1. B Cells

Question 1

Immunoglobulin (Ig): Key Features

Answer 1

2 heavy chains

2 light chains

disulphide bonds

Question 2

heavy chain

Answer 2

3 constant domains = CH1, CH2, CH3

1 variable domain = VH

Question 3

light chain

Answer 3

1 constant domain = CL1

1 variable domain = VL

Question 4

IgM

Answer 4

secreted as a pentamer

held together by a J chain

10 binding sites

efficient at agglutinating bacteria

1st antibody produced in an infection

found on B cell as an antigen receptor

Question 5

IgG

Answer 5

4 subclasses: IgG1, IgG2, IgG3 and IgG4

most prevalent antibodies in serum

only antibodies that can cross the placenta

Question 6

IgA

Answer 6

secreted as a dimer

held together by a J chain

contains a “secretory component” (SC)

protects the mucosa

secreted locally by plasma cells e.g. in saliva, milk and tears

Question 7

IgD

Answer 7

present in low levels in the serum

B cell antigen receptor

Question 8

IgE

Answer 8

involved in inflammation

protection from parasitic worms

low serum levels

binds to IgE receptors on a mast cell associated with antibody-mediated allergy

Question 9

Isotypes

Answer 9

present in all healthy individuals – Ig classes and subclasses

Question 10

Allotypes

Answer 10

genetically restricted variation within CH region

Question 11

Idiotypes

Answer 11

individual antigenic characteristics of a given antibody

based on its variable region

Question 12

Four main mechanisms for Antibody Diversity

Answer 12

1. Combinational diversity 2. Junctional diversity 3. Heavy/light chain pairings 4. Somatic hypermutation

Question 13

2 types of light chains

Answer 13

1. Kappa 2. Lambda

Question 14

Junctional diversity

Answer 14

RAG enzymes cleave DNA at random positions along the region

Random nucleotides are added (or deleted) for extra variability

This somatically recombined DNA is then processed

Question 15

Transcription and Splicing

Answer 15

somatically recombined DNA is transcribed into pre mRNA

introns are spliced out, combining the V,J and C regions

translated into the light chain in the ER

Question 16

Class Switching

Answer 16

Somatic recombination at Switch (S) regions replace IgM

Question 17

Somatic hypermutation

Answer 17

AID converts cytosine to uracil

Hyper-mutation occurs when cells try to fix the error

B cells producing antibodies with higher affinity for antigen are selected to survive

Question 18

Answer 18

Defect in somatic recombination

Omenn Syndrome

Curable by bone marrow transplantation

Question 19

B-cell development

Answer 19

B cell precursor rearranges its immunoglobulin genes

Generation of B cell receptors in the bone marrow

Negative selection in the bone marrow

B cell is activated when foreign antigen binds

B cells migrate to the peripheral lymphoid organs

give rise to plasma cells and memory cells

Antibody secretion

Question 20

B cell function

Answer 20

secretes antibodies

Question 21

B-cell receptor (antibody) signalling

Answer 21

IgM or IgD

Kinase activation (tyr phosphorylation)

Ca2+ release

TF activation

Question 22

Immunological memory

Answer 22

memory cells

Re-exposure of antigen = more rapid response