Lecture 24

Question 1

What antigens cause T cell independent antibody production?

Answer 1

T independent antigens are highly repetitive structures e.g. flagellin, polysaccharides. This causes crosslinking between BCRs and sends a strong signal to the B cell

Question 2

What antigens cause T cell dependent antibody production?

Answer 2

All non-repetitive antigens e.g. peptides, proteins

Question 3

True or false: B cells express MHC I

Answer 3

False. B cells express MHC II so they can act as antigen-presenting cells to CD4 T cells

Question 4

What are the steps for B cell activation when T cells produce cytokines?

Answer 4

1. B cell receptor binds antigen/pathogen and takes it up to process it.
2. Processed antigen is presented on the MHCII.
3. CD4T cell activated by B cell acting as an APC
4. T cells produce cytokines
5. B cell responds to the cytokines by developing into plasma cells and begin producing antibody

Question 5

What are the steps for B cell activation by T cells via CD40L

Answer 5

1. B cell receptor binds antigen/pathogen and antigen is taken up and processed
2. B cell presents antigen and upregulates CD40 expression
3. T cell activated by B cell acting as an APC
4. T cell upregulates CD40L which binds to CD40 on the B cell
5. B cell develops into a plasma cell and produces antibody

Question 6

Where does B cell expansion happen?

Answer 6

Spleen and lymph nodes

Question 7

What immune cells are the main inhabitor of the paracortical area of the lymph node?

Answer 7

T cells

Question 8

What immune cells are the main inhabitor of the lymphoid follicle in the lymph node?

Answer 8

Mostly B cells

Question 9

Where are germinal centers found in the body?

Answer 9

Germinal centers are found in B cell regions of lymph nodes or spleens

Question 10

What occurs during B cell activation in the lymph node? Where do the B cells go when theyre activated?

Answer 10

During activation, B cells encounter antigen specific T cells in the T cell areas outside of the B cell follicles. Acitvated B cells move into the follice and form a germinal center.

Question 11

What types of cells make up germinal centers?

Answer 11

Germinal centers are mostly composed of proliferating B cells and around 10% antigen specific T cells as well as follicular dendritic cells.

Question 12

Why do your lymph nodes grow when youre sick?

Answer 12

Because the germinal centers in the lymph nodes are growing because the B cells are undergoing clonal expansion.

Question 13

What is clonal expansion?

Answer 13

When B cells encounter their antigen through the BCR and begin to divide into identical daughter cells.

Question 14

What is somatic hypermutation? When does it occur?

Answer 14

Somatic hypermutation is where point mutations are introduced during clonal expansion. Occurs after the antigen driven B cell activation as a part of the gernimal center response.

Question 15

What % chance at each division that a B cell will acquire a mutation in the antibody it encodes?

Answer 15

50%

Question 16

Where are mutations introduced in somatic hypermutations?

Answer 16

Point mutations are introduced into rearranged V region genes at a high rate. Occurs at ‘hotspots’ in the genes.

Question 17

What protein is required for somatic hypermutation?

Answer 17

Activation induced cytidine deaminase (AID)

Question 18

What is affinity maturation?

Answer 18

Good mutations are introduced during somatic hypermutation. Higher affinity interaction with antigen. This causes the b cell to survive, proliferate, and mature into antibody producing cells and outcompetes B cells with lower affinity antibody/BCR.

Question 19

What happens when a bad mutation is introduced through somatic hypermutation?

Answer 19

Bad mutations cause lower affinity interactions with antigen. Can’t compete with better B cells so they die by apoptosis.

Question 20

Somatic hypermutation and antibody class switching both occur in…

Answer 20

The germinal centre

Question 21

What are 6 functions of antibodies

Answer 21

1. neutralisation
2. opsonisation
3. complement activation
4. agglutination
5. antibody-dependent cell mediateed cytotoxicity
6. degranulation

Question 22

What is antibody class switching? What happens?

Answer 22

When antibodies change classes e.g. from IgG to IgE.

Variable region stays the same (antibody retains the same specificity) but different isoforms of constant region of heavy chain.

Question 23

What two types of antibodies are expressed on naive B cells?

Answer 23

IgM and IgD

Question 24

What is the first antibody secreted by activated B cells?

Answer 24

IgM

Question 25

Later on during the immune response, what antibodies are being secreted?

Answer 25

IgA and IgG. IgE produced in small amounts, driven by IL-4.

Question 26

What enzyme is required for antibody class switching?

Answer 26

acitvation induced cytidine deaminase (AID) (same as somatic hypermutation)

Question 27

When does antibody class switching occur?

Answer 27

Occurs after antigen driven B cell activation as a part of the germinal center response

Question 28

What causes class switching?

Answer 28

Caused by gene rearrangements triggered by cytokines

Question 29

Draw the two forms of IgM

Answer 29

Question 30

Answer 30

Question 31

IgD is found where?

What is its function?

Answer 31

IgD is abundant on the B cell surface

Function unknown

Question 32

Answer 32

Question 33

Answer 33