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Year 2 Semester 1 > CMB2004 Cell and Molecular Biology of the Immune System > Flashcards

CMB2004 Cell and Molecular Biology of the Immune System Flashcards

1
Q

What is specific immunity mediated by?

A

B and T lymphocytes

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2
Q

What are BCR expressed by?

A

B lymphocytes

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3
Q

What are TCR expressed by?

A

T lymphocytes

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4
Q

Which are found only in the membrane form, BCR or TCR?

A

TCR

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5
Q

What do BCRs bind?

A

“Free” antigens

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6
Q

What do TCRs bind?

A

Peptide fragment (epitope) bound to MHC expressed by APC

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7
Q

Describe the structure of antibodies

A

-Paired Variable (V) regions form two identical antigen binding site
-Constant regions are responsible for antibody structure and interacting with other molecules (FcR) and cells of innate system.

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8
Q

What are antibodies responsible for?

A

-Agglutination (against pathogens)
-Activating complement
-Activating effector cells

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9
Q

What are the two types of Light chain in antibodies?

A

Lambda or Kappa

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10
Q

What are the 5 isotypes of antibodies?

A

IgM, IgD, IgA, IgG and IgE

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11
Q

How many domains are found in the Light chain of an antibody?

A

2

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12
Q

How many domains are found in the Heavy chain of an antibody?

A

4 or 5

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13
Q

What comprises each domain in an antibody?

A

~110 amino acids
-Two Beta sheets
-Linked by a disulphide bridge
-Domains are paired

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14
Q

Name some compounds found in the immunoglobulin superfamily

A

TCR, MHC class I and II, CD4, CD8

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15
Q

How many hyper variable regions are found in antibodies?

A

3 in Variable Heavy and Variable light domains

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16
Q

What do the hyper variable regions found in antibodies contribute to?

A

Complementary determining regions (CDR1-3)

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17
Q

What types of epitopes are there?

A

Continuous or conformational

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18
Q

Describe the structure of TCRs

A

-Heterodimer of ⍺ or β chain (sometimes γ or 𝛿)
-Each chain has a V and a C region
-Domains are Ig like

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19
Q

Which cell types are MHC Class I molecules expressed by?

A

Nearly all cell types in body

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20
Q

Which cell types are MHC Class II molecules expressed by?

A

Specialised group of immune cells
-ANTIGEN PRESENTING CELLS

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21
Q

Describe the structure of MHC Class I molecules

A

Heterodimer of ⍺ chain (consisting of ⍺1, ⍺2, and ⍺3) and β2-microglobulin

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22
Q

What are the three different MHC Class I molecules?

A

HLA-A, HLA-B and HLA-C

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23
Q

What are the different HLA molecules encoded by?

A

Separate ⍺ chain genes

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24
Q

What do the ⍺1 and ⍺2 domains of MHC class I fold to form?

A

β sheet structure known as peptide binding site

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25
Q

Describe the structure of MHC Class II molecules

A

Heterodimer of ⍺ chain (⍺1 and ⍺2 domains) and β chain (β1 and β2 domains)

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26
Q

What are the three different MHC Class II molecule types?

A

HLA-DP, HLA-DQ and HLA-DR

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27
Q

What do both the ⍺2 and β2 domains of MHC Class II form?

A

Ig-like structure

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28
Q

How many gene segments make up the H chain and TCRβ in an TCR or BCR?

A

3 - V, D and J

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28
Q

How many gene segments make up the L chain and TCR⍺ in an TCR or BCR?

A

2 - V and J

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29
Q

What occurs to the different gene segments during lymphocyte differentiation?

A

They will rearrange

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30
Q

Describe the rearrangement of Immunoglobulin genes during B cell development.

A

-DNA containing the Ig gene segments is deliberately broken and rearranged to form functional genes
-Each individual B cell will perform both the breakage and rearrangement randomly

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31
Q

What is the process whereby Ig Gene segments rearrange

A

Non-homologous End Joining (NHEJ) recombination

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32
Q

Describe the recombination of gene segments to encode the V region of the light chain of an immunoglobulin

A

-After DNA breaks, a single V and a single J gene segment are joined together

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33
Q

What are the two loci containing L chain immunoglobulin genes?

A

κ and 𝞴

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34
Q

In what order do Immunoglobulin rearrangements occur?

A

-First H chain gene segments rearrange
-Then light chain gene segments rearrange forming κ segments first. If this is unsuccessful then 𝞴 segments rearrange.

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35
Q

Describe the recombination of gene segments to encode the V region of the heavy chain of an immunoglobulin

A

After DNA breaks, a single random V, D and J segments are randomly joined together

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36
Q

There multiple V, D and J immunoglobulin segments, but where are they encoded?

A

At 3 different loci
-H (on chromosome 14)
-κ (on chromosome 2)
-𝞴 (on chromosome 22)

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37
Q

What is Immunoglobulin gene segment rearranged guided by?

A

Recombination signal sequences

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38
Q

What complex is involved in the immunoglobulin gene segment rearrangement?

A

V(D)J recombinase

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39
Q

What genes activate the recombination process in immunoglobulin gene rearrangement?

A

RAG1 and RAG2 (recombination activating gene)

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40
Q

What occurs if mutations occur in RAG genes?

A

Immunodeficiency

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41
Q

What is immunoglobulin light chain isotype exclusion

A

-Each B cell expresses either a rearranged κ or 𝞴 light chain but never both
-Ensures that each individual B cell produces just one randomly generated BCR that is different from every other BCR

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42
Q

Give the mechanisms for generation of antibody diversity

A

1) Multiple gene segments for each chain
2) Combinatorial diversity
3) Different combinations of heavy and light chains
4) Junctional diversity
5) Somatic hypermutation

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43
Q

Describe how junctional diversity increases immunoglobulin diversity

A

imprecise joining (small differences in sequences where V-D and D-J segments join)
-N regions (random addition of nucleotides at junctions of V-D and D-J by terminal transferase)

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44
Q

Describe how somatic hypermutation increases immunoglobulin diversity

A

-Mutation frequency in antibody, V genes us orders of magnitude higher than that seen in all other areas of the genome
-SHM occurs in germinal centres

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45
Q

What carries out Somatic hypermutation in immunoglobulin diversity?

