Adaptive Immunity: T Cells

Question 1

Outline the features of adaptive immunity

Answer 1

• Specificity- ensures distinct antigens elixir specific responses
• Diversity- enables immune system to respond to large variety of antigens
• Memory- enhanced responses to repeated exposures to same antigen
• Clonal expansion- increases number of antigen- specific lymphocytes from a small number of naïve lymphocytes

Question 2

Outline TCR

Answer 2

• ~90% T cells have TCRαβ (divided into CD4+ and CD8+)
• ~5-10% T cells have TCRγδ (enriched in skin and gut)
• Variable and constant region on both α and β chain
• Associated with CD3 complex of invariant chains (γ,δ,ε,ξ)-> signal transduction
• Signal activation requires costimulation- APC must have B7 (/CD80(B71)/CD86(B72)) which binds CD28 and causes T cell to proliferate

Question 3

What are the T cell subsets?

Answer 3

• CD4 T cells- interact with MHC II- see antigens taken up exogenously

• Helper T cells promote certain immune responses
• Regulatory T cells suppress immune responses and prevent autoimmunity

• CD8 T cells- interact with MHC I- see endogenous peptides

Question 4

What are Cytotoxic T lymphocytes CTLs?

Answer 4

An important CD8 cell type
• Have cytotoxic granules containing perforin and granzymes
• Perforin facilitates entry of the granzymes which cause apoptosis
• CTL bind to MHC I and death receptors such as Fas

Question 5

Give examples of CD4 Helper T cells

Answer 5

Once T cell is activated and clonally expands it will differentiate:
• Th1-> INFγ-> macrophages-> intracellular pathogens
• Th2-> IL-4, IL-5, IL-13-> eosinophils-> parasites (helminths)
• Th17-> IL-17, IL-22-> neutrophils-> extracellular pathogens