BIO - TERMS - ANTIGEN Flashcards
ABO blood group system
The classification of red blood cells based on the presence or absence of A and B carbohydrate antigens.
accessory effector cells
Cells that aid in an adaptive immune response but are not involved in specific antigen recognition. They include phagocytes, neutrophils, mast cells, and NK cells.
acellular pertussis vaccines
A formulation of pertussis used for vaccination containing chemically inactivated antigens, including pertussis toxoid.
activated macrophage
A macrophage that has increased phagocytic ability and other functions after exposure to mediators released by T cells after stimulation by antigens.
afferent lymphatic vessels
Vessels of the lymphatic system that drain extracellular fluid from the tissues and carry antigen, macrophages, and dendritic cells from sites of infection to lymph nodes or other peripheral lymphoid organs.
agnathan paired receptors resembling Ag receptors (APARs)
Multigene family of genes containing immunoglobulin domains present in hagfish and lamprey, that possibly represent ancestral predecessors of mammalian antigen receptors.
allelic exclusion
In a heterozygous individual, the expression of only one of the two alternative alleles of a particular gene. In immunology, the term describes the restricted expression of the individual chains of the antigen receptor genes, such that each individual lymphocyte produces immunoglobulin or T-cell receptors of a single antigen specificity.
allergic asthma
An allergic reaction to inhaled antigen, which causes constriction of the bronchi, increased production of airway mucus, and difficulty in breathing.
allergic reaction
A specific response to an innocuous environmental antigen, or allergen, that is caused by sensitized B or T cells. Allergic reactions can be caused by various mechanisms, but the most common is the binding of allergen to IgE bound to mast cells, which causes the cells to release histamine and other biologically active molecules that cause the signs and symptoms of asthma, hay fever, and other common allergic responses.
allergy
The state in which a symptomatic immune reaction is made to a normally innocuous environmental antigen. It involves the interaction between the antigen and antibody or primed T cells produced by earlier exposure to the same antigen.
alloantibodies
Antibodies produced against antigens from a genetically nonidentical member of the same species.
alloantigens
Antigens from another genetically nonidentical member of the same species.
alum
Inorganic aluminum salts (for example aluminum phosphate and aluminum hydroxide); they act as adjuvants when mixed with antigens and are one of the few adjuvants permitted for use in humans.
anchor residues
Specific amino acid residues in antigenic peptides that determine peptide binding specificity to MHC class I molecules. Anchor residues for MHC class II molecules exist but are less obvious than for MHC class I.
anergy
A state of nonresponsiveness to antigen. People are said to be anergic when they cannot mount delayed-type hypersensitivity reactions to a test antigen, whereas T cells and B cells are said to be anergic when they cannot respond to their specific antigen under optimal conditions of stimulation.
antibody response
Adaptive immune response in which B cells are activated to secrete antibodies that circulate in the bloodstream or enter other body fluids, where they can bind specifically to the foreign antigen that stimulated their production.
antigen presentation
The display of antigen on the surface of a cell in the form of peptide fragments bound to MHC molecules. T cells recognize antigen when it is presented in this way.
antigen processing
The intracellular degradation of foreign proteins into peptides that can bind to MHC molecules for presentation to T cells. All protein antigens must be processed into peptides before they can be presented by MHC molecules.
antigen receptor
The cell-surface receptor by which lymphocytes recognize antigen. Each individual lymphocyte bears receptors of a single antigen specificity.
AP-1
A heterodimeric transcription factor formed as one of the outcomes of intracellular signaling via the antigen receptors of lymphocytes and the TLRs of cells of innate immunity. Most often, contains one Fos-family member and one Jun-family member. AP-1 mainly activates the expression of genes for cytokines and chemokines.
autoantibodies
Antibodies specific for self antigens.
autoantigens
A self antigen to which the immune system makes a response.
autoimmune hemolytic anemia
A pathological condition with low levels of red blood cells (anemia), which is caused by autoantibodies that bind red blood cell surface antigens and target the red blood cell for destruction.
autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy (APECED)
A disease characterized by a loss of tolerance to self antigens, caused by a breakdown of negative selection in the thymus. It is due to defects in the gene AIRE, which encodes a transcriptional regulatory protein that enables many self antigens to be expressed by thymic medullary epithelial cells. Also called autoimmune polyglandular syndrome type I.
autoimmunity
Adaptive immunity specific for self antigens.
