B cells

Question 1

How much of all WBCs do B cells constitute

Answer 1

~5%

Question 2

Primary role of B cells

Answer 2

secrete antibodies as plasma cells

Question 3

What 2 components is BCR composed of

Answer 3

1. Antibody (Y-shaped structure) –> light & heavy chains
2. Signalling transduction moiety –> IgA & IgB

Question 4

BCR vs TCR -
* no. binding sites
* secreted/not secreted

Answer 4

BCR:
- 2 Ag binding sites
- Secreted (Ab)

TCR:
- 1 Ag binding site
- Not secreted

Question 5

Major difference between BCR and secreted Ab

Answer 5

Secreted Abs lack a cytoplasmic tail

Question 6

Antibody structure - 2 regions (+ roles)

Answer 6

Fab region: “for antigen binding”
Fragment crystallizable (Fc) region: interacts with Fc receptors on immune cells & recruits complement

Question 7

Where is the antigen binding site of an antibody located?

Answer 7

between the variable region of heavy & light chains

Question 8

What is the difference between the recombination of VH and VL regions

Answer 8

• VH - comprises 1 variable, 1 diversity, 1 joining segment
• VL - only contains 1 variable & 1 joining (lacks diversity)

Question 9

Can T cells activate B cells?

Answer 9

Yes, T cells provide CD40 ligation (supply CD40 ligand) & cytokines

Question 10

What is clonal selection?

Answer 10

When a B cells binds an Ag that it is specific for, it becomes activated and clonally expands

Question 11

When naive B cells are activated/clonally expanded, what can they differentiate into?

Answer 11

1. Plasma cells - secrete Abs
2. Memory B cells - remember specific antigen for long time (immunological memory)

Question 12

Does an Antigen’s affinity for a specific Ab increase or decrease in germinal centres?

Answer 12

Ags affinity for a specific Ab INCREASES in germinal centres
* Affinity maturation - “natural selection for B cells”

Question 13

What is an immunoglobulin (Ig)

Answer 13

Antibody

Question 14

Most important function of the constant region of an antibody

Answer 14

Dictate the isotype/class of the Ab
* and therefore determines effector functions

Question 15

What is the most abundant Ab isotype

Answer 15

IgG - 80% in serum

Question 16

First Ab isotpye to be expressed during an immune response

Answer 16

IgM

Question 17

Avidity vs Affinity

Answer 17

Avidity - Combined strength of multiple binding sites
Affinity - Strength of one binding site

Question 18

Does IgM or IgG have higher avidity? why?

Answer 18

• IgM has higher avidity due to its pentamer conformation.
• Both IgM and IgG have 2 binding sites on each Ab
• However, IgM exists as a pentamer (therefore, 5x2 = 10 binding sites), whereas IgG exists as a monomer (1x2 = 2 binding sites)

Question 19

REMEMBER: Fab fragments have similar affinity, but avidity varies (depends on Ab isotype)

Answer 19

Remember that fucker

Question 20

What region of the Ab is altered in isotype switching

Answer 20

Constant domain of the heavy chain

Question 21

Is isotype switching reversible?

Answer 21

No, it is irreversible
Involves deletion (DNA recombination)

Question 22

What is affected in isotype switching

Answer 22

Constant region of heavy chain (CH) is AFFECTED
- Variable region of Heavy chain, & light chain remain unaffected
-Therefore, Ab retains its specificity for Ag

Question 23

Immune deficiency disorder where B cells cannot isotype switch

Answer 23

X-Linked hyper IgM syndrome –> Mostly affects males (x-linked)
- T cells do not express CD40 ligand
- Susceptible to upper respiratory tract infection