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Clinical Immunology > Organisation & Expression of Immune Genes (Antibody Diversity) > Flashcards

Organisation & Expression of Immune Genes (Antibody Diversity) Flashcards

1
Q

function of heterochromatin

A

closed DNA structure not actively transcribed

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2
Q

function of Euchromatin

A

open structure allowing access to transcription machinery

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3
Q

Epigenetics (post-transcriptional) –methylation and acetylation account for…

A

… genome

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4
Q

post-transcriptional events (RNA) editing also
account for…

A

… differential gene expression

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5
Q
A
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6
Q

what do hydrophobic leader sequences allow?

A

(~20 amino acids) allows nascent poly
peptide transport through ER -> Golgi -> membrane (cleaved )

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7
Q

where is IgD expressed?

A

B cell surface

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8
Q

what does IgD engage with

A

engages with Ag during specific immune response activation

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9
Q

what receptor does IgD bind to?

A

B cell receptor

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10
Q

Ig have enormous

A

diversity, there are 10^ 15 to 10^ 18 B cells expressing different Ag specificities (more B cells than base pairs in the genome)

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11
Q

number of gene encoding B cell is in the…

A

… 100’s, not billions

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12
Q

How do you explain 10
15
to 10
18
different B cells?

A

genes encoding for the variable regions within the V
H
and V
L
chains rearrange within the genome of differentiating B cells (somatic
recombination)

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13
Q

Genetic recombination during
meiosis 1 creating…

A

genetically
diverse daughter (2n) cells

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14
Q

Meiosis 2 creates…

A

…four genetically distinct (1n) cells

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15
Q

go look at slide 10 and 11

A
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16
Q

The λ and κ light-chains are encoded by

A

V, J and C segments

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17
Q

Heavy-chain are encoded by

A

V, D, J and C segments

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18
Q

(kb denote

A

the genomic distance between segments)

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19
Q

There are two light-chains whic h are…

A

κ and λ

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20
Q

The Ig protein has…

A

… two major light chain domains:

1) Variable region (VL)
2) Constant region (CL)

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21
Q

How many amino acid residues in VL ?

A

VL = 108 amino acid residues

a) V (variable) = 95 residues
b) J (joining) = 13 residues

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22
Q

One V gene segment and one J gene segment are…

A

… brought together in the genome which then combine with a C (constant) gene segment.

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23
Q

One V gene segment and one J gene segment are brought together in the genome which then combine with a C (constant) gene segment.

This unique rearrangement if known as …

A

… V(D)J recombination

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24
Q

There are two light-chains….

