| T-cell lymphoma | A cancer of the immune system that appears in the skin; also called mycosis fungoides. (12 Dec 1998) |
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| T-cell protein tyrosine phosphatase | <enzyme> Contains a single ptp domain and possesses a c-terminal region that may play a role in enzymatic regulation and/or targeting to discrete intracellular sites; amino acid sequence known Registry number: EC 3.1.3.- Synonym: tc-ptp (26 Jun 1999) |
| T-cell receptor | <immunology> The antigen recognising receptor on the surface of T-cells. Heterodimeric (disulphide linked), one of the immunoglobulin superfamily of proteins, binds antigen in association with the major histocompatibility complex (MHC), leading to the activation of the cell. There are two subunits (_ and _, 42-44 kD in mouse, 50-40 kD in humans), each with variable and constant regions, that are associated noncovalently with T3 (20-30 kD). A second heterodimer on CD3 cells with _ (35 kD in mice, 55 kD in humans) and _ (45 kD in mice, 40 kD in humans) chains is a second T-cell antigen receptor that is not MHC restricted. The __ T-cell receptors (TCRs) are formed on very early T-cells in the thymus. (18 Nov 1997) |
| T-cell-rich, B-cell lymphoma | <tumour> A B-cell lymphoma in which more than 90% of the cells are of T-cell origin, masking the large cells that form the neoplastic B-cell component. See: adult T-cell lymphoma. (05 Mar 2000) |
| T-dependent antigen | An antigen that requires T helper cells in addition to appropriate B-cells. Most antigens are T-dependent. (05 Mar 2000) |
| T-E fistula | A congenital anomaly where the upper oesophagus ends (atresia) and does not connect with the stomach and the lower oesophagus connects to the trachea (tracheoesophageal fistula). A common complication seen shortly after birth is an aspiration pneumonia. Infants will demonstrate excessive salivation, gagging and coughing with feeding, poor feeding and a bluish discolouration to the skin (cyanosis). Treatment involves the surgical repair of the oesophagus before the child can take anything by mouth. (27 Sep 1997) |
| t-helper cell | Immune cells that are triggered by antibodies to seek and attack invading organisms. Cells called macrophanges summon t-helper cells to the site of the infection and present a protruding antigen onto which the t-helper cell locks, thus recognizing the invading substance. The t4-helper cell then reproduces and secretes its potent lymphokine hormones that stimulate B-cell production of antibodies; signal natural killer or cytotoxic (cell-killing) T-cells; and summon more macrophanges to the site of the infection. T-helper cells are also called t4 cells and are normally twice as common as t8 cells. If a person has aids, the proportion of t4 to t8 cells is often reversed. (12 Dec 1998) |
| t-lymphocyte | A white blood cell made in the thymus gland, a lymphoid structure in the upper chest. T lymphocytes are also called T-cells. (the t in T-cell stands for thymus). These cells coordinate the immune system by secreting lymphokine hormones. There are 3 fundamentally different types of t lymphocytes : helper, killer, and suppressor. (12 Dec 1998) |
| t-lymphocyte subsets | A classification of T-lymphocytes, especially into helper/inducer, suppressor/effector, and cytotoxic subsets, based on structurally or functionally different populations of cells. (12 Dec 1998) |
| T-lymphocytes | Lymphoid cells concerned with cell-mediated immunity. They originate from lymphoid stem cells that migrate from the bone marrow to the thymus and differentiate under the influence of the thymic hormones. Various subpopulations have been described. (12 Dec 1998) |
| T-lymphocytes, cytotoxic | Immunised T-lymphocytes which can directly destroy appropriate target cells. These cytotoxic lymphocytes may be generated in vitro in mixed lymphocyte cultures (mlc), in vivo during a graft-versus-host (gvh) reaction, or after immunization with an allograft, tumour cell or virally transformed or chemically modified target cell. The lytic phenomenon is sometimes referred to as cell-mediated lympholysis (cml). These cells are distinct from natural killer cells (killer cells, natural) and from killer cells mediating antibody-dependent cell cytotoxicity. (12 Dec 1998) |
| T-lymphocytes, helper-inducer | Subpopulation of CD4+ lymphocytes that cooperate with other lymphocytes (either t or b) to initiate a variety of immune functions. For example, helper-inducer T-cells cooperate with B-cells to produce antibodies to thymus-dependent antigens and with other subpopulations of T-cells to initiate a variety of cell-mediated immune functions. (12 Dec 1998) |
| T-lymphocytes, suppressor-effector | Subpopulation of CD8+ T-lymphocytes which suppress antibody production or inhibit cellular immune responses. Suppressor-effector cells execute the message received from suppressor-inducer cells (T-lymphocytes, suppressor-inducer). (12 Dec 1998) |
| T-lymphocytes, suppressor-inducer | Subpopulation of CD4+ lymphocytes which induce CD8+ suppressor T-cells (T-lymphocytes, suppressor-effector) to suppress antibody production by B-cells. They also stimulate other cellular immune responses. (12 Dec 1998) |
| t-lymphocytopenia, idiopathic CD4-positive | Reproducible depletion of CD4+ lymphocytes below 300 per cubic millimeter in the absence of HIV infection or other known causes of immunodeficiency. This is a rare, heterogeneous syndrome and does not appear to be caused by a transmissible agent. (12 Dec 1998) |