Cell-Mediated Immunity

Question 1

What are 2 types of CD4+ T Cells?

Answer 1

1. Helper T Cells (cytokine secreting)

2. Regulatory T Cells

Question 2

What is the function of Regulatory T Cells?

Answer 2

They suppress T cell-mediated immunity at the end of an immune reaction and also suppress auto-reactive T cells that escaped negative selection.

Question 3

What is the function of Cytotoxic T Cells?

Answer 3

They release cytolytic substances such as perforin and granzyme that ligand directly into target cells and promote apoptotic cell death.

*Destroy virally-infected and tumor cells.

Question 4

Memory T Cells

Answer 4

May be either CD4 or CD8 that are antigen-specific T cells. They quickly expand upon re-infection.

Question 5

Double-Negative Thymocytes

Answer 5

Immature T cells which do not express CD4 or CD8.

Question 6

What are two processes of Thymic Education?

Answer 6

1. MHC Restriction

2. Self-Tolerance

Question 7

Describe MHC Restriction

Answer 7

• Occurs in Cortical Epithelium of Thymus
• Positive Selection Occurs
• DP CD4+ CD8+ cells that don’t bind or has too low affinity for self-MHC undergo apoptosis.

Question 8

Describe Self-Tolerance

Answer 8

• Occurs in Medulla Epithelium of Thymus
• Negative Selection Occurs
• SP CD4+ or SP CD8+ cells that bind self-peptides or has a high affinity for MHC I or II undergo apoptosis.

Question 9

What are Naive T Cells

Answer 9

Single positive thymocytes (either CD4+ or CD8+) that leave the thymus in an unactivated state.

• They die within 6 weeks if don’t bind to an antigen+MHC complex for differentiation.

Question 10

What second co-stimulatory signal is required for T-Cell Activation?

Answer 10

CD28 receptor on Native T Cell must bind to B7 protein on APC.

Question 11

What happens in the absence of a co-stimulatory signal 2?

Answer 11

The naive T cell becomes Anergy (no longer responsive to antigen-MHC stimulation).

• Self-Tolerance mechanism

Question 12

What happens upon TCR binding to the MHC+peptide complex?

Answer 12

Protein Tyrosine Kinase (PTK) phosphorylate ITAM on CD3 near the TCR complex. This starts signal transduction of T cells to secrete cytokines.

Question 13

What happens after co-stimulation of T-Cell Activation Occurs?

Answer 13

1. Activated T cell secretes IL-2 cytokine that is bound by itself in an autocrine manner.
2. IL-2 promotes cell proliferation (clonal expansion) & differentiation of all types of T cells.
3. Differentiated effector T cells leave lymphoid tissues and enter circulation.

• Both CD4+ and CD8+ T cells secrete IL-2.

Question 14

What Is The Function of CD4+ Helper T Cells?

Answer 14

They release cytokines

Question 15

What are subtypes of CD4+ Helper T Cells?

Answer 15

1. TH1
2. TH2
3. TH17

Question 16

Describe TH1 T Cells

Answer 16

• Pro-inflammatory
• Responds to Intracellular microbes
• Cytokines Required: IL-12
• Cytokines Produced: IFN-Y
• Function: Activate Macrophages; increase MHC expression; inhibits Th2 cell differentiation

Question 17

Describe TH2 T Cells

Answer 17

• Anti-inflammatory
• Responds to Helminthic parasites
• Cytokines Required: IL-4
• Cytokines Produced: IL-4, 5, 10, 13
• Function: Neutralize IgG and mast cells; Activate eosinophils (parasitic infection); B cell switching to IgE

Question 18

Describe TH17 T Cells

Answer 18

• Pro-inflammatory
• Responds to Extracellular bacteria, fungi
• Cytokines Required: TGF-B
• Cytokines Produced: IL-17, 22
• Function: Enhance neutrophil and monocyte response