B Cell Diversity-L5

Question 1

Types of light chains

Answer 1

lambda and kappa (only seen in V and J regions)

Question 2

Gene segment types

Answer 2

• J region
• D region
• V region

Question 3

How are V, D, and J brought together?

Answer 3

Recombinase genes RAG1 and RAG2

Question 4

Signal sequences

Answer 4

Determines which immunoglobulin gene segments can be joined to each other

Question 5

Generation of functional diversity

Answer 5

• RAG cleaves heptamer RSSs from the D and J gene segments to yield DNA hairpins
• RAG opens hairpins and generates palindromic P-nucleotides
• N-nucleotide additions by TdT
• Strands paired
• Unpaired nucleotides removed by exonuclease
• Gaps filled and ligated

Question 6

TdT

Answer 6

• Terminal deoxynucleotidyl transferase
• Only found in developing B cells in the pro B stages after birth
• Add random nucleotides to V-D and D-J joins.

Question 7

Rearrangement in early pro-B cells

Answer 7

• H chain rearrangement

- D-J regions on both chromosomes

Question 8

Rearrangement in late pro-B cells

Answer 8

• H chain rearrangement

- V-DJ rearrangement on both chromosomes

Question 9

Rearrangement in pre-B cells

Answer 9

• L chain rearrangement
• kappa chain on both chromosomes, then gamma
• No N regions (added by TdT) found in light chains

Question 10

IgD formation

Answer 10

• Selective splicing of an RNA transcribed from both IgM and IgD constant regions
• Splicing determines whether membrane bound or secreted Ig

Question 11

Class switching and somatic mutations

Answer 11

• Variable region joined to a new constant region
• Doesn’t occur for IgD
• Variable region undergoes a high rate of mutation–yields amino acids that improve antigen binding
• Somatic mutations limited to variable region of Ig
• Enzyme: Activation induced cytidine deaminase (AID)

Question 12

T cell receptor

Answer 12

-NO somatic hypermutation, most other mechanisms the same as the B-cell.