Copy of `MicrobiologyBytes - Glossary of Immunology`
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MicrobiologyBytes - Glossary of Immunology
Category: Health and Medicine > Infection & Immunity
Date & country: 13/07/2008, US Words: 158
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Accessory cellCell required for, but not actually mediating, a specific immune response. Often used to describe antigen-presenting cells (APC; see below).
AffinityA measure of the binding constant of a single antigen combining site with a monovalent antigenic determinant.
AgglutinationThe aggregation of particulate antigen by antibodies. Agglutination applies to red blood cells as well as to bacteria and inert particles covered with antigen.
AllelicRelating to one of a series of two or more alternate forms of a gene that occupy the same position or locus on a specific chromosome.
Allelic exclusionThe ability of heterozygous lymphoid cells to produce only one allelic form of antigen-specific receptor when they have the genetic endowment to produce both. Genes other than those for the specific receptors are usually expressed codominantly.
AllergenAn antigen responsible for producing allergic reactions by inducing IgE formation.
AllergyA term covering immune reactions to non-pathogenic antigens, which lead to inflammation and deleterious effects in the host.
AllogeneicHaving a genetic dissimilarity within the same species.
AllograftA tissue transplant (graft) between two genetically nonidentical members of a species.
AllotypesAntigenic determinants that are present in allelic (alternate) forms. When used in association with immunoglobulin, allotypes describe allelic variants of immunoglobulins detected by antibodies raised between members of the same species.
Alternate (Alternative) pathwayThe mechanism of complement activation that does not involve activation of the C1, C4, C2 pathway by antigen-antibody complexes, and begins with the activation of C3.
AnaphylatoxinSubstance capable of releasing histamine from mast cells.
AnaphylaxisImmediate hypersensitivity response to antigenic challenge, mediated by IgE and mast cells. It is a life-threatening allergic reaction, caused by the release of pharmacologically active agents.
AntibodySerum protein formed in response to immunization; antibodies are generally defined in terms of their specific binding to the immunizing antigen.
AntigenAny foreign material that is specifically bound by specific antibody or specific lymphocytes; also used loosely to describe materials used for immunization. Antigens may also be immunogens if they are able to trigger an immune response, or haptens if not.
Antigen processingLarge molecules are broken down (processed) within macrophages into peptides and presented within the groove of MHC molecules.
Antigen receptorThe specific antigen-binding receptor on T or B lymphocytes; these receptors are transcribed and translated from rearrangements of V genes.
Antigen-binding siteThe part of an immunoglobulin molecule that binds antigen specifically.
Antigen-presenting cell (APC)A specialized type of cell, bearing cell surface class II MHC (major histocompatibility complex) molecules, involved in processing and presentation of antigen to inducer, or helper , T cells. Examples: macrophage, dendritic cells.
Antigenic determinantA single antigenic site or epitope on a complex antigenic molecule or particle.
AtopyA term used by allergists to describe IgE-mediated anaphylactic responses in humans, usually genetically determined.
AutograftA tissue transplant from one area to another on a single individual.
Autoimmunity (autoallergy)An immune response to 'self' tissues or components. Such an immune response may have pathological consequences leading to autoimmune diseases.
AvidityThe summation of multiple affinities, for example when a polyvalent antibody binds to a polyvalent antigen.
B lymphocyte (B cell)The precursors of antibody-forming plasma cells; these cells carry immunoglobulin and class II MHC (major histocompatibility complex) antigens on their surfaces.
BasophilA polymorphonuclear leukocyte., whose basophils granules contain heparin, histamine and other vasoactive amines. Within tissues, these cells are known as mast cells q.v.
Bence-Jones proteinDimers of immunoglobulin light chains in the urine of patients with multiple myeloma.
Blocking antibodyA functional term for an antibody molecule capable of blocking the interaction of antigen with other antibodies or with cells.
Bursa of FabriciusAn outpouching of the cloaca in birds; site of development of B cells in birds.
Carcinoembryonic antigen (CEA)Antigen present during embryonic development which normally disappears but reappears in malignant tissue.
CarrierA large immunogenic molecule or particle to which an antigenic determinant is attached, allowing the determinant to become immunogenic.
Cell-mediated cytotoxicity (CMC)Killing (lysis) of a target cell by an effector lymphocyte.
Cell-mediated immunity (CMI)Immune reaction mediated by T cells; in contrast to humoral immunity, which is antibody mediated. Also referred to as delayed-type hypersensitivity.
ChemotaxisMigration of cells along a concentration gradient of an attractant.
