Lecture 24 - Cell Mediated Immunity

Question 1

What are the parts of a T-cell receptor?

Answer 1

alpha and beta chain
Top half is variable region
Bottom half is constant region
One antigen binding site

Question 2

What are three differences between Th and Tc cells?

Answer 2

CD4 vs CD8 surface molecule
MHCII vs MHCI
secrete cytokines vs perforin

Question 3

What are the 2 signals required to activate Th cells?

Answer 3

1. Specific antigen binding of TCR to MHCII
2. Co-stimulatory peptide B7 binds to CD28 on Th cell (B7 indicates it is a pathogen)

Question 4

Why is it important that two signals are needed to activate Th cells?

Answer 4

It ensures that they are only activated by phagocytes that have engulfed pathogens

Question 5

What is the difference between “naive” cells and “effector” cells?

Answer 5

Naive = inactive
Effector = activated

Question 6

What is the main function of effector Tc cells?

Answer 6

Effector Tc cells follow chemokine trails, binds infected cell showing antigen, and releases cytotoxins (like perforin) to induce apoptosis

Question 7

Why does Tc activation require stronger ligand recognition than Th?

Answer 7

Because once activated, Tc cells are tissue-destructive

Question 8

What are three function of effector Th cells?

Answer 8

1. Stimulate proliferation and differentiation of B cells
2. Binds MHCII of macrophages and secretes cytokines
3. Proliferate and differentiate by auto stimulatory cytokines

Question 9

What are special features of activated macrophages

Answer 9

More lysosomes, nitric oxide, and giant cells/granulomas form

Question 10

Why are T-regulatory and T-memory cells necessary?

Answer 10

T-regulatory cells reduce the T cell response
T-memory cells can be directly reactivated (no B7 needed)

Question 11

How are Treg cells produced?

Answer 11

produced in response to presence of products from the gut

Question 12

How do Treg cells decrease immune response?

Answer 12

1. produce anti-inflammatory IL-10
2. Destabilize low-affinity DC-Tc cell interactions
3. Stop division of self-recognizing Tc cells
4. Produce surface molecule CTLA-4 (CD152)

Question 13

What is the two-stage process of T-cell clonal deletion to achieve T-cell immune tolerance

Answer 13

T cells screened in thymus
1. Positive selection- T cells should be able to bind MHC I
2. Negative selection- T cells should not bind to thymus cells

Question 14

What is the function of NK cells in killing other cells?

Answer 14

1. bind to bacterial surface (spec vaccenic acid) or bind Fc of antibody (attached to bacteria)
2. release cytotoxins

Question 15

Compare NK and Tc cell functions

Answer 15

Both release cytokines
Does not need MHC

Question 16

Why do NK cells not kill all the cells in the human body?

Answer 16

NK cells spare healthy cells that express high self-MHC I and low stress-induced molecules