(Section B: Immunology) Lecture 14: T-Cell Immunity I

Question 1

What components are T-Cell Receptors made up of?

Answer 1

1. Variable region (V)
2. Constant region (C)
3. Transmembrane region
4. Cytoplasmic tail

Question 2

What protein subunits for the TCR?

Answer 2

Alpha and Beta

Question 3

What does the V-region in TCRs contain?

Answer 3

The antigen binding site

Question 4

True or False:

TCRs don’t directly recognize antigens

Answer 4

True

Question 5

What do TCRs recognize?

Answer 5

Mostly recognize peptides (from proteins) presented by MHC molecules

Question 6

Epitope

Answer 6

Part of antigen actually recognized

Question 7

What is the epitope for TCRs?

Answer 7

Peptides

Question 8

How are peptides presented to TCRs?

Answer 8

1. Antigen broken down into peptide fragments
2. Carried by MHC to TCRs

Question 9

Give examples of:

Peptides interacting with MHC

Answer 9

Inside the cell:
1. Self proteins
2. Virus infections

Outside the cell:
1. Bacterial infections
2. Parasitic infections
3. Self proteins

Question 10

What are the classes of MHC?

Answer 10

• Class II MHC
• Class I MHC

Question 11

Class II MHC

Answer 11

• Recognized by TH cells (CD4+)
• Made up of two protein chains (alpha and beta)

Question 12

Class I MHC

Answer 12

• Recognized by TC Cells (CD8+)
• Made up of one protein chain (alpha)

Question 13

What is the MHC presenting peptide fragments known as?

Answer 13

Antigen Presentation

Question 14

MHC Restriction

Answer 14

T cells can only recognize antigens presented by MHC

Question 15

Why is a large diversity of MHC molecules necessary?

Answer 15

Increases the range of peptides that can be recognized by T Cells

Question 16

What advantage does MHC diversity impart?

Answer 16

Evolutionary survival advantage against infectious disease

Question 17

Describe the structure of the peptide binding groove in both classes of MHCs

Answer 17

1. Beta sheets on the floor of the groove
2. Alpha helices on the walls of the groove

Question 18

How does the composition of peptide-binding groove differ between MHC Class II and MHC Class I?

Answer 18

MHC Class II:
* Alpha and Beta domains form peptide-binding groove

MHC Class I:
* Alpha and Alpha domains form peptide-binding groove

Question 19

What size of peptides can the classes of MHC proteins present to T Cells?

Answer 19

Class I proteins:
* “Closed” peptide-binding groove
* Binds peptides of 8-10 amino acids

Class II proteins:
* “Open” peptide-binding groove
* Binds peptides of 13-24 amino acids

Question 20

Where are the classes of MHC proteins expressed?

Answer 20

MHC Class I
* Inside the cell
* Expressed by all nucleated cells (not in RBCs)

MHC Class II
* Outside the cell
* Expressed by specialized cells (“Antigen presenting cells”, all have phagocytic ability)
* E.x. B Cells, Macrophage, Dendritic cells, Epithelial Thymic Cells

Question 21

What types of Antigen-presenting cell types are there?

Answer 21

• Professional
• Nonprofessional

Question 22

What are examples of professional Antigen-Presenting Cells?

Answer 22

• Dendritic cells
• Macrophages
• B cells

Question 23

What are examples of nonprofessional Antigen-presenting cell types?

Answer 23

• Fibroblasts (skin)
• Glial cells (brain)
• Pancreatic beta cells
• Thymic epithelial cells
• Intraepithelial lymphocytes
• Vascular endothelial cells

Question 24

Professional Antigen-Presenting cells

Answer 24

Express Class II MHC molecules at high levels
* Delivers activating signals to T cells

Question 25

Nonprofessional Antigen-presenting cells (APCs)

Answer 25

Can express Class II MHC and coostimulatory molecules **when stimulated by infection**

Question 26

What role do thymic epithelial cells play?

Answer 26

Play a role in clonal selection during T cell development

Question 27

How do peptide antigens get to Class I MHCs?

Answer 27

1. Protein gets degraded by proteosome 2. Peptide fragments go through TAP into ER 3. MHC I carries peptide through Golgi to outside the cell

Question 28

How do peptide antigens get to Class II MHCs?

Answer 28

1. Antigen gets carried into cell via Vesicle and receptors 2. MHC Class II goes from ER to Golgi and to cytoplasm 3. Peptides are broken down from early to late endosome, receptors are recycled 4. MHC Class II and peptide endosomes are merged together 5. MHC Class II leaves cell

Question 29

What is unique about Dendritic Cells?

Answer 29

They can initiate both CD4 and CD8 T Cell Activation by Cross-Presentation of Antigen

Question 30

Allorecognition

Answer 30

Recognition of "other" (non-self)

Question 31

Direct vs. Indirect allorecognition

Answer 31

Direct: * T cell recognition of **donor (nonself) MHC presenting donor (nonself)** *or* **recipient (self) peptides** Indirect: * T cell recognition of **recipient (self) MHC presenting donor (nonself) peptide** (allopeptide)

Question 32

What disease exploit the MHC Class II Pathway?

Answer 32

* Flesh eating disease * Toxic shock syndrome Diseases caused by Bacterial Infections

Question 33

What is inflammation caused by in diseases that exploit the MHC Class II Pathway?

Answer 33

Superantigen proteins (SEA, SEB etc.)

Question 34

What does the superantigen protein do?

Answer 34

Essentially prevents the MHC protein and the T cell from separating (causing overexpression)