Week 13

Question 1

What are the 5 classes of Ig?

Answer 1

IgM
IgD
IgE
IgA
IgG

Question 2

Abs are the secreted form of what?

Answer 2

the BCR

Question 3

What is the Ab repertoire?

Answer 3

The total number of Ab specificities available to an individual - is at least 10^11 in humans

Question 4

What are hyper-variable regions?

Answer 4

Designated/concentrated regions of sequence variability in the variable regions of both the heavy and light chain

Question 5

What are complementarity determining regions (CDRs)?

Answer 5

Same as hyper variable regions (concentrated areas of sequence variability on VH and VL)

Question 6

How many hyper variable regions are there within the heavy and light chain?

Answer 6

6 (2 sets of HV1, HV2, HV3 combination)

Question 7

What determines the antigen specificity of an Ab?

Answer 7

The combination of the 6 HV regions on the VH/VL chains (combinatorial diversity)

Question 8

What are the 3 key things that create diversity in the Ig repertoire?

Answer 8

Combinatorial diversity
Junctional diversity
Somatic hyper-mutation

Question 9

How does combinatorial diversity create Ig repertoire diversity?

Answer 9

Mx copies of each gene segment type, different combinations of gene segments
Different combinations of H and L V regions

Question 10

How does junctional diversity create Ig repertoire diversity?

Answer 10

Can have addition/subtraction of nucleotides at joints b/w different gene segments

Question 11

How does somatic hypermutation create Ig diversity?

Answer 11

After an immune response is initiated, point mutations are introduced into the rearranged V region genes

Question 12

How does B-cell DNA differ to gremlin DNA?

Answer 12

V and C regions have been brought closer in B cell DNA

Question 13

What are the 3 DNA segments that encode VH?

Answer 13

V D and J

Question 14

What are the DNA segments that encode VL?

Answer 14

V and J

Question 15

What are the 3 DNA segments that encode alpha chains of the TCR?

Answer 15

V D and J

Question 16

What are the DNA segments that encode beta chains of the TCR?

Answer 16

V and J

Question 17

What are RAG1 and RAG2?

Answer 17

Genes encoding for proteins that are part of the V(D)J recombinase protein complex

Question 18

How are RAG1 and RAG2 involved in gene rearrangement?

Answer 18

Encode lymphoid specific parts of the V(D)J recombinase protein complex, which helps effect somatic recombination

Question 19

What happens in the early pro-B cell stage of B development?

Answer 19

Heavy chain locus rearranged - D segment joined to J segment

RAG1 and RAG2 genes induced

Question 20

What happens in the late pro-B cell stage of B development?

Answer 20

Rearrangement so V segment added to the DJ sequence - if successful μ heavy chains produced in cytoplasm
Pre-BCR produced –> signals transition to pre-B cells

Question 21

Out of the heavy and light chains, which is rearranged first in B cell development?

Answer 21

Heavy chain is rearranged first (D to J joining = first step)

Question 22

What happens in the pre-B cell stage of B development?

Answer 22

Pre-BCR signalling enforces allelic exclusion
Further rearrangement of H chain locus halted, begin L chain locus rearrangement
Many able to generate progeny w/ IgM molecules (=immature B cells)
L chains display isotypic exclusion (express only one type of light chain)

Question 23

What is allelic exclusion?

Answer 23

Only one of the two alleles of a gene is expressed in a diploid cell

Question 24

At the pre-B cell stage of B cell development, L chains display isotypic exclusion - what does this mean?

Answer 24

They only express one type of light chain (κ or λ)

Question 25

Roughly what is the ratio of κ to λ light chain expressing B cells in humans?

Answer 25

65% : 35%

Question 26

The BCR is composed of two key parts - what are they?

Answer 26

Membrane-bound Ig molecule of one isotype (D, M, A etc) | Ig⍺/Igβ heterodimer (CD79)

Question 27

What is central tolerance?

Answer 27

The process of eliminating any developing T or B cell that is autoreactive

Question 28

What are the general stages of B cell development?

