L3-4 - Antigens, Presentation and Receptors

Question 1

What is an antigen?

Answer 1

Any molecule that can bind specifically to an antibody or T cell receptor

Question 2

Define antigenicity

Answer 2

The ability of a chemical structure to bind specifically to T or B cell receptors

Question 3

What is an immunogen?

Answer 3

Molecule that elicits an adaptive immune reaction

Question 4

Define immunogenicity

Answer 4

Ability of a molecule to induce a humoral or cell-mediated immune response

Question 5

What is the difference between antigenicity and immunogenicity?

Answer 5

Antigenicity involves ability to bind, immunogenicity involves ability to elicit an immune response

Question 6

What happens during the innate immune response when there is a local infection?

Answer 6

Pathogen enters the body, phagocytes are recruited to kill invaders

Question 7

What happens during the innate immune response when an infection penetrates tissues?

Answer 7

Dendritic cells phagocytise the pathogens, then activate the adaptive immune system

Question 8

How do antibodies facilitate the removal of extracellular pathogens and toxins?

Answer 8

They bind the pathogen/toxin, bind to macrophage, taken in by macrophage and destroyed

Question 9

What is the main role of the B cell?

Answer 9

Processing and presenting antigens

Question 10

What are the variable domains of an antibody?

Answer 10

Regions in the Fab domain that are highly variable and specific for target antigens

Question 11

What is the name of the antigen binding site of an antibody, and what does this consist of?

Answer 11

Complementarity-determining region (CDR) - 3 variable regions of heavy and light chains (6 total) that are paired in an antibody

Question 12

How is antibody diversity generated?

Answer 12

Heavy and light chain genes are rearranged

Question 13

What are the 5 major antibody isotypes?

Answer 13

IgM, IgG, IgE, IgA and IgD

Question 14

What antibody provides initial response?

Answer 14

IgM

Question 15

What is the major antibody in serum?

Answer 15

IgG

Question 16

What antibody provides the majority of the defence against pathogens?

Answer 16

IgG

Question 17

Which antibody prevents microbial colonisation of mucosal surfaces?

Answer 17

IgA

Question 18

Which antibody aids in the defence against parasites? How does it do this?

Answer 18

IgE - triggers mast cells to destroy parasite

Question 19

What is the constant domain of an antibody, and what is its role?

Answer 19

The non-variable part of the antibody that is responsible for activating different effector mechanisms

Question 20

What 2 types of protein chain are antibodies made up of? How many of each are there in IgG?

Answer 20

Heavy and light chains

IgG has 2 of each

Question 21

What is the name of the structure within an antigen that the antibody recognises?

Answer 21

Epitope

Question 22

What happens within lymph nodes during activation of the adaptive immune system?

Answer 22

Dendritic cells migrate here and present processed antigens (from phagocytised pathogens) to T cells

Question 23

What area of an antibody does a T cell receptor (TCR) resemble?

Answer 23

Fragment antigen binding (Fab) region

Question 24

What are the names of the protein chains that make up the majority of T cell receptors (TCRs)?

Answer 24

Alpha and beta chains

Question 25

What are the 2 main ways a T cell receptor differs from a B cell receptor or antibody?

Answer 25

They have 1 antigen binding domain | They are never secreted

Question 26

What type of molecule are CD4 and CD8?

Answer 26

Cell surface proteins

Question 27

What is another name for CD4 and CD8 molecules? and how do they get this name?

Answer 27

Co-receptors - they associate with T cell receptors to help bind to MHC

Question 28

What cell types are CD4+?

Answer 28

Helper T cells and regulatory T cells

Question 29

What MHC class do CD4+ T cells bind to?

Answer 29

Class II

Question 30

What are the 3 main types of helper T cell?

Answer 30

Th1, Th2 and Th17

Question 31

What is the role of Th1?

Answer 31

Co-ordinates inflammatory response against intracellular pathogens

Question 32

What is the role of Th2?

Answer 32

Helps B cells produce antibodies against extracellular parasites

Question 33

What is the role of Th17?

Answer 33

Protects against extracellular bacteria or fungi

Question 34

What cell types are CD8+?

Answer 34

Cytotoxic T cells

Question 35

What MHC class do CD8+ T cells bind to?

Answer 35

Class I

Question 36

What are the two groups of protein chains that can make up a T cell receptor? Which is the most common?

Answer 36

Alpha and beta chains Gamma and delta chains Alpha and beta are most common

Question 37

Where are gamma delta T cells localised?

Answer 37

Gut mucosa

Question 38

What 3 receptors are expressed on natural killer cells?

Answer 38

Fc receptors Killer-activating receptors (KAR) Killer-inhibiting receptors (KIR)

Question 39

Describe how natural killer cell receptors influence the cell's activation

Answer 39

The killer-activating receptors (KAR) bind to common molecules on cell surface. Whether the cell is targeted for destruction depends on the binding of killer inhibiting receptors (KIR) to MHC class I. If bound - cell is not infected, so is not destroyed In-bound - cell is infected, destroyed

Question 40

In what organ to T cells mature?

Answer 40

Thymus

Question 41

Describe the process of T cell maturation in the thymus

Answer 41

Immature T cells are exposed to thymic cells expressing self MHC. Those with a strong affinity are removed, those with a weak affinity survive and enter the peripheral T cell repertoire

Question 42

Which type of T cell has a role in the prevention of autoimmune responses? How does it do this?

Answer 42

Regulatory T cells - releases cytokines which inhibit CD4+ Th cells when it encounters MHC class II displaying self antigen

Question 43

What are co-stimulatory molecules in T cell activation?

Answer 43

Cell surface proteins present on T cells and antigen presenting cells

Question 44

What is the role of co-stimulatory molecules in CD4+ T cell activation?

Answer 44

T cells need 2 signals to activate - bind to MHC class II on antigen presenting cell, binding of co-stimulatory molecule to receptor on T cell This reduces risk of self responses

Question 45

What are the co-stimulatory molecules / receptors involved in CD4+ T cell activation?

Answer 45

CD28 receptor on naïve T cell binds to B7 molecule on antigen presenting cell (APC)

Question 46

What is required for antigen presenting cells to become activated?

Answer 46

Binding of antigen to a pattern recognition receptor (PRR)

Question 47

What happens after antigen presenting cells are activated?

Answer 47

They upregulate the production of co-stimulatory molecules required for T cell activation and phagocytise the pathogen