Glossary of Immunology

Glossary of Immunology - Accessory cell: Cell required for,...

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Accessory cell: Cell required for, but not actually mediating, a specific immune response. Often used to describe antigen-presenting cells (APC; see below). Affinity: A measure of the binding constant of a single antigen combining site with a monovalent antigenic determinant. 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. Allergen: An antigen responsible for producing allergic reactions by inducing IgE formation. Allergy: A term covering immune reactions to non-pathogenic antigens, which lead to inflammation and deleterious effects in the host. Allogeneic: Having a genetic dissimilarity within the same species. Allograft: A tissue transplant (graft) between two genetically nonidentical members of a species. Allotypes: Antigenic 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) pathway: The 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. Anaphylatoxin: Substance capable of releasing histamine from mast cells. Anaphylaxis: Immediate 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. Antibody: Serum protein formed in response to immunization; antibodies are generally defined in terms of their specific binding to the immunizing antigen. Antibody-dependent, cell-mediated cytotoxicity (ADCC): A phenomenon in which target cells, coated with antibody, are destroyed by specialized killer cells (NK cells and macrophages), which bear receptors for the Fc portion of the coating antibody (Fc receptors). These receptors allow the killer cells to bind to the anti-body-coated target. Antigen: Any 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-binding site: The 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. Antigen receptor: The specific antigen-binding receptor on T or B lymphocytes; these receptors are transcribed and translated from rearrangements of V genes. Antigenic determinant:
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Glossary of Immunology - Accessory cell: Cell required for,...

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