Lecture 1 - B cells - Immune Deficiencies 1 Flashcards Preview

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Flashcards in Lecture 1 - B cells - Immune Deficiencies 1 Deck (70):
1

What are RSSs?

In which cells are they found in the DNA?

Recombination signal sequences
• These flank the V, D & J mini gene segments
• Nucleotide sequences recognised by the enzymes RAG-1 and RAG-2 → cleavage

RSS are found in all cells, as the immunoglobulin gene loci are present in all cells. The reason that the genes are not rearranged in all cells is that they do not express RAG1/RAG2

2

What are the various enzymes that perform gene recombination of immunoglobulins?

1. Site recognition and cleavage
• Recombination-activating genes (RAG-1, RAG-2
• HGM1

2. NHE joining
• Artemis
• PKcs (protein kinases)
• Ku70 and Ku80

3. Ligation
• TdT (addition of nucleotides to form N regions)
• DNA Ligase IV

3

Describe the function of RAG1 & RAG2

1. Recognition of RSS sequences

2. Cleavage
• Induction of cleavage by making nicks in dsDNA

4

What are the three steps in VDJ recombination?

1. Site recognition and cleavage
2. NHE joining
3. Ligation

5

Describe NHE joining

Enzymes bring the two ends together
• Artemis
• PKcs
• Ku70 and Ku80

These enzymes and the process are ubiquitous, i.e. this is how DNA is joined everywhere in the body

6

Describe the stage of ligation

1. TdT randomly adds extra nucleotides to the broken ends at VDJ junctions

2. DNA Ligase IV joins up the DNA

7

Which enzymes in the process of VDJ recombination are unique to B lymphocytes?

• RAG1/2
• TdT (NB Process unique to the heavy chain)

8

When do immature B cells leave the bone marrow?

Once they have a successful IgM and IgD on their surface
(i.e. once they are mature)

9

List the mutations that can disrupt B cell development

What two categories do they fall into?

-- Mutations in the enzymes that drive recombination and development--

• RAG
• PAX5
• E2A

-- Mutation in genes that transmit success signals --
• Igα/β
• BLNK
• BTK
• Syk

10

Describe the structure of an immunoglobulin

Light chain:
• VL
• CL

Heavy chain:
• VH
• CH1
• CH2
• CH3

Chains held together by disulphide bonds
• 1x between heavy and light chain
• 2x at hinge region between the two heavy chains

11

What are the features of large Pre-B cells?

Has Pre-B cell receptor:
• VDJ(h) + surrogate light chains
• Igα and Igβ signalling chains

NB Light chain in germ line configuration

12

What are the features of pre-pro B cells?

Rearranging heavy chain: D(h) → J(h)

13

What is a pro-B cell?

Successfully rearranged DJ(h)

Rearranging V(h) → DJ(h)

14

What are SLCs?
Where are they seen?
Which transcription factor is required for their expression?

Surrogate light chains
• They are the same in every B cell
• They are seen in pre-B cells
• E2A required for their expression

15

What are the different immunoglobulin loci in humans?

• H
• L(κ)
• L(λ)

16

Which locus, κ or λ, is rearranged first?

κ
(alphabetical order)

17

What do the 'signalling' molecules do in VDJ rearrangement?
Describe the mechanism of the pre-BCR checkpoint

Signal that rearrangement of the heavy chain was successful

1. Heavy chain + SLC join with Igα and Igβ
2. Signal transduction, involving:
• Btk
• BLNK
• Syk
3. 'Success' signal

18

What is the structure of the pre-B cell receptor?

Heavy chain + SLC

The immunoglobulin is bound to the surface, but the light chains are yet to be made; SLCs take their place

19

What are Igα and Igβ?

Signal transduction molecules
Transmit signal from the surface by a sequential cascade into the nucleus

20

Describe the pathogenesis of agammaglobulinaemia

1. Mutation in part of 'success signal'
• Btk (→ leads to XLA)
• Igα & Igβ
• μ heavy chain
• SLC
• BLNK

2. Even though Ig is successfully rearranged, the signal is not there

3. B cells development is halted

4. No B cells in circulation, no Ab

5. Recurrent infections

21

What is the pathogenesis XLA?

1. Mutation in Btk

2. No transduction of success signal at the pre-BCR checkpoint

3. B cell development does not occur

4. No B cells (and thus Ab in circulation)

NB No problem with rearrangement of immunoglobulin

22

What are the symptoms and features of XLA and other agammaglobulinaemias without B cells?

At what age do people with agammaglobulinaemia present?

• Recurrent infections: Strep. pneumonia, H. influenzae, otitis, sinusitis

• Serum lacking immunoglobulin
• No circulating B cells

Presentation at 3 years

23

What happens to T cells in XLA?

Not affected

24

What is a combined immune deficiency?

Both humoral and cellular immunity is lost

25

Describe Intravenous immunoglobulin treatment

• Administration
• Components
• Efficacy

• IgG derived from sera of other people
• Given intravenously

• High dose once a month
• By end of month, the amount is still quite high despite decay

Efficacy:
• Not great
• Only 20% of people remained infection free over a period of 5 years
• This is because the Ab is static and can not be improved over the course of an infection

26

What is Subcutaneous immunoglobulin treatment?

• Immunoglobulin self administered once a week

• Much more convenient

• Dosage can be better controlled

27

Which molecules in the pre-B cell receptor are vital for success signals?

Igα
Igβ
Btk
BLNK

28

What is Btk?

A kinase involved in signal-transduction at Pre-BCR checkpoint

29

What is BLNK?

