TCR Recognition

Question 1

What are the branches of the adaptive immune system?

Answer 1

1. Cell-mediated - T cells

2. Humoral - B cells

Question 2

What are TCR characteristics?

Answer 2

TCR:
membrane only
req APC to present Ag
Monovalent (1 binding site)
Bind peptide Ag in MHC pocket on APC surface
Made of 2 polypeptide chains
Similar in size and structure to single Fab of Ig

Question 3

What are APC examples?

Answer 3

macrophages, dendritic cells, B cells

Question 4

What are Ig characteristics?

Answer 4

Membrane bound and secreted
Bind free Ag (no APC required)
Bivalent (2 Ag binding sites)
Bind proteins, carbohydrates, lipids, nucleic antigens
Made of 4 polypeptide chains: 2 heavy and 2 light

Question 5

Explain TCR structure

Answer 5

A membrane protein with short cytoplasmic tails
Each chain has an amino terminal variable region and carboxy terminal constant region
Always with another protein called CD3 complex
Heterodimers with either alpha-beta chains (most T cells) or gamma-delta chains (1-5%, don’t req MHC and APCs)

Question 6

What does CD3 do?

Answer 6

Mediates signal transductions when the T cell is stimulated after Ag recognition

Question 7

Explain TCR gene organization and rearrangement

Answer 7

Specificity is associated with the variable region
VDJ recombination during development in thymus
VJ for alpha region, VDJ for beta
RAG1/RAG2 recombinase protein mediates gene rearrangment
Other diversity mechanisms in rearrangement: N&P additions

Question 8

What mechanisms do Igs have that TCRs do not?

Answer 8

Affinity maturation

Isotype switching

Question 9

How does diversity compare between TCR and Ig?

Answer 9

TCR has much greater diversity: ~10^18

Ig ~5x10^13