A

-Activation induced deaminase
-Acts on DNA to deaminate cytosine to uracil
-Uracil is Recognised by error prone DNA repair pathways leading to mutations

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46
Q

The constant region of each immunoglobulin heavy chain is encoded by?

A

-Different C region gene segment (eg C𝛿, Cµ, Cε)
-Four γ chain gene segments correspond to the four IgG subclasses

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47
Q

What is the first isotype of BCR expressed by developing B cells?

A

IgM

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48
Q

What can IgM be coexpressed with, and why?

A

C𝛿 is next to Cµ, hence IgD can be coexpressed with IgM, by differential processing of the RNA from the two C region genes

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49
Q

What are the variable regions in T cell receptors encoded by?

A

V, D and J segments

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50
Q

Where does Gene segment rearrangement occur in the body in TCRs?

A

The thymus

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51
Q

In what lymphocytes does somatic hypermutation occur?

A

ONLY in BCR

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52
Q

Does gene rearrangement occur in MHC molecules

A

NO

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53
Q

What are the subtypes of genes encoding MHC Class II

A

HLA-DP, HLA-DQ, HLA-DR

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54
Q

If heterozygous at each MHC Class I molecule, how many different Class I molecules can be expressed (and likewise for Class II)?

A

6

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55
Q

What is the benefit to having a high level of MHC polymorphism?

A

-Allows a wide range of epitopes to bind
-Increasing variety of APCs
-Population can respond to almost unlimited number of pathogens/antigens

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56
Q

What is the drawback(s) of having a high level of MHC polymorphism?

A

-Increased risk of immune-mediated disease (eg autoimmune)
-Reduces pool of available donor organs (as reduced matching)

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57
Q

Where are peptides derived from antigens synthesised/processed inside the cell presented?

A

Usually by Class I MHC molecules

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58
Q

Where are peptides derived from antigens synthesised/processed outside the cell presented?

A

Usually by Class II MHC molecules

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59
Q

Describe the process by which antigens are processed and presented by MHC Class I molecules

A

1 - Antigen synthesised in cytoplasm
2 - Protein cleaved to peptides by proteasome
3 - Peptides transported to endoplasmic reticulum by TAP transporter
4 - Peptides bind to MHC Class I molecules
5 - MHC-1/peptide complex then transported to cell surface

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60
Q

What transports antigens cleaved to epitopes into the endoplasmic reticulum?

A

TAP transporter

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61
Q

How may proteasomes involved in antigen processing change during inflammation?

A

Proteasomes receiving inflammatory cytokines signals produce altered peptides

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62
Q

Describe the process by which antigens are processed and presented by MHC Class I molecules

A

1 - Antigens are endocytose into intracellular vesicles inside the cell
2 - Protein cleaved to peptides by acid proteases
3 - Vesicles fuse with vesicles containing MHC class II molecules
4 - Peptides bind MHC Class II molecules
5 - MHCII/peptide complex then transported inside vesicles to cell surface

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63
Q

Describe how MHC Class II molecules prevent inappropriate binding?

A

-MHC Class II molecules bind to invariant chain in the endoplasmic reticulum
-Preventing peptides binding in the groove
-In endocytic pathway lysosomal enzymes degrade this leaving CLIP peptide associated with the binding groove
-Peptides from antigen displace CLIP when they bind
-HLA-DM is required for loading of peptides into the groove

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64
Q

What is the role of HLA-DM, a molecule encoded in the Class II region of the MHC HLA?

A

Required for loading of peptides into the groove of MHC Class II molecules

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65
Q

What do MHC I and II molecules bind and present in normal healthy cells?

A

Peptides from self proteins

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66
Q

Where are each accessory molecules involved in antigen processing and presenting encoded?

A

They are all encoded in the MHC

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67
Q

What will happen to any cell expressing MHC Class I molecules with a non-self antigen?

A

They will be recognised and killed by cytotoxic CD8+ T cells

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68
Q

What will happen to any cell expressing MHC Class II molecules with a non-self antigen?

A

They will be recognised and activated helper CD4+ T cells

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69
Q

What do B cells develop from?

A

-Haematopoietic stem cells in bone marrow
-Which express PAX5 transcription factor

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70
Q

What B cell specific markers are expressed?

A

CD45

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71
Q

What is expressed after B cells are matured?

A

CD19

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72
Q

Describe how pre B cells mature

A

-H chain genes rearrange first (µ chain), which then moves to cell surface with Ig⍺ and Igβ and expressed with surrogate light chain
-Then light chains rearrange, displacing the surrogate light chain

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73
Q

What makes up the surrogate light chain expressed in pre-B cells?

A

VpreB and 𝞴5 chains

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74
Q

Once pre-BCRs are functional, what does the signal sent to preB cells do?

A

-Turns off RAG1 and RAG2
-5 or 6 rounds of cell division
-Surrogate light chain expression stops
-RAG1 and RAG2 turned on again for gene rearrangement
-L chain rearrangement starts

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75
Q

What occurs if cell fails to productively rearrange both H and L genes?

A

It dies

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76
Q

Following successful H chain rearrangement, what happens if pre-B cells initially fail to generate non-productive rearrangements of light chain κ genes?

A

-They can be rescued by up to 10 further rearrangements at the same locus
-If after these attempts and still out of frame, then 𝞴 locus will begin to rearrange

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77
Q

What happens to immature B cells that bind multivalent self antigens?

A

-Clonal deletion (cell apoptosises)
OR
-Receptor editing (further light chain gene rearrangements of variable regions)

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77
Q

What happens to immature B cells that bind soluble self antigens?

A

Cell becomes unresponsive (anergic)

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78
Q

Where do premature T cells rearrange receptor genes?

