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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

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