Immunology Glossary


Ab Abbrev. for antibody

ABA Acron. for azobenzenearsonate

Accessory cell Cell required for, but not actually mediating, a specific immune response. Often used to describe antigen-presenting cells.

Acquired cell-mediated immunity. An immune state mediated by T cells and characterized by the development of activated macrophages

Acquired immune deficiency syndrome (AIDS) A disease caused by the human immunodeficiency virus that causes destruction of key components of the immune system. As a result, infected individuals become very susceptible to infections and cancers

Activated macrophage A macrophage in a state of enhanced metabolic and functional activity

Active immunity. Immunity produced as a result of the administration of an antigen

Acute phase proteins Serum proteins whose levels increase during infection or inflammatory reactions. Examples of acute phase proteins: C- Reactiveprotein , proteínas do sistema complemento

Adaptive Immunity Immune responses mediated by antibodies and / or T cells that are specific and has memory for the antigen that elicited it.

ADCC Acron. for : Antibody- Dependent Cell- Mediated Citotoxicity

Addressins Proteins on lymphocyte surfaces that bind to homing receptors on blood vessel walls and so regulate lymphocyte emigration from blood.

Adjuvant A substance added to increase the immune response to the inoculant, in immunizations. Ex. Freund’s complete adjuvant

Adoptive immunity The development of immunity as a result of the transfer of cells from an immunized animal to an unimmunized recipient

AFC or AFCs Acron. for: Antibody-Forming Cell(s)

Affinity chromatrography A method to isolate antigens or antibodies based upon antigen-antibody binding

Affinity The strength of binding between two molecules such as an antigen and antibody. Usually expressed as an association constant (Ka).

Ag Abbrev. for antigen

Agammaglobulinemia Refer to Hypogammaglobulinemia Agammaglobulinemia was used in earlier years before the development of methods sufficiently sensitive to detect relatively small quantities of gamma globulin in the blood

Agglutination The aggregation of particulate antigen by antibodies. Agglutination applies to red blood cells as well as to bacteria and inert particles covered with antigen.

Agglutination Reactions The reaction of aggregation of particulate antigen by antibodies. Agglutination applies to red blood cells, bacteria and inert particles covered with antigen (see difference with precipitation reactions)

AIDS Acron. for : Acquired Immunodeficiency Syndrome

AIDS-related complex (ARC) A preamble to AIDS that consists od various symptoms and sigsm including, fever > 380C , loss of body weight (> 10%), lymphadenopathy, diarrhea, night sweats (> three months duration) and fatigue.

Allele Alternative form of a gene from a single locus

Allelic Relating 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.

Allergen A substance that induces an allergy (mold, grasses, certain food, antibiotics, etc.)

Allergy A disease or reaction triggered by an immune response to allergens. Characterized by the release of pharmacological agents as a result of mast cell and basophil degranulation, which is usually mediated by antibodies of the IgE class. Also called Immediate (Type I) hypersensitivity.

Allogeneic Refers to intraspecies genetic variations, i.e., a genetic dissimilarity within the same species

Allograft A tissue / organ graft between two genetically nonidentical members of a given species

Allotype A protein that is detectable as an antigen by other members of the same species

Alternative complement pathway A series of enzyme reactions triggered by interactions on activating surfaces leading to activation of the complement system

ANA Acron. for antinuclear antibodies

Anaphylatoxin Some peptides from the complement system (C3a and C5a) which cause mast cell degranulation and smooth muscle contraction.

Anergy The failure to respond to an antigen, upon contact with it.

Antibody A molecule that binds/ react specifically with antigens. Sometimes it is also referred as immunoglobulins although antibody is a more specific term

Antibody-dependent, cell-mediated cytotoxicity (see ADCC) A type of cytotoxicity in which target cells, coated with antibody, are destroyed by certain lymphocytes (e.g. Killer cells), which bear receptors for the Fc portion of the coating antibody (Fc receptors). These receptors allow the killer cells to bind to the antibody-coated target.

Antigen A substance which can induce a detectable immune response (specific antibodies ot T cell response) when introduced into an animal

Antigen Presenting Cell (see APC) A cell that can present the antigen to lymphocytes, through their cell surface class II MHC (major histocompatibility complex) and stimulate the lymphocytes to provide a specific immune response. Examples of APCs are macrophages and dendritic cells)

Antigen processing Large molecules are broken down (processed) within macrophages into peptides and presented within the groove of MHC molecules.

Antigen receptor The specific antigen-binding receptor on T or B lymphocytes; these receptors are transcribed and translated from rearrangements of V genes.

Antigen-binding site The part of an immunoglobulin molecule that binds antigen specifically.

Antigenic Determinant An area on the surface of an antigen that stimulates a specific immune response and against which that response is directed – same as epitope

Antiglobulin Antibody directed against an immunoglobulin. Usually obtained by injecting immunoglobulin into an animal of another species

Antinuclear antibodies Antibodies directed against nuclear constituents (usually nucleoproteins) found in the blood of patients with some disorders, mainly lupus erythematosus

Antiserum ( plural Antisera) Serum containing antibodies against a specific antigen.

Antistreptolysin O test A laboratory technique that serves as an indicator of infection by group A.

