L19

Question 1

How is the ab response to antigen different after immunisation?

Answer 1

Unimmunised donor primary response:

• frequency of antigen specific B cells 1x10^4
• isotype of ab produced IgM>IgM
• affinity of ab low
• somatic hyerpmutation low

Immunised donor secondary response:

• frequency of ag specific B cells 1x10^3
• isotype of ab produced IgG, IgA
• affinity of ab high
• somatic hypermutation high

Question 2

What is the response like to T cell dependent vaccines?

Answer 2

Regular bump on graph after first, then taller and longer lasting bump on secondary vaccine.

Question 3

What is the response like to T cell independent vaccines?

Answer 3

Regular bump to both vaccines. E.g. in capsular polysacch vaccines.

Question 4

Why are T cells essential in relation to B cells?

Answer 4

they are NEEDED for:

• switching to IgG, IgA and IgE
• high affinity ab production
• essential for the longest lived ab responses
• for B cell memory

This is because T and B cells are needed for productive GCs.

Question 5

What happens in T independent ab responses?

Answer 5

Shorter lived, less IgG, virtually no memory, no affinity maturation because there are no GCs.

Question 6

Ab responses can develop through 2 pathways:

Answer 6

Extrafollicular giving modest affinity ab, memory? TD and TI

GC best boy, yes to all. TD response.

Question 7

How do ab responses to protein antigens being? (DCs and B cells)

Answer 7

Ag specific B celsl binds ag, specific ag efficiently internalised by receptor mediated endocytosis.

DC aren’t specific in antigen uptake. They prime T cells.
B cells are highly specific in what antigen they take up. T cells license B cells.

Question 8

Why and where is priming of T follicular helper cells by DC important?

Answer 8

Essential for T dependent ab responses.

Question 9

Why are germinal centres important?

Answer 9

For long lived ab production (nearly all B cell memory) and CLASS SWITCHED and HIGH AFFINITY Ab

Question 10

What does the B cells need to undergo in terms of recombination?

Answer 10

Further Ig V recombo but needs to be regulated to not recognise self

Question 11

What is affinity maturation?

Answer 11

Process by which B cell produce Abs of increased affinity for Ag. Parts of affinity maturation include somatic hypermutation and clonal selection of the best B cell. B cells can undergo many rounds of GC to get the best one.

Question 12

What is somatic hypermutation

Answer 12

The process used to achieve affinity maturation, involved mutations in the variable regions of the Ig

Question 13

What happens in terms of competition of B cells and fDCs?

Answer 13

The best B cell with the strongest affinity for Ag that the fDC has will be selected, Other low affinity ones will be outcompeted or deleted

Question 14

What happens in the dark zone of the GC?

Answer 14

Lots of proliferation of the centroblast and also somatic hypermutation

Question 15

What B cells are in the light zone?

Answer 15

They leave dark zone as centrocytes having somatic hypermutated.

Question 16

What do fDCs do? Where are they found?

Answer 16

They have intact Ag in its native conformation bound to their surface and CC has to compete to bind this Ag. In light zone.

Question 17

What do follicular T helper cells do?

Answer 17

They give survival signals to CC after they come out of light and dark zone. they are GC involved T cells.

Question 18

What is AID?

Answer 18

Activation induce cytidine deaminase when expressed in B cells allows class switch recombination and IgV hypermutation.

Question 19

Why is CD4O/CD40L important?

Answer 19

CD40 on B cells and CD40L on T cells. It’s important to establish a germinal centre reaction. Important survival signal for B cells ‘licensing’

Question 20

When can class switching occur?

Answer 20

After encountering Ag and only after activation by T cells

Question 21

Where does class switching occur?

Answer 21

Both in primary foci in periphery and in GC

Question 22

What 2; gene and CD are important for class switching?

Answer 22

AID and CD40

Question 23

Why is IL-21 important?

Answer 23

For generation of T follicular helper cells

Question 24

What is cognate interaction? What important cytokines are there?

Answer 24

CD4 T follicular helper cell are vital for efficient generation of Abs. They are primed by DCs. They then positively select B cells they recognise peptide presented on MHC2 by them. ICOSL (B cells) and ICOS (T cells) is also important. IL-6, IL-21, IL-4 and IFNγ.