Antibody Genetics I

Question 1

Where are B cells derived from in adult mammals?

Answer 1

Bone marrow

Question 2

Where do B cells originally develop?

Answer 2

In foetal liver at 8-9 weeks gestation

Question 3

What cells line the bone endosteum?

Answer 3

Progenitor cells

Question 4

What do stromal reticular cells do?

Answer 4

Produce IL-7 to sustain B cell differentiation
Support B cell development

Question 5

How many progeny can be produced by each progenitor?

Answer 5

64

Question 6

What happen to the progeny?

Answer 6

They migrate to the centre of spongy bone
Adventitial reticular cells aid egress to the venous sinusoid then out into circulation

Question 7

What percentage of B cells do not make it out of the bone?

Answer 7

75%

Question 8

What happens to the B cells that do not leave the bone?

Answer 8

Apoptosis or phagocytosis by macrophages

Question 9

What allows survival of B cells after selection?

Answer 9

Successful rearrangement of Ig gene (BCR)

Question 10

How are autoreactive B cells removed?

Answer 10

By negative selection

Question 11

What was Ehrlich’s side-chain theory?

Answer 11

That each B cell had multiple specificities (side chains)

Question 12

What are the mechanisms of diversity?

Answer 12

Somatic recombination and somatic mutation

Question 13

What does somatic recombination allow?

Answer 13

Joining of one segment of the gene to another

Question 14

What does somatic mutation allow?

Answer 14

Sloppy joining of the gene segments

Question 15

What happens when there is somatic recombination and mutation together?

Answer 15

Generate heavy and light chains of Ig
Pairing of unique heavy and light chains add diversity

Question 16

What is the order of diversity generation?

Answer 16

First heavy chain rearranged
If successful then kappa light chain rearranges
If no kappa chain then lambda chain rearranges

Question 17

What chromosome are the VDJ heavy chain segments on?

Answer 17

Chromosome 14

Question 18

How is the functional heavy chain VDJ region formed?

Answer 18

Recombination of any one V with any one D and any one J

Question 19

What does each V region code for?

Answer 19

A single peptide which directs the polypeptide to the RER, golgi and the out the cell

Question 20

What happens first in heavy chain rearrangement?

Answer 20

Joining of Jh to Dh

Question 21

What does the VDJ region constitute?

Answer 21

Highly diverse 3rd hypervariable region (CDR3)

Question 22

What happens if the DJ rearrangement is productive?

Answer 22

DhJh now signals rearrangement to a Vh gene segment

Question 23

What does the VDJ recombine to?

Answer 23

C mu

Question 24

What happens in light chain rearrangement?

Answer 24

Kappa light chain locus on chromosome 2
No D regions so VJ joining, forming primary RNA transcript
Additional J regions spliced out to form mRNA
Remaining J region spliced out to form kappa chain

Question 25

What happens if both kappa gene rearrangements are unsuccessful?

Answer 25

Moves to lambda chain locus on chrom 22

Question 26

What happens in lambda rearrangement?

Answer 26

VJ joining Intron between VJ and C lambda is cleaved

Question 27

How is extra diversity created?

Answer 27

Imprecise joining

Question 28

What enzymes are involved in recombination?

Answer 28

RAG-1 and 2

Question 29

What creates N-region junctional diversity?

Answer 29

TdT

Question 30

What do recombination signal sequences do?

Answer 30

Flank all V, D and J segments

Question 31

What are the recombination signal sequences?

Answer 31

CACAGTG heptamer downstream 3' of Vh, VL and Dh Followed by a spacer of 12 or 23 non-conserved bases Then a ACAAAAACC nonamer Upstream 5' of Jh, Dh and JL is a corresponding nonamer, spacer and heptamer sequence

Question 32

What is the 12/23 rule?

Answer 32

Only 12 will combine with 23 and vice versa No 12 will combine with another 12, no 23 will combine with another 23 - ensures correct recombinations occur

Question 33

What is the mechanism of recombination?

Answer 33

Portions of the gene made available to recombination machinery 2 selected coding segments and their RSSs are brought together forming chromosomal loop Double strand breaks generated at RSS sequence junctions by RAG1/RAG2 complex Creates a hairpin end on coding region Opening of hairpin by artemis Addition or removal of bases by TdT to add extra diversity Coding ends are rejoined by number of factors including DNA ligase

Question 34

What is combinational diversity?

Answer 34

Random pairing of VH and VL chains Not all pairings will form functional receptors

Question 35

Describe junctional diversity

Answer 35

Asymmetric breakage of hairpin loop so one DNA loop is longer than the other Shorter strand extended with complimentary nucleotides called P nucleotides TdT adds N nucleotides This adds non-germline sequences These junctional sequences form CDR3

Question 36

What do pro B cells express?

Answer 36

CD19 and CD10

Question 37

What do pre B cells express?

Answer 37

Mu chain TdT RAG CD19 CD10

Question 38

What do immature B cells express?

Answer 38

Mu chain Light chain RAG CD19 IgM

Question 39

What do mature B cells express?

Answer 39

Mu chain Delta chain Light chain CD19 IgM IgD

Question 40

What is an idiotype?

Answer 40

The region that is specific for an antibody

Question 41

How does an immature B cell respond to an antigen?

Answer 41

Negative selection Receptor editing

Question 42

How do mature B cells respond to antigens?

Answer 42

Activation, proliferation, differentiation

Question 43

What happens if idiotypes go wrong?

Answer 43

SCID

Question 44

What does SCID affect?

Answer 44

Mainly T cells but some forms affect both T and B

Question 45

How does autoimmunity occur?

Answer 45

During B cell maturation in BM, allows non-functional BCR to be deleted or replaced

Question 46

How can IgM be autoreactive?

Answer 46

If IgM switches to IgG = pathogenic, e.g. rheumatoid arthritis (RA)

Question 47

What is the function of RAG1/2?

Answer 47

Production of T and B cells

Question 48

What happens if there are mutations in RAG1/2?

Answer 48

No production of T and B cells