A

κ and λ

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25
First step of recombination is
...the joining of a V segment to a J segment (VJ complex) any DNA in between is deleted
26
RNA splicing removes
introns and leftover V and J segments
27
Lambda (λ) gene recombination is similar in principle to
κ gene recombination – only expressed when κ are not recombined correctly
28
whats the principle step of Lambda gene recombination?
Principle step involves rearranging the genomic DNA to join V and J segment together crating a λ-VJ complex
29
How many Vλ and Jλ in the human λ locus?
40 Vλgene segments and 4 Jλ gene segments
30
Organisation of these segments in lambda genes differs from...
the κ locus
31
how many Cλ gene segments and J segments associate with?
There are four different Cλ gene segments that the J segment can associate with, thus four different λ chain isotypes produced
32
How many gene segments involved in the heavy chain variable region?
There are three gene segments involved in the heavy-chain variable region; VH (Variable), DH (Diversity) and JH (Joining)
33
The D and J segments encode for
the amino acid residues that constitute the complementary determining region 3 (CDR3) of the heavy-chain
34
Heavy-chain locus (Ch. 14) includes...
50 VH gene segments 20 DH gene segments 6 JH gene segments
35
Heavy-chain germ line contains ...
... multiple gene segments encoding for the constant (C) region
36
C region determines ...
... class and biological function
37
In the early stages of B cell differentiation, how many gene arrangement processes occur?
two gene arrangement processes occur
38
In the early stages of B cell differentiation two gene arrangement processes occur
1) one D segment associates with one J segment 2) one V segment associates with the DJ complex
39
The new V(D)J complex is closest to...
Cμ and Cδ segments which form the primary transcript.
40
Alternative splicing of the primary transcript yields ...
two different mature mRNA; V(D)J-μ and V(D)J-δ
41
A resting B cell may express...
...both IgM and IgD with identical Ag specificity
42
what is the first step of recombination of heavy chains?
First step of recombination is the joining of a D segment to a J segment (DJ complex)
43
DJ complex joins with
an upstream V segment (VDJ) complex
44
Primary RNA contains
μ and δ constant segments – alternative splicing produces two Ab classes
45
RSS has three elements which are...
1) a conserved heptamer 5’-CACAGTG-3’ 2) a less conserved spacer (either 12 or 23 bp) 3) a second conserved nonamer5’-ACAAAAACC-3’
46
RAG1/2 proteins bind to...
... DNA at RSS and mediate VDJ recombination by bringing together one 12-bp spacer with one 23-bp spacer.
47
V(D)J recombination mechanism steps
Step 1 RAG1/2 complexes with heptamer and RAG1 with nonamer Step 2 RAG1/2 create single strand nicks Step 3 V and J hairpin structures form due to RAG1/2 mutual affinity and a blunt end cut formed Step 4 ligation of 12 bp and 23 bp signal ends Step 5 Hairpin cleavage Step 6 overhang extension (palindromic hairpins) Step 7 ligation of V and J segments
48
In theory any B cell has
numerous gene segments from which to select for the synthesis
49
Each B cell has one set of [...] and one type of [...]
V(D)J genes and one type of VJ light gene (either κ or λ)
50
Each B cell rearranges these segments in a unique way, therefore
each B cell produces antibodies with only one antigenic specificity
51
B cells are
diploid (have 2 sets of chromosomes)
52
In contrast to all other cells, Ig chains are coded for by...
... only one set of genes
53
In contrast to all other cells, Ig chains are coded for by only one set of genes – e.g....
- Heavy-chain maybe from the paternal chromosome - Light-chain may be from the maternal chromosome
54
B cell may create one single...
Ag specific Ig – VJ (light) and VDJ (heavy) are fixed
55
B cells can switch class to...
make different Ig’s  IgA, IgG or IgE
56
B cells can switch class to make different Ig’s  IgA, IgG or IgE while
retaining the same Ag specificity (isotype switching)
57
What does isotope switching invovle?
involves rearranging the VDJ gene segment complex, juxtaposing the rearranged VDJ complex with a different C chain gene segment
58
In Isotype class switching,
Double stranded DNA breaks occur at consensus regions known as switch-regions, upstream of C gene segment
59
Switch-regions occur ...
adjacent all C genes except δ
60
Activation Induced (cytidine) Deaminase (AID) mediates
DNA at two selected switch regions, eliminating unwanted C genes
61
Non-homologous end joining links
VDJ with new C
62
Isotype class switching ocurs in...
mature B cells and is Ag stimulation dependent
63
Factors (CYTOKINES) that regulate this process are secreted from...
T cells
64
what are cytokines?
Cytokines are peptides that bind cognate cell surface receptors and alter cell activity and function
65
What are the other mechanisms to create antibody diversity?
1) Presence of multiple V genes in the germ line 2) Random assortment of H and L chains 3) Junctional and insertional diversity 4) Somatic hypermutation
66
1) Presence of multiple V genes in the germ line Number of different V gene segments in...
the germ line forms the baseline from which Ig is derived and represents the minimum number of different Ig that can be produced
67
Describe 2) Random assortment of H and L chains
Any distinct H chain may associate with any distinct L chain
68
Describe 3) Junctional and insertional diversity
The precise position at which the gene for the V and J or the V, D and J segments are fused together are not constant -> imprecise DNA recombinations can cause frame shift mutations  alter amino-acid sequence at the regions -> diversifying further
69
Describe 4) Somatic hypermutation
After secondary Ag exposure, Ag:Ab affinity increases -> analysis shows SNPs in VDJ region -> fine tuning of the immune system
70

Clinical Immunology (9 decks)

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