B-1 B cells
A class of atypical, self-renewing B cells (also known as CD5 B cells) found mainly in the peritoneal and pleural cavities in adults and considered part of the innate rather than the adaptive immune system. They have a much less diverse antigen-receptor repertoire than conventional B cells and are the major source of natural antibody.
B-cell co-receptor complex
A transmembrane signaling receptor on the B-cell surface composed of the proteins CD19, CD81, and CD21 (complement receptor 2), which binds complement fragments on bacterial antigens also bound by the B-cell receptor. Co-ligation of this complex with the B-cell receptor increases responsiveness to antigen about 100-fold.
B7 molecules, B7.1 and B7.2
Cell-surface proteins on specialized antigen-presenting cells such as dendritic cells, which are the major costimulatory molecules for T cells. B7.1 (CD80) and B7.2 (CD86) are closely related members of the immunoglobulin superfamily and both bind to the CD28 and CTLA-4 proteins on T cells.
BDCA-2 (blood dendritic cell antigen 2)
A C-type lectin expressed selectively as a receptor on the surface of human plasmacytoid dendritic cells.
cancer-testis antigens
Proteins expressed by cancer cells that are normally expressed only in male germ cells in the testis.
cathepsins
A family of proteases using cysteine at their active site that frequently function in processing antigens taken into the vesicular pathway.
caveolins
Family of unusual integral membrane proteins that are the major structural proteins in caveolae, CD4 Co-receptor protein on helper T cells and regulatory T cells that binds to a nonvariable part of class II MHC proteins (on antigen-presenting cells) outside the peptide-binding groove.
CD (cluster of differentiation)
Number assigned to an epitope on a single antigen, for example, CD4 protein, which is found on T helper cells.
CD1
Small family of MHC class I-like proteins that are not encoded in the MHC and can present glycolipid antigens to CD4 T cells.
CD103
Integrin αE:β7, a cell-surface marker on a subset of dendritic cells in the gastrointestinal tract that are involved in inducing tolerance to antigens from food and the commensal microbiota.
CD28
An activating receptor on T cells that binds to the B7 co-stimulatory molecules present on specialized antigen-presenting cells such as dendritic cells. CD28 is the major co-stimulatory receptor on naive T cells.
CD30, CD30 ligand
CD30 on B cells and CD30 ligand (CD30L) on helper T cells are co-stimulatory molecules involved in stimulating the proliferation of antigen-activated naive B cells.
CD4
The co-receptor for T-cell receptors that recognize peptide antigens bound to MHC class II molecules. It binds to the lateral face of the MHC molecule.
CD40, CD40 ligand
CD40 on B cells and CD40 ligand (CD40L, CD154) on activated helper T cells are co-stimulatory molecules whose interaction is required for the proliferation and class switching of antigen activated naive B cells. CD40 is also expressed by dendritic cells, and here the CD40–CD40L interaction provides co-stimulatory signals to naive T cells.
CD45
A transmembrane tyrosine phosphatase found on all leukocytes. It is expressed in different isoforms on different cell types, including the different subtypes of T cells. Also called leukocyte common antigen, it is a generic marker for hematopoietically derived cells, with the exception of erythrocytes.
CD69
A cell-surface protein that is rapidly expressed by antigen-activated T cells. It acts to down-modulate the expression of the sphingosine 1 phosphate receptor 1 (S1PR1), thereby retaining activated T cells within T-cell zones of secondary lymphoid tissues as they divide and differentiate into effector T cells.
