MHC And Ag Presentaiton To T Cells

Question 1

T cells have evolved to protect us against ____ microbes.

Answer 1

Intracellular microbes (viruses and some bacteria)

Question 2

T cells have evolved to protect us against intracellular microbes. They also help to mount a robust Ab-mediated humoral immune response against ____ pathogens.

Answer 2

Extracellular

Question 3

True or false: t cells cannot directly recognize unprocessed Ags or bind to microbes.

Answer 3

True

Question 4

What are Ags in host cells broken up into?

Answer 4

Linear peptides.

They are displayed by MHC molecules expressed on the cell surface.

Question 5

True or false: each T cell recognizes many specific foreign peptides.

Answer 5

False, each T cell recognizes one specific foreign peptide.

This occurs during normal thymus development.

Question 6

CD4 T helper cells recognize Ags in the context of what MHC class of molecules?

Answer 6

MHC class II.

These are expressed by DCs, macrophages and B cells.

Question 7

CD8 cytotoxic T cells recognize peptides associated with what MHC class of molecules?

Answer 7

MHC class I

Question 8

CD4 and CD8 attach to what part of the MHC class I and II molecules?

Answer 8

The non-polymorphic (non-variant) part.

Question 9

In order for naive T cells to carry out their functions, what needs to occur?

Answer 9

They need to be activated.

Recognition of the peptide Ag by the TCR is not sufficient to activated the cells.

Question 10

T cell activation leads to ____ of specific T cells.

Answer 10

Clonal expansion.

Question 11

What is the function of T helper cells?

Answer 11

They help macrophages to get rid of intracellular microbes and help the development of cytotoxic T cells to kill virus infected cells.

Question 12

What substance produced by Th1 cells activates macrophages?

Answer 12

IFN-gamma

Question 13

What is the primary role of Th2 cells?

Answer 13

They are involved in helping B cells to develop into memory cells and plasma cells that produce antibodies.

Question 14

What substance produced by Th2 cells is important for B cell proliferation?

Answer 14

IL-4

Question 15

Where is the TCR for an Ag only found?

Answer 15

On the T cell membrane.

Question 16

What is the TCR composed of?

Answer 16

Two polypeptide chains (alpha and beta), which are made up of constant and variable regions.

Question 17

What constitutes the Ag binding sites of T cell receptors (TCRs)?

Answer 17

The alpha and beta chain variable regions.

Question 18

What is the difference between alpha-beta T cells and gamma-delta T cells?

Answer 18

The gamma-delta T cells have some of the characteristics of alpha-beta T cells, but have a broader specificity for unconventional Ag such as HSPs and phospholipids.

Question 19

The genes coding for TCR polypeptide chains are members of what superfamily?

Answer 19

Ig superfamily

Question 20

What is a difference between Abs and TCRs?

Answer 20

Unlike Abs, TCRs do not recognize native antigens, but can only bind processed Ag presented in MHC molecules.

Question 21

What does the T cell receptor complex consist of?

Answer 21

The TCR

Alpha beta or gamma delta dimer in association with CD3

Question 22

What is CD3?

Answer 22

A signaling complex composed of gamma, delta and sigma chains. It is associated with TCRs

Question 23

What is the significance of co-dominant expression of the MHC gene?

Answer 23

It increases the number of different MHC molecules that can present peptides to T cells.

Question 24

What is the significance of polymorphic genes of the MHCs?

Answer 24

They ensure that different individuals are able to present and respond to different microbial peptides.

Question 25

What do CD4 helper T lymphocytes interact with?

Answer 25

DCs, macrophages and B lymphocytes

Question 26

What is CD8 capable of?

Answer 26

Killing an virus-infected cell.

Question 27

What is contained on the heavy chain of MHFC molecules?

Answer 27

A binding groove for peptides to be recognized by T cells. They are derived from class I genes.

Question 28

What do Class II genes encode?

Answer 28

Molecules composed of two dissimilar polymorphic polypeptide chains, both of which contribute to the peptide-binding groove.

Question 29

What cells express class I MHC?

Answer 29

All nucleated cells

Question 30

What cells express class II MHC?

Answer 30

DCs, phagocytes, B lymphocytes, endothelial cells, thymic epithelium

Question 31

What is the source of protein antigens in the class II MHC pathway?

Answer 31

Endosomal/lysosomal proteins

Question 32

What is the source of proteins found in the class I MHC pathway?

Answer 32

Cytosoloic proteins

Question 33

What is the site of peptide loading for the class II MHC pathway?

Answer 33

Specialized vesicles

Question 34

What is the site of peptide loading of MHC for the class I MHC pathway?

Answer 34

Endoplasmic reticulum

Question 35

True or false: anchor residues on the peptides bind to residues in the class I and II grooves and vary for different MHC alleles.

Answer 35

True

Question 36

Where are the polymorphic residues of class I and class II MHC molecules located?

Answer 36

In the peptide-binding clefts and the alpha helices around the clefts.

Question 37

The cleft of class I MHC molecule is closed, whereas that of the class II molecule is open. As a result, what happens?

Answer 37

Class II molecules accommodate longer peptides than do class I molecules.

Question 38

Where are MHC class I molecules expressed?