Antitoxins Protective antibodies that neutralize soluble toxins

APC or APCs Acron. for Antigen Presenting Cell(s)

Apoptosis A form of programmed cell death, characterized by endonuclease digestion of DNA

ARC Acron. for AIDS-related complex

ASLT Abbrev. for antistreptolysin O test

Atopy A term used by allergists to describe IgE-mediated anaphylactic responses in humans, usually genetically determined.

attenuated rendered less virulent

Autoantibody Antibody to self antigens

Autocrine Producing effects on the cell of origin

Autograft A tissue graft from one area to another on a single individual.

Autoimmune disease Disease caused by an immune reaction against an individual's own tissues

Autoimmunity (autoallergy) An immune response to "self" tissues or components. Such an immune response may have pathological consequences leading to autoimmune diseases.

Autoradiography A technique for detecting radioactive isotopes in tissues

Avidin a glycoprotein found in egg white who has a very high affinity and binds to biotin ( a water-soluble vitamin)

Avidin-biotin peroxidase complex technique A method useful for the localization of peptide hormones or other antigens in formalin-fixed tissues

Avidity The summation of multiple affinities, for example when a polyvalent antibody binds to a polyvalent antigen.

B lymphocytes or B cells Lymphoid cells that express surface immunoglobulin proteins and are responsible for the antibody production

BALT Acron. for Bronchial- Associated Lymphoid Tissue

Basophil A polymorphonuclear leukocyte., whose basophils granules contain heparin, histamine and other vasoactive amines. Within tissues, these cells are known as mast cells q.v.

BCG Bacille Calmette Gyérin An atenuated strain of Mycobacterium tuberculosis var. bovis

Bence-Jones proteins (BJ proteins) Immunoglobulin light chains present in the urine of some multiple myeloma patients.

BGG Acron. for Bovine Gamma Globulin

Blast Cells Cells prior to division when they have large amounts of cytoplasm

Blocking antibodies Antibodies that by binding to a target cell, serve to protect it from immune destruction.

Blood Groups Antigens found on the surface of red blood cells. Their expression is inherited.

blot the transfer of DNA, RNA or protein molecules from na electrophoretic gel to a nitrocellulose or nylon membrane (by osmosis or vacuum)

booster a second administration of immunogen to na individual primed months or years ago

BSA Acron. for Bovine Serum Albumin

BSFs Acron. for B Cell Stimulating Factors earlier terms for interleukin 4 ( BSF-1) and interleukin 6 (BSF-2)

Bursa of Fabricius An outpouching of the cloaca in birds; site of development of B cells in birds.

C (See Complement System) Abbrev. for Complement

C region Constant region of the Ig molecule (carboxi-terminal part of the molecule)

Cachectin An old designation for Tumor Necrosis Factor a (TNF a ).

Capping The active clustering of surface structures such as antigens or receptors in a small area on the cell surface.

Carcinoembryonic antigen An antigen present in fetal tissue and is reexpressed on the surface of neoplastic cells.

Carrier An immunogenic macromolecule to which a hapten may be bound so making the hapten immunogenic. This part of the molecule is recognized by T cells.

Cascade reaction A series of enzyme reactions in which the products of one reaction catalyze a second reaction, and so forth. Typical example is the Complement System cascade reactions.

Cationic Proteins Antimicrobial substances present within granules of phagocytes.

CD Acron. for Cluster of Differentiation. CD molecules are leukicyte surface molecules classified according to the internationally accepted CD systemand identified by monoclonal antibodies

CD4 A cell surface marker, on T cells, mainly helper T cells, that recognizes MHC class II molecules on antigen presenting cells.

CD8 An antigenic marker on T cells, mainly cytotoxic T cells, that recognizes MHC class I molecules on target cells.

CEA Acron. for Carcinoembryonic antigen

Cell-mediated cytotoxicity

Cell-mediated immunity A form of immune response mediated by T lymphocytes and macrophages; it can be conferred on an animal by adoptive transfer

CFU Acron. for Colony Forming Unit

CH50 unit The quantity or dilution of the serum which required to lyse 50% of the red cells in a standard hemolytic complemement assay

Chemotaxis Migration of cells or organism toward increasing concentrations of a chemical substance

Chromatography A variety of techniques useful for the separation of proteins

Class I MHC Protein Heterodimeric surface glycoproteins encoded by the A,B and C locus of the major histocompatibility complex , which functions mainly in antigen presentation to CD8 + T cells.

Class switch See isotype switch.

Classical Pathway (of complement activation) A series of enzyme reactions classically triggered by antigen-antibody complexes, leading to activation of the complement system

Clonal deletion The loss of lymphocytes of a particular specificity due to contact with either "self" or artificially introduced antigen.

Clonal selection theory The 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.

Cluster of Differentiation A designation to one or more cell surface proteins

CMI Acron. for Cell Mediated Immunity

Combinatorial joining The 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.

Complement A 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 components An enzymatic system of serum proteins triggered by the classical and alternative pathways, and resulting in target cell lysis, phagocytosis, opsonization and chemotaxis.

Complement fixation (CF) test An assay for detecting the presence of antibodies reactive against

Complement receptor A structure found on erythrocytes, lymphocytes, neutrophils, monocytes and macrophages that binds C3 fragments.

Complement System A group of serum proteins, some of which act in an enzymatic cascade, that is activated by factors such as the combination of antigen and antibody and results in a variety of biological consequences including cell lysis and opsonization

Con A Abbrev. for Concanavalin A

Concanavalin A A lectin derived from the jack bean that stimulates predominantly T lymphocytes.

