Glossary DEF

• Fungi: Organisms made up of eukaryotic cells with rigid walls composed of chitin, mannan, and sometimes cellulose.
• Decay - accelerating factor (DAF): A glycoprotein found on peripheral red blood cells (RBCs), endothelial cells, fibroblasts, and epithelial cell surfaces that is capable of dissociating C3 convertases formed by both the classical and alternative pathways of complement.
• Defensins: Small cationic proteins that, when released from lysosomal granules, can kill bacteria and many fungi by destroying their cell walls.
• Delayed hypersensitivity: Type IV or T - cell – mediated hypersensitivity; so named because its manifestations are not seen until 24 to 48 hours after exposure to the inducing antigen.
• Delta check: A QA procedure that compares a patient’s test results with the previous results
• Dendritic cell: Tissue cells covered with long membranous extensions that make them resemble nerve cell dendrites
• Deoxyribonucleic acid (DNA): The nucleic acid whose sugar is deoxyribose. It is the primary genetic material of all cellular organisms and DNA viruses
• Dermatomyositis (DM): A systemic autoimmune rheumatic disease that involves the skin
• Diagnostic sensitivity: The proportion of people who have a specific disease or condition and who have a positive test result
• Diagnostic specificity: The proportion of people who do not have a disease or condition and who have a negative test result
• Diapedesis: The process by which cells are capable of moving from the circulating blood to the tissues by squeezing through the wall of a blood vessel
• DiGeorge syndrome: A congenital defect of the third and fourth pharyngeal pouches that affects thymic development, leading to a T - cell deficiency
• Diluent: One of two entities needed for making up a solution. It is the medium into which the solute is added
• Direct agglutination: A clumping of cells that occurs when antibodies react with antigens that are naturally found on the surface of the cells
• Direct allorecognition: Pathway in which recipient T cells recognize intact human leukocyte (HLA) molecules on donor cells
• Factor H: A control protein in the complement system that acts as a cofactor with factor I to break down C3b formed during complement activation.
• Fab fragment: Fragment of an immunoglobulin molecule obtained by papain cleavage that consists of a light chain and one-half of a heavy chain held together by disulfide bonding.
• Flow cytometry: An automated system for identifying cells based on the scattering of light as cells flow single file through a laser beam.
• Fluorochrome: See fluorophores.
• Forward-angle light scatter (FSC): Light scattered at an angle of less than 90 degrees, which indicates the size of a cell.
• Flow cytometer: An automated system in which single cells in a fluid are analyzed in terms of intrinsic light-scattering characteristics as well as extrinsic properties.
• Factor I: A serine protease that cleaves C3b and C4b formed during complement activation; a different cofactor is required for each of these reactions.
• Fluorescence in situ hybridization (FISH): A technique used to identify a specific region of DNA in a chromosome through binding of fluorescent-tagged complementary DNA probes.
• Flocculation: The formation of downy masses of precipitate that occurs over a narrow range of antigen concentration.
• Extractable nuclear antigen (ENA): A member of a family of small nuclear proteins associated with uridine-rich ribonucleic acid (RNA) that can stimulate the production of autoantibodies; examples are Sm and RNP.
• F(ab’) 2: Fragment of an immunoglobulin molecule obtained by pepsin cleavage that consists of two light chains and two heavy-chain halves held together by disulfide bonding.
• Fluorescent anti-nuclear antibody (FANA) testing: Testing to identify the presence of antibody to nuclear antigens, using human epithelial cells and a fluorescent-labeled anti-human immunoglobulin.
• Fluorophores: Compounds that absorb energy from an incident light source and convert that energy into light of a longer wavelength and lower energy as the excited electrons return to the ground state.
• Fluorescence polarization immunoassay (FPIA): An immunoassay based on the change in polarization of fluorescent light emitted from a labeled molecule when it is bound by antibody.
• Extrinsic parameter: In flow cytometry, properties of a cell such as a surface protein that require addition of a fluorescent-labeled antibody for their detection.
• Fc fragment: Fragment of an immunoglobulin molecule obtained by papain cleavage that consists of the carboxy-terminal halves of two heavy chains; these two halves are held together by disulfide bonds.
• Fibrinogen: An acute-phase reactant that changes to fibrin and forms clots in the bloodstream.
• Fluorescent treponemal antibody absorption (FTA-ABS) test: A confirmatory test for syphilis, which detects antibodies to Treponema pallidum by using anti-human immunoglobulin with a fluorescent label.
• Fomite: An inanimate object that can become contaminated with an infectious agent and transmit the agent to a new host.
• Direct antiglobulin test (DAT): A technique to determine in vivo attachment of antibody or complement to red blood cells (RBCs), using anti - human globulin to cause a visible agglutination reaction
• Direct immunofluorescence assay: A technique to identify a specific antigen using an antibody that has a fluorescent tag attached
• Domain: Region of an antibody molecule that consists of approximately 110 amino acids
• Double - negative (DN) thymocyte: Stage in the development of T cells when neither CD4 nor CD8 is expressed
• Double - positive (DP) thymocyte: Stage in the development of T cells when both CD4 and CD8 antigens are expressed
• Double - stranded DNA (dsDNA) antibodies: Autoantibodies produced against double - stranded DNA that are diagnostic for systemic lupus erythematosus (SLE)