• An adaptor protein
• Involved in signal transduction of the success signal in Ig gene rearrangement

30

What is a PID?
How many are there?

What are the classes?
Give some examples of each class

Primary immune deficiency
• Immune deficiency, not secondary to something else (e.g. infection, treatment, environmental exposure etc.)

There are over 200

8 classes:
1. Combined immune deficiencies
• Both humoral and cellular immunity affected
e.g.
• SCID
• HIGM

2. Antibody deficiencies
• Humoral immunity affected
e.g.
• CVID
• HIGM
• XLA

31

Are there such things as solely T cell deficiencies?

No, there aren't.

B cell function is dependent on T cell function (especially CD4 T cells)

If there is a T cell deficiency, the B cell compartment will also be affected → combined immune deficiency

32

What is gammaglobulin?

aka Immunoglobulin
aka Antibody

33

Where do RAGs cut?

Between the gene segment and the RSS
i.e. the RSSs are cleaved out, leaving only the gene segments

34

What are the different classes of heavy chain?

(9 classes)
Alpha1, Alpha2
Delta
Epsilon
Gamma1, Gamma2, Gamma3, Gamma 4
Mu

35

What are the different classes of light chain?

Kappa
Lambda

36

Is Ig gene rearrangement conserved?
What does this mean?

Why would this be so?

Yes
This means that similar Ig gene loci are seen in many different mammals:
• Sharks
• Platypus
• Chicken
• Mouse

This is because it is a very effective system

37

How many different VDJ(h)/VJ(k) combinations are there?

1,100,000

38

Which things contribute to Ig diversity?

1. Ig gene rearrangement

2. Combinatorial diversity: (heavy and light chain combination)

3. Junctional diversity

39

What other molecule is important for Ig gene recognition and cleavage?

How is it different from RAG?

HGM1

It is not unique to Ig gene rearrangement

40

What is the function of Artemis?

Recognition and synapsis of NHE

41

Describe the components of the BCR

• Heavy chain
• Light chain
• Igα and Igβ

42

What is the difference between XLA and HIGM?

XLA: no antibody or mature B cells
HIGM: only IgM, no CSR or SHM

43

What is the mean age of diagnosis of XLA?
What normally leads to the diagnosis?

Mean age of 3

Recurrent infections:
• S. pneumoniae
• H. influenzae

44

What determines which cells are affected in combined immune deficiencies?

Which gene is mutated
i.e. if the gene product is vital for NKs, B and T cells, then there will be a deficiency of all three

45

Which mutation leads to T-B-NK-?

ADA

46

Mutations in which genes lead to T-B+NK-?

γc chain
JAK3

47

Mutations in which genes lead to T-B+NK+

IL7Ra

48

Mutations in which genes lead to T-B-NK+?

RAG1/2
Artemis

49

What is the phenotype of mutation in ADA?

T-B-NK-

50

What is the phenotype of mutation in JAK3?

T-B+NK-

51

What is the phenotype of mutation in IL7Ra?

T-B+NK+

52

What is the phenotype of mutation in Artemis?

T-B-NK+

53

What is the phenotype of mutation in γc chain?

T-B+NK-

54

What is the phenotype of mutation in RAG?

T-B-NK+

55

What are the various treatments for XLA and HIGM?

IVIg

56

What is contained in Intragam?

IgG (all subtypes), with trace amounts of IgM and IgA

57

Describe the features of SCID

What mutations give rise to SCID?
Which mutation is most common?

(Severe combined immunodeficiency disease)
A combined PID, thus affecting both humoral and cellular immunity

Susceptible to recurrent infections

Mutations:
• Common gamma chain (most common)
• ADA (2° most common)
• Artemis
• RAG-½
• JAK3
• IL-7Ra

58

Describe diversity of odorant receptors

Odorant receptors are germ line encoded (unlike BCRs / Ig, which are rearranged)

Human have 400 functional odorant receptor genes (600 pseudogenes)

This is 1/30th of our genes (if we accept we have 30 000 genes)

59

V regions differ between ...

C regions differ between ...

... all Ig molecules (unless they are from the same B cell)

... different classes of Ig

60

How are the heavy and light chains of Ab joined?

Disulfide bonds

Between:
• 1x between Heavy and Light chain
• 2x at hinge region between heavy chains

61

Describe the process of differentiation into mature B cells

At which stage does heavy chain rearrangement commence?

What about light chain rearrangement?

1. ELP
2. Pre-pro-B cell
3. Pro-B cell
4. Pre-B cell large
5. Pre-B cell small
6. Immature B cell
7. Mature B cell

Heavy chain rearrangement: pre-pro-B cell

Light chain rearrangement: Pre-B cell small

62

At which stage is Ig rearrangement complete?

Immature B cell

63

What is the difference between immature and mature B cells?

Immature: completed Ig rearrangement

Mature: expressed IgD and IgM on the surface

64

Why do predominantly boys get XLA?

Because the gene for Btk is on the X-chromosome

65

What is the most common mutation causing agammaglobulinaemia without B cells?

XLA: i.e. Btk mutation

66

How rare is XLA?

Rare: 1/250 000

67

What is XLA due to?

Mutation in Btk

68

List genes in which mutation causes combined immune deficiencies

• ADA
• Common γ chain
• JAK3
• IL-7Ra
• RAG1/2
• Artemis

69

Compare SCIg and IVIg

Efficacy:
• SCIg might be better because it is administered weekly

Convenience:
• SCIg much more convenient, because it can be done at home

70

Which mutation leads to X-SCID?

Mutation in the common gamma chain (encoded on the X chromosome)