A

In the thymus

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79
Q

How is T cell development similar to that of B cells?

A

-Originate from bone marrow stem cells
-Rearrange receptor genes
-Express pre-T receptor
-Elimination of self reactive T cells by negative selection

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80
Q

T cells expressing ⍺β TCR must do what to be selected?

A

Bind with self MHC (through positive selection)

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81
Q

What occurs after T cells migrate to the thymus?

A

Develop into thymocytes by
-Rearranging TCR genes (β first) and express TCR
-Acquire other markers eg CD3, CD4, CD8
-Undergo positive and negative selection

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82
Q

Describe the thymus

A

-Bi lobed organ in anterior mediastinum
-Each lobe divided into many lobules
-Each lobule has outer cortex and inner medulla

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83
Q

Once inside the thymus, describe how thymocytes rearrange TCR genes

A

-Firstly they rearrange TCRβ genes
-Expressed along with pre-T cell receptor
-Cells proliferate and then rearrange TCR⍺ genes

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84
Q

What does TCR expression require?

A

The CD3 complex
-CD3 transmits signal to T cell nucleus following TCR recognition of peptide-MHC

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85
Q

What will some thymocytes express instead of ⍺β TCR?

A

γ𝛿

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86
Q

T cells expressing a randomly rearranged ⍺/β TCRs may

A

-Recognise self MHC plus peptide from “foreign” Antigen (immunity) - KEPT
-Recognise self MHC plus peptide from “self” Antigen (autoimmunity) - ELIMINATED
-Not be able to recognise self MHC - ELIMINATED

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87
Q

Describe positive selection of T cells

A

-Positive selection of cells which recognise MHC+Self peptide
-Occurs when double positive (DP, CD4 CD8) T cells recognise MHC on cortical epithelial cells in thymus
-Apoptosise if not recognised

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88
Q

Describe negative selection of T cells

A

-Negative selection of T cells which recognise MHC+self peptide on thymic dendritic cells/macrophages with high affinity
-TCR binding to MHC/self peptide with high affinity causes T cell to die apoptosis (clonal deletion)

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89
Q

Where does the positive selection of ⍺:β T cells occur?

A

In the cortical epithelial cells in the thymus

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90
Q

Where does the negative selection of ⍺:β T cells occur?

A

In the
-Dendritic cells
-Macrophages
-Other cells in the thymus

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91
Q

How does TCR affinity for self peptide-MHC affect selection?

A

-All T cells recognising self MHC are positively selected
-Those with the highest affinity for MHC+self peptide are then negatively selected

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92
Q

Describe the T cells that survive thymic selection

A

-Express TCR capable of binding self MHC
-Are depleted of self reactive cells
-Exit the thymus as mature, single positive T cells

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93
Q

Which T cells recognise antigens in association with MHC Class I?

A

CD8+ T cells

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94
Q

Which T cells recognise antigens in association with MHC Class II?

A

CD4+ T cells

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95
Q

Following exit from the thymus, through what do naive T cells recirculate, and where to?

A

-Via blood/lymphatics through High Endothelial Venules (HEV)
-To secondary lymphoid tissue

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96
Q

What occurs when naive T cells make contact with specific APC-Ag?

A

Clonal proliferation and differentiation

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97
Q

What may naive T cells differentiate into following contact with specific APC-Ag?

A

-Effector T cells (CD4 or CD8)
-Memory T cells

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98
Q

Following activation in the secondary lymphoid tissue, where may T cells go?

A

Effectors will migrate to sites of infection

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99
Q

Apart from presenting antigens, how may APCs activate lymphocytes?

A

Using cytokines

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100
Q

What occurs to T cells that are not activated?

A

Leave the lymph node via cortical sinuses into the lymphatics, reentering circulation and being recycled for another day.

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101
Q

How may T cells get to where they need to be?

A

Chemokine receptors expressed on surface of T cells bind chemokines expressed by other cells

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102
Q

Once T cells are physically close to other cells, what will mediate cell/cell interactions?

A

Cell adhesion molecules

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103
Q

Describe the process that occurs when T lymphocytes contact APC

A

-T cells contact APCs using CAMs
-TCR scans APC peptide/MHC complexes
-If no recognition they may disengage, if there is recognition CD3 signal activates
-Increasing affinity of CAM interactions
-T cell divides and progeny differentiate to effector cells

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104
Q

What is LFA-1?

A

Leukocyte function-associated antigen

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105
Q

What is ICAM-1?

A

Intercellular adhesion molecule

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106
Q

Describe the process by which T cells bind and become activated on a molecular level.

A

-T cells initially bind APC through low affinity LFA1:ICAM1 interactions
-Subsequent binding of T cell receptors signals LFA1
-Conformational change in LFA1 increases affinity and prolongs cell cell contact

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107
Q

Name the signals involved in T cell costimulation

A

Signal 1 - TCR contacting MHC-Epitope on APC, involving CD3
Signal 2 - APC express B7.1/2 that bind CD28 on T cells
Signal 3 - APC release cytokines that bind cytokine receptors on T cells

108
Q

Once activated by costimulation, describe negative feedback in T cell proliferation

A

-Activated T cells now proliferate and express ICOS and CTLA4
-Binding of CTLA4 to B7.1/2 on APC delivers a negative signal to the activated T cell

109
Q

What does ICOS on activated T cells bind to?

A

ICOS (related to CD28) binds ICOSL on APC to induce cytokine secretion by T cells

110
Q

What does CTLA-4 on activated T cells bind to?

A

CTLA-4 is highly related to CD28, and shows stronger binding to B7.1/2 than CD28

111
Q

What are mutations in CTLA-4 associated with?

A

Autoimmune diseases eg Type I diabetes

112
Q

APCs activate T cells, but what activates APCs?

A

-APCs express receptors for microbial molecules (PRR)
-Binding these pathogen associated molecules activates APC
-Leading to up regulation of MHC and Costimulatory molecules
-Ensuring signal 2 to activate T cell mediated response only occurs during infection

113
Q

How do different cytokines affect differentiation?

