| CD4 | <immunology> 55-kD glycoproteins originally defined as differentiation antigens on T-lymphocytes, but also found on other cells including monocytes/macrophages. CD4 antigens are members of the immunoglobulin supergene family and are implicated as associative recognition elements in MHC (major histocompatibility complex) class II-restricted immune responses. On T-lymphocytes they define the helper/inducer subset. Cd4 antigens also serve as HIV receptors, binding directly to the envelope protein gp120 on HIV. The protein structure on the surface of a human cell that allows HIV to attach, enter, and thus infect a cell. CD4 receptors are present on CD4 cells (helper T-cells), macrophages and dendritic cells, among others. Normally, CD4 acts as an accessory molecule, forming part of larger structures (such as the T-cell receptor) through which Tcells and other cells signal each other. (12 Dec 1998) |
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| CD4 cell | T helper cells which are targets for HIV infection. (09 Oct 1997) |
| CD4 cell count | The most commonly used surrogate marker for assessing the state of the immune system. As CD4 cell count declines, the risk of developing opportunistic infections increases. The normal range for CD4 cell counts is 500 to 1500 per cubic millimetre of blood. CD4 count should be rechecked at least every six to twelve months if CD4s are greater than 500/mm3. If the count is lower, testing every three months is advised. (09 Oct 1997) |
| CD4 count, absolute | The number of helper T-lymphocytes in a cubic millimeter of blood. With HIV, the absolute CD4 count declines as the infection progresses. The absolute CD4 count is frequently used to monitor the extent of immune suppression in persons with HIV. Also called a T4 count. (12 Dec 1998) |
| CD4 immunoadhesins | <immunology> Chimeric molecules resulting from the fusion of recombinant soluble CD4 to the fc portion of immunoglobulins. These have potential use in the therapy of aids since they possess both the gp120-binding and HIV-blocking properties of rCD4 as well as the long plasma half-life and fc receptor-binding functions of immunoglobulin. (12 Dec 1998) |
| CD4 lymphocyte | A specific type of lymphocyte, derived from the thymus gland, that plays an important role in cellular immunity. T4 lymphocytes (CD4 cells) are decreased (absolute counts less than 200) in patients with AIDS resulting in compromised immune function. (27 Sep 1997) |
| CD4 lymphocyte count | A count of the number of CD4-positive lymphocytes in the blood. Determination requires the use of a fluorescence-activated flow cytometer. (12 Dec 1998) |
| CD4-positive T-lymphocytes | A critical subpopulation of regulatory T-lymphocytes involved in the induction of most immunological functions. The HIV virus has selective tropism for the t4 cell which expresses the CD4 phenotypic marker, a receptor for HIV. In fact, the key element in the profound immunosuppression seen in HIV infection is the depletion of this subset of T-lymphocytes, which includes both the helper-inducer (T-lymphocytes, helper-inducer) and suppressor-inducer (T-lymphocytes, suppressor-inducer) T-cells. (12 Dec 1998) |
| CD4/CD8 count | The ratio of the number of helper-inducer T lymphocytes to cytotoxic-suppressor T lymphocytes, as measured by monoclonal antibodies to the CD4 surface antigen found on helper-inducer T-cells, and the CD8 surface antigen found on cytotoxic-suppressor T-cells. In healthy individuals, the H/S ratio ranges between 1.6 and 2.2.When the body mounts an immune response, as against a virus or a transplant, the ratio is almost always reduced because of a decrease in the number of circulating helper-inducer cells and an increase in suppressor cells. The CD4/CD8 count has been used to monitor for signs of organ rejection after transplants, and more recently has become a tool for assessing the relative condition of HIV patients. With the CD4 absolute count and the CD4 lymphocyte percentage, it provides a way of gauging the progression from HIV to AIDS. (05 Mar 2000) |
| CD40 | <immunology> Differentiation antigens found on all mature B-lymphocytes and some epithelial cells, carcinomas, and lymphoid dendritic cells. This is a member of the tumour necrosis factor superfamily. Evidence suggests that CD40-dependent activation of B-cells is important for generation of memory B-cells within the germinal centres. (12 Dec 1998) |
| CD44 | <immunology> Acidic sulfated integral membrane glycoproteins expressed in several alternatively spliced and variable glycosylated forms on a wide variety of cell types including mature T-cells, B-cells, medullary thymocytes, granulocytes, macrophages, erythrocytes, and fibroblasts. Cd44 antigens are the principle cell surface receptors for hyaluronate and this interaction mediates binding of lymphocytes to high endothelial venules. (12 Dec 1998) |
| CD45 | <immunology> High-molecular weight glycoproteins uniquely expressed on the surface of all leukocytes and their haemopoietic progenitors. The CD45 family consists of multiple members that are all products of a single gene. Cd45 expression is necessary for signalling through the T-cell receptor. (12 Dec 1998) |
| CD45 phosphatase | <enzyme> Reverses glycoprotein cd3-induced microtubule-associated protein-2 kinase activity in jurkat t-cells Registry number: EC 3.1.3.- Synonym: glycoprotein-cd45 phosphatase, cd45 ptpase, cd45 phosphotyrosine phosphatase (26 Jun 1999) |
| CD4:CD8 ratio | The ratio of CD4 to CD8 cells. A common measure of immune system status that is around two in healthy individuals. The ratio of T-lymphocytes that express the CD4 antigen to those that express the CD8 antigen. This value is commonly assessed in the diagnosis and staging of diseases affecting the immune system including HIV infection. (12 Dec 1998) |
| absolute CD4 count | The number of helper T-lymphocytes in a cubic millimeter of blood. With HIV, the absolute CD4 count declines as the infection progresses. The absolute CD4 count is frequently used to monitor the extent of immune suppression in persons with HIV. Also called a T4 count. (12 Dec 1998) |
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| antigens, CD4 | <immunology> 55-kD glycoproteins originally defined as differentiation antigens on T-lymphocytes, but also found on other cells including monocytes/macrophages. CD4 antigens are members of the immunoglobulin supergene family and are implicated as associative recognition elements in MHC (major histocompatibility complex) class II-restricted immune responses. On T-lymphocytes they define the helper/inducer subset. Cd4 antigens also serve as HIV receptors, binding directly to the envelope protein gp120 on HIV. The protein structure on the surface of a human cell that allows HIV to attach, enter, and thus infect a cell. CD4 receptors are present on CD4 cells (helper T-cells), macrophages and dendritic cells, among others. Normally, CD4 acts as an accessory molecule, forming part of larger structures (such as the T-cell receptor) through which Tcells and other cells signal each other. (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) |