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' test A 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-reaction The reaction of an antibody directed against one antigen, with a second antigen. This occurs because the two antigens possess epitopes in common or similar epitopes.

Cross-reactivity The ability of an antibody, specific for one antigen, to react with a second antigen; a measure of relatedness between two different antigenic substances.

CTL(s) Acron. for cytotoxic T lymphocyte(s)

Cytokines Soluble polypeptides (hormones) that mediate cellular interactions and regulate cell growth and function. As a result, they regulate the immune response.

Cytotoxic (Cytolytic) T cell Cell 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.

Cytotoxic T Cell A cell , usually a CD8+ T cell, that can injure or kill other cells

D gene A small segment of immunoglobulin heavy-chain and T-cell receptor DNA, coding for the third hypervariable region of most receptors.

Degranulation The process in which cytoplasmic storage granules fuse with fagosomes, discharge their contents and disappearsfrom the cytoplasm.

Delayed type Hypersensitivity A cell-mediated inflammatory reaction in the skin, so-called because it takes 24 to 48 hours to reach maximum intensity. Typical example: tuberculin reaction

Dendritic cells An heterogenous macrophage-like cells that function as antigen-trapping and antigen-presenting cells, including: Langerhans cells, blood dendritic cells, interdigitating cells , among others.

Determinant Part of the antigen molecule which binds to an antibody-combining site or to a receptor on T cells (see hapten and epitope).

Diapedesis The emigration of blood cells through intact cell walls, that occurs mainly during inflammation

DIC Acron for Disseminated intravascular coagulation

Differentiation antigen A cell surface antigenic determinant found only on cells of a certain lineage and at a particular developmental stage; used as an immunologic marker.

Disseminated intravascular coagulation Activation of the clotting cascade within the circulation. A severe post transfusional reaction.

Domain A 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 antigens MHC class II molecules found on B cells and antigen-presenting cells of humans.

DTH Acron. for Delayed Type Hypersensitivity

DTP Acron for Diphteria, tetanus and pertussis vaccine.

Dysgammaglobulinemia The abnormal production of gammaglobulins in blood: usually a selective immunoglobulin deficiency

EDTA Acron. for ethylene-diaminetetraacetic acid

Effector cells Cell that carry out an immunologic attack or is able to "effect" an immune response. These include cytotoxic T cells and plasma cells.

EIA Acron for Immunoenzimatic assay

Electroimmunodiffusion An immunodiffusion technique run over a slide in which antigens and antibodies are driven toward each other in an electric field resulting in precipitation lines.

Electrophoresis The separation of molecules in a mixture by subjecting them to an electric field

ELISA Acron for Enzyme-linked immunosorbent assay. An immunologic assay for detection or quantitation of antigens or antibodies that uses ligands (e.g. anti-immunoglobulins) conjugated to an enzyme. This conjugate changes the color of a substrate bound to an inert surface

Enchancing antibodies Antibodies which enhance the survival of a graft or of a tumour.

Endocytosis The uptake of extracellular macromolecules by cells and subsequent production of na intracellular vesicle which encloses the ingeste material.

Endogenous antigen An antigen synthesized within body cells (e.g., a virus protein)

Endosomes Cytoplasmic vesicles formed by invagination of the outer cell membrane. They contain endocytosed substances

Endotoxins Pathogenic lipopolysaccharide components of gram-negative bacterial cell walls

Enzyme-linked immunosorbent assay (ELISA) An assay in which an enzyme is linked to an antibody and a coloured substrate is used to measure the activity of bound enzyme and, hence, the amount of bound antibody.

Eosinophil A polymorphonuclear leukocyte with large eosinophilic (i.e. red) cytoplasmic granules.

Eosinophilia Increased numbers of eosinophils in the blood

Epithelioid cells Macrophages that accumulate around a tubercle and resemble epithelial cells in histological sections

Epitope An alternative term for antigenic determinant.

Epstein Barr virus (EBV) The causal agent of Burkitt's lymphoma and infectious mononucleosis

Equivalence zone In a precipitin reaction, the region in which the concentration of antigen and antibody leads to maximal precipitation.

Erythema Redness produced during inflammation due to red blood cells entering tissue spaces

Exocytosis The export of material from a cell by the fusion of cytoplasmic vesicles with the outer cell membrane.

Exogenous antigen A foreign antigen that originates at a source outside the body (e.g., bacterial antigens)

Exon A segment of DNA that contains expressed genes

Exotoxins Soluble protein toxins, usually produced by gram-positive pathogenic bacteria

Exudate The extracellular fluid containing proteins and celular debris which accumulates during inflammation

F(ab')2 A fragment of an antibody containing two antigen-binding sites generated by cleavage of the antibody molecule with the enzyme pepsin which cuts at the hinge region C-terminally to the inter-H-chain disulphide bond.

F1 or F1 Abbrev. for First generation

F2 or F2 Abbrev. for Second generation

Fab Fragment 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.

Fab fragment  Monovalent antigenbinding fragment of a partially digested antibody. It consists of a light chain and the N-terminal half of heavy chain.

FACS Acron. for Fluorescent activated cell sorter

Facultative intracellular organism. An organism that can, if necessary, grow within cells

Fc Fragment 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 A cell-surface receptor that specifically binds antibody molecules through their Fc region

Fc region Crystallizable, non-antigen binding fragment of an immunoglobulin molecule partially digested. It consists of the C-terminal halves of both heavy chains and it is responsible for the biological activities of the molecule, through binding to Fc receptors.