Answer 38

On all nucleated cells.

Question 39

The expression of class I and/or II molecules is modulated by what?

Answer 39

Cytokines

Question 40

Peptide Ags that bind to class I MHC molecules are derived from what?

Answer 40

They are derived from viruses that have infected host cells and move as the complexes to the surface.

Question 41

Peptide Ags that bind to class I MHC are recognized by what?

Answer 41

CD8 cytotoxic T lymphocytes.

Question 42

Where are MHC class II molecules expressed?

Answer 42

On professional APCs

Question 43

Where are peptide Ags that bind to class II MHC taken from the environment primarily presented to?

Answer 43

CD4 helper T cells.

Question 44

What are the functions of DCs?

Answer 44

Native t cell activation Clonal expansion and differentiation into effector T cells

Question 45

What are the primary functions of macrophages?

Answer 45

Effector T cell response: macrophage activation (cell mediated immunity).

Question 46

What is the primary functio of B cells?

Answer 46

Effector T cell response: B cell activation and and antibody production (humoral immunity).

Question 47

What increases class II MHC of dendritic cells?

Answer 47

IFN-gamma

Question 48

What induces class II MHC of macrophages?

Answer 48

IFN-gamma

Question 49

What increases class II MHC of B lymphocytes?

Answer 49

IL-4

Question 50

Microbial Ags commonly enter through the skin and GI and respiratory tracts, where they are captured by ___ and transported to regional lymph nodes.

Answer 50

Dendritic cells

Question 51

Ags that enter the blood stream are captured by APCs in the ____.

Answer 51

Spleen

Question 52

When do NK cells produce IFN-gamma?

Answer 52

During innate immune reactions to microbes or by T cells during adaptive immune responses.

Question 53

IFN-gamma stimulates the expression of what class of MHCs?

Answer 53

Class II MHC

Question 54

Alpha beta cells recognize only peptides. Why is this so?

Answer 54

Only peptides bind to MHC molecules.

Question 55

Alpha beta cells recognize linear peptides. Why is this so?

Answer 55

Conformation is lost during enzymatic processing of protein Ags into peptides.

Question 56

Alpha beta T cells recognize cell-associated and not soluble Ags. Why is this so?

Answer 56

MHC stably bound peptides stably and complexes are located on the cell surface.

Question 57

CD4+ T cells recognize extracellular Ags. Why is this so?

Answer 57

MHC class II molecules display peptides that are taken up from the extracellular enviroment of APCs by pinocytes (DCs and B cells) and phagocytosis (macrophages)

Question 58

CD8 T cells recognize intracellular Ags. Why is this so?

Answer 58

MHC class I molecules present peptides from cytosolic proteins including intracellular pathogens.

Question 59

What organelle is associated with the class I MHC pathway?

Answer 59

Endoplasmic reticulum

Question 60

What is the class I MHC pathway?

Answer 60

Production of proteins in the cytosol Proteolytic degradation of proteins Transport of peptides from cytosol to ER Assembly of peptide class I complexes in the ER Surface expression of peptide class I complexes.

Question 61

What is the class II MHC pathway?

Answer 61

Uptake of extracellular proteins into vesicular compartments of APC Processing of internalized proteins in endosomal/lysosomal vesicles Biosynthesis and transport of class II MHC molecules to endosomes Association of processed peptides with class II MHC molecules in vesicles Expression of peptide MHC complexes on cell surface

Question 62

What is the function of the HLA-DM editing mechanism?

Answer 62

It works to ensure the presentation of only the most relevant Ags for eliciting an immune response.

Question 63

What ar the three major functions of the HLA-DM editing mechaism?

Answer 63

It causes the dissociation of CLIP from the peptide binding groove of MHC II. It stabilizes and prevents degradation of the empty MHC II. It faciliattes the binding of Ag fragments to the open, stabilizes binding groove.

Question 64

What is the pathway of HLA-DM?

Answer 64

Synthesis of class II MHC in ER Transport of class II MHC and Ii to vesicle Binding of processesd peptides to class II MHC Transport of peptide0class II MHC complex to cell surface Expression of peptide MHC complex on cell surface.

Question 65

What do DCs ingest?

Answer 65

Fragments of cells infected with intracellular microbes.

Question 66

Where are Ags of infectious microbes transported?

Answer 66

Into the cytosol and processed and presented in association with class I MHC molecules to CD8 T cells. Thus, DCs are able to present extracellular Ags by the class I pathway.

Question 67

What is the class I MHC pathway?

Answer 67

Production of proteins in the cytosol Proteolytic degradation of proteins Transport of peptides from cytosol to ER Assembly of peptide-class I complexes in ER Surface expression of peptide class I complexes

Question 68

Where are immunodominant peptides obtained?

Answer 68

By proteases available in cells. The peptides bind best to the available class I and class II MHC molecules. Applies to peptides presented by both class I and class II MHC molecules.

Question 69

What is the pathway of immunodominant peptides?

Answer 69

Internalization of antigen into APC Antigen processing Processing generates multiple peptides, one of which can bind to class II allele T cells respond to immunodominant peptide epitope.

Question 70

Cell mediated immunity is due to the direct action of what type of cells?

Answer 70

T cells