Glossary T

• T-dependent antigen: An antigen that requires T-cell help in order for B cells to respond
• Typhus: Diseases characterized by fever, rash, and a cough caused by Rickettsiae bacteria.
• T follicular helper (Tfh) cell: A subpopulation of T helper cells that remain in the lymph nodes, where they interact with B cells and plasma cells
• T helper (Th) cells: Lymphocytes that express the CD4 antigen
• Their function is to provide help to B cells in recognizing foreign antigen and producing antibody to it
• T helper 1 (Th1) cells: T cells that are developed through the expression of interleukin - 12 (IL - 12) by dendritic cells and that are primarily responsible for cell-mediated immunity
• T helper 2 (Th2) cells: T cells that are developmentally regulated by interleukin - 4 (IL - 4) and whose main function is to drive antibody-mediated immunity
• T helper 17 (Th17) cells: A subset of T cells that play an important role in host defense against bacterial and fungal infections at mucosal surfaces
• They secrete interleukin - 17 (IL - 17), which attracts neutrophils to the site of infection
• T-independent antigens: Antigens that are able to elicit antibody formation in the absence of T cells
• T lymphocytes: Cells that mature in the thymus which play important roles in cell-mediated immunity and produce cytokines that assist the humoral immune response
• T-pallidum particle agglutination (TP-PA) test: A particle agglutination test that detects antibodies to Treponema pallidum to aid in the diagnosis of syphilis
• T regulatory (Treg) cell: A subpopulation of T cells that play an important role in suppressing the immune response to self-antigens
• Tertiary syphilis: The last stage of syphilis that appears months to years after secondary infection
• Tetrapeptide: The basic four-chain unit common to all immunoglobulin molecules, consisting of two large heavy chains and two smaller light chains
• The Joint Commission (TJC): An independent body that certifies and accredits health-care organizations in the United States
• Thymocyte: Immature lymphocyte, found in the thymus, that undergoes differentiation to become a mature T cell
• Thymus: A small, flat, bilobed organ found in the thorax of humans, which serves as the site for differentiation of T cells
• Thyroglobulin (Tg): A large iodinated glycoprotein from which the active thyroid hormone triiodothyronine (T3) and its precursor, thyroxine (T4), are synthesized
• Thyroid peroxidase (TPO): An enzyme that oxidizes iodine ions to form the iodine atoms that are incorporated into thyroglobulin to facilitate the synthesis of the thyroid hormones T3 and T4
• Thyroid-stimulating hormone (TSH): A hormone produced by the pituitary gland that binds to specific receptors, on the thyroid gland causing thyroglobulin to be broken down into secretable T3 and T4
• Thyroid-stimulating hormone receptor antibodies (TRAbs): Antibodies that are directed against the receptor for thyroid-stimulating hormone.
• Trend: A gradual change in the mean in one direction that may be caused by a gradual deterioration of reagents or deterioration of instrument performance
• Type III hypersensitivity: An immune reaction
• Toxoid: A chemically inactivated bacterial toxin used in some vaccines
• Tumor - infiltrating lymphocyte (TIL): Lymphocyte within a tumor mass that are able to react with antigens on tumor cells to help destroy them
• TP - PA test: See Tpallidum particle agglutination (TP - PA) test
• 22q11.2 deletion syndrome: An autosomal dominant disorder caused by a deletion in chromosome 22, region q11, resulting in underdevelopment of the thymus and a T- cell deficiency
• Turnaround time (TAT): The amount of time required between the point at which a test is ordered by the health-care provider and the results are reported to the health-care provider
• Tumor: An abnormal cell mass that can either be benign or malignant
• Translation: The process by which messenger ribonucleic acid (RNA) is used to make functional proteins
• Tumor suppressor genes: Genes that control the entry of cells into the cell cycle and prevent cells from completing the cycle if they contain damaged DNA or other abnormalities
• Transcription: The process of generating a messenger ribonucleic acid (RNA) strand from DNA
• Type I hypersensitivity: An allergic reaction in which antigen-specific immunoglobulin E (IgE) antibody binds to mast cells and basophils, triggering degranulation and the release of chemical mediators; also known as anaphylactic hypersensitivity
• Tumor necrosis factor (TNF): Family of cytokines that mediate the innate defense against gramnegative bacteria and effect adaptive immune responses
• Treponema pallidum: A spirochete that is the causative agent of syphilis
• Treponemal tests: Serological tests for syphilis that detect antibodies directed against Treponema pallidum
• Type 1 diabetes mellitus (T1D): A chronic autoimmune disease characterized by insufficient insulin production, caused by progressive destruction of the beta cells of the pancreas.
• Type II hypersensitivity: An immune reaction in which immunoglobulin G (IgG) or immunoglobulin M (IgM) antibodies are produced to cell surface receptors, causing damage to the cells, dysfunction of the cells, or overstimulation of the function of the cells; also known as antibody-mediated cytotoxic hypersensitivity
• Tumor marker: Biological substances found in increased amounts in the blood, body fluids, or tissues of patients with a specific type of cancer