First-set reaction The initial rejection of a foreign tissue graft

FITC Acron for Fluorescein isothiocyanate

Fluorescein isothiocyanate Freen fluorescent dye that can be conjugated to proteins (antigens or antibodies) for use in immunofluorescence reactions.

Fluorescent antibody An antibody chemically conjugated to a fluorescent dye, such as FITC.

Freund's adjuvant An adjuvant which is na emulsion of aqueous antigen in mineral water containing heat-killed mycobacteria.

Freund's complete adjuvant A 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.

GALT Acron. for gut-associated lymphoid tissue

Gamma globulins A group of serum proteins that migrate toward the cathode on electrophoresis and that incluedes most of the serum immuneglobulins.

Gammopathies Abnormalitiy in gamma globulin levels

Gel diffusion An immunoprecipitation technique that involves letting antigen and antibody meet and precipitate in a clear gel such as agar

Gene complex A cluster of related genes occupying a restricted area of a chromosome

Genotype All of the genes possessed by an individual; in practice it refers to the particular alleles present at the loci in question.

Germ line Refers 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.

Germinal center Discrete areas within lymph nodes and spleen where B-cell maturation and immunological memory development occur.

Glomerulonephritis Pathological lesions in the glomeruli of the kidney, usually as a result of immune complex depositions.

gp Abrev. for glicoprotein

Graft-versus-host reaction (or disease)  Reaction occuring when grafted T cells recognize and attack host cells.

Granulocyte. Any myeloid cell containing prominent cytoplasmic granules, including neutrophils, eosinophils and basophils.

Granuloma. A localized- nodular inflammatory lesion characterized by chronic inflammation with mononuclear cell infiltration and extensive fibrosis.

Growth factors Biologically active molecules that promote cell growth.

Gut-associated lymphoid tissue A lymphoid tisue which includes Peyer's patches, appendix, and solitary lymph nodes in the submucosa

H-2 complex The mouse major histocompatibility complex (MHC). It is situated on chromosome 17 of the mouse and contains subregions K, I and D

Haplotype A particular combination of closely linked alleles on a chromosome. Since these alleles are genetically linked, they are usually inherited together

Hapten A small molecule that cannot initiate an immune response unless first bound to an immunogenic carrier molecule. Thus although not immunogenic, it is able to react with na antibody of the appropriate specificity ( elicited by immunization ot the hapten + carrier molecule)

H-Chain Abbrev. for Heavy chain

Heavy chain (H chain) The larger of the two types of chains that comprise a normal immunoglobulin or antibody molecule

Heavy-chain disease A group of immunological disorders characterized by the presence of monoclonal but incomplete H chains without L-chains in the sera and urine

Helper T cells The class of T cells whose primary function is to promote the activation and functions of other T cells, B cells and macrophages. T helper cells are also called CD4+ cells and they help trigger B cells to make antibody against thymus-dependent antigens. Helper T cells also help generate cytotoxic T cells.These functions are mediated by releasing cytokines such as interleukin 2 or interleukin 4.

Hemagglutination inhibition A technique to detect small amounts of antigen in which the agglutination of antigen bonded red cells is inhibited by homologous antigen.

Hemagglutination The agglutination of red blood cells

Hemagglutinin Any molecule (usually antobodies) that aglutinates red bllod cells.

Hematopoiesis The production of blood cells of all types.

Hematopoietic system All cells and tissues responsible for the formation of blood cells.

Hemolymph The fluid that fills the body cavities of invertebrates. It has analogous functions to blood.

Hemolysin Any substance (but usually refers to an antibody) that can lyse red blood cells.

Hemolytic disease Disease occurring as a result of the destruction of red blood cells by antibodies transferred to the young individual from its mother. Also called hemolytic disease of the newborn.

Heterodimer A molecule consisting of two different subunits.

Heterophile antigen A cross-reacting antigen that appears in widely ranging species such as humans and bacteria.

High endothelial venules. Post capillary venules lined with specialized cuboid epithelal cells that mediate specific binding and migration of blood lymphocytes into tissues.

Hinge region A flexible region in the heavy chains of some immunoglobulin molecules that permits them to bend freely.

Histamine A peptide present in basophils and mastocytes granules which is a mediator of imflammation and causes increased vascular permeability and smooth muscle contraction.

Histiocyte A tissue macrophage.

Histocompatibility molecules Cell membrane proteins that are required to present antigen to antigen sensitive cells.

Histocompatibility The ability of tissues to get along; in immunology, it means identity in all transplantation antigens. These antigens, in turn, are collectively referred as histocompatibility molecules or histocompatibility antigens.

HIV Abbrev. for Human Immunodeficiency Virus, the cause of AIDS.

HLA Abbrev. for Human Leukocyte Antigens – the human major histocompatibility complex (MHC).

HLA complex See 'Major histocompatibility complex'.

Homodimer A molecule consisting of two identical subunits. Example, the antibody molecule has two L-Chains and two H-chains, thus 2 homodimers.

HPLC Abbrev. for High-Performance Liquid chromatography

Humoral immunity Immunity or immune responses mediated by soluble factors in body fluids, especially by antibodies.

Hybridoma A hybrid cell line formed by the fusion of a malignant cell ( usually a myeloma cell) with a normal antibody producing cell.

