complement-fixing antibody

antibody

 [an´tĭ-bod″e] an immunoglobulin" >immunoglobulin molecule having a specific amino acid sequence that gives each antibody the ability to adhere to and interact only with the antigen that induced its synthesis. This antigen-specific property of the antibody is the basis of the reaction" >antigen-antibody reaction that is essential to an immune response" >immune response. The antigen-antibody reaction begins as soon as substances interpreted as foreign invaders gain entrance into the body. See also immunity" >immunity. Abbreviated Ab.
Antibodies are synthesized by the plasma cells formed when antigen-specific groups (clones) of lymphocytes" >B lymphocytes respond to the presence of antigen. The developmental process of antibody production begins when stem cells are transformed into B lymphocytes; this transformation usually is completed a few months after birth, at which time the lymphocytes migrate to lymphoid tissue primarily located in the lymph nodes, although they are also found in the spleen, gastrointestinal tract, and bone marrow.
Antibody production, its interaction with a specific antigen, and the activation of complement (C), an interrelated group of eleven proteins, are the major components of the humoral system of immunity.Antibody-mediated immunity. From Applegate, 2000. Fortunately, the immune response of antibody and complement can be transferred passively from one individual to another, as for example the transfer of maternal antibody across the placental barrier to the fetus, who has not yet developed a mature immune system. An antibody present in an individual without known prior exposure to the corresponding red cell antigen is termed an isoagglutinin. (Examples are the ABO antibodies anti-A, anti-B, and anti-A,B.)
Antibodies can be classified according to their mode of action as they react to and set about defending the body against foreign invaders. Some cause clumping together of bacterial cells (agglutination" >agglutination) and are called agglutinins. Those antibodies that cause bacterial cells to dissolve or liquefy are called bacteriolysins. This activity is assisted by complement, which interacts with the antigen-antibody complex in such a way that the cell ruptures and there is dissolution (lysis) of the cell body. Opsonins coat the outside of bacteria, making them more attractive to phagocytes. Other types of antibodies include those that neutralize the toxins of antigens (antitoxins) and those that cause precipitation of antigens in a fluid medium (precipitins).anaphylactic antibody a substance formed as a result of the first injection of a foreign anaphylactogen and responsible for the anaphylactic symptoms following the second injection of the same anaphylactogen.antinuclear a's (ANA) autoantibodies directed against components of the cell nucleus, e.g., DNA, RNA, and histones; they may be detected by immunofluorescence. A positive ANA test is characteristic of systemic lupus erythematosus. Antinuclear antibodies also occur in patients with rheumatoid arthritis, Sjögren's syndrome, and scleroderma.blocking antibody any antibody that by combining with an antigen blocks another immunologic reaction with the antigen. Immunotherapy (hypersensitization) for allergic disorders induces in most treated patients IgG blocking antibodies that can bind the allergen and prevent it from binding to cell-fixed IgE and trigger immediate hypersensitivity; thus it can induce partial immunologic tolerance. Blocking antibodies can prevent agglutination in serologic tests.complement-fixing antibody antibody (primarily IgM and the IgG subclasses 1, 2, and 3) that activates complement when reacted with antigen.complete antibody antibody capable of agglutinating cells in physiologic saline solution.cross-reacting antibody one that combines with an antigen other than the one that induced its production.cytophilic antibody cytotropic antibody.cytotoxic antibody any specific antibody directed against cellular antigens, which when bound to the antigen, activates the complement pathway or activates killer cells, resulting in cell lysis.cytotropic antibody any of a class of antibodies that attach to tissue cells (such as mast cells and basophils) through their Fc segments to induce the release of histamine and other vasoconstrictive amines important in immediate hypersensitivity reactions. In humans this antibody, also known as reagin, is of the immunoglobulin class known as IgE. Called also cytophilic antibody.heterophil antibody a characteristic antibody found with many cases of infectious mononucleosis; see also heterophil antibody.immune antibody a type of isoantibody induced by immunization, either by pregnancy or by transfusion, in contrast to natural antibodies.incomplete antibody 1. antibody that binds to erythrocytes or bacteria but does not produce agglutination; in blood banking, the nonagglutinating antibody is detectable in serum by using the antiglobulin (Coombs') test. For example, IgG anti-Rh antibodies do not agglutinate erythrocytes in physiologic saline whereas IgM antibodies do.2. a univalent antibody fragment.monoclonal a's (MOAB) proteins produced from a single clone of lymphocytes" >B lymphocytes; used as laboratory reagents in radioimmunoassays, ELISA assay, and immunofluorescence assays, and also as modifiers" >biological response modifiers fused with rapidly reproducing myeloma cells, resulting in a hybridoma capable of synthesizing a massive amount of one specific antibody; the antibody is made in response to tumor cells injected into mice and is produced from mouse serum. Monoclonal antibodies may be used alone (unconjugated) or bound (conjugated) to radioisotopes, toxins, or other biological response modifiers. When bound to radioisotopes they may also be used as a diagnostic tool to locate tumors and metastatic disease.natural a's (naturally occurring a's) antibodies present in the serum of normal individuals in the apparent absence of any contact with the specific antigen, probably induced by exposure to cross-reacting antigens; examples are the ABO antibodies, anti-A and anti-B. Such antibodies may play a major role in resistance to infection.neutralizing antibody one that reduces or destroys infectivity of a homologous infectious agent by partial or complete destruction of the agent.protective antibody one responsible for immunity to an infectious agent, observed in passive immunity.Rh a's those directed against Rh antigen(s) of human erythrocytes. Not normally present, they may be produced when Rh-negative persons receive Rh-positive blood by transfusion or when an Rh-negative person is pregnant with an Rh-positive fetus.saline antibody complete antibody.

com·ple·ment-fix·ing an·ti·bod·y

antibody that combines with antigen leading to the binding and activation of complement, which may result in opsonization or cell lysis. Synonym(s): CF antibody

com·ple·ment-fix·ing an·ti·bod·y

(kom'plĕ-mĕnt-fiks'ing an'ti-bod-ē) Antibody that combines with and sensitizes antigen leading to the activation of complement, which may result in cell lysis.