Lecture 12. T-cell Activation and Differentiation Flashcards
What is one of the first things that T-cells do ?
Produce IL2
What is the induction of response in cell mediated immunity ?
Naive CD4+ T-cells and CD8+ T-cells recognise peptides and that are derived from protein antigens and presented by antigen-presenting cells in peripheral lymphoid organs. The T-lymphocytes are activated to proliferate and differentiate into effector cells ehich enter the circulation
Where do effecter T-cells go ?
The site of the antigen
How do effector T-cells travel ?
They migrate through blood vessels in peripheral tissues by binding to endothelial cells
What are endothelial cells activated by ?
Cytokines
What are T-cell effector functions ?
CD4+ T-cells recruit and activate phagocytes to destroy microbes and CD8+ cytotoxic T lymphocytes kill infected cells
What are the steps in activation of T-cells ?
- Antigen recognition
- Activation
- Clonal expansion
- Differentiation
- Effector functions
How do T-cells respond to antigen recognition ?
By producing cytokines and expressing receptors for these cytokine leading to an autocrine pathway of cell proliferation resulting in clonal expansion
What does naive T-cell activation require ?
Two signals
What are the two signals that naive t-cell activation requires ?
- T-cell receptor
- Co-stimulatory molecules
What is the purpose of requiring two signals for naive T-cell activation ?
Ensures only appropriate activation occurs - microbes induce expression of signal 2 so full T cell activation should only occur in presence of infection
What does the co-stimulatory molecule B7 do ?
Binds CD28 on the naive T cell
What does CTLA-4 provide and why ?
Negative signals to help regulate T-cell responses
What does CTLA-4 binding to B7 achieve ?
Inhibitory signals to activated T- cells
What may present peptide antigens, but do not express costimulators and are unable to activate naive T-cells ?
Resting antigen presenting cells which have not been exposed to microbes or adjuvants
What may T cells that recognise antigen without costimulation become ?
Tolerant to subsequent exposure to the antigen (anergy
What induces the expression of costimulators on the antigen presenting cells ?
Microbes as well as cytokines produced during the innate immune responses
What happens once a naive T cell has been properly activated ?
Undergoes prolliferation/clonal expansion
What is initital activation of naive T cells ?
An important checkpoint
How do naive CD8+ T cells become activated if MHC class I presenting cells dont express costimulatory molecules ?
Cross presentation
What is cross presentation needed for ?
Activation of naive CD8+ T-cells
How is cross presentation thought to occur ?
By cytosolic diversion
What is cytosolic diversion ?
Where proteins are transported out of phagosomes into the cytosol and then enter the class I pathway as usual
What is the function of CD3 ?
Signal transduction by TCR complex