Hypersensitivity An immunologically-mediated damaging inflammatory response to a normally innocuous antigen.

Hypervariable regions Small areas within immunoglobulin or TCR variable regions where the greatest variations in amino acid sequence occur.

Hypogammaglobulinemia A immunodeficiency in which low levels of all classes of immunoglobulins are found in blood.

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.

Ia antigen Mouse MHC class II antigen.

ICAM Acron. for Intracellular adhesion molecule

Idiotope An epitope formed by the variable amino acid sequences located in or close to the antigen binding site of an immunoglobulin.

Idiotype networks The series of reactions between idiotypes, anti-idiotypes and anti-anti-idiotypes that plays a role in controlling immune responses.

Idiotype The unique collection of idiotopes on an immunoglobulin molecule. Idiotype of the immunoglobulin distinguishes it from from all other immunoglobilins.

IFN Acron. for Interferon.

IgA Immunoglobulin A – the predominant immunoglobulin in secretions (e.g., saliva).

IgD Immunoglobulin D – an immunoglobulin present in the surfaces of B cells.

IgE The immunoglobulin class that is the predominant mediator of immediate hypersensitivity reactions (allergies).

IgG The predominant immunoglobulin class produced during secondary immune responses. The most conspicuous immunoglobulin in the blood.

IgM The predominant immuneglobulin class expressed by virgin B lymphocytes and secreted during primary immune responses.

IL Acron. for Interleukin

Immediate (Type I) hypersensitivity See allergy

Immediate-type hypersensitivity Hypersensitivity tissue reaction occurring within minutes after the interaction of antigen and antibody.

Immune adherence The adherence of particulate antigen coated with C3b to tissue having cells with C3b receptors

Immune complex Antigen bound to antibody.

Immune elimination The enhanced removal of an antigen from the bloodstream by circulating antibodies and phagocytic cells.

Immune modulators Substances that control the expression of the immune response.

Immune response (Ir) gene A gene controlling the 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.

Immune surveillance The concept that lymphocytes survey the body for cancerous or abnormal cells and then eliminate them.

Immunodeficiency Disease condition in which immune function is defective.

Immunoelectrophoresis A technique involving electrophoresis to separate protein from a mixture followed by immunodiffusion; it is used to identify the proteins in a complex solution such as serum

Immunofluorescence Immunologic tests that make use of antibodies conjugated to a fluorescent dye (e.g. anti-immunoglobulin conjugated to a fluorescein isothyacyanate).

Immunogen Any substance which elicits na immune response. Although all immunogens are antigens, not all antigens are immunogens (see haptens for antigens that are not immunogens).

Immunoglobulin A glycoprotein with antibody activity. Immunoglobulins are classified according to the H-chain structure in classes: IgG, IgM, IgA, IgD and IgE.

Immunoperoxidase Immunologic test that uses antibodies chemically conjugated to the enzyme peroxidase.

Immunosuppression Inhibition or elimination of the immune responses by drugs or other processes.

Inactivated vaccine A vaccine containing an agent that has been treated in such a way that it is no longer

Incomplete antibody An antibody that can bind to a particulate antigen but is incapable of causing its agglutination.

Inflammation The complex series of responses of tissues to trauma. It is characterized by increased blood flow and entry of leukocytes into the injured tissues, resulting in swellness, redness, elevated temperature and many times pain. These responses generally act to enhance tissue defenses and initiate repair processes.

Integrins A family of adhesion proteins found on cell membranes that bind to connective tissue proteins such as collagen or fibronectin.

Interferons (IFNs) A group of cytokines having antiviral activity and capable of enhancing and modifying the immune response. IFN-a andb are also called leukocyte IFN. IFN-g is the immune IFN.

Interleukin (IL) Any cytokine secreted by leukocytes that act as growth, differentiation and function factors for the cells of the immune system.

Internal image A spatial configuration of the combining site of an anti-idiotype antibody which resembles the epitope to which the idiotype is directed.

Intron A segment of DNA that separates exons and that does not contain expressed genes (non-coding segment). Introns are transcribed into RNA with the exons but are not translated into protein.

Isogeneic Genetically identical

Isograft A tissue transplanted between two genetically identical individuals.

Isohemagglutinins Antibodies to major red blood cell antigens present normally as a result of inapparent immunization by cross-reactive antigens in bacteria, food, etc.

Isotype switching The change in immunoglobulin isotype that occurs during the course of the immune response as a result of heavy chain gene switching.

Isotype Synonymous with immunoglobulin class and subclass. The types of immunoglobulin molecules common to all members of a species.

J chain A short glycopeptide that joins two monomers in the polymeric immunoglobulins IgM and IgA.

K cell (Killer cell) A killer lymphocyte with Fc receptors which allow it to bind to and kill antibody-coated target cells. It mediates ADCC (antibody-dependent cell-citotoxicity)

Killer T cell A T cell with a particular immune specificity and an endogenously produced receptor for antigen, capable of specifically killing its target cell after attachment to the target cell by this receptor. Also called cytotoxic T cell.

Kinins Peptides that increase vascular permeability (thus, vasodilactors) produced in injured or inflamed tissue.

Kupffer cells Macrophages lining the sinusoids of the liver

L chain Abbrev. for Light chain.

Lactoferrin An iron-containing molecule that has antimicrobial action by binding iron needed for microbial growth.