A

Different cytokines dictate the differentiation of activated CD4 cells into different subsets of effector cells

114
Q

What transcription factor does TGFβ act upon, and what subtype of CD4 does it cause differentiation into?

A

-Acts on FoxP3
-Differentiating into Treg cells

115
Q

What transcription factor does IL6 act upon, and what subtype of CD4 does it cause differentiation into?

A

-Acts on Bcl6
-Differentiating into T follicular helper cells

116
Q

What transcription factor does TGFβ-IL6 act upon, and what subtype of CD4 does it cause differentiation into?

A

-Acts on RORγT
-Differentiating into TH17 cells

117
Q

What transcription factor does IL12-IFNγ act upon, and what subtype of CD4 does it cause differentiation into?

A

-Acts on T bet
-Differentiating into TH1 cells

118
Q

What transcription factor does IL-4 act upon, and what subtype of CD4 does it cause differentiation into?

A

-Acts on GATA3
-Differentiating into TH2 cells

119
Q

Give some APCs that express MHC Class II molecules II

A

-Dendritic cells
-Macrophages
-B cells

120
Q

Name some types of dendritic cells

A

-Myeloid (conventional DC2,3)
-Plasmacytoid DC (pDC, DC6)

121
Q

Describe myeloid Dendritic cells (DC2,3)

A

-Key APC that initiates T cell responses
-Bone marrow derived
-Do not express B7 until activated/matured
-Induced to mature and migrate to lymph node following “danger signal” activation

122
Q

How may mature myeloid dendritic cells (DC2,3) differ from inactivated DC?

A

-Found in T cell areas of lymphoid tissues
-DC MHC Class I and II will be loaded with peptides from pathogens they encountered in peripheral tissues
-Their levels of costimulatory molecules will be very high
-They will express high levels of adhesion molecules

123
Q

What is special about dendritic cells (DC1)?

A

-They take up and process exogenous antigens and present it via MHC Class I molecules
-This allows these DCs to activate naive CD8 T cells, meaning these (which don’t need co-stim) can kill infected cells that are not APC

124
Q

Describe macrophages

A

-Function as scavengers of pathogens but also important APC for extracellular pathogens
-Highly phagocytic
-Express MHC II and B7 which increases following T cell help
-Resident in many tissues at peripheral sites as well as in lymphoid tissue
-Once activated by T cells secrete many inflammatory cytokines

125
Q

Describe B lymphocytes as antigen presenting cells

A

-Very poor at phagocytosis
-Internalise soluble Ag for processing and presentation by BCR (act as Ag specific APC)
-Ag binding to BCR up regulates B7 (can provide signal 2 to activate T cells)

126
Q

What is Interleukin 2?

A

-A key cytokine for T cell survival
-Autocrine T cell Growth factor
-Once activated T cells express a high affinity IL2R and secrete IL2
-Leading to lots of T cell proliferation

127
Q

How may Interleukin 2 receptors change once T lymphocytes are activated?

A

-Naive T cells express a low affinity form of the IL2R
-Activated T cells express a high affinity IL2R and secrete IL2

128
Q

What is the target of cyclosporin, an immunosuppressive drug?

A

Interleukin 2

129
Q

Describe activation of CD8 T cells

A

-Requires high levels of costimulator activity
-CD8 T cells can be activated directly by infected or cross presenting APC
-Or may require additional help from CD4 T cells.

130
Q

How are B lymphocytes and T lymphocytes similar in terms of activation?

A

Both require costimulation ie multiple signals

131
Q

What is signal 1 in B lymphocyte activation?

A

Binding of antigen to B cell receptor

132
Q

What immunoglobulins are expressed on the surface of B cell receptors?

A

IgM and IgD

133
Q

What does crosslinking of BCRs in B lymphocyte activation activate?

A

Intracellular kinases

134
Q

What is associated with membrane BCRs?

A

Ig⍺ and Igβ, which contain Immunoreceptor tyrosine based activation motifs (ITAM)

135
Q

What can enhance signal 1 in B lymphocyte activation?

A

-Activated complement cascade
-ie lots of C3b
-binding to complement receptor (CR2) on B cell surface
-Aids in forming the BCR coreceptor complex
-Augmenting the signal

136
Q

What are the two types of antigens that B cells can bind to?

A

-Thymus independent antigen (TI)
-Thymus dependent antigen (TD)

137
Q

How do B cells receive signal 2 when activating by TI antigens?

A

Signal 2 is provided by the antigen itself or extensive cross linking of BCR

138
Q

How do B cells receive signal 2 when activating by TD antigens?

A

Signal 2 is provided by CD4 T cells

139
Q

Describe thymus independent (TI) antigens

A

Lead to antibody production (only IgM) with no requirement for T cell involvement

140
Q

Describe the TI1 isotype of Thymus independent antigens

A

-Binds to other receptors (as well as BCR) on B cells providing signal 2
-The two signals lead to B cell activation, proliferation and antibody secretion

141
Q

In high concentrations, what do TI1 thymus independent antigens do?

A

Act as polyclonal activators (mitogens) for B cells

142
Q

Describe the TI2 isotype of thymus independent antigens

A

-Often repeated epitopes (eg polysaccharides)
-Will therefore cross link many BCR molecules on same B cell surface
-Take longer to induce B cell activation

143
Q

At what age do antibody responses to TI2 thymus independent antigens develop?

A

After 5 years of age

144
Q

Describe Thymus dependent antigens?

A

-Antibodies to these antigens require CD4 T cells
-Antibody responses are much better

145
Q

Describe how all classes of antibodies can be produced to neutralise Thymus dependent antigens

A

-T cells activated by MHC-epitope on APC
-BCR binds antigen (signal 1)
-Then B cell internalises antigen, processes and presents Ag to CD4 T cells (signal 2) via CD40-CD40L
-Cytokines secreted by T cell aid B cell to class switch

146
Q

How may we improve the efficiency of a vaccine against pathogens that have T1 antigens?

