T Cell Activation and Immunity (Lec 7)

Question 1

Extravasation of T Cells

Answer 1

• only done if T cell is in the bloodstream, not necessary if it is in lymphatic system
• T cells in bloodstream have proteins that interact with proteins on epithelial cells in blood vessels
• T cells start to roll on blood vessel due to protein interactions
• once strong enough interaction occurs, T cell will perform diapedesis and go from bloodstream into lymph node

Question 2

T Cell Co-Receptors

Answer 2

• CD4 and CD8 proteins
  are co-receptors to the
  TCR
• ensure that CD4 (helper) T cells bind to MHC Class II and CD8 (Cytotoxic) T cells bind to MHC Class I

Question 3

1st Signal of T Cell activation

Answer 3

TCR and CD4 or CD8 co-receptor recognizing a specific peptide presented
on MHC Class II/I

Question 4

2nd Signal of T Cell activation

Answer 4

Costimulatory receptor, CD28, binding to B7 on APC that is presenting antigen

Question 5

3rd Signal of T cell activation

Answer 5

Cytokines (differentiation)
- IL-2 = Interleukin-2

Question 6

T Cell Inhibitory Co Receptors

Answer 6

• have both CD28 and CTLA-4, which affect T cell activation
• CD28 = positive (activation)
• CTLA-4 = negative (no activation)
• CTLA-4 binds B7 more avidly than CD28 and delivers inhibitory signals to activated T cells

Question 7

IL-2

Answer 7

• after getting 1st and 2nd signals, T cell starts making own IL-2
• autocrine action = acts on same T cell that made it
• promotes T cells to
  proliferate many times and
  produce many clones with
  same peptide:MHC recognition

Question 8

T Cell Anergy

Answer 8

• Lack of costimulation =
  lack of IL-2 = T cell anergy
• irreversible
• stays anergic even after it gets correct combination of signals after it was already made anergic

Question 9

Activation of CD8 T Cells

Answer 9

• activated by cross presentation
• requires a stronger co-stimulation signal from a professional antigen
  presenting cell (pAPC) to prevent CD8 T cells from doing unnecessary damage
• Once Naïve CD8 T cells recognizes antigen presented on MHC Class I by a pAPC → activated and differentiates into an effector CD8 T cell

Question 10

Effector CD8 T cells

Answer 10

no longer require co-stimulation and can recognize a wide variety
of target cells (not just pAPCs like naïve CD8 T cells)

Question 11

Example of Effector CD8 T Cell Function

Answer 11

Cytotoxic T cells (CD8 T cells)
create an immunological
synapse with the target cell to release harmful granules that induce apoptosis without spreading to other cells

Question 12

Superantigens

Answer 12

• have properties that allow
  them to activate many
  different T cells with
  different peptide:MHC
  recognition
• cross-link receptors together to trigger broad T cell activation
• Results in non-specific T cell
  activation = less effective
  immune response