Langerhans cells Dendritic cells found in the skin, able to act as effective antigen presenting cells.

Lectins Proteins, usually of plant origin, that can bind specifically to carbohydrates. Many lectins are mitogenic (i.e., can induce lymphocytes to divide), such as Com A and PHA.

Leukotrienes Vasoactive metabolites of arachidonic acid produced by the actions of lipoxygenase and proudced by mast cells, basophils and macrophages. Leukotrienes promote inflammatory processes, such as chemotaxixs and increased vascular permeability).

Ligand A generic term for the molecules that bind specifically to a receptor.

Light chain (L chain) The smaller of the two types of chains that comprise a normal immunoglobulin or antibody molecule. Light chains occur in two forms: kappa and lambda.

Linkage disequilibrium A situation where a pair of alleles are found in a population at an unexpectedly greater frequency when compared with the frequency of the individual genes.

Lipopolyssacharide (LPS) Endotoxin derived from the cell wall of Gram negative bacteria which presents inflammatory and mitogenic actions.

Lymph The tissue fluid that into and through the lymphatic systema through the lymphatic vessels.

Lymphadenopathy  Enlarged lymph nodes.

Lymphocyte A small mononuclear cell with a round nucleus containing densely packed chromatin and a thin rim of cytoplasm.

Lymphokine-activated killer cells (LAK) Killer and natural killer cells activated in vitro by exposure to cytokines such as IL-2

Lymphokines Soluble substances secreted by lymphocytes, which have a variety of effects on lymphocytes and other cell types

Lymphotoxins Synonim for TNF-a. Cytotoxic cytokines secreted by lymphocytes.

Lysosomes Cytoplasmic organelles found within phagocytic cells that contain hydrolitic enzymes involved in the digestion of phagocytosed material

Lysozyme An enzyme present in tears, saliva, and neutrophils. It digests mucopeptides in the cell wall of gram-positive bacteria

Macrophage A large phagocytic cell of the mononuclear series found within tissues. Main functions are phagocytosis, and antigen presentation to T cells.

Macrophage-activating factor (MAF) Actually several lymphokines, including interferon, released by activated T cells, which together induce activation of macrophages, making them more efficient in phagocytosis and cytotoxicity.

Major histocompatibility complex (MHC) A cluster of genes, encoding cell surface molecules that are polymorphic and that code for antigens which lead to rapid graft rejection between members of a single species which differ at these loci. MHC molecules are involved in antigen presentation. Several classes of protein such as MHC class I and II proteins are encoded in this region. These in humans, are known as "Human leukocyte antigens" (HLA).

MALT Acron for Mucosal Associated Lymphoid Tissue

Mast cell Tissue located cell of hematopietic origin. Possesses receptor for Fc of IgE and is the main effector of the "Immediate hypersensitivity" reactions.

Membrane attack complex (MAC) The multicomponent complement complex which assembles on the surface of a target cell and causes their lysis.

Memory (imunonological)  In the immune system, memory denotes an active state of immunity to a specific antigen, such that a second encounter with that antigen leads to a larger, faster and more specific response.

Memory cells T and B lymphocytes formed as a result of exposure to antigen (primary immune response). They have the ability to mount a secondary immune response which is enhanced to antigen as compared to lymphocytes that had not previously encountered antigen.

MHC Abbrev. for Major histocompatibility complex.

MHC class I molecule A molecule encoded to genes of the MHC which participates in antigen presentation to cytotoxic T (CD8+) cells.

MHC class II molecule A molecule encoded by genes of the MHC which participates in antigen presentation to helper T (CD4+) cells.

MHC restriction The ability of T lymphocytes to respond only when they recognize the appropriate antigen in association with "self" MHC class I or class II proteins on the antigen presenting cells.

Migration inhibition factor (MIF) A lymphokine that inhibits the motility of macrophages in culture.

Minor histocompatibility antigens These antigens, encoded outside the MHC, are numerous, but do not generate rapid graft rejection or primary responses of T cells in vitro. They do not serve as restricting elements in cell interactions.

Mitogen A substance that stimulates the proliferation of many different clones of lymphocytes.

Mitogen Any substance that estimulate that can stimulate resting cells to proliferate.

Mixed lymphocyte culture An in vitro test for cellular immunity in which lymphocytes from two individuals are cultured together and when these cells are expressing allogeneic MHC a proliferative response is generally observed.

Monoclonal antibody An antibody derived from the progeny of a single B-cell. Thus a monoclonal antibody preparation is homogenous and all antiobdies present identical antigen binidng sites and isotype.

Monocytes Large circulating phagocytic cells which are the precursors of the tissue macropages.

Monokines Cytokines secreted by macrophages and monocytes.

Monomer Any molecule composed of a single unit, such as a single polypeptide chain.

Mononuclear phagocyte system. A system that comprises tissue macrophages and their precursors (monocytes).

Myeloma A tumour of plasma cells, generally secreting a single species of immunoglobulin.

Myeloma protein The immunoglobulin product secreted by a myeloma cell

Natural alloantibodies Antibodies against foreign antigens found in the serum of normal, unimmunized individuals. Most probably arise as a result of exposure to cross-reacting bacterial antigens (e.g. anti-A and B blood cell antigens)

Natural killer cells Non-T, non-B lymphocytes found in normal individuals and capable of killing some tumor cells and some virus-infected cells independently of bound antibody to the target cell.

