Generation of Antigen receptor diversity

Question 1

The variable region of the light chain is encoded which gene segments

Answer 1

V , J segments

*constant regoin is encoded by C segments

Question 2

The variable region of the heavy chain of the antibody molecule is encoded by ——– discrete gene segments (——–)

Answer 2

The variable region of the heavy chain of the antibody molecule is encoded by three discrete gene segments (V, D, J)

Question 3

———— is responsible for the receptor repertoire of naïve B cells

Answer 3

Somatic Recombination

Question 4

what is somatic recombination

Answer 4

Segments of genomic DNA within the immunoglobulin genes are rearranged in cells of the B cell lineage but not in other cells
( therfore, these rearrangements cannot be inherited)

Question 5

which is produced first, the heavy chain or light chain?

Answer 5

Heavy chain
(if the rearrangement is incorrect, then the cell dies via apoptosis)

Question 6

Genes required for the initiation of V(D)J recombination

Answer 6

RAG1 and RAG2
(Recombination activating gene)

Question 7

where are RAG1 and RAG2 expressed?

Answer 7

In developing lymphocytes

Question 8

what is junctional diversity ?

Answer 8

Junctional diversity –> when the enzyme TdT randomly inserts bases at the junctions of V,D and J segments , when heavy chain gene segments are undergoing recombiantion

Question 9

When heavy chain gene segements are undergoing recombination, the enzyme —— randomly inserts bases at the junctions of V,D and J segments –> this creates ————

Answer 9

When heavy chain gene segements are undergoing recombination, the enzyme TdT randomly inserts bases at the junctions of V,D and J segments –> this creates Junctional diversity

Question 10

TdT is [Active/not active] during the rearrangement of the light chain

Answer 10

Not active

* its only active during heavy chain rearrangement

Question 11

Mutations in RAG1 and RAG2 indicate?

Answer 11

SCID- Sever combined immunodeficiency

Question 12

function of TdT enzyme

*terminal deoxy nucleotidyl transferase

Answer 12

establishes Junctional diversity in heavy chain gene segements undergoing recombination

Question 13

Describe the steps of B-cell receptor expression

Answer 13

1) 1st, heavy chain rearrangemnet (if successful) –> light chain genes rearranged
2) Second, only one heavy chain and light chain must be synthesised in each B cell, this is established through Alleic exclusion
3) 3rd, the receptor undergoes negative and positive selection (tested for binding to self-Ag)

Question 14

During B cell development only one heavy chain and light chain must be synthesised, what process ensures that?

Answer 14

Allelic exclusion

Question 15

TCRs are ——–

Answer 15

Heterodimers

Question 16

most TCRs posses an —- and —– chain

Answer 16

most TCRs posses an a (alpha) and β (beta) chain

Question 17

markers for T cells that have recently emigrated from the thymus

Answer 17

TRECs (T cell receptor excision circles)

Question 18

Functional TCR genes are produced by rearrangements of?

Answer 18

• V & J segments in the α-chain & γ-chain chains (like Ig L chains)
• V, D & Jsegments in the β-chain & δ-chain chains (like Ig H chains)

Question 19

Activity of TdT enzyme in T cells vs B cells

Answer 19

• B-cells–> only active in Heavy chain rearrangement (inactive in light chain rearrangement) so ‘N’ nucelotides are seen at the heavy chain only
• T-cells –> TdT is active during the rearrangement of both α- and β- chains, so ‘N’ nucelotides are seen at similar frequencies in all the TCR chains