Class I, II and III MHC moleculesProteins encoded by genes in the major histocompatibility complex (q.v.). Class I molecules are designated HLA-A, B, or C. Class II molecules are designated DP, DQ or DR.
Class switchSee isotype switch.
Classical pathwayThe mechanism of complement activation initiated by antigen-antibody aggregates and proceeding by way of C1, C4 and C2.
Clonal deletionThe loss of lymphocytes of a particular specificity due to contact with either 'self' or artificially introduced antigen.
Clonal selection theoryThe prevalent concept that specificity and diversity of an immune response are the result of selection by antigen of specifically reactive clones from a large repertoire of preformed lymphocytes, each with individual specificities.
Cluster determinant (CD)Cluster of antigens with which antibodies react that characterize a cell surface marker.
Combinatorial joiningThe joining of segments of DNA to generate essentially new genetic information, as occurs with Ig genes during the development of B cells. Combinatorial joining allows multiple opportunities for 2 sets of genes to combine in different ways.
ComplementA series of serum proteins involved in the mediation of immune reactions. The complement cascade is triggered classically by the interaction of antibody with specific antigen.
Complement componentsAn enzymatic system of serum proteins triggered by the classical and alternative pathways, and resulting in target cell lysis, phagocytosis, opsonization and chemotaxis.
Complement receptorA structure found on erythrocytes, lymphocytes, neutrophils, monocytes and macrophages that binds C3 fragments.
Constant region (C region)The invariant carboxyl-terminal portion of an antibody molecule, as distinct from the variable region which is at the amino-terminal of the chain.
Coombs' testA test named for its originator, R.R.A. Coombs, used to detect non-agglutinating antibodies on red blood cells by addition of an anti-immunoglobulin antibody.
Cross-reactivityThe ability of an antibody, specific for one antigen, to react with a second antigen; a measure of relatedness between two different antigenic substances.
CytokinesSoluble substances secreted by cells, which have a variety of effects on other cells, e.g. Interleukin 1 (Il-1).
Cytotoxic (Cytolytic) T cellCell that kills target cells bearing appropriate antigen within the groove of an MHC class I molecule that is identical to that of the T cell.
D geneA small segment of immunoglobulin heavy-chain and T-cell receptor DNA, coding for the third hypervariable region of most receptors.
Delayed type hypersensitivity (DTH)A T cell-mediated reaction to antigen, which takes 24-48 hours to develop fully, and which involves release of lymphokines and recruitment of monocytes and macrophages. Also called c cell-mediated immunity.
DeterminantPart of the antigen molecule which binds to an antibody-combining site or to a receptor on T cells (see hapten and epitope).
Differentiation antigenA cell surface antigenic determinant found only on cells of a certain lineage and at a particular developmental stage; used as an immunologic marker.
DomainA compact segment of an immunoglobulin molecule, made up of about 110 amino acids around an S-S bond, and encoded by a unique segment of DNA, surrounded by nontranslated sequences.
DR antigensMHC class II molecules found on B cells and antigen-presenting cells of humans.
Enchancing antibodiesAntibodies which enhance the survival of a graft or of a tumour.
EosinophilA polymorphonuclear leukocyte with large eosinophilic (i.e. red) cytoplasmic granules.
EpitopeAn alternative term for antigenic determinant.
Equivalence zoneIn a precipitin reaction, the region in which the concentration of antigen and antibody leads to maximal precipitation.
ExonThe region of DNA coding for a protein or a segment of a protein.
FabFragment of antibody containing the antigen-binding site, generated by cleavage of the antibody with the enzyme papain, which cuts at the hinge region N-terminally to the inter-H-chain disulphide bond and generates two Fab fragments from one antibody molecule.
FcFragment of antibody without antigen-binding sites, generated by cleavage with papain; the Fc fragment contains the C-terminal domains of the heavy immunoglobulin chains.
Fc receptor (FcR)A receptor on a cell surface with specific binding affinity for the Fc portion of an antibody molecule. Fc receptors are found on many types of cells.
Fluorescent antibodyAn antibody coupled with a fluorescent dye, used with a fluorescence microscope to detect antigen on cells, tissues, or microorganisms.
Freund's complete adjuvantA water-in-oil emulsion that contains an immunogen, an emulsifying agent, and killed mycobacteria which enhance the immune response to the immunogen; termed 'incomplete' Freund's adjuvant if mycobacteria are not included.
GenotypeAll of the genes possessed by an individual; in practice it refers to the particular alleles present at the loci in question.
Germ lineRefers to genes in germ cells as opposed to somatic cells, that is, genes in their unrearranged state rather than those rearranged for production of a protein.