NK Abbrev. for Natural killer cells, it is Naturally occurring, large, granular, lymphocyte-like killer cells that kill various tumour cells; they may play a role in resistance to tumours. Also, they participate in ADCC. They do not exhibit antigenic specificity, and their number does not increase by immunization. 

Northern blot A technique for detection of specific RNA species within a mixture after separation by gel electrophoresis.

Nude mice A mutant strain of mice that have no thymus and are hairless. This strain of mouse is very useful in immunological research.

Null cells An early population of lymphocytes that lacks T-and B-cell differentiation antigens, so they cannot be assignet to the B nor to the T lineage.

Oncogene Any gene whose protein product plays a key role in cell division, thus contributing to excessive cell growth and tumor formation. Oncogenes may be found in normal cells as well as in cancer-causing viruses.

Opportunistic pathogen Organisms of low virulence that are unable to cause disease in a healthy individual, but may invade and cause disease in an individual whose immunological defenses are impaired.

Opsonin Any substance that facilitates phagocytosis of a particle to which it is bound.

Opsonization The coating of a particle with antibody and/or complement (opsonins) that leads to enhanced phagocytosis of the bacterium by phagocytic cells.

PAF Acron for Platelet Activating Factor An organic medioator of inflammation that is released during platelet activation.

Paracortex The region located between the cortex and medulla of lymph nodes in which T cells predominate.

Paratope The antigen combining site on an immunoglobulin that is complementary to na epitope (part of the antigenic determinant).

Passive agglutination The agglutination of inert particles by antibodies directed against antigens bound to their surface.

Passive immunization Immunization of one individual by introduction of preformed antibodies or immune cells from another individual.

Perforins Molecule produced by T cells and NK cells that when polymerized can insert themselves into target cell membranes and provoke cell lysis and consequent death. The component C9 of the complement system is also a perforin.

Phagocytes Cells whose prime function is to engulf cells and particulate matters (phagocytosis). They include macrophages and related cells, neutrophils, and eosinophils.

Phagocytosis The engulfment of a particle or a microorganism by leukocytes.

Phagolysosome A structure produced by the fusion of a phagosome and a lysosome following phagocytosis.

Phagosome The cytoplasmic vesicle that encloses an ingested organism during phagocytosis.

Phenotype The physical expression of an individual's genotype.

Phytohemagglutinin (PHA) A lectin derived from the red kidney bean. It acts as a T-cell mitogen.

Pinocytosis Ingestion of liquid or very small particles by vesicle formation in a cell.

Plasma cell A fully diferentiated B cell able to procude and secrete large amounts of antibodies.

Polyclonal activator A substance that induces activation of many individual clones of either T or B cells. See Mitogen.

Polyclonal gammopathies The appearance in serum of a high level of immunoglobulins of many different specificities originating from many different clones.

Polyclonal mytogen  A substance that induces activation of many individual clones of either T or B cells.

Polymerase Chain Reaction An in vitro technique used to exponentially replicate specific short regions of DNA.

Polymorphism Literally, "having many shapes"; in genetics polymorphism means occurring in more than one form within a species; the existence of multiple alleles at a particular genetic locus. Example: MHC loci, genes for blood cell alotypes.

Polymorphonuclear leukocyte White cell, granular cytoplasm. There are three tyoes, classified according to is ability to be stained by different dies. Neutral staining (neutrophil) most frequent, phagocytic. Basophilic staining – basophil. Eosinophilic staining – eosinophil.

PPD Acron. for Purified Protein Derivative, Synonim of tuberculin.

Primary immunodeficiencies Inherited immunodeficiency diseases.

Primary lymphoid organs Organs in which the maturation of T and B lymphocytes take place and antigen-specific receptors are first acquired.

Primary responses The immune response to a first encounter with antigen. The primary response is generally small, has a long induction phase or lag period, consists primarily of IgM antibodies, and generates immunologic memory.

Primary responses The immune response resulting from an individual first encounter with an antigen. The primary response is generally small, has a long induction phase or lag period, consists primarily of IgM antibodies, and generates immunologic memory.

Privileged sites Some (rare) locations within the body where foreign grafts are not rejected. An example is the cornea of the eye.

Prophylaxis Protection.

Prostaglandins Small molecules derived from the lipid metabolism. These molecules are mediators of inflammation.

Radioallergo sorbent test (RAST) A radioimmunoassay for detecting IgE antibody specific for a particular allergen.

Radioallergosorbent test (RAST) A solid-phase radioimmunoassay for detecting IgE antibody specific for a particular allergen.

Radioimmunoassay (RIA) A group of immunological techniques that requires the use of an isotope-labeled reagent. These techniques are used for measurement of antigen-antibody interactions, and for the determination of the level of important biological substances in mixed samples. RIA takes advantage of the specificity of the antigen-antibody interaction and the sensitivity that derives from measurement of radioactively labelled materials.

Radioimmunodiffusion A type of immunodiffusion in which a radioactive amtibody is incorporated in order to increase the sensitivitu of the method.

Radioimmunosorbent test (RIST) A solid-phase radioimmunoassay that can detect extremely low levels of IgE.

Reagin The name allergists use for IgE antibodies.

Receptor A structure on cell membranes that binds specifically to ligands in the surrounding media.

Recombinant vaccine A vaccine containing antigen prepared by recombinant DNA techniques.

