T cells Flashcards
2 Types of T cell
CD4 (T helper- Th, immune regulation) and CD8 (cytotoxic T cell, kill intracellular pathogens)
What types of antigens stimulate T cells
Peptide antigens on MHC1 (CD8) and MHC2 (CD4). T cells are only activated by interacting with other cells don’t recognise antigens not on MHC receptors. Activated by only 1 specific antigens for it’s unique TCR (t cell receptor)
Where do T cells develop
Thalamus (primary lymphoid tissue). Go from immature to mature (but still not activated). Assigned CD8 or CD4 function
Where are t cells activated
Lymph nodes (secondary lymphoid tissue). Interacts with specific antigens on APCs to go from naive to activated
3 steps of T cell development
TCR presence, positive (MHC) selection and negative (self) selection
T cell Receptors Outline
Millions of unique receptors (complementary to specific antigen). Each T cell contains only 1 type. Consists of 2 chains (alpha and beta) each made up of 2 different regions. Top region = variable (substrate binding site) and bottom region = constant (attached to cell membrane)
How are so many uniquely antigen specific TCR binding regions created
VDJ (TCR coding genes) recombination done randomly. There’s 10^4 possible combinations
Positive Selection Outline
TCR binds to MHC receptors in thalamus cells. A signal is sent to the T cell telling it to keep living. If TCR fails to bind MHC T cell is defective and is killed (doesn’t recieve positive signal). Positive selection is point at which cell either becomes CD8 (MHC1) or CD4 (MHC2)
Negative Selection Outline
TCR should only bind moderately/weakly to cell in thalamus as MHC only contains self (non-infected cell) antigen. If binding is strong the cell receives a secondary signal to undergo apoptosis. Protects against autoimmunity
Benefits of T cell activation in lymph nodes
Lymph nodes are present all over body. There should never be a sit of infection where T cells are very far
Result of T cell activation
Clonal expansion - T cell activated releases an autocrine IL-2 that stimulates production of identical clones
3 signals required for T cell activation (dendritic + T cell)
MHC x + TCR (T cell recognises it’s specific antigen), CD40 antigen + CD40L receptor (co-stimulatory activates transduction pathway for altered gene expression) and instructive cytokine (creates subclasses of T cells eg IL-12 and Th1)
Do T cells produce memory cells
A % T cells produced are relegated to memory cells
T cell activated by cytokine IL-12
Th1
What do Th1 cells secrete
interferon gamma. Activates macrophages and cytotoxic T cells
T cell activated by IL-10
Th2
What does Th2 secrete
IL-4, IL-5 and IL-13. Activates eosinophils, mast cells and b cells (antibodies)
T cell activated by IL-23
Th17
Cytokines released by Th17
IL-17 and IL-22. Activates neutrophils
T regulatory cells secretion and function
Secretes IL-10. Switches off Th1, Th2 and Th17 response
CD8 Secretion and Function
Granzymes (stimulate apoptosis) and perforin (damages cell membrane). Kill cells infected by pathogens