CD86 (B7-2)
A transmembrane protein of the immunoglobulin superfamily that is expressed on antigen-presenting cells and binds to CD28 expressed by T cells.
cellular hypersensitivity reactions
A hypersensitivity reaction mediated largely by antigen-specific T lymphocytes.
cellular immunity (cell-mediated immunity)
An immune response that involves T cells binding to antigens presented on antigen-presenting cells; T cells then differentiate into several types of effector T cells.
central tolerance
Immunological tolerance to self antigens that is established while lymphocytes are developing in central lymphoid organs. Cf. peripheral tolerance.
chimeric antigen receptor (CAR)
Engineered fusion proteins composed of extracellular antigen-specific receptors (e.g., single-chain antibody) and intracellular signaling domains that activate and co-stimulate, expressed in T cells for use in cancer immunotherapy.
class II MHC protein
One of two classes of major histocompatibility complex (MHC) protein. Found on the surface of various antigen-presenting cells, where it presents peptides to helper and regulatory T cells.
classical MHC class I genes
MHC class I genes whose proteins function by presenting peptide antigens for recognition by T cells. Cf. nonclassical MHC class Ib.
clonal expansion
The proliferation of antigen-specific lymphocytes in response to antigenic stimulation that precedes their differentiation into effector cells. It is an essential step in adaptive immunity, allowing rare antigen-specific cells to increase in number so that they can effectively combat the pathogen that elicited the response.
clonal selection theory
The central paradigm of adaptive immunity. It states that adaptive immune responses derive from individual antigenspecific lymphocytes that are self-tolerant. These specific lymphocytes proliferate in response to antigen and differentiate into antigen-specific effector cells that eliminate the eliciting pathogen, and into memory cells to sustain immunity. The theory was formulated by Macfarlane Burnet and in earlier forms by Niels Jerne and David Talmage.
clonotypic
Describes a feature unique to members of a clone. For example, the distribution of antigen receptors in the lymphocyte population is said to be clonotypic, as the cells of a given clone all have identical antigen receptors.
co-stimulatory molecules
Cell-surface proteins on antigen-presenting cells that deliver co-stimulatory signals to naive T cells. Examples are the B7 molecules on dendritic cells, which are ligands for CD28 on naive T cells.
co-stimulatory receptors
Cell-surface receptors on naive lymphocytes through which the cells receive signals additional to those received through the antigen receptor, and which are necessary for the full activation of the lymphocyte. Examples are CD30 and CD40 on B cells, and CD27 and CD28 on T cells.
co-stimulatory signal
In immunology: a secreted or membrane-bound signal protein that helps activate an antigenresponding B cell or T cell.
combinatorial diversity
The diversity among antigen receptors generated by combining separate units of genetic information, comprising two types. First, receptor gene segments are joined in many different combinations to generate diverse receptor chains; second, two different receptor chains (heavy and light in immunoglobulins; α and β, or γ and δ, in T-cell receptors) are combined to make the antigen-recognition site.
complement fixation
The process in which complement combines with an antigen–antibody complex.
complement receptors (CRs)
Cell-surface proteins of various types that recognize and bind complement proteins that have become bound to an antigen such as a pathogen. Complement receptors on phagocytes enable them to identify and bind pathogens coated with complement proteins, and to ingest and destroy them. See CR1, CR2, CR3, CR4, CRIg, and the C1 complex.
complementarity-determining regions (CDRs)
Parts of the V domains of immunoglobulins and T-cell receptors that determine their antigen specificity and make contact with the specific ligand. The CDRs are the most variable part of antigen receptor, and contribute to the diversity of these proteins. There are three such regions (CDR1, CDR2, and CDR3) in each V domain.
conformational epitopes, discontinuous epitopes
Antigenic structure (epitope) on a protein antigen that is formed from several separate regions in the sequence of the protein brought together by protein folding. Antibodies that bind conformational epitopes bind only native folded proteins.
conjugated vaccine
A vaccine consisting of the desired antigen and other proteins.
continuous epitope, linear epitope
Antigenic structure (epitope) in a protein that is formed by a single small region of amino acid sequence. Antibodies that bind continuous epitopes can bind to the denatured protein. The epitopes detected by T cells are continuous. Also called a linear epitope.
conventional (or classical) dendritic cells (cDCs)
The lineage of dendritic cells that mainly participates in antigen presentation to, and activation of, naive T cells. Cf. plasmacytoid dendritic cells.