Rejection An immune response with both cellular and humoral components directed against transplants and grafts.

Respiratory burst The oxygen dependent increase in metabolic activity that occurs in phagocytic cells while particles are being ingested.

Reticuloendothelial system (RES). A network of phagocytic cells. Macrophages are the most important cells of this system.

Reverse transcriptase An enzyme that reversely transcribes RNA to DNA. It is found in retroviruses such as HIV.

Rheumatoid factor (RF) An autoantibody (usually IgM) which reacts with the individual's own IgG. Present in rheumatoid arthritis.

Second set rejection Accelerated rejection of an allograft in an already immune recipient.

Secondary immunodeficiencies Immunodeficiency diseases resulting from a known but non-genetic cause

Secondary lymphoid organs Organs in which antigen-driven proliferation and differentiation of B and T lymphocytes takes place (example lymph nodes and spleen).

Secretory component A protein found on mucosal cells that functions as an IgA receptor and, on binding to IgA, protects IgA against proteolytic digestion in the intestine.

Selectins A family of cell surface adhesion proteins that bind cells to glycoproteins on vascular endothelium.

Sensitization Ntural or artificial induction of an immune response by exposure to an antigen. Same as immunization.

Serology The science of antibody detection.

Serum sickness A type of hypersensitivity response (hypersensitivity type III) to the administration of foreign serum as a result of the development of immune complexes in the bloodstream, which in turn result in an inflammatory reaction. Serum sickness was originally induced following therapy with large doses of antibody from a foreign source e.g. horse serum.

Serum The clear, yellow fluid that is expressed when blood has clotted and the clot contracts, i.e., plasma without fibrinogen.

Skin test A diagnostic procedure, usualy applied to detect allergy, that induces a local inflammatory response following intradermal inoculation of an antigen or allergen.

Slow-reacting substance of anaphylaxis (SRS-A): A group of leukotrienes released by mast cells during anaphylaxis which induces a prolonged constriction of smooth muscle. This prolonged constriction is not reversible by treatment with antihistamines.

Somatic antigens Antigens associated with bacterial bodies.

SRBC Acron for Sheep Red Blood Cells

Stem cell A cell that can give rise to many different differentiated cell lines.

Suppression A mechanism for producing a specific state of immunologic unresponsiveness by the induction of suppressor T cells. This type of unresponsiveness is passively transferable by suppressor T cells or their soluble products.

Suppressor cells T lymphocytes that are claimed to suppress the response of other cells to antigen, thus being involved in the immuneregulation. Their existence is disputed

Syngeneic Literally, genetically identical. ( same as isogeneic)

Syngraft Same as isograft.

Systemic lupus erithematosus (SLE) An auto-immune disease in which antibodies against nuclear cells are found.

T cell A lymphocyte which undergoes a developmental stage in the thymus.

T-dependent antigen An antigen that is able to induce antibody synthesis only in the presence of lymphokines released by helper T cells.

Th1 A subset of the T helper cells that elaborates cytokines (such as g-IFN), , which selectively promote cell-mediated immune reposnses.

Th2 A subset of the T helper cells that elaborates cytokines (such as IL-4, IL-5, IL-6 and IL-10) , which selectively promote humoral immune reposnses.

Thymocyte An immature thymic T cell.

T-independent antigen An antigen which induces antibody synthesis in the absence of lymphokines released by T cells; the antibodies are generally of the IgM isotype.

Titration The measurement of the level of specific antibodies in a serum by testing increasing dilutions of the serum for antibody activity.

Titre The reciprocal of the last dilution of a titration giving a measurable effect; e.g. if the last dilution giving significant positive reaction is 1:256, the titre is 256.

Tolerance Diminished or absent capacity to make a specific response to an antigen; usually produced as a result of contact with that antigen under nonimmunizing conditions.

Toxoid A nontoxic derivative of a toxin used as an immunogen for the induction of antibodies capable of cross- reacting with the toxin.

Transcription The conversion of a DNA nucleotide sequence into a RNA nucleotide sequence by complementary base pairing.

Transduction The conversion of a signal from one form to another.

Translation The conversion of the RNA codon sequence into an amino acid sequence in a ribosome.

Transporter protein Proteins that bind fragments of endogenous antigen and carry them to newly assembled MHC class I molecules in the endoplasmic reticulum.

Tuberculin A protein fraction of the Mycobacterium tuberculosis that is used in a skin test for tuberculosis.

Tumor necrosis factors (TNF) Macrophage and lymphocyte-derived cytokines that can exert a direct toxic effect on neoplastic cells. There are two maun types of TNF, namely TNF-a and TNF-b

Unresponsiveness Inability to respond to antigenic stimulus. Unresponsiveness may be specific for a particular antigen (see tolerance), or broadly nonspecific as a result of damage to the immune system, for example after whole body irradiation.

Vaccination The administration of an antigen (vaccine) to stimulate a protective immune response against an infectious agent. The term originally referred to protection against smallpox.

Vaccine A suspension of living, dead or inactivated organisms used as an antigen in order to confer immunity.

Variable region (V region) That part of the immunoglobulin or TCR peptide chains where the amino acid sequence shows significant variation between molecules.

Western Blot A technique for detecting specific proteins (usually by using specific antibodies) within a complex mixture of proteins after separation by gel electrophoresis.

Xenograft A tissue or organ transplantation from a different species.