Recognition of antigen by the adaptive immune system

Question 1

What are the cells of the adaptive immune system?

Answer 1

B cells, T cells

Question 2

What are antigens?

Answer 2

Molecules that induce an immune response through the activation of antigen specific lymphocytes

Question 3

What are the three groups of molecules that work together to recognise antigen for the adaptive immune system?

Answer 3

MHC, B cell receptors, T cell receptors

Question 4

What is combinatorial diversity?

Answer 4

Diversity achieved through a process of gene rearrangement of the different parts encoding the receptor

Question 5

How do B cell receptors achieve further diversity and specificity for antigen?

Answer 5

Through a process of rapid mutation called hypermutation

Question 6

What do T lymphocytes recognise?

Answer 6

Short peptide sequences from antigens, not whole pathogens

Question 7

What does an APC have to do in order for a T lymphocyte to be able to recognise a pathogen?

Answer 7

Break down the pathogen and process into smaller peptides within the APC

Question 8

How do T lymphocytes recognise peptides?

Answer 8

The peptides must be presented on the APC cell surface

Question 9

How are peptides presented on the APC cell surface for recognition by T cells?

Answer 9

By a peptide-presenting molecule - Major histocompatibility complex (MHC)

Question 10

What do B lymphocytes recognise?

Answer 10

whole antigen

Question 11

How do B lymphocytes recognise antigen?

Answer 11

Through their B cell receptor which binds to cell surface molecules or patterns.

Question 12

What is the difference between a B cell receptor and an antibody/immunoglobulin?

Answer 12

Antibodies/immunoglobulins are soluble antigen receptors secreted from terminally differentiated B cells (plasma cells)

Question 13

What do B cells/antibodies do once they have bound to antigens?

Answer 13

Present to T cells

Question 14

What does MHC class I recognise?

Answer 14

Peptides derived from endogenous proteins

Question 15

What does MHC class II recognise?

Answer 15

Peptides processed from exogenous proteins

Question 16

Where are MHC class I molecules found?

Answer 16

All nucleated cells, except neurones

Question 17

What is a proteosome?

Answer 17

A large cytoplasmic complex involved in the breakdown of proteins

Question 18

Where do the broken down peptides (antigens) go?

Answer 18

Through the endoplasmic reticulum to the surface and loaded into the peptide-binding groove of a MHC class I molecule

Question 19

What type of cell recognises the MHC class I: peptide complex?

Answer 19

Cytotoxic T cells

Question 20

What do cytotoxic T cells express that facilitate the interaction between the T cell and the MHC class I?

Answer 20

CD8 - a co-receptor for the T cell receptor (TCR)

Question 21

What does the process of specific antigen recognition trigger the cytotoxic T cell to do?

Answer 21

Kill the virally infected cell by inducing apoptosis

Question 22

What does the TAP protein do?

Answer 22

Controls the movement of these intracellular proteins into the endoplasmic reticulum

Question 23

What two proteins assist the folding of MHC?

Answer 23

calnexin and calreticulin

Question 24

Why are calnexin and calreticulin needed?

Answer 24

Because the protein is relatively unstable before it has bound peptide

Question 25

What retains a pool of MHC in the ER?

Answer 25

Protein Tapasin

Question 26

Why is there a need for a pool of MHC to be retained in the ER?

Answer 26

So that a rapid increase in surface peptide/MHC complexes can occur following peptide bonding

Question 27

Which cells express MHC class II on their surface?

Answer 27

Antigen presenting cells e.g. dendritic cells, monocytes/macrophages, B cells

Question 28

What is the peptide binding groove of the MHC class II complexed with, before it reaches the ER?

Answer 28

Invariant chain

Question 29

Where is the invariant chain degraded?

Answer 29

in the ER

Question 30

What does HLA-DM do?

Answer 30

Catalyse the insertion of the antigenic peptide or epitope into the peptide binding groove of an MHC class II molecule

Question 31

What does MHC class II interact with?

Answer 31

CD4 receptor on T cell

Question 32

What does the cytokine environment following interaction with CD4 cause the T cell to do?

Answer 32

Polarise to become either a memory cell or one of a number of effector cell phenotypes

Question 33

What are the commonest effector cell phenotypes for T cells?

Answer 33

Th1, Th2, Tregulatory and Th17 cells

Question 34

Where do B cells develop?

Answer 34

Firstly within the bone marrow and then secondly in secondary lymphoid organs when they encounter antigen

Question 35

What is a molecule of immunoglobulin composed of?

Answer 35

a pair of identical heavy chains and a pair of identical light chains

Question 36

What type of bond connects the pair of heavy chains?

Answer 36

Disulphide bond

Question 37

What type of bond connects each heavy chain to a light chain?

Answer 37

Disulphide bond

Question 38

What is the gross structure of IgG molecule?

Answer 38

three globular regions linked together by a flexible hinge region

Question 39

What enzyme digests the globular regions?

Answer 39

papain

Question 40

What do accessory/signalling molecules do?

Answer 40

Required to signal the inside of the cell when antigen is bound

Question 41

Why can't surface Ig molecules signal the inside of the cell when antigen is bound?

Answer 41

The cytoplasmic tail is too short

Question 42

What is the best known accessory molecule often used in labs to identify B cells?

Answer 42

CD19

Question 43

How many hypervariable regions does each variable domain have?

Answer 43

3

Question 44

What forms the surface that binds to the antigen on an immunoglobulin molecule?

Answer 44

The hypervariable regions

Question 45

What are the two types of light chain?

Answer 45

Kappa or lamda

Question 46

What are the five types of heavy chain?

Answer 46

mu, gamma, delta, epsilon, alpha

Question 47

What do the constant domains determine?

Answer 47

the function of the antibody molecule

Question 48

What is a TCR compose of?

Answer 48

two non-identical Ig-domain polypeptide chains

Question 49

What are the two types of T cells distinguished by?

Answer 49

Expression of either alpha and beta TCR chains or gamma and delta chains

Question 50

What accessory signalling molecule is used by the TCR?

Answer 50

CD3 complex

Question 51

What is somatic recombination?

Answer 51

Mechanism by which the immune system can combat the diversity of pathogens

Question 52

What are the gene segments encoding for variable regions of the heavy and light chains of Ig and the alpha-beta or gamma-delta chains of the TCR?

Answer 52

``` Variable domain gene (V) Diversity gene (D) Joining gene (J) Constant domain genes (C) ```

Question 53

What enzymes are required for gene rearrangement?

Answer 53

RAG-1 and RAG-2

Question 54

What happens in the absence of RAG-1 and RAG-2?

Answer 54

Neither B nor T cells develop and infants suffer severe life threatening infections due to Severe Combined Immunodeficiency Disease

Question 55

What is the first step of gene rearrangement?

Answer 55

Combine the D and J segments of the heavy chain or TCRβ chain

Question 56

What is the second step of gene rearrangement?

Answer 56

Join the V segment to the DJ.

Question 57

What happens once the mRNA for the V and C segments have been synthesised?

Answer 57

They are spliced together and translated

Question 58

What is different about the gene rearrangement for the light chain and TCRα chain?

Answer 58

There are only V and J segments for the variable region

Question 59

How is additional diversity created in the light chain and TCRα chain?

Answer 59

By the addition of nucleotides at the junctional site by the enzyme terminal deoxynucleotidyl transferase (tdt)