A

By converting a TI antigen to a TD antigen

147
Q

Describe how we may convert a TI antigen to a TD antigen in a vaccine?

A

-Using a conjugate vaccine
-Coupling a pathogen to a protein on a TD antigen
-Allows young children to be immunised and protected

148
Q

Describe the process through which B lymphocytes and CD4 T cell interactions occur in the thymus

A

-B cells enter lymph node from blood
-If a B cell comes into contact with its specific Ag it can then be activated
-If Ag is TD, B cell presents peptide from Ag to CD4 Th cells at the boundary of the T/B areas forming a B/T cell conjugate

149
Q

Describe the molecular processes through which B lymphocytes and CD4 T cells interact

A

-B cell presents Ag-BCR to activated CD4 Th cell
-T cell expresses CD40 ligand, secreting cytokines
-B cell receives signal 2 via CD40/CD40L binding and via cytokine from T cells binding receptors causing proliferation
-CD40 signal also induces activation induced deaminase (AID) which causes class switching and SHM

150
Q

Where in the thymus do B/CD4 T cell interactions occur?

A

In the boundary between the B cell follicle and T cell zone

151
Q

Following conjugation of B lymphoblasts and T cells, what occurs?

A

-These conjugates move to primary follicles (B cell areas) forming Germinal centres within a B cell follicle in secondary lymphoid tissues
-B cells divide rapidly to become centroblasts and then differentiate into non dividing centrocytes

152
Q

How do B cells differentiate into centrocytes from centroblasts?

A

Through - Somatic hypermutation of Ig genes
- Isotype switching

153
Q

Once in a germinal centre, what do B cells do?

A

-Differentiate into plasma cells (secreting various isotypes)
-or Form long-lived memory cells and recirculate
-or Die within lymphoid tissue, if BCR no longer binds antigen because of somatic hypermutation

154
Q

Name the enzymes involved in somatic hypermutation?

A

Activation induced deaminase (AID) and DNA repair genes

155
Q

Where are follicular dendritic cells present?

A

In Germinal centres

156
Q

What do follicular dendritic cells capture Antigens via?

A

Fc receptors and Complement receptors

157
Q

What oversees B cell affinity maturation?

A

Follicular dendritic cells

158
Q

Describe how follicular dendritic cells oversee B cell affinity maturation

A

-Centrocytes that have undergone somatic hypermutation express mutated BCR on surface
-Centrocytes thus compete with each other for antigen on FDC and for signals from Tfh cell
-If mutated BCR binds Ag on FDC better than unmutated, it will present more efficiently and receive CD40 signal from Tfh

159
Q

Describe the function of Follicular T helper cells

A

-Recently defined subset of CD4 Th cells
-Specialised to help B cells
-By secreting either TH1 or TH2 type cytokines

160
Q

What is the role of CD40 signal?

A

CD40 signal via CD40L expressed on Tfh
-Protects centrocytes from apoptosis
-Inducing isotype switching (different cytokines induce different isotopes)

161
Q

What is the function of Activation induced deaminase (AID)?

A

Induces DNA breakage forming new constant region of antibody joined without affecting existing VDJ region

162
Q

Describe the different isotopes of immunoglobulins that different antigens produce

A

-Polysaccharides (TI) produce IgM
-Proteins (TD) produce IgG1 and IgG3 or IgG4
-Ag at mucosal surfaces induce IgA
-Some Ag elicit IgE

163
Q

Why do we need immunological tolerance

A

-Without tolerance, the immune system would attack the body’s own healthy cells as self reactive species are developed
-Prevents overreactions to harmless substances
-Helps regulate immune responses, ensuring the body doesn’t damage itself too much
-Important for accepting beneficial transplants and microbes (eg microbiota)

164
Q

Describe how random TCR gene rearrangement can lead to T cells expressing TCR that are tolerant

A

-A fail to recognise self MHC (useless), B recognise self MHC+self peptide (dangerous), C recognise MHC+other peptide (useful)
-A die by neglect (no positive selection survival signals), B and C are expanded by positive selection, then B are eliminated by negative selection
-Leading to only C surviving

165
Q

Since not all self antigens (eg insulin) are expressed in the thymus, how are these antigens introduced to naive T cells?

A

-Autoimmune Regulator Protein is a transcription factor that allows the expression of many tissue-specific antigen in the thymus
-So negative selection of T cells that recognise these antigens occurs

166
Q

Describe how random BCR gene rearrangement can lead to no autoreactive B cells

A

-Autoreactive B cells are negatively selected in bone marrow
-B cells get a second chance to rearrange self reactive BCR through receptor editing

167
Q

What occurs when immature B cells bind to self antigens?

A

Anergy (downregulating til unresponsive) or death or editing

168
Q

How may T lymphocytes be made anergic?

A

-Unstimulated macrophages do not deliver a costimulatory signal to T cells recognising a non bacterial antigen

169
Q

Name some other mechanisms of immunological tolerance

A

-Immunological ignorance (Ag not presented at sufficient levels)
-Privileged sites (Ag hidden away from immune system or suppressive cytokines)
-No T cells = No B cell response
-Regulatory T cells and B cells

170
Q

What transcription factor do T regulatory cells express?

A

Foxp3

171
Q

Describe regulatory T cells

A

-CD4 T cell subset that suppresses immune responses
-Crucial for preventing autoimmune responses
-Arise in thymus from T cells with high affinity TCR fro self AG

172
Q

What are the types of regulatory T cells?

A

Natural T reg (nTreg) - arising in thymus
Induced T reg (iTreg) - Induced in periphery

173
Q

How do regulatory T cells work?

A

-Suppressing anti inflammatory cytokines (eg IL10 and TGFβ) that inhibit self reactive T cells
-Binding directly to cells through cell surface receptors, eg blocking costimulatory molecules on dendritic cells

174
Q

What are the different types of effector CD4 T cells?