CR2 (CD21)
Complement receptor that is part of the B-cell co-receptor complex. It binds to antigens coated with breakdown products of C3b, especially C3dg, and, by cross-linking the B-cell receptor, enhances sensitivity to antigen at least 100-fold. It is also the receptor used by the Epstein–Barr virus to infect B cells.
CRAC channel
Channels in the lymphocyte plasma membrane that open to let calcium flow into the cell during the response of the cell to antigen. Channel opening is induced by release of calcium from the endoplasmic reticulum.
cross-priming
Activation of CD8 T cells by dendritic cells in which the antigenic peptide presented by MHC class I molecules is derived from an exogenous protein (i.e., by cross-presentation), rather than produced within the dendritic cells directly. Cf. direct presentation.
cryptic epitopes
Any epitope that cannot be recognized by a lymphocyte receptor until the antigen has been broken down and processed.
CTL (cytotoxic T lymphocyte)
An activated CD8+ T cell; kills cells presenting endogenous antigens.
Cutaneous immune system
The lymphocytes and scavenger antigen-presenting cells (Langerhans cells) that comprise the skinassociated lymphoid tissue. (Chapter 4)
cutaneous lymphocyte antigen (CLA)
A cell-surface molecule that is involved in lymphocyte homing to the skin in humans.
cyclophosphamide
A DNA alkylating agent that is used as an immunosuppressive drug. It acts by killing rapidly dividing cells, including lymphocytes proliferating in response to antigen.
Delayed-type hypersensitivity
A reaction caused by CD4 T cells that recognizes antigens in the skin; the reaction typically occurs hours to days aft er antigen is injected, hence its name; it is partially responsible for characteristic local responses to virus infections, such as rashes. (Chapter 4)
delayed-type hypersensitivity reactions
A form of cell-mediated immunity elicited by antigen in the skin stimulating sensitized Th1 CD4 lymphocytes and CD8 lymphocytes. It is called delayed-type hypersensitivity because the reaction appears hours to days after antigen is injected. Referred to as type IV hypersensitivity in the historic Gell and Coombs classification.
differentiation antigens
Referring to a category of genes with restricted expression patterns that can be targeted as antigens by immunotherapies in treatment of cancers.
direct agglutination test
The use of known antibodies to identify an unknown cell-bound antigen.
direct allorecognition
Host recognition of a grafted tissue that involves donor antigen-presenting cells leaving the graft, migrating via the lymph to regional lymph nodes, and activating host T cells bearing the corresponding T-cell receptors.
direct fluorescent-antibody (DFA) test
A fluorescent-antibody test to detect the presence of an antigen.
direct presentation
The process by which proteins produced within a given cell give rise to peptides presented by MHC class I molecules. This may refer to antigen-presenting cells, such as dendritic cells, or to nonimmune cells that will become the targets of CTLs.
DNA vaccination
Vaccination by introduction into skin and muscle of DNA encoding the desired antigen; the expressed protein can then elicit antibody and T-cell responses.
draining lymph nodes
A lymph node downstream of a site of infection that receives antigens and microbes from the site via the lymphatic system. Draining lymph nodes often enlarge enormously during an immune response and can be palpated; they were originally called swollen glands.
effector lymphocytes
The cells that differentiate from naive lymphocytes after initial activation by antigen and can then mediate the removal of pathogens from the body without further differentiation. They are distinct from memory lymphocytes, which must undergo further differentiation to become effector lymphocytes.
endogenous
(1) Infection caused by an opportunistic pathogen from an individual’s own normal microbiota. (2) Surface antigens on human cells produced as a result of infection.
Endogenous antigen presentation
Th e cellular process by which viral proteins are degraded inside the infected cell, and the resulting peptides are loaded onto major histocompatibility complex class I molecules that move to the cell surface. (Chapter 4)
epitope spreading
Increase in diversity of responses to autoantigens as the response persists, as a result of responses being made to epitopes other than the original one.
equilibrium phase
Stage of anti-tumor immune response when immunoediting allows the immune response to continuously shape the antigenic character of cancer cells.
