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helper T-cell


Helper T-Cell (CD4+)
CD8 T-Cell

  T-Cell or T-Lymphocyte

A lymphocyte that matures in the thymus and expresses a T-cell receptor, CD3, and CD4 or CD8. Several distinct T-cell subpopulations are recognized.

A lymphocyte (white blood cell) that develops in the bone marrow, matures in the thymus, and works as part of the immune system in the body.

different type of T-cell: T-helper cell (T4 cell, CD4 cell), T-killer cell (cytoxic T cells), T-suppressor cell (T8 cell, CD8 cell).

produce cytokine to help B-Lymphocyte to produce immunoglobuline

  T cells also express what appear to be antibody molecules on their surfaces, but unlike B cells, these molecules cannot be secreted. This is TCR T-Cell Receptor

Cytotoxic (Cytolytic) T cell: Cell that kills target cells bearing appropriate antigen within the groove of an MHC class I molecule that is identical to that of the T cell.

Helper T cells A class of T cells which help trigger B cells to make antibody against thymus-dependent antigens. Helper T cells also help generate cytotoxic T cells.

Killer T cell: A T cell with a particular immune specificity and an endogenously produced receptor for antigen, capable of specifically killing its target cell after attachment to the target cell by this receptor. Also called cytotoxic T cell.

Suppressor T-cells The existance of these cells stems from recent discoveries and the functioning of these cells is still somewhat debated. The basic concept of suppressor T-cells is a cell-type that specifically suppresses the action of other cells in the immune system, notably the B-cells and the T-cells. Thereby preventing the establishment of an immune response. How this is done is not known with certainty, but it seems that certain specific antigens can stimulate the activation of the suppressor T-cells. Discrete epitopes have been found, that have suppressor activity on T-helper-cells and B-cells. The suppressor effection is thought to be mediated by some inhibitory factor, secreted by suppressor T-cells. It is not any of the known lymphokines. Another fact that renders the study of this cell-type difficult is the lack of a specific surface marker. Most suppressor T-cells are CD8 positive just as cytotoxic T-cells.

A subpopulation of T cells which act to reduce the immune responses of other T cells or B cell suppression. May be antigen-specific, idiotype-specific, or non-specific in different circumstances.

Cytotoxic T-cell The cytotoxic T-cell has the simplest mode of action of the T-lymphocytes known. It has got the role of recognizing cells infected with virus, or tumorcells, that produce proteins, that do not normally constitute the cell. The recognition takes place, when a cytotoxic T-cell encounters a cell that display a Major-Histo-Compatibility-molecule class I (MHC-molecule classI) on the surface. The MHC-molecule class I, shown bound to a nona-peptide (blue) below, can bind a specific peptide sequence of a foreign protein, that is being synthesized intracellularly as a result of viral infection or by transformation into a tumor state.This way, the infected cell signals to the surroundings, that it is infected and that it better be eliminated in order not to spread the infection. Membranebound T-cell-Receptors ( TcR's) on the cytotoxic CD8+ T-cells intercept this signal by specifically recognizing the MHC-molecule complexed with the foreign peptide. The T-cells must just as B-cells have the ability to recognize a very wide spectra of MHC-peptide complexes. This task is overcome by the T-cell by recombining the different gene segments, that encode the TcR. A feature also known from the immunoglobulin genes present in the B-cell. In fact the TcR's are member of the immunoglobulin superfamily. This way a very broad array of TcR's can be produced with virtually any kind of specificity. Some of the T-cell-receptors will initially have self-specificity, meaning, they recognize MHC-molecules class I, complexed with part of a protein stemming from the normal cell. These T-cells however, are eliminated during the T-cell maturation in the thymus. Once the MHC-classI-foreign peptide has been recognized by the TcR, a signal is transmitted to the interior of the T-cell and the cytotoxic T-cell effectuate the cell-kiling by a lysis mechanism or by inducing programmed cell death (apoptosis) in the target cell just like NK-cells. For this mechanism to start a signal must also come from the co-receptor molecule CD8. The CD8 molecule serves as a marker of cytotoxic cells. As most cells are at risk for infections, MHC-molecules class I are present on nearlyt all celltypes in the body in contrast to MHC-molecules class II, that are only present on the so-called antigen presenting cells, primarily macrophages and B-cells.

T-Cells or Cytotoxic T-Cells (CD8+):
are responsible for Cell-Mediated Immune Responses (Cellular Immunology) - used to fight Virual Infections. #22
- Cytotoxic T-Cells (CD8+) are responsible for the destruction of host cells which have become infected by Viruses or other InterCellular Pathogens. #30

Helper T-Cells (CD4+) - heighten the production of AntiBodies by B-Cells.
- A functional subclass of T-Cells which can help to generate Cytotoxic T-Cells (CD8+) and cooperate with B-Cells in the production of AntiBody responses. Helper T-Cells recognize Antigens in association with Class II MHC molecules.

Suppressor T-Cells - supress B-Cell activity and seem to be in short supply during a MS attack (exacerbation). #28
- A functionally defined population of T-Cells which reduce the Immune Responses of other T-Cells or B-Cells, or switch the response into a different pathway. #30

Helper T-cell links:
HON Allergy Glossary T-Cell
B Cells and T Cells

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