T-Cell Activation

T-Cell Response Some types of antigens are recognized by T-cells after being processed by other cells in the immune system, once T-cells recognize an antigenic sequence, they are first activated, then respond to the antigen. T-cells typically respond to intracellular pathogens (such as viruses and intracellular bacteria)

T-Cells T-Cells are characterized by a surface receptor, the T-cell receptor (TCR) T-cells are named such because they mature in the thymus (while B-cells mature in bone marrow) T-cells cannot bind antigen directly, and must interact with processed antigenic peptides

Types of T-cells There are four different types of T-cells Helper T-cells Helper T-Cells are involved in activating and detecting other cells of the immune system and ‘help’ the boost the immune response Cytotoxic T-cells Cytotoxic T-cells kill other cells by releasing granules with cell-death inducing proteins Regulatory T-cells Regulatory T-cells regulate the immune response, to prevent an overactivation of the immune system Memory T-cells Memory T-cells are used to ‘remember’ specific foreign pathogens

T-Cell Development While T-cells originate in the bone marrow, they mature in the thymus In the thymus, the T-cell undergoes several changes in cell surface molecules, going from double negative to double positive for CD4 and CD8, and ultimately to single positive

T-cell Activation In order for T-cells to be activated, two different receptors must be engaged: one is TCR, and the other is CD 28 Both receptors initiate intracellular signal processes

T-Cell Activation, continued The TCR and CD 28 receptors activate intracellular proteins, notably tyrosine kinase Inositol phospholipids in the plasma membrane are hydrolized Cellular Ca2+ levels are increased, so that calcineurin can be activated Calcineurin regulates the transcriptions of genes in the T-cell, and promotes T-cell activation

T-Cell Activation Diagram

T-Cell Response The response of the T-Cell depends on the type of T-Cell Cytotoxic T-Cells immediately release perforinand granulysin , which form holes on a target cells plasma membrane, when activated Helper T-Cells proliferate and release cytokines to stimulate growth of T-cells

References http://www.cartage.org.lb/en/themes/sciences/LifeScience/GeneralBiology/Immunology/ImmunityInfection/CellActivation/TCellMaturation/figure12-05.jpg http://www.biochemj.org/bj/371/0015/bj3710015f01.jpg