A

-TH1
-TH2
-TH17
-Treg + Breg
-TFH

174
Q

What do regulatory B cells secrete?

A

IL10 cytokines

175
Q

Describe the role of TH1 cells

A

-Activate macrophages via the secretion of cytokines (eg IFNγ)
-Express CD40L which binds to CD40 on macrophage (activating it)
-Can kill chronically infected macrophages through Fas ligand induced apoptosis

176
Q

Describe the role of TH17 cells

A

-Secrete IL17 cytokines
-Recruits neutrophils early in fungal infections

177
Q

What subtypes of CD cells can Treg cells be?

A

-CD4
-CD25
-CD8

178
Q

What does IL10 inhibit?

A

APC function

179
Q

Describe the role of TH2 cells

A

-Secrete IL4, IL5, and IL13
-Promoting responses mediated by eosinophils and mast cells

180
Q

Describe what TH1 cytokines promote and inhibit in terms of T cell development

A

-Promote commitment to TH1
-Inhibit development of TH2 and TH17

181
Q

Describe what TH2 cytokines promote and inhibit in terms of T cell development

A

-Promote commitment to TH2
-Inhibit development of TH1 and TH17

182
Q

Describe what TH17 cytokines promote and inhibit in terms of T cell development

A

-Promote commitment to TH17
-Inhibit development of Treg

183
Q

Describe what Treg cytokines promote and inhibit in terms of T cell development

A

-Inhibit TH1, TH2 and TH17 responses

184
Q

How are Tregs significant in pregnancy?

A

Suppress activation of the immune system, allowing for successful placentation

185
Q

What are polarised responses

A

The pathways of immune activation that the body chooses based on the type of threat it faces (eg prioritising TH1 cells)

186
Q

Why are polarised immune responses important?

A

-Allows tailoring immune response to types of threats, maximising efficiency whilst minimising damage to the body
-Prevents autoimmunity (excessive TH1)
-Prevents allergies (excessive TH2)
-Allows pregnancy

187
Q

Do effector T cells (ie not naive anymore) require costimulation?

A

No!

188
Q

What has an effect on the type of effector mechanisms required?

A

-Cellular site of pathogen
-Type of pathogen
-Stage of infection

189
Q

Name some sites where infection may occur

A

-Extracellular interstitial spaces (eg blood, lymph)
-Extracellular epithelial surfaces
-Cytoplasmic spaces
-Vesicular

190
Q

Describe innate defence mechanisms

A

-Rapid
-Utilises barriers, the complement system, phagocytosis, NK cells, antimicrobial peptides
-Non specific
-Ineffective against many pathogens

191
Q

Describe host defence mechanisms

A

-Acquired/adaptive defence mechanisms
-Utilises antibodies, cell mediated immunity
-Takes longer to develop but exhibits memory
-Enhances and focuses innate defences

192
Q

What are TH1 CD4 cells active against?

A

-Active against intracellular pathogens
-Activates macrophages and stimulate cytotoxic T cells

193
Q

What are TH2 CD4 cells active against?

A

-Active against extracellular pathogens
-Support antibody production, particularly class switching to IgE
-Activates eosinophils, basophils and mast cells

194
Q

What are TH17 CD4 cells active against?

A

-Active against extracellular bacteria and pathogens
-Important in attractive inflammatory cells such as neutrophils

195
Q

Name some gram positive bacteria

A

-Staphylococcus aureus
-Streptococcus spp

196
Q

Name some gram negative bacteria

A

-Campylobacter
-Salmonella
-Shigella
-Haemophilus
-Neisseria

197
Q

How do bacterial cell walls affect the immune response?

A

-Components eg LPS, peptidoglycan bind to Toll like responses on macrophages

198
Q

Describe Toll like receptors

A

Binding of pathogen associated molecular patterns (PAMPs) to TLR can
-Promote inflammation
-Promote dendritic cell maturation
-Influence differentiation of T cells
-Activate B cells

199
Q

Give some examples of molecules that bind to intracellular toll like receptors

A

-dsRNA
-ssRNA
-CpG DNA

200
Q

Give some examples of molecules that bind to extracellular toll like receptors

A

-Diacyl lipopeptides
-Triacyl lipopeptides
-Flagellin
-LPS

201
Q

Describe the role of antibodies in bacterial infection

A

-Opsonisation (bind Fc receptors in phagocytes)
-Complement activation (promote inflammation, opsonise, lyse using MAC)
-Bind to and neutralise toxins
-Bind to surface structures to prevent mucosal adherence

202
Q

What do defects in terminal complement components lead to?

A

Susceptibility to Neisseria spp

203
Q

What effector cell is used against bacteria surviving within phagocytes?

A

TH1

204
Q

What is the difference between normal and activated macrophages?

A

-Activated macrophages are better at phagocytosis and killing
-More efficient antigen presenting cells
-May stimulate inflammation

205
Q

What activates a macrophage?

A

-The binding of CD40 on a macrophages surface to CD40 ligand secreted by TH1 cell
OR
-IFNγ secreted by TH1 binding to its receptor on the macrophage cell surface

206
Q

Give an example of the different outcomes of a disease (in this case leprosy) depending on types of immune response

A

-Tuberculoid leprosy develops from a strong TH1 response, containing the bacteria within the skin and nerves, limiting bacterial spread.

-Lepromatous leprosy develops from a weak TH1 response, allowing the bacteria to multiply and spread throughput the body, often due to STRONGER TH2 response

207
Q

What are the innate defences against virus infected host cells?

A

Interferons (IFN⍺ and IFNβ) and Natural killer cells

208
Q

What is the action of IFN⍺ and IFNβ secreted by virus infected host cells on healthy cells?

A

-Induces resistance to viral replication in all cells by inducing Mx proteins, 2’-5’ linked adenosine oligomers and the PKR kinase
-Increases MHC class I expression and antigen presentation in all cells
-Activate dendritic cells and macrophages
-Activate NK cells to kill virus infect cells
-Induces chemokines to recruit lymphocytes

209
Q

What do natural killer cells and T cells do in response to a viral infection?

