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1. Immunology > The Adaptive Immune System > Flashcards

The Adaptive Immune System Flashcards

1
Q

What are the three main features of the adaptive immune system?

A

It responds to a specific pathogen

It has a ‘memory’ of specific antigens

It improves upon re-exposure

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2
Q

What is an antigen?

A

A molecule that provokes an immune response

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3
Q

What does the adaptive system require to become activated?

A

It requires the innate system

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4
Q

What are the cells of the adaptive immune system?

A

Lymphocytes

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5
Q

What are the two different types of lymphocytes?

A

B and T

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6
Q

How does the adaptive system response differ upon re-exposure?

A

It will be more rapid and more intense

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7
Q

Where do both types of lymphocytes originate from?

A

From progenitors in the bone marrow

Their precursor cell is the common lymphoid precursor

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8
Q

Where do B-cells mature?

A

In the bone marrow

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9
Q

Where do T-cells mature?

A

In the thymus

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10
Q

What does maturing mean in terms of lymphocytes?

2

A

Forming of a receptor

Gaining the ability to recognise and respond to specific antigens

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11
Q

What are cells called before they have matured?

A

Immature

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12
Q

What percentage of cells that go to the thymus die?

A

98%

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13
Q

What is it called when cells audition to become T cells?

A

T-cell education

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14
Q

What happens if a cell fails to become a T cell?

A

It is killed

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15
Q

What happens if a cell succeeds in becoming a T cell?

A

It enters the medulla

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16
Q

How many copies of its receptor does each lymphocyte have?

A

about 104 to 106 receptors

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17
Q

What is the receptor on a T cell called?

A

a T-cell receptor

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18
Q

What is the receptor on a B cell called?

A

a B cell receptor

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19
Q

What is present as the receptor on B cell?

A

antibodies

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20
Q

What are the two types of T cells?

A

Killer T cells

Helper T cells

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21
Q

What is the ratio between helper T cells and killer T cell?

A

You have twice as many helpers as you do killers

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22
Q

How are T cell receptors made?

A

They are made by a totally random process of gene shuffling

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23
Q

How do B cell receptors work?

2

A

The antibody molecule can be reproduced many times

These antibodies can be released from the cell at a distance

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24
Q

What are lymphocytes called after they have gotten their receptors?

A

Naive cells

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25
Q

What happens to lymphocytes once they have become naive cells?

A

They travel to the lymph nodes, spleen or other lymphoid organs to await activation

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26
Q

Describe the structure of the T-cell receptor.

4

A

Made of 2 polypeptide chains

Usually an alpha and a beta chain

Rarely a gamma and theta chain

Has variable regions that dictate what it will bind to

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27
Q

Describe the structure of an antibody.

A

Made of 4 protein chains

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28
Q

What type of cell secretes antibodies?

A

Plasma cells

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29
Q

What is the process by which clonal lymphocytes form?

A

Clonal expansion

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30
Q

What is clonal expansion?

A

The process by which a lymphocyte with the correct receptor replicates to form clonal lymphocytes

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31
Q

How do T cells become activated?

A

T cells need antigen presenting cells to show them their target

32
Q

Name the three antigen presenting cells.

A

Dendritic cells

Macrophages/monocytes

B-cells

33
Q

How does antigen presentation work?

4

A

The antigen presenting cells phagocytose pathogens

The pathogens are killed and chopped up into peptides

The antigen presenting cell display peptide fragments of the pathogens on their surfaces

The antigen presenting cell then approaches the T cells and if its receptor binds to the peptide the T cell will become activated

34
Q

What does MHC stand for?

A

Major Histocompatibility Complex

35
Q

Why do T cells need MHC molecules?

A

antigen presenting cells need to present their pathogen’s peptide in an MHC molecule to the T cells

36
Q

Why are T cells known as MHC restricted cells?

A

Because T cells can only recognise antigens in the context of MHC

37
Q

Where does antigen presentation and T-cell activation usually occur?

A

In peripheral lymphoid organs such as lymph nodes

38
Q

What happens when an APC takes up a pathogem?

A

It becomes activated and migrates to a regional lymph node

39
Q

What is the main function of lymph nodes?

A

They act as organising centres for immune responses

40
Q

How does an APC know it has made contact with a pathogen?

3

A

APCs have pattern recognition receptors on their surface

These are called Toll Like Receptors (TLRs)

TLRs recognise specific pathogen associated molecular structures (PAMS)

41
Q

What are the receptors on APCs called?

A

Toll Like Receptors

42
Q

What does PAMS stand for?

A

Pathogen associated molecular structures (PAMS)

43
Q

What does TLR stand for?

A

Toll like receptors

44
Q

Give some examples of PAMS.

A

LPS

Double stranded RNA

Flagellin

45
Q

What happens to an antigen presenting cell when a toll like receptor is activated?
(2)

A

The APC becomes activated

This allows it to migrate to a lymph node and interact with T cells

46
Q

Is antigen presentation needed for memory cells?

A

Yes

47
Q