Graft versus host reaction (GVH)The pathologic consequences of a response initiated by transplanted immunocompetent T lymphocytes into an allogeneic, immunologically incompetent host. The host is unable to reject the grafted T cells and becomes their target.
H-2 complexThe major histocompatibility complex situated on chromosome 17 of the mouse; contains subregions K, I and D.
HaplotypeA particular combination of closely linked genes on a chromosome inherited from one patient.
HaptenA compound, usually of low molecular weight, that is not itself immunogenic but that, after conjugation to a carrier protein or cells, becomes immunogenic and induces antibody, which can bind the hapten alone in the absence of carrier.
Heavy chain (H chain)The larger of the two types of chains that comprise a normal immunoglobulin or antibody molecule.
Helper T cellsA class of T cells which help trigger B cells to make antibody against thymus-dependent antigens. Helper T cells also help generate cytotoxic T cells.
Heterophile antigenA cross-reacting antigen that appears in widely ranging species such as humans and bacteria.
Hinge regionA flexible, open segment of an antibody molecule that allows bending of the molecule. The hinge region is located between Fab and Fc and is susceptible to enzymatic cleavage.
HistocompatibilityLiterally, the ability of tissues to get along; in immunology, it means identity in all transplantation antigens. These antigens, in turn, are collectively referred to as histocompatibility antigens.
HLA complexSee 'Major histocompatibility complex'.
Humoral immunityAny immune reaction that can be transferred with immune serum is termed humoral immunity (as opposed to cell-mediated immunity). In general, this term refers to resistance that results from the presence of specific antibody.
HybridomaA hybrid cell that results from the fusion of an antibody-secreting cell with a malignant cell; the progeny secrete antibody without stimulation and proliferate continuously both in vivo and in vitro.
HypersensitivityState of reactivity to antigen that is greater than normal for the antigenic challenge; hypersensitivity is the same as allergy and denotes a deleterious outcome rather than a protective one.
Hypervariable regionsPortions of the light and heavy immunoglobulin chains that are highly variable in amino acid sequence from one immunoglobulin molecule to another, and that, together, constitute the antigen-binding site of an antibody molecule. Also, portions of the T-cell receptor which constitute the antigen-binding site.
Ia'Immune response-associated' proteins, found on B cells and antigen-presenting cells of mice; an old term now replaced with MHC (major histocompatibility complex) class II molecules.
IdiotypeThe combined antigenic determinants (idiotopes) found on antibodies of an individual that are directed at a particular antigen; such antigenic determinants are found only in the variable region.
Immediate-type hypersensitivityHypersensitivity tissue reaction occurring within minutes after the interaction of antigen and antibody.
Immune adherenceThe adherence of particulate antigen coated with C3b to tissue having cells with C3b receptors.
Immune complexAntigen bound to antibody.
Immune modulatorsSubstances that control the expression of the immune response.
Immune response (Ir) geneA gene controlling an immune response to a particular antigen; most genes of this type are in the MHC (major histocompatibility complex), and the term is rarely used to describe other types of Ir genes outside the MHC.
ImmunogenA substance capable of inducing an immune response (as well as reacting with the products of an immune response). Compare with antigen.
Immunoglobulin (Ig)A general term for all antibody molecules. Each Ig unit is made up of two heavy chains and two light chains and has two antigen- binding sites.
InterferonA group of proteins having antiviral activity and capable of enhancing and modifying the immune response.
InterleukinsGlycoproteins secreted by a variety of leukocytes which have effects on other leukocytes.
Internal imageA spatial configuration of the combining site of an anti-idiotype antibody which resembles the epitope to which the idiotype is directed.
IntronA segment of DNA that does not code for protein; the intervening sequence of nucleotides between coding sequences or exons.
IsograftA tissue transplanted between two genetically identical individuals.
IsohemagglutininsAntibodies to major red blood cell antigens present normally as a result of inapparent immunization by cross-reactive antigens in bacteria, food, etc.
Isotype switchThe shift of a B cell or its progeny from the secretion of antibody of one isotype or class of antibody with the same V regions but a different heavy- chain constant region and, hence, a different isotype (class switch).
IsotypesClasses of antibody that differ in the constant region of their heavy chain (Fc portion); distinguishable also on the basis of reaction with antisera raised in another species. These differences also result in different biological activities of the antibodies.
J chain (joining chain)A polypeptide involved in the polymerization of immunoglobulin molecules IgM and IgA.
J geneA gene segment coding for the J or joining segment in immunoglobulin DNA; V genes translocate to J segments in L chains, and to D and J segments in H chains. Also, codes for a portion of the T-cell receptor.