A

Secrete IFNγ which
-inhibits TH2 response and promotes TH1
-Recruits macrophages

210
Q

How do natural killer cells kill virus infected cells?

A

Kill by extracellular mechanism using perforion and granzyme

211
Q

How do Natural Killer cells distinguish between infected and uninfected host cells?

A

-Activated by carbohydrate ligand receptors, triggering lysis
-Inhibited by MHC class I molecules (only TCRs can bind)

212
Q

What are the two mechanisms of cell mediated specific immunity to viruses?

A

-Cytotoxic T cells (CD8+) recognising viral peptide
-Cytokines with antiviral activity eg IFNγ

213
Q

Describe the mechanisms by which Cytotoxic T cells may apoptosise a viral infected cell

A

-Secretion of cytotoxic granules (eg perforin, granzymes)
-Fas ligand binds to Fas receptors (CD95) on the cell surface of infected cells, triggering caspases

213
Q

In influenza, what do antibodies recognise?

A

Viral haemagglutinin and Neruaminidase

214
Q

What immune cell does HIV target?

A

CD4

215
Q

How does our body control the HIV infection?

A

-Antibodies to HIV do not seem to protect against the virus
-Instead, patient with higher levels of Cytotoxic T cell activity show slower disease progression

216
Q

How may antibodies protect against parasites?

A

-May opposonise
-Activate complement, leading to MAC formation and lysis
-ADCC (antibody dependent cell mediated cytotoxicity)

217
Q

Name some methods that pathogens have developed to evade the immune response?

A

-Concealment of antigens
-Antigenic variation
-Immunosuppression
-Interference with effector mechanisms

217
Q

What is the role of IgE antibodies in fighting parasites?

A

-Mast cell mediated inflammation
-Eosinophil antibody-dependent cell mediated cytotoxicity

218
Q

Describe how pathogens may conceal antigens

A

-Viruses may inhibit antigen presentation by MHC Class I (eg HSV)
-May occupy immune privileged sites (eg chickenpox may develop into shingles)
-May uptake host molecules, as a disguise (eg schistosomes)

219
Q

Describe how pathogens may use antigenic variation to evade the immune system

A

-They may have a large number of antigenic types (eg streptococcus pneumoniae)
-Pathogens may mutate frequently, undergoing small changes/antigenic drift and larger recombination events/antigenic shift
-Pathogens may switch on different genes at different times, producing different antigens, via genetic rearrangement

220
Q

What antigen changes in trypanosome’s gene switching to avoid the immune system?

A

Variant specific glycoprotein

220
Q

Describe how many antigens that Streptococcus pneumoniae vaccines must be active against?

A

23 capsule antigens

221
Q

Describe methods that viruses suppress the immune system

A

-Pathogens may infect immune cells directly (eg HIV infecting CD4)
-Pathogens may induce regulatory T cells, secreting immunosuppressive cytokines (IL10)

222
Q

Describe how pathogens may evade immune defences by interfering with effector mechanisms

A

-May secrete molecules that interfering with antibody function (eg IgA proteases secreted by Streptococcus pneumoniae)
-May secrete molecules interfering with complement (eg enzymes that break down C3a by pseudomonas)
-May secrete molecules by binding cytokines
-May secrete molecules that inhibit cytokine activity (eg IL10)

223
Q

Describe how host responses may contribute to immunopathology

A

-Infections may cause chronic immune cell activation, leading to granulomas
-Infections may lead to cytokines storms, where excessive cytokines are released leading to a hyper inflammatory state, damaging tissues and organs

224
Q

Describe the effects of Interferon gamma (IFNγ)

A

-Enhances expression of MHC class I, meaning more sites for TCR to bind and activate T cells
-NK cells are more likely to kill cells that lack MHC I

225
Q

Name a method of natural active immunity?

A

Natural infection

226
Q

Name a method of artificial active immunity?

A

Immunisation

227
Q

Name a method of natural passive immunity?

A

Placental transfer of maternal IgG

228
Q

Name a method of artificial passive immunity?

A

Human IgG transfusion

229
Q

Describe passive immunity

A

-Short lived
-Hypogammaglobulinaemia in infants as maternal IgG declines
-examples of artificial is Tetanus antitoxin

229
Q

Describe active immunity

A

-Exploits immunological memory
-Faster to develop, greater in magnitude, may be qualitatively better

230
Q

Describe herd immunity

A

-Disease spread is limited as a significant portion of a population becomes immune to an infectious disease
-Based on that vulnerable people are protected as those who they interact with are immune

231
Q

What are the main types of vaccines?

A

-Inactivated dead organisms
-Attenuated (live but virulence disabled)
-Subunit vaccines (protein fragments)
-Toxoid
-Conjugate something with low antigenic property with high

231
Q

Give some requirements of an effective vaccine

A

-Safe
-High level of protection
-Long lasting protection
-Correct response
-Low cost
-Easy to administer
-Stable

232
Q

Describe inactivated vaccines

A

-Made from viruses or bacteria that have been inactivated so they cannot cause disease
-Usually with heat, chemicals or radiation, so their structure is preserved
-Do not revert to virulent form, making them safe
-Require booster doses in most cases

233
Q

Describe attenuated vaccines

A

-Made from live viruses or bacteria that have been modified to replicate slowly or not at all
-Does not cause illness but gives long lasting immunity
-However must be stored correctly, and not recommended for immunocompromised individuals

234
Q

Describe subunit vaccines

A

-Contain only specific parts of a pathogen, typically proteins, sugars or other antigens
-Cannot cause disease and have a low risk of side effects
-Often requires booster doses

235
Q

Describe toxoid vaccines

A

-Specific to bacteria that release harmful toxins, preparing for neutralisation
-Inactivated toxins using heat or chemicals
-Often require emulsion in aluminium solutions

236
Q

Describe conjugate vaccines

A

-Protein carrier is linked to polysaccharide antigens so that this is more easily recognised in immunocompromised people.
-Converts TI-2 to a thymus dependent form

237
Q

What is reverse vaccinology?

