5. Adaptive Immune Response: B Cells

Question 1

Which immune cells produce antibodies?

Answer 1

B cells and only B cells (plasma cells too but they’re derived from B cells)

Question 2

Where are B cells produced and matured?

Answer 2

The bone marrow

Question 3

What is a naive B cell?

Answer 3

B cell which has not yet met an antigen

Question 4

What is the difference in receptor of B and T cells?

Answer 4

B cells use antibody as receptor whereas T cells use T cell receptor

Question 5

What are the five classes of antibody?

Answer 5

IgM, IgA, IgE, IgD, IgG

Question 6

What are the two initial classes of antibody produced are present on the B cell surface?

Answer 6

IgM and IgD (both specific for the same antigen) - 50,000 copies of each

Question 7

What else is expressed on the B cell surface other than transmembrane version of antibodies?

Answer 7

Ig-alpha, Ig-beta, CD19 (B cell marker), CD20, CD40 (not present only on B cells)

Question 8

What is another name for the transmembrane version of the antibody present on the surface of the B cell?

Answer 8

BCR (B cell receptor)

Question 9

What is the structure of the BCR?

Answer 9

Contains variable (recognises native/natural antigen) and constant regions

Question 10

How does the BCR recognise antigen?

Answer 10

Recognises the natural form of the antigen (unaltered), just binds it as it flows past

Question 11

How many different BCR variable regions are possible with gene rearrangement?

Answer 11

10^15

Question 12

What is clonal selection?

Answer 12

The antigen selects the most appropriate B-cells and then those proliferate in an infection

Question 13

What do most B cells differentiate into? What does this cell do?

Answer 13

Plasma cells, secrete correct antibody

Question 14

How are plasma cells different structurally to B cells?

Answer 14

Large amounts of cytoplasm, rough endoplasmic reticulum and mitochondria so they can pump out lots of proteins (antibodies)

Question 15

What do some of the B cells differentiate into?

Answer 15

Memory cells (smaller amount)

Question 16

What occurs genetically when B cell differentiates into the plasma cell?

Answer 16

It splices out the transmembrane region of the antibody so the antibody can be secreted/soluble

Question 17

What is the benefit of using the antibodies from plasma cells derived from memory cells?

Answer 17

More antibodies made (as more memory cells) and due to somatic hypermutation the cells fit stronger to the antigen

Question 18

Immunological memory can vary. Give an examples of diseases with long and short immunological memories

Answer 18

Long: Yellow fever
Short: Tetanus

Question 19

What helps B cells to undergo class switching? What is class switching?

Answer 19

T helper cells

Class switching is the ability of B cells to produce IgG, IgA and IgE (instead of only IgM and IgD)

Question 20

What is the best helper T cells for enabling B class switching?

Answer 20

Th2

Question 21

How do T cells activate class switching?

Answer 21

Cell surface interactions/soluble communicators

CD80 and CD86 on B cell interact with CD28 of T cell

CD19 and CD20 (B cell markers)

CD40 of B cell interacts with CD40 ligand of T Cell

Interactions send signals into both B and T cells causing B cell to divide and proliferate

Question 22

What defines the class of antibody produced by the B cell?

Answer 22

The type of cytokine produced by T helper cells

Question 23

Give an example of a cytokine released by T helper cells which causes B cells to switch to a specific Ig?

Answer 23

Interleukin 4 and 13 cause B cell to class switch to IgE production

Question 24

What is somatic hypermutation?

Answer 24

Accompanies antigen induced proliferation, involves rearranging of the variable region genes - allows you to better bind the antigen

Question 25

How are the somatically hyper mutated cells selected?

Answer 25

If mutated B cell has little antigen stimulation then survival rates will be low, but if cells bind antigen stronger then survival rate increases

Question 26

What is a professional antigen presenting cell?

Answer 26

Cell which shows antigen to a T cell using MHCII - B cells can do this

Question 27

What is the difference between antigen presenting cells and professional antigen presenting cells?

Answer 27

APCs include all nucleated cells and are cells which contain MHCI for presenting antigen to T cells, professional antigen presenting cells (e.g. B cells) also contain MHCII to present antigen to T cells (this is a much more efficient method

Question 28

How do B cells present antigen?

Answer 28

1. Recognise antigen and bind it with transmembrane antibodies
2. Antigen and transmembrane antibody entocytosed into cell
3. This is then chopped up with proteases (from endosomes) into peptides
4. This leads to a co-stimulatory signal along with the presentation of antigen in the MHCII

Question 29

How is the signal of the antigen binding transduced into the B cell?

Answer 29

Whilst the BCR recognises/binds the antigen, it does not transduce the signal.

The signal transduction is carried out by Ig-alpha and Ig-beta associated to the BCR (not immunoglobulin molecules but associated with them), these have long cytoplasmic tails with ITAMs. ITAMs and Src family tyrosine kinases initiate signalling into the nucleus to tell the B cell to proliferate and divide

Question 30

What is a T independent antigen?

Answer 30

An antigen that can stimulate B cells without need for helper T cell

Question 31

Give an example of T-independent antigen

Answer 31

polysaccharide antigen - if antibody has physically repeated structure then can cross-link with others so can send signal into B cell which overcomes reliance on T cell.

But T cells required for class switching so large IgM response but no class switching