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Study Notes - Principles > *Immunology 3 (lectures 5 and 6) > Flashcards

*Immunology 3 (lectures 5 and 6) Flashcards

1
Q

What is an antigen?

A

An substance which can cause an adaptive immune response by activating B cells and T cells

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2
Q

Where are T cells and B cells found?

A

Constantly circulate through the blood, lymph and secondary lymphoid tissues
Inactive until meet an antigen

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3
Q

What is the purpose of B cells?

A

Key role in defence against intracellular pathogens via production of antibodies

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4
Q

Purpose of T cells?

A

Key role in defence against intracellular pathogens (viruses, mycobacteria)

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5
Q

What are the 2 different types of T cells?

A

Helper T cells

Cytotoxic T cells

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6
Q

What is the role of helper T cells?

A

Key regulators of the entire immune system

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7
Q

What is the role of cytotoxic T cells?

A

kill virally infected body cells

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8
Q

How do T cells recognise antigens?

A

Through their T cell antigen receptor

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9
Q

What is the T cel antigen in terms of proteins?

What chains does it have?

A

Membrane-Bound protein heterodimer
1 X Alpha chain
1 X beta chain

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10
Q

How does B cells recognise antigens?

A

Through their b cell antigen receptor

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11
Q

What are B cell antigen receptors?

What chains does this have?

A

Membrane bound antibody (IgM or IgD)
2 X light chains
2 X heavy chains

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12
Q

What is another name for antibodies?

A

Immunoglobulins

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13
Q

What are antibodies?

A

proteins that are produced by B cells in response to an antigen and which bind specifically to that particular antigen

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14
Q

What are the 2 different forms of antibodies?

A

Those expressed on the surface of B cells

Those secreted as soluble proteins in extracellular fluids

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15
Q

What type of pathogens do antibodies provide defence against?

A

Extracellular pathogens (most bacteria, viruses and toxins)

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16
Q

What type of regions do both the heavy and light chains have on immunoglobulins?

A

Constant regions

Variable regions

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17
Q

Does the constant region or the variable region form the antigen binding site?

A

Variable region

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18
Q

What are the 5 different types of antibodies that exist?

What makes them different?

A 
IgM
IgG
IgA
IgE
IgD
Different heavy chain constant regions
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19
Q

Heavy chain constant region of IgM?

A

μ heavy chain

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20
Q

Heavy chain constant region of IgG?

A

γ heavy chain

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21
Q

Heavy chain constant region of IgA?

A

α heavy chain

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22
Q

Heavy chain constant region of IgE?

A

ε heavy chain

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23
Q

Heavy chain constant region of IgD?

A

δ heavy chain

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24
Q

What is the epitope?

A

the part of an antigen molecule to which an antibody attaches itself

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25
Q

What are antibody heavy and light chain proteins encoded for by?

A

Segmented genes in the germ-line genome of haematopoietic stem cells

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26
Q

What happens to gene segments as individual B cells develop?

A

They randomly rearrange (this also happens in TCR alpha and beta chains in developing T cells)

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27
Q

How is there more antibodies in the human body that there are entire genes in the human genome?

A

There is radom rearrangement of the segments of genes that code for antibody heavy and light chain proteins in individual developing B cells (a similar process also occurs in developing T cells)

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28
Q

What type of lymphoid tissues do adaptive immune responses occur in?

A

Secondary lymphoid tissues

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29
Q

What do mature antigen-specific T cells and B cells constantly re-circulate between?

A

Different primary lymphoid tissues, the blood and lymphatic vessels

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30
Q

Where are mature dendritic cells, pathogens, antigens, debris, etc. trapped?

A

In secondary lymphoid tissues (lymph in lymph nodes, blood in spleen)

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31
Q

What are the 2 different zones within lymph nodes?

A

T cell zone

B cell zone (around the edges)

32
Q

What happens if after several days of being in the lymph node, T cells and B cells don’t encounter their specific antigen?

A

They return to the blood system

33
Q

How do antigens from a pathogen enter a lymph node?

A

Particles and antigens derived from pathogens are release by phagocytes
The pathogen also releases inflammatory TNF alpha that stimulates immature tissue-resident dendritic cells to express B7
Dendritic cells phagocytose these (by joining via PPR and PAMP)
Dendritic cells digests pathogen-derived protein and display small peptides on surface in complex with MHC proteins
Pathogen derived particles, antigens and mature dendritic cells travel to local draining lymph nodes

34
Q

What do stromal cells do to opsonised antigens in the B cell zone?

A

Trap them

35
Q

How many signals does B cell activation require?

A

2

36
Q

What are the 2 signals that B cells must receive to be activated by a protein antigen?

A

BCR + antigen

T cell help

37
Q

What are the 2 signals that B cells must receive to be activated by any antigen?

A

BCR + antigen

PRR + PAMP

38
Q

What are the 2 signals that B cells must receive to be activated by antigens with repetitive antigenic epitopes?

A

Multiple

BCRs + antigens engaged

39
Q

What are the only peptide antigens that T cells can recognise?

A

Those presented by MHC

40
Q

What do MHC proteins do?

A

Display peptide antigens to T cells

41
Q

What are MHC proteins also referred to as?

A

Human Leucocyte antigens (Human leucocyte antigens)

42
Q

What are the 2 classes of MHC proteins?

A

Class I MHC

Class II MHC

43
Q 
What is class I MHC expressed on?
What does it do?
A

All nucleated cells

Presents peptide antigens to cyctotoxic T cells

44
Q

What is Class II MHC expressed on?

What does it do?

A

Only expressed on professional antigen presenting cells (dendritic cells, macrophages and B cells)
Present peptide antigens to helper T cells

45
Q

How many signals does T cell activation require?

A

2

46
Q

What are the 2 signals required for B cell activation?

A

Signal 1 = MHC peptide and TCR

Signal 2 = B7 and CD28

47
Q

What happens once B cells are activated?

A

They undergo clinical expansion and differentiate into memory B cells and plasma effector B cells

48
Q

What type of antibody is produced by B cells which are activated by protein antigen: BCR and PRR:PAMP?
Are memory cells produced

A

Low affinity, antigen-specific IgM

No memory cells

49
Q

What type of antibody is produced by B cells which are activated by protein antigen: BCR and T helper cells?
Are memory cells produced

A

High affinity, antigen-specific antibodies (IgM initially and then all types)
Memory cells are produced

50
Q

What is the most abundant Ig in plasma?

A

IgG

51
Q

How amen subtypes of IgG are there?

A

4

52
Q

What type of Ig is actively transported across the placenta?

A

IgG

53
Q

What is the second most abundant Ig type?

A

IgA

54
Q

Where is IgA found? (4)

A

Monomeric form = blood

Dimeric form = breast milk, saliva, tears, mucosal secretions

55
Q

How do mothers provide protective antibodies to their young?

A

IgG through the placenta (levels decrease when the baby is born = transiently low IgG between 3 months and a year when the baby is still making own)
Dimeric IgA through breast milk

56
Q

What is the first Ig to be produced during an immune response?

A

IgM (present only in plasma/ secretion)

57
Q

Where is IgD found?

A

Extremely low levels in blood

58
Q

Where is IgE found?

What is it produced in response to?

A

Extremely low levels normally

Produced in response to parasitic infections and allergic responses

59
Q

What is the constant region of the heavy chains of an antibody called?

A

Fc

60
Q

What are the 2 purposes of antibodies?

A

Binding to antigens

Clearance mechanisms mediated by interaction of Fc region with effector molecules (complement, Fc receptors)

61
Q

What does the binding of high affinity neutralising antibodies to viruses prevent?

A

The virus infecting host cells

Microbial toxins from disrupting normal cell function

62
Q

What complement pathway can antibodies activate?

A

The classical complement pathway

63
Q

What 3 molecules can act as opsonins?

A

C3b
CRP
Antibodies

64
Q

How do bacteria opsonised by antibodies bind to phagocytes?

A

Through Fc receptors that bind to the constant region of the Ig

65
Q

How can antibody binding cause NK cells to kill target cells

A

Antibody-dependent Cell-mediated Cytotoxicity

66
Q

How can IgE lead to allergic responses?

A

IgE binds an allergen and then binds to a mast cell via an Fc receptor
This causes degranulation

67
Q

What is the name of helper T cells when they are resting and not effector cells?

A

CD4+ cells

68
Q

What is the name of cytotoxic T cells when they are resting and not effector cells?

A

CD8+ cells

69
Q

What 2 things cause CD4+ to become Th?

A

Peptide

MHC II

70
Q

What 2 things cause CD8+ cells to become Tc?

A

Peptide

MHC I

71
Q

What is the purpose of T helper cells?

A

To help stimulate other immune cells (CD8+, macrophages, B cells through cytokines and direct cell contact)

72
Q

How do Th cells stimulate CD8+?

A

Through IL-2

73
Q

How do effector Th cells help macrophages?

A

Th cells migrate from lymph node into sites of infection/ inflammation
The cells are re-activated by macrophages in an antigen-specific manner
The cells express co-stimulatory molecules and hyper-activate macrophages enhancing their killing activities and pro-inflammatory responses (through IFNgamma)

74
Q

How do effector Th cells help B cells?

A

Protein antigen bound to BCR is internalised by the B cell
Antigen is degraded and peptides are presented on the B cell surface in complex with MHC-IIEffector Th cells move into B cell zone of the Lymph node where they are re-stimulated by B cells in an antigen-specific manner and start to express CD40L
Re-activated effector Th cells stimulate the B cell to proliferate and survive (via CD40L : CD40 interactions)
Effector Th cells secrete cytokines that further activate the B cell and stimulate the Germinal Centre response

75
Q

What is the germinal centre response?

A

B cell proliferation
Antibody heavy chain switching
Generation of high affinity antibodies
Differentiation into Plasma cells and Memory B cells

76
Q

What happens to effector cytotoxic T cells?

A

they exit lymph nodes, migrate to sites of infection, recognise and kill infected tissue cells in an antigen specific manner (target cells die by apoptosis)

77
Q

What is immunological memory?

What type of memory cells are produced?

A 
Once the adaptive immune system has recognised and responded to a specific antigen, it exhibits life-long immunity to this antigen
Memory Th cells
Memory Tc cells
Memory B cells
Long-lived plasma cells

Study Notes - Principles (39 decks)

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