Wednesday, September 30, 2009

T cells

A T cell is a leukocyte which belongs to the lymphocytes group. This white blood cell is called T cell because it matures in the thymus, which is a small organ located in the chest cavity. T cells are differentiated from other lymphocyte cells, such as B cells and natural killer cells, by the presence of a special receptor on their cell surface. This receptor is called T cell receptors, or TCR.

T cells are subdivided into three types of T cells: T helper cell, or Th cell; T suppressor cell, or Ts cell; T cytotoxic cell, or Tc cell. T helper cells assist other leukocytes in immunological processes. T suppressor cells shut down T cell-mediated immunity toward the end of an immune reaction and stop specific immune reactions from occurring. T cytotoxic cells kill virally infected cells and cancerous cells.

T helper cells: they establish and maximize the capabilities of the immune system. T helper cells do not have cytotoxic or phagocytic activity. They do not kill infected host cells or pathogens, and without other immune cells they would be useless against an infection. Nevertheless T helper cells activate and direct other immune cells, such as natural killer cells, macrophage cells, and T cytotoxic cells, to carry out the task of destroying foreign microorganisms.