B cell development Flashcards Preview

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Flashcards in B cell development Deck (31):
1

V region exons

300 bp sections at the 5' end of each Ig locus that are separated by non-coding DNA

2

Joining segments

Downstream of the V region, they have additional coding sequences that are about 30-50 bp long

3

Diversity segments

Additional coding sequences present downstream of V and J regions, but ONLY IN HEAVY CHAINS

4

Location of C region genes

Varying distances in the 3' direction from the V genes

5

How many exons are in the Ch region?

Three to four, plus another one for either the cytoplasmic/transmembrane domain

6

Ig genes are only expressed where?

In B cells

7

Heavy chain: DJ

The first Ig gene rearrangement occurs here; joins one D and one J segment and deletes intervening DNA

8

Heavy chain: VDJ

After DJ rearrangement, one of the many V genes is attached to the DJ complex. All segments 5' to the DJ complex are deleted

9

What is significant about the VDJ rearrangement step?

Only happens in cells committed to be B cells, and it is a highly regulated step because V transcription begins right after deletion of the unused D segment

10

Light chain: VJ

VJ complex is formed in the light chain after complete VDJ rearrangement of the heavy chain.

11

When does transcription begin for the light chain?

When the C region is joined to the VJ complex

12

Formation of immature B cell

The kappa chain completed after light chain rearrangement joins with mu segment from heavy chain rearrangment, making IgM, which is then expressed on the cell surface

13

Major rule of antibody production

One B cell makes only one kind of antibody because of allelic exclusion

14

How does the B cell bypass the major rule of antibody production?

Alternative splicing after mRNA production

15

ProB cells

Precursor of PreB cells; have heavy chain DJ rearrangements and no light chain rearrangements

16

PreB cell

Earliest cell that produces mu heavy chain with variable and constant domains; only found in hematopoietic tissues.

17

What comprises a preB receptor?

Mu chains, surrogate light chains, Ig-alpha and Ig-beta

18

Immature B cell

Kappa or lambda light chains are now produced, associating with the previously made mu chains and expressing IgM on the surface
Cannot respond to antigens

19

Mature B cell

Complete Ig; migrate out into the periphery and can respond to antigens

20

How do B cell IgM and IgD respond to the same antigens?

They both have the same V region and therefore the same antigen specificity

21

Recognition sequences

DNA sequence that mediates the recombination of V, D, and J gene segments; located on either side of the D segments and after V or before J

22

RAG1 and RAG2

Recognize RSSes, loop them together, and excise them out, leaving just the exons that are joined by DNA ligase

23

Are all rearrangements functional?

No

24

BRECs

The excision loops that are left behind after RAG1/RAG2 activity. Clinically important for testing B cell proliferation after bone marrow transplants

25

TdT

Mediates random addition of new nucleotides added to the junctions during VDJ rearrangement

26

Junctional diversity by N-region addition

N sequences are added into the junctions during VDJ arrangement

27

What happens to B cells that have nonfunctioning VDJ?

They are deleted

28

What happens when B cells have anti-self reactivity?

Can become anergic, can be deleted, or can try and be salvaged by receptor editing

29

Receptor editing

When anti-self is detected, B cell maturation arrests and new combination is used. If that new specificity also is self-reactive, the cell is killed. If not, it can continue as a functional B cell

30

Most T cells have what type of receptors?

Alpha/beta receptors (5% have delta-gamma)

31

Functional structure of a T cell receptor

Has two alpha and two beta domains, variable domains on the periphery