Glossary A

• Accuracy: The ability of a test to actually measure what it claims to measure
• Acquired immunodeficiency syndrome (AIDS): A disease affecting the immune system caused by HIV
• Activation unit: The combination of complement components C1, C4b, and C2b that form the enzyme C3 convertase, whose substrate is C3
• Active immunity: Immunity resulting from natural exposure to an infectious agent or administration of a vaccine
• Acute - phase reactants: Normal serum proteins that increase rapidly because of infection, injury, or trauma to the tissues
• Acute rejection (AR): A type of rejection that occurs days to weeks after transplantation as a result of cellular mechanisms and antibody formation
• Acute rheumatic fever: A disease that develops as a sequel to Group A streptococcal pharyngitis, characterized by the presence of antibodies that cross-react with heart tissue
• Adaptive immunity: A type of resistance that is characterized by specificity for each individual pathogen, or microbial agent, and the ability to remember a prior exposure, which results in an increased response to that pathogen upon repeated exposure
• Adaptive T regulatory 1 (Tr1) cells: CD4+ T cells induced from antigen-activated naïve T cells under the influence of interleukin-10.
• Adjuvant: A substance administered with an immunogen that enhances and potentiates the immune response
• Adoptive immunity: Immunity resulting from the transfer of cells of the immune system (usually lymphocytes) from an immunized host to a nonimmune individual
• Adoptive immunotherapy: Administration of immune cells to treat patients with conditions such as immunodeficiency diseases or cancer
• Affinity: The initial force of attraction that exists between a Fab site on an antibody and one epitope or a determinant site on the corresponding antigen
• Affinity maturation: Process during the immune response whereby somatic mutations in B cells result in immunoglobulin receptors that can bind the antigen more strongly
• Agammaglobulinemias: Immunodeficiency diseases in which antibody levels in the blood are significantly decreased
• Agglutination: The process by which particulate antigens such as cells aggregate to form large complexes when a specific antibody is present
• Agglutination inhibition: An agglutination reaction based on competition between antigen-coated particles and soluble patient antigens for a limited number of antibody-combining sites.
• Agglutinin: An antibody that causes clumping or agglutination of the cells that triggered its formation. Lack of agglutination is a positive test result.
• Allele: An alternate form of a gene that codes for a slightly different form of the same product
• Allelic exclusion: The selection of an allele on one chromosome only
• Allergen: An antigen that triggers a type I hypersensitivity response (i.e., an allergy)
• Allergy immunotherapy (AIT): Therapy involving administration of increasing doses of an allergen with the goal of inducing immune tolerance to the allergen
• Autoimmune hemolytic anemia is an autoimmune disorder in which patients form antibodies that destroy their own red blood cells (RBCs).
• Anti-nuclear antibodies (ANA) are antibodies produced to different components of the nucleus in several autoimmune diseases, including anti-DNA, anti-deoxyribonucleoprotein, and antiribonuclear protein antibodies, all of which may be present in systemic lupus erythematosus.
• Autoimmune hepatitis (AIH) is an autoimmune disease in
• Autocrine is an effect produced by a cell that stimulates the same cell.
• Arthus reaction is a type III hypersensitivity skin reaction that occurs when an individual has a large amount of circulating antibody and is exposed to the antigen intradermally, resulting in localized deposition of immune complexes.
• Anti-RNP antibodies are autoantibodies directed against ribonucleoprotein (RNP), which consists of several nonhistone proteins complexed to a small nuclear RNA called U1-nRNP.
• Apoptosis is a normal process of programmed cell death.
• ASO titer is a test for the diagnosis of poststreptococcal sequelae, based on the neutralization of streptolysin O by antistreptolysin O found in patient serum.
• Attenuation is a process of producing nonpathogenic bacteria or viruses for use in vaccines; these organisms have been weakened by treatment with a chemical, exposure to elevated or cold temperatures, or repeated passage in cell culture.
• Anti-phospholipid antibodies are a heterogeneous group of autoantibodies that bind to phospholipids or phospholipids-protein complexes.
• Atypical hemolytic uremic syndrome (aHUS) is a rare genetic disorder associated with defects in complement regulation that cause microvascular thrombosis and affect the kidneys.
• Autoimmune disease is a condition in which damage to body organs results from the presence of autoantibodies or autoreactive cells.
• Aspergillosis is an opportunistic fungal infection predominantly caused by Aspergillus fumigatus.
• Autoantigen is an antigen that belongs to the host and is not capable of eliciting an immune response under normal circumstances.
• Ataxia-telangiectasia (AT) is an autosomal recessive syndrome that results in a combined defect of cellular and humoral immunity.
• Anti-toxin antibodies are used in passive immunization for the purpose of neutralizing a bacterial toxin.
• Autoantibody is an antibody produced against an antigen found in an individual’s own cells, tissues, or organs.
• Autograft is tissues removed from one location of an individual’s body and reintroduced in another location in the same individual.