T Cells at Work

Question 1

Effector Th cells have two main functions:

Answer 1

• remain in circulation, travelling among lymph nodes to provide help to B cells and CTLs
• exit the blood at the battle site and provide help for ‘soldiers’ of the innate and adaptive immune system

Question 2

‘Quarterbacks’ of the immune system

Answer 2

Th cells

- use cytokines to ‘call the plays’

Question 3

PAMPs detected by different TLRs

Answer 3

• TLR4: LPS on gram neg
• TLR2: gram pos cell wall ‘signatures’
• TLR3: double-stranded RNA from viral infections
• TLR9: unmethylated DNA dinucleotide, CpG

Question 4

How do the DCs (coaches) know the proper instructions to give the Th cells?

Answer 4

• what kind of pathogen is invading based on PAMPs

- where are the Th cells needed?; regional identity learned from local tissue cells

Question 5

Main cytokines produced by Th1 cells locally at site of infection

Answer 5

• IFN-gamma: activates macs; primes B cells to produce IgG3; Th2 antagonist
• TNF activates primed macs and NK cells
• IL-2 a growth factor for CTLs, NK, and Th1 cells; recharges NK cells
• GM-CSF growth and differentiation of granulocytes and monocytes

Question 6

Effects of cytokines produced by Th1 cell

Answer 6

fights virus or bacteria attack

Question 7

Main cytokines produced by Th2 cells locally at site of infection

Answer 7

• IL-3 stimulates growth of polymorphonuclear cells
• IL-4, a growth factor of Th2 cells, B cells and switch for IgE
• IL-5 stimulates B cell to switch to IgA
• IL-10 B cell proliferation and Th1 antagonist
• IL-13 stimulates mucus production in intestines

Question 8

Effects of cytokines produced by Th2 cell

Answer 8

fights parasites or mucosal infections

Question 9

Th17 cell

Answer 9

• IL-17 recruits neutrophils
• IL-21 a growth factor for Th17 cells
• fights fungi and extracellular bacteria

Question 10

Th0 cell

Answer 10

• remain ‘unbiased’ when first activated in the lymph node

- commit to a particular cytokine profile AFTER arriving at a battle scene ; influenced by local battle cytokines

Question 11

The case of delayed-type hypersensitivity (DTH)

Answer 11

• tuberculin protein (PPD)
• DCs process this and present peptides in MHC II and provide B7 costimulation to experienced Th1 cells
• if have/had TB or BCG vaccine = T cells secrete TNF and INF-gamma
• T cells react and proliferate but then macs and neutrophils are recruited to injection site = raised, red bump

Question 12

How CTLs kill their targets through FasL

Answer 12

• FasL on effector CTL binds to Fas protein on surface of its target cell
• Caspase-8 is activated and triggers a cascade that leads to apoptosis

Question 13

How CTLs kill their targets through perforins and granzyme B

Answer 13

• these are exocytosed from CTL and endocytosed into target cell
• perforin allows granzyme B to enter the cytoplasm of the target cell and activated a cascade that leads to apoptosis