Explain the mechanism of action of T cells to antigens.
Mechanism of Action of T-cells: Like B-lymphocytes, T-cells are also antigen specific as each Tcell recognises a specific antigen. Thus, different types of T-cells are stimulated by different types of antigens.
When a T-cell comes in contact with an antigen, the T-lymphocyte divides rapidly to form a clone of Tcells. A clone of T-cells has four types of cells. These are helper T-cells, killer T-cells, supressor Tcells and memory T-cells. Out of these, the first three are also called effector cells.Cytotoxic T-cells or Killer T-cells (Tc cells) destroy infected cells having foreign antigens attached to their surface. They become active on receiving signal molecules from helper T-cells and antigenpresenting cells or by foreign antigen. They secrete perforin molecules and granzymes.
(a) Perforins form pores in the cell membrane of infected cells. Water and ions enter the infected cells through these pores and cause their bursting.
(b) Granzymes enter the infected cells by endocytosis and initiate its apoptosis (cell death) leading to fragmentation of its nucleus and cytoplasm. Memory T-cells are sensitised by antigens and retain sensitisation for the future. Suppressor T-cells inhibit immune response by releasing cytokines that suppress activity of other Tcells and B-cells. Helper T-cells secrete substances that enhance or activate immune response.
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