Adaptive immunity

Question 1

Describe the overview of the adaptive response roughly

Answer 1

1. infection
2. transport of antigen to lymphoid organs
3. recognition by native T and B cells
4. clonal expansion and differentiation to effector cells
5. removal of infectious agent

Question 2

Why is the adaptive response advantageous?

Answer 2

• generation time for bacteria can only take 20 mins and our generation time is 20 years
• rapid evolution of pathogens means that new receptors will be required continuously
• to compete, new receptors are continuously generated as lymphocytes develop in the bone marrow and thymus

Question 3

What is an antigen?

Answer 3

any molecule that is specifically recognised by either T cell receptors (TCR) or antibodies

Question 4

What is an epitope?

Answer 4

the site on an antigen that directly binds to an antibody or TCR

Question 5

what is a T cell antigen?

Answer 5

peptide derived from an antigenic protein

Question 6

What is a B cell antigen?

Answer 6

Proteins, carbohydrates

Question 7

What is an antibody made up of and where does the antigen bind?

Answer 7

• variable region (antigen binding site)

- constant region

Question 8

How is the structure of the variable region decided?

Answer 8

• in the germ-line DNA there are small segments of DNA in groups V,J and D
• bone marrow cell will randomly select one V, D and J segment which will form the gene that determines the variable region
• this is how diversity is created, by random gene recombination

Question 9

What happens to newly produced B and T cells?

Answer 9

they are constantly recirculated through lymph nodes, lymphatic vessels and blood which improves the likelihood of encounter of a rare antigen specific cells with the antigen

Question 10

What type of antibodies are produced at the start of an immune response and why?

Answer 10

• IgM antibodies because they are pentameric so have 10 binding sites
• low affinity

Question 11

What types of antibodies due you produce later on in the immune response?

Answer 11

• IgA (secreted to mucous membranes)
• IgD (membrane receptor)
• IgE (Localised on Mast cells)
• IgG (highest concentration in serum)
• smaller molecules (find it easier to move into tissue)
• more specific
• all have different roles

Question 12

In terms of antibodies, what happens when a B cell differentiates into a plasma cell?

Answer 12

-lots of antibodies are released over a long period of time

Question 13

What are the functions of antibodies?

Answer 13

• neutralisation (prevent bacterial adherence)
• opsonisation (promotes phagocytosis)
• complement activation (antibody activates complement which enhances opsonisation and lyses some bacteria)

Question 14

Where do T cells differentiate?

Answer 14

in the thymus gland

Question 15

How are naive T cells produced?

Answer 15

• T cell precursor leaves bone marrow and does into the thymus gland
• in the thymus gland the cells proliferate and undergo TCR gene rearrangement
• selection occurs (removal of self-reactive cells)

Question 16

What cell type presents antigens to T cells?

Answer 16

Dendritic Cell

Question 17

How do dendritic cells transport the antigens ti lymph nodes?

Answer 17

1. immature dendritic class reside in peripheral tissues
2. dendritic cells migrate via lymphatic vessels to regional lymph nodes
3. mature dendritic cells activate naive T cells in the lymphoid organs such as lymph nodes

Question 18

When is the only time that TCR will recognise antigens?

Answer 18

if they are presented on MHC proteins

Question 19

How does antigen presentation occur?

Answer 19

1. the epitopes recognised by T cell receptors are often buried
2. the antigen must first be broken down into peptide fragments
3. the epitope peptide binds to a self MHC molecule
4. the T cell receptor binds to a complex of MHC molecule and epitope peptide

Question 20

What will CD4+ T cells recognise?

Answer 20

exogenous peptides bound to MHCII proteins

Question 21

What is the consequence of CD4+ T cell recognising an antigen?

Answer 21

production of cytokines

Question 22

What is the role of Th1?

Answer 22

provides help signals for macrophages

Question 23

What is the role of Th2?

Answer 23

help signals to B cells, in particular for production of IgE

Question 24

What is the role of Th17?

Answer 24

inflammation

Question 25

What is the role of Tfh?

Answer 25

support B cell differentiation?

Question 26

What will CD8+ cells recognise?

Answer 26

antigenic peptides bound to MHC I proteins

Question 27

What is a CD8+ cell also known as?

Answer 27

a cytotoxic T cell (kills infected cells)

Question 28

How does a cytotoxic T cell cause apoptosis?

Answer 28

1. Cytotoxic T-cell recognises and binds to virally infected cell
2. T-cell programs the target for death by inducing DNA fragmentation
3. T-cell binds to its next target
4. The target cell dies by apoptosis

Question 29

What are the four tasks that the immune system needs to carry out?

Answer 29

• distinguish self from non-self
• effective removal of pathogens
• self regulation
• memory of pathogens encountered in the past