A

-Using genomic information to identify potential antigens directly from the DNA sequence of a pathogen
-Removes the pathogen cultivation in a lab aspect of vaccinology
-Useful for complex pathogens that have numerous strains

238
Q

What are adjuvants?

A

-Substances added to vaccines to enhance the body’s immune response to the vaccine’s antigen
-Often aluminium in humans

239
Q

In what area of blood are antibodies found?

A

In the plasma

240
Q

What is blood serum?

A

Plasma once the blood clot has been removed

241
Q

What is serum from an immunised person/animal known as?

A

Antiserum

242
Q

What does blood antiserum contain?

A

-Antibodies that bind a certain Ag
-Other soluble blood components eg growth factors, proteins
-NO CELLS OR CLOTTING PROTEINS

243
Q

Describe the antibodies found in antiserum

A

-Many different antibodies that bind the same antigen
-Different antibodies may bind different regions (epitopes) of the same antigen

244
Q

How may different antibodies be purified from antiserum?

A

Using gel filtration chromatography or affinity chromatography

245
Q

Simplify gel filtration chromatography

A

-Separates molecules based on size
-Uses column filled with porous beads, through which molecules of different sizes pass at different rates

246
Q

Simplify affinity chromatography

A

-Separates molecules based on specific interactions between a target molecule and a ligand attached to a stationary phase (resin)
-Used to purify a certain substance

247
Q

Give some weaknesses of using antiserum in immunisation

A

-Antibodies created will never be the same
-Short lived immunity, lasting only a few weeks or months
-Limited efficacy against mutating pathogens
-Does not induce memory

248
Q

Describe the production of hybridomas

A

-Animal is IMMUNISED against an antigen
-B cells are HARVESTED and FUSED with MYELOMA cells (cancerous cells), which produce antibodies indefinitely
-Fused cells are placed in a SELECTIVE medium (HAT medium) which only allows hybridomas
-MONOCLONAL ANTIBODIES are produced

249
Q

Describe labelled antibodies

A

-Labelled using an enzyme (HRP,AP) or a fluorochrome (PE, FITC)
-Allows confirmation of the presence of antigens
-Label does not affect antibody/Ag binding

250
Q

What can you use antibodies for in research?

A

-Purifying biological molecules from a mixture using AFFINITY CHROMATOGRAPHY
-Identifying the location of a protein within a cell using IMMUNOFLUORESCENCE MICROSCOPY
-WESTERN BLOTTING
-ENZYME LINKED IMMUNOSORBENT ASSAY (ELISA)
-FLOW CYTOMETRY

250
Q

Describe secondary antibodies

A

-Secondary antibodies bind specifically to primary antibodies (which bind to the targeted antigen)
-This increases the sensitivity and reducing costs

251
Q

Describe the types of ELISA

A

-Direct ELISA (detect antigens directly with an enzyme linked antibody)
-Indirect ELISA (Uses a primary antibody to bind the antigen and a secondary enzyme linked for detection)
-Sandwich ELISA (uses two antibodies for detection: a capture immobilising antigen and a secondary enzyme linked antibody)

252
Q

Describe the steps of ELISA

A

-Plate wells are COATED with either an antibody or antigen
-Non specific sites are blocked to prevent background noise
-Sample containing the target antigen or antibody is added and allowed to bind
-Substrate specific to an enzyme is added, producing a detectable signal
-Colour intensity is measured using a spectrophotometer

253
Q

Describe the basic principles of flow cytometry

A

-Forward light scattering indicate cell size, side light scattering indicate reflects cell granularity
-Cells are passed through a laser beam, and the intensity of forward and size scattering

254
Q

Describe FACS (Fluorescence activated cell sorting) cytometry

A

Sorts cells based on fluorescent labelling, which target specific markers on the cell surface or within the cell

255
Q

Describe how we can use FACS to determine which immune cell has been examined

A

-Antibodies specific for certain molecules (eg CD3, CD4, CD8) can be conjugated with fluorescent dyes
-and used to identify the number of antibody “positive cells” in a mixed population

256
Q

Give the steps in FACS data analysis

A

-GATING select specifics cells based on FSC and SSC, reducing noise from dead or unwanted cells
-FLUORESCENCE COMPENSATION removes overlapping signal of multiple fluorophlores
-Use GATES to exclude doublets or clumped cells, ensuring only single cells are analysed
-IDENTIFY CELL POPULATIONS
-VISUALISE DATA
-QUANTIFY

257
Q

Give the biological components that make up innate immunity

A

-Physical barriers (skin, mucous membranes)
-Immune cells (macrophages, neutrophils, dendritic cells)
-Complement system
-Inflammatory responses

258
Q

Give the biological components that make up adaptive immunity

A

-Lymphocytes (T+B)
-Antibodies (produced by B cells)
-Antigen presenting cells (eg Dendritic cells)

259
Q

Give the key differences in primary and secondary immune responses

A

-Primary Response: Slower, lower intensity, and involves the generation of memory cells. Initially IgM are produced, followed by IgG and others
-Secondary Response: Faster, stronger, with a more efficient and robust immune reaction due to the presence of memory cells. IgG are produced much faster and at higher levels

260
Q

Give a summary of the three signals required to activate B cells (Signal, Source, Role)

A

Summary of the Three Signals
Signal Source Role
Signal 1: BCR Engagement, Antigen, Initial activation and antigen presentation.
Signal 2: CD40-CD40L Interaction, Th cell (CD4+), Costimulation for full activation.
Signal 3: Cytokines, Th cell (CD4+), Drives class switching and effector function.

261
Q

What are plasmacytoid dendritic cells specialised for ?

A

Specialized for recognizing viral infections via Toll-like receptors (TLR7 and TLR9)

Year 2 Semester 1 (5 decks)

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