by the HLA-DPA and HLA-DPB genes, respectively; all the genes are in the MHC
HLA type
the combination of HLA Class I and Class II allotypes that a person expresses
homing
the directed migration of subsets of circulating lymphocytes into particular tissue sites; this for lymphocytes is regulated by the selective expression of adhesion molecules on the lymphocytes and the tissue-specific expression of endothelial ligand for the receptors; typically involve the movement of naive T cells into secondary lymphoid tissues, or of effector T cells to an effector site
human immunodeficiency virus
the causative agent of the acquired immune deficiency syndrome (AIDS); a retrovirus of the lentivirus family that infects CD4 T cells, leading to their slow depletion, which eventually results in immunodeficiency
human leukocyte antigen (HLA) complex
the human major histocompatibility comples (MHC)
macrophages
large mononuclear phagocytic cells resident in most tissues; derived from blood monocytes and contribute to innate immunity and early nonadaptive phases of host defenses; function as professional antigen-presenting cells and as effector cells in humoral and cell-mediated immunity
major histocompatibility complex
a cluster of genes on the short arm of human chromosome 6 that encodes a set of polymorphic membrane glycoproteins called the MHC molecules, which are involved in presenting peptide antigens to T cells
mannose-binding lectin (MBL)
an acute-phase protein in the blood that binds to mannose residues on pathogen surfaces and when bound activates the complement system; aka mannose-binding protein (MBP) and mannan-binding lectin
mannose receptor
a carbohydrate binding receptor (lectin) expressed by macrophages that binds mannose and fucose residues on microbial cell walls and mediates phagocytosis of the organisms
mast cells
large bone marrow derived cells found resident in connective tissues throughout the body; contain large granules that store a variety of chemical mediators including histamine; have high-affinity Fc? receptors that bind free IgE; antigen binding to these associated with IgE triggers their activation and degranulation, producing a local or systemic immediate hypersensitivity reaction; have crucial role in allergic reactions
mature dendritic cell
dendritic cells in secondary lymphoid tissues that express co-stimulatory molecules and other cell-surface molecules that enable them to present antigen to naive T cells and activate them
membrane-attack complex
the complex of terminal complement components that forms a pore in the membrane of the target cell, damaging the membrane and leading to cell lysis
memory B cells
long-lived antigen-specific B cells that are produced from activated naive B cells during the primary immune response to an antigen; on subsequent exposure to their specific antigen they are reactivated to differentiate into plasma cells as part of the secondary and subsequent immune responses
memory cells
general term for lymphocytes that are responsible for the phenomenon of immunological memory and protective immunity
humoral immunity
the type of adaptive immunity that is mediated by antibodies; the principal defense mechanism against extracellular microbes and their targets; can be transferred to a non-immune recipient by serum
hybridomas
hybrid cell lines that make monoclonal antibodies of defined specificity; formed by fusing a specific antibody-producing B lymphocyte with a myeloma cell that grows in tissue culture and does not make any immunoglobulin chains of its own
hypersensitivity reactions
immune responses to innocuous antigens that lead to symptomatic reactions on re-exposure; can cause hypersensitivity disease if they occur repetitively; this state of heightened reactivity to an antigen is called hypersensitivity; classified by mechanism: Type I involve the triggering of mast cells by IgE antibodies; Type II involved IgG antibodies against cell-surface or matrix antigens; Type III involve antigen-antibody complex, and type IV are mediated by effector T cells
hypervariable regions
small regions of high amino acid sequence diversity within the variable regions of immunoglobulin and T-cell receptors; correspond to the complementarity-determining regions
IgA
the class of immunoglobulin having alpha heavy chains; these antibodies are those in dimeric form present in mucosal secretions; present in the blood in monomeric form
IgD
the class of immunoglobulin having delta heavy chains; appears as surface immunoglobulin on mature naive B cells but its function is unknown
IgE
the class of immunoglobulin having epsilon heavy chains; involved in allergic reactions
IgG
the class of immunoglobulin having gamma heavy chains; the most abundant class of immunoglobulin in plasma
IgM
the class of immunoglobulin having mu heavy chains; the first immunoglobulin to appear on the surface of B cells and the first antibody secreted during an immune response; secreted in pentameric form
immature dendritic cells
dendritic cells present in tissues, which take up antigen but do not express co-stimulatory molecules and cannot yet act as professional antigen-presenting cells to naive T cells
lymph nodes
a type of secondary lymphoid tissue found at many sites in the body where lymphatic vessels converge; antigens are delivered by the lymph and presented to the lymphocytes within these where adaptive immune responses are initiated
lymphatic system
a system of vessels throughout the body that collects tissue fluid (lymph) originally derived from the blood, and returns it, via the thoracic duct to the circulation; lymph nodes are interspersed along these vessels to trap and retain antigens present in the lymph
lymphatic vessels (lymphatics)
thin-walled vessels that carry lymph from tissues to secondary lymphoid tissues (with the exception of the spleen) and from secondary lymphoid tissues to the thoracic duct
lymphocytes
a class of white blood cells that consist of small and large lymphocytes; small ones bear variable cell-surface receptors for antigen and are responsible for adaptive immune responses; two main classes of small ones--B lymphocytes (B cells) and T lymphocytes (T cells); large granular ones are natural killer (NK) cells, ones of innate immunity
lymphoid
containing lymphocytes, or pertaining to lymphocytes
lymphoid lineage
all types of lymphocytes, and the bone marrow cells that give rise to them
lymphoid organs
organized tissues that contain very large numbers of lymphocytes held in a non-lymphoid stroma; primary ones, where lymphocytes are generated, are the thymus and bone marrow; the main secondary ones, in which adaptive immune responses are initiated, are the lymph nodes, spleen, and mucosa-associated lymphoid tissues such as tonsils, Peyer's patches, and the appendix
lymphoid progenitor
stem cell in bone marrow cell that gives rise to all lymphocytes
lysosome
a membrane-bound, acidic organelle abundant in phagocytic cells, which contains proteolytic enzymes that degrade proteins derived mainly from the extracellular environment
lytic granules
intracellular storage granules of cytotoxic T cells and NK cells that contain perforin and granzymes
M cells
specialized cells in intestinal epithelium through which antigens and pathogens enter gut-associated lymphoid tissue from the intestines; short for microfold cells
macrophage activation
stimulation of macrophages, which increases their phagocytic, antigen-presenting, and bacterial killing functions; occurs in the course of infection