B Lymphocytes

Question 1

What are antigens?

Answer 1

Proteins/molecules present on pathogens that induce an adaptive immune response

Question 2

What are epitopes?

Answer 2

Regions of antigens where receptors bind

Question 3

What are the two different types of epitopes?

Answer 3

Linear: SEQUENCE recognised by T-cells
Structural: STRUCTURE recognised by antibodies

Question 4

What is the humoral response?

Answer 4

B-Cell and antibody activity

Question 5

What is the cell-mediated response?

Answer 5

T-cells and cytokines with killing

Question 6

What are B-Lymphocytes?

Answer 6

WBCs derived from haematopoietic stem cells that are effector cells of humoral immune system, secreting antibodies and becoming memory cells

Question 7

What are B-Cell receptors?

BCRs

Answer 7

Antibodies - Unique binding sites that bind to epitopes, attached to transmembrane domains that cause a cascade upon binding.

Question 8

How many BCRs are there on a single B-cell?

Answer 8

Thousands

Question 9

What is the structure of a BCR?

Answer 9

Transmembrane complex comprised of monomeric immunoglobulin, and couple of disulphide linked IgAlpha and IgBeta heterodimers each side.

Question 10

Does the monomeric immunoglobulin in the BCR have a signalling domain?

Answer 10

No

Question 11

How does the monomeric immunoglobulin in the BCR initiate a signal upon reaction w/epitope?

Answer 11

Structural changes occur in mIg that cause conformation changes in IgAlpha/Beta. Their cytoplasmic tails can then start intracellular signalling

Question 12

How many antibodies does a human need to produce?

Answer 12

10^10

Question 13

How many genes code for the production of all antibodies

Answer 13

~25,000

By recombination

Question 14

What are the 3 types of variable gene segment involved in Antibody production?

Answer 14

Variable (V)
Diversity (D)
Joining (J)
Constant (C)

Question 15

Describe the structure of Germline DNA that encodes the Ig Light Chain.

Answer 15

In germline DNA 30-40 Variable regions encoded, followed by 5 Joining regions and a constant region

Question 16

How is the Ig Light chain expressed?

3 Steps

Answer 16

1. Germline DNA rearranged as B-cell develops (in marrow)
   2 V regions and a J region randomly selected along with constant region.
2. Gene transcribed to RNA with alternative splicing patterns. Results in mature mRNA w/ one V, J, and C region
3. Translated into Kappa chain polypeptide.

Question 17

What is the enzyme that produced recombinant DNA?

Answer 17

V(D)J Recombinase

Question 18

What gene codes for V(D)J Recombinase?

Answer 18

Rag genes

Question 19

What does Rag gene deficiency lead to?

Answer 19

SCID

Severe combined immunodeficiency

Question 20

What is the structure of Heavy chain germline DNA?

Answer 20

65 V
27 D
6 J
9 C

Question 21

How is the Ig Heavy chain expressed?

Answer 21

Rearrangement of germline DNA
Transcription (1 V, 1 D, 2 J, 2 C)
Alternative splicing (V,D,J,C)
Translation

Question 22

What are the differences in expression between the light and heavy chain?

Answer 22

D region only found in heavy chain.

Question 23

Name the stages of B-cell development

Answer 23

Haematopoietic Stem Cell
Early pro-B cell
Late pro-B cell
Large pre-B cell
Small pre-B cell
Immature B cell
Mature B cell

Question 24

What happens to Ig that recognises self?

Answer 24

Selected out during maturation to mature B cell

Question 25

When is surface Ig first present on a B-cell?

Answer 25

Immature B-cell (IgM present)

Question 26

In what stage of development of the B-cell are Light Ig chains first rearranged?

Answer 26

Small pre-B cell

Rearranged by Immature B-cell

Question 27

In what stage of development of the B-cell are Heavy Ig chains first rearranged?

Answer 27

DJ rearranging in Early pro-B cell

V-DJ rearranging in Late pro-B cell

Question 28

What are the 3 possible pathways when a B-cell binds to an antigen?

Answer 28

Affinity maturation: Antibody response improves
Memory Cell: stored for later exposure
Plasma cell: Produced to secreet antibodies

Question 29

How can a plasma cell be identified?

Answer 29

Many ER and ribosomes present to produce antibodies

Question 30

What is required for Naïve B-cells to react with antigens?

Answer 30

Signal from T helper cell or microbial constituents

Question 31

What are the 2 types of antigen a B-cell can recognise?

Answer 31

Thymus dependent: All Ig classes w/memory

Thymus independent: IgM without memory. Requires microbial constituent signal

Question 32

What do T helper cells do when the recognise antigens on B-cell surface?

Answer 32

Release cytokines to drive B-cells to undergo clonal expansion

Question 33

What effect do might cytokines have on B-cells?

Answer 33

Different cytokines lead to different types of antibody (Ig) production by changing the type of Constant region (variable region remains same)

Question 34

What is Ig Class Switch?

Answer 34

When the constant region of an antibody is changed by the effect of cytokines secreeted by T helper cells

Question 35

When does somatic hypermutation and affinity maturation occur?

Answer 35

Inbetween exposures - Response improves

Question 36

What is Somatic hypermutation and affinity maturation?

Answer 36

AID (activation-induced deamination) causes point mutations in the VDJ region.

Question 37

What problems can B-cells cause?

Answer 37

Autoimmunity, allergy, cancer