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MicrobiologyBytes - Glossary of Immunology
Category: Health and Medicine > Infection & Immunity
Date & country: 13/07/2008, US
Words: 158


K cell
An effector lymphocyte with Fc receptors which allow it to bind to and kill antibody-coated target cells.

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.

Light chain (L chain)
The light chain of immunoglobulin is a structural feature that occurs in two forms: kappa and lambda.

Linkage disequilibrium
The frequency, in a population of linked genes, which is governed by factors other than change.

Lymphocyte
Small cell with virtually no cytoplasm, found in blood, in all tissue, and in lymphoid organs, such as lymph nodes, spleen, and Peyer's patches, and bears antigen-specific receptors.

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

Macrophage
A large phagocytic cell of the mononuclear series found within tissues. Properties include 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.

Mast cell
Tissue located cell probably derived from basophils. Possesses receptor for Fc of IgE. Participates in 'Immediate hypersensitivity' reactions.

Memory
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 and more rapid response.

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 'see' 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.

Mixed lymphocyte reaction (MLR)
When lymphocytes from two individuals are cultured together, a proliferative response is generally observed, as the result of reactions of T cells of one individual to MHC antigens on the other individual's cells.

Monoclonal
Literally, coming from a single clone. A clone is the progeny of a single cell. In immunology, monoclonal generally describes a preparation of antibody that is monogenous, or cells of a single specificity.

Monocyte
Large circulating white cell, 2-10% of total white cells, phagocytic, indented nucleus. Migrates to tissues, where it is known as a macrophage.

Monokines
Soluble substances secreted by monocytes, which have a variety of effects on other cells.

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

NK cell
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.

Null cells
An early population of lymphocytes bearing neither T-cell nor B-cell differentiation antigens.

Opsonin
A substance, usually antibody or complement component, which coats a particle such as a bacterium and enhances phagocytosis by phagocytic cells.

Opsonization
Literally means 'preparation for eating'. The coating of a bacterium with antibody and/or complement that leads to enhanced phagocytosis of the bacterium by phagocytic cells.

Paratope
An antibody combining site that is complementary to an epitope.

Passive immunization
Immunization by the administration of preformed antibody into a nonimmune individual.

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

Phenotype
The physical expression of an individual's genotype.

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

Plasma cell
End-stage differentiation of a B cell to an antibody-producing cell.

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

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.

Polymorphonuclear leukocyte
White cell, granular cytoplasm. Neutral staining (neutrophil) - most frequent, phagocytic. Basophilic staining - basophil q.v. Eosinophilic staining - eosinophil q.v.

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.

Prophylaxis
Protection.

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

Radioimmunoassay (RIA)
A widely used technique for measurement of primary antigen-antibody interactions, and for the determination of the level of important biological substances in mixed samples. It takes advantage of the specificity of the antigen-antibody interaction and the sensitivity that derives from measurement of radioactively labelled materials.

Reagin
Allergist's term for IgE antibodies.

Respiratory burst
Oxygen dependent increase in metabolic activity within phagocytic cells stimulated by bacteria or parasites, to be microbicidal.

Reticuloendothelial system
A network of phagocytic cells.

Rheumatoid factor
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 lymphoid organs
Organs in which antigen-driven proliferation and differentiation of B and T lymphocytes takes place.

Secretory component
A surface receptor on epithelial cells lining mucosal surfaces which binds dimeric IgA and transports it through the cell into mucosal secretions.

Serum sickness
A hypersensitivity reaction consisting of fever, rashes, joint pain and glomerulonephritis, resulting from localization of circulating, soluble, antigen-antibody complexes, which induce inflammatory reactions. Serum sickness was originally induced following therapy with large doses of antibody from a foreign source - e.g. horse serum.

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.

Syngeneic
Literally, genetically identical.

Syngraft
Same as isograft.

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

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

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

Titre
The reciprocal of the last dilution of a titration giving a measurable effect; e.g. if the last dilution giving significant agglutination is 1:128, the titre is 128.

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.

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 entire immune system, for example after whole body irradiation.

Vaccination
Originally referred to immunization against smallpox with the less virulent cowpox (vaccinia) virus; more loosely used for any immunization against a pathogen.