Answer 28

``` Early pro-B cell Late pro-B cell Pre-B cell Immature B cell Mature B cell ```

Question 29

What happens in the immature B cell stage of B cell development?

Answer 29

Rearranged light chain paired w/ μ chain IgM can be expressed on cell surface - associates w/ Ig⍺/Igβ to form a functional BCR Central tolerance - tested for auto reactivity in bone marrow Peripheral tolerance - does same in periphery, secondary check in case any escape central If successful can continue to mature and are carried to spleen

Question 30

What is CD79 also known as?

Answer 30

Ig⍺/Igβ

Question 31

What is the Ig⍺/Igβ heterodimer also known as?

Answer 31

CD79

Question 32

What does the Ig⍺/Igβ heterodimer do?

Answer 32

Associates with IgM to form a functional BCR

Question 33

Where do B cells complete their maturation?

Answer 33

B cell follicles in the spleen

Question 34

What happens if cells are self-reacting in development?

Answer 34

Receptor editing - autoreactive receptor replaced | Clonal deletion

Question 35

What happens in the mature B cell stage of B cell development?

Answer 35

Complete their maturation in B cell follicles in the spleen Follicles release signals for survival - weak, constitutive signals through BCR and BAFF (cytokine) produced through follicular DCs

Question 36

What is BAFF?

Answer 36

A cytokine released by follicular DCs to mature B cells for cell survival

Question 37

Over-expression of BAFF has been linked to what?

Answer 37

Development of autoimmune disease

Question 38

What do naive B cells need for activation?

Answer 38

Accessory signals from Tfh cells (or microbial constituents)

Question 39

What signals do Tfh cells provide to B cells for activation?

Answer 39

CD40L + various cytokines eg. IL-21, IL-6, TGF-β, IL-4 and IFN-γ

Question 40

What is linked recognition?

Answer 40

T cells are activated by the same Ag recognised by the B cell (peptide recognised by T cell must physically associated with the Ag recognised by the BCR)

Question 41

What are germinal centres?

Answer 41

Areas of lymphoid follicles where there is intense proliferation of B cells

Question 42

What are the 3 key constituents of GCs?

Answer 42

A mantle zone contacting resting Bc ells | Two areas of activated B cells - light and dark zone

Question 43

What are GCs composed of?

Answer 43

Mainly rapidly proliferating B cells + ≈10% Ag-specific T cells helping

Question 44

Where do centroblasts proliferate?

Answer 44

In the dark zone of the GC

Question 45

When centroblasts reduce proliferation and move over to the light zone, what do they become?

Answer 45

Centrocytes

Question 46

What do centrocytes do?

Answer 46

Increase Ig production

Question 47

What happens in the dark zone of the GC?

Answer 47

Centroblasts rapidly proliferate

Question 48

What happens in the light zone of the GC?

Answer 48

Centrocytes increase Ig production

Question 49

What are the 3 key processes GC B cells undergo that produce Ab and are more effective in eliminating infections?

Answer 49

Somatic hypermutations Affinity maturation Class switching

Question 50

Where are centroblasts found?

Answer 50

In the dark zone of the GC

Question 51

Where are centrocytes found?

Answer 51

In the light zone of the GC

Question 52

What's found in the mantle zone of the GC?

Answer 52

Resting B cells

Question 53

Where are resting B cells found in the GC?

Answer 53

Mantle zone

Question 54

How do somatic hypermutations make GC B cells more effective?

Answer 54

Introduces random mutations in the V genes which are initiated by activation-induced cytidine deaminase (AID) The B cell clones produced have subtle differences in specificity and Ag affinity Mostly have negative effect on BCR ability to bind to original Ag and so are eliminated by apoptosis - prevents rapidly dividing B cells from dividing to excessive no.s

Question 55

What is the name of the enzyme which initiate somatic hypermutations in B cells?

Answer 55

Activation-induced cytidine deaminase (AID)

Question 56

What is affinity maturation in the context of B cells?

Answer 56

Selection of B cells with improved affinity for Ag - centrocytes whose BCR binds Ag better will present more peptides one their MHC II surface and so receive stronger survival signals from Tfh Those w/ weaker binding receive weaker survival signals and => apoptotic

Question 57

What are the first Ag receptors expressed by B cells?

Answer 57

IgM and IgD

Question 58

What is the first Ab produced in an immune response?

Answer 58

IgM

Question 59

When does switching from IgM to other Ig classes occur?

Answer 59

After B cells have been stimulated by Ag

Question 60

How is Tfh involved in class switching?

Answer 60

Produces cytokines which regulate the selection of the particular C region

Question 61

IL-4 promotes switching to which isotype antibody?

Answer 61

IgE

Question 62

IL-4 signalling in class switching activates which TF?

Answer 62

STAT6

Question 63

How does IL-4 lead to IgE isotype antibody being made?

Answer 63

IL-4 activates STAT6 STAT6 promotes transcription upstream of the Sε region This creates IgE isotype Ab

Question 64

What does IL-21 promote switching to?

Answer 64

IgG1 and IgG3

Question 65

What does TGF-β promote switching to?

Answer 65

IgG2b and IgA

Question 66

What does IL-5 promote switching to?

Answer 66

IgA

Question 67

In humans, what is the marker of memory B cells?

Answer 67

CD27

Question 68

What is a primary antibody response characterised by? (in terms of Ig)

Answer 68

Rapid production of IgM, slightly delayed production of IgG

Question 69

What is a secondary antibody response characterised by? (in terms of Ig)

Answer 69

Production of small amounts of IgM and much larger amounts of IgG, with some IgA and IgE

Question 70

Which of the Ig classes is the most abundant in healthy adult humans and mice?

Answer 70

IgG

Question 71

What is the main function of IgA?

Answer 71

Defence at mucosal sites

Question 72

What is the main function of IgG?

Answer 72

Most abundant in serum and strongly induced during an immune response

Question 73

What is the main function of IgD?

Answer 73

Function not well known; may serve as auxiliary BCR

Question 74

What is the main function of IgE?

Answer 74

Defence against parasites but also involved in allergic diseases

Question 75

What is the main function of IgM?

Answer 75

First one produced after B cell activation

Question 76

Give 4 key features of the immunopathogenesis of SLE

Answer 76

Aberrant immune regulation Immune complexes are trapped inside tissue and fix complement, causing inflammation B cells produce autoantibodies (typically have high ANAs) T cells produce pro-inflammatory cytokines IL-2 production is low meaning Treg cells are reduced Immune complexes may trigger IFN production which favours class switching and Ab production