1. T-Cell Activation

2. 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)

3. 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

4. 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

5. 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

6. 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

7. 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

8. T-Cell Activation Diagram

9. 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

10. References