CMB2004/L02 Antigen Recognition Systems I

Question 1

How is it possible that the number of possible antibodies is more than the number of genes?

Answer 1

Gene rearrangement

Question 2

What 3 gene segments encode the H chain and TCRB (V region)?

Answer 2

V, D and J

Question 3

Which 2 gene segments encode the L chain and TCRa (V region)?

Answer 3

V and J

Question 4

How are Ig genes found in the genome?

Answer 4

As gene segments

Question 5

Describe briefly rearrangement of Ig genes.

Answer 5

In B cells, DNA containing Ig gene segments broken and rearranged randomly to form functional Ig genes

Question 6

What are the 2 loci containing L chain genes?

Answer 6

Lambda and kappa

Question 7

In which order are the chains made in antibody formation?

Answer 7

Heavy then light

Question 8

Describe the order of Ig rearrangements during B cell development. (3)

Answer 8

H chain gene segments rearrange (D-J then V-DJ)
Light chain segments rearrange (k segments V-j first)
If k rearrangement is unsuccessful, lambda gene segments rearrange

Question 9

Which gene segments are involved in light chains?

Answer 9

V, J and C

Question 10

Which gene segments are involved in heavy chains?

Answer 10

V, D, J and C

Question 11

At which chromosome is the H chain locus found?

Answer 11

14

Question 12

At which chromosome is the kappa chain locus found?

Answer 12

2

Question 13

At which chromosome is the lambda chain locus found?

Answer 13

22

Question 14

What are recombination signal sequences?

Answer 14

Sequences flanking each of the V, D and J gene segments that guide Ig gene segment rearrangement

Question 15

What complex of enzymes is involved in gene rearrangement?

Answer 15

V(D)J recombinase

Question 16

Which 2 genes encode lymphoid-specific components of the recombinase?

Answer 16

RAG-1
RAG-2
(Recombination activating genes)

Question 17

What is the result of mutations in RAG genes?

Answer 17

Immunodeficiency

Question 18

How many rearranged H chain genes are expressed in each B cell?

Answer 18

Only one

Question 19

How many rearranged L chains from one chromosome is expressed by each B cell?

Answer 19

Only one

Question 20

What does allelic exclusion ensure in B cells?

Answer 20

That each individual B cell produces just one randomly generated BCR/antibody that is different to that of every other B cell

Question 21

Give 2 mechanisms for generation of antibody diversity.

Answer 21

Multiple gene segments for each chain
Combinatorial diversity
Combinations of heavy and light chains
Junctional diversity
Somatic hypermutation

Question 22

Explain somatic hypermutation (SHM).

Answer 22

Mutation frequency in antibody (H/L) V genes in orders of magnitude higher than that seen in all other areas of the genome
Occurs in germinal centres (GC) as B cells recognise Ag and proliferate/become activated

Question 23

Explain the role of enzymes in somatic hypermutation.

Answer 23

Activation-induced deaminase (AID)
Acts on DNA to deaminate cytosine to uracil
Uracil recognised by error-prone DNA repair pathways leading to mutations

Question 24

Howa re the membrane and secreted forms of antibodies produced by B cells?

Answer 24

Alternative RNA processing

Question 25

How does the secreted form of antibody differ from the BCR?

Answer 25

Has an alternative constant region that lacks a transmembrane region
Same antigen specificity (VDJ not altered)

Question 26

At the heavy chain locus, which segment is closest to the V, D and J gene segments and what does this mean?

Answer 26

C(mew) segment
IgM is the first class expressed by each developing B cell

Question 27

What segment is next to C(mew) on DNA and what effect can this have?

Answer 27

C(delta)
IgD can be coexpressed with IgM by differential processing of the RNA from the two C region genes

Question 28

Give the 3 steps to isotype switching.

Answer 28

Looping out
Switch-region recombination
Further rearrangement (potentially)

Question 29

What is a key difference in class switching between VDJ and B cells?

Answer 29

B cells do not class switch randomly

Question 30

Where do V region genes undergo SHM?

Answer 30

Specialised areas of secondary lymph organs