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► Med Misc 39 > *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
What are antibody heavy and light chain proteins encoded for by?
Segmented genes in the germ-line genome of haematopoietic stem cells
26
What happens to gene segments as individual B cells develop?
They randomly rearrange (this also happens in TCR alpha and beta chains in developing T cells)
27
How is there more antibodies in the human body that there are entire genes in the human genome?
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)
28
What type of lymphoid tissues do adaptive immune responses occur in?
Secondary lymphoid tissues
29
What do mature antigen-specific T cells and B cells constantly re-circulate between?
Different primary lymphoid tissues, the blood and lymphatic vessels
30
Where are mature dendritic cells, pathogens, antigens, debris, etc. trapped?
In secondary lymphoid tissues (lymph in lymph nodes, blood in spleen)
31
What are the 2 different zones within lymph nodes?
T cell zone | B cell zone (around the edges)
32
What happens if after several days of being in the lymph node, T cells and B cells don't encounter their specific antigen?
They return to the blood system
33
How do antigens from a pathogen enter a lymph node?
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
What do stromal cells do to opsonised antigens in the B cell zone?
Trap them
35
How many signals does B cell activation require?
2
36
What are the 2 signals that B cells must receive to be activated by a protein antigen?
BCR + antigen | T cell help
37
What are the 2 signals that B cells must receive to be activated by any antigen?
BCR + antigen | PRR + PAMP
38
What are the 2 signals that B cells must receive to be activated by antigens with repetitive antigenic epitopes?
Multiple | BCRs + antigens engaged
39
What are the only peptide antigens that T cells can recognise?
Those presented by MHC
40
What do MHC proteins do?
Display peptide antigens to T cells
41
What are MHC proteins also referred to as?
Human Leucocyte antigens (Human leucocyte antigens)
42
What are the 2 classes of MHC proteins?
Class I MHC | Class II MHC
43
``` What is class I MHC expressed on? What does it do? ```
All nucleated cells | Presents peptide antigens to cyctotoxic T cells
44
What is Class II MHC expressed on? | What does it do?
Only expressed on professional antigen presenting cells (dendritic cells, macrophages and B cells) Present peptide antigens to helper T cells
45
How many signals does T cell activation require?
2
46
What are the 2 signals required for B cell activation?
Signal 1 = MHC peptide and TCR | Signal 2 = B7 and CD28
47
What happens once B cells are activated?
They undergo clinical expansion and differentiate into memory B cells and plasma effector B cells
48
What type of antibody is produced by B cells which are activated by protein antigen: BCR and PRR:PAMP? Are memory cells produced
Low affinity, antigen-specific IgM | No memory cells
49
What type of antibody is produced by B cells which are activated by protein antigen: BCR and T helper cells? Are memory cells produced
High affinity, antigen-specific antibodies (IgM initially and then all types) Memory cells are produced
50
What is the most abundant Ig in plasma?
IgG
51
How amen subtypes of IgG are there?
4
52
What type of Ig is actively transported across the placenta?
IgG
53
What is the second most abundant Ig type?
IgA
54
Where is IgA found? (4)
Monomeric form = blood | Dimeric form = breast milk, saliva, tears, mucosal secretions
55
How do mothers provide protective antibodies to their young?
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
What is the first Ig to be produced during an immune response?
IgM (present only in plasma/ secretion)
57
Where is IgD found?
Extremely low levels in blood
58
Where is IgE found? | What is it produced in response to?
Extremely low levels normally | Produced in response to parasitic infections and allergic responses
59
What is the constant region of the heavy chains of an antibody called?
Fc
60
What are the 2 purposes of antibodies?
Binding to antigens | Clearance mechanisms mediated by interaction of Fc region with effector molecules (complement, Fc receptors)
61
What does the binding of high affinity neutralising antibodies to viruses prevent?
The virus infecting host cells | Microbial toxins from disrupting normal cell function
62
What complement pathway can antibodies activate?
The classical complement pathway
63
What 3 molecules can act as opsonins?
C3b CRP Antibodies
64
How do bacteria opsonised by antibodies bind to phagocytes?
Through Fc receptors that bind to the constant region of the Ig
65
How can antibody binding cause NK cells to kill target cells
Antibody-dependent Cell-mediated Cytotoxicity
66
How can IgE lead to allergic responses?
IgE binds an allergen and then binds to a mast cell via an Fc receptor This causes degranulation
67
What is the name of helper T cells when they are resting and not effector cells?
CD4+ cells
68
What is the name of cytotoxic T cells when they are resting and not effector cells?
CD8+ cells
69
What 2 things cause CD4+ to become Th?
Peptide | MHC II
70
What 2 things cause CD8+ cells to become Tc?
Peptide | MHC I
71
What is the purpose of T helper cells?
To help stimulate other immune cells (CD8+, macrophages, B cells through cytokines and direct cell contact)
72
How do Th cells stimulate CD8+?
Through IL-2
73
How do effector Th cells help macrophages?
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
How do effector Th cells help B cells?
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
What is the germinal centre response?
B cell proliferation Antibody heavy chain switching Generation of high affinity antibodies Differentiation into Plasma cells and Memory B cells
76
What happens to effector cytotoxic T cells?
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
What is immunological memory? | What type of memory cells are produced?
``` 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 ```

► Med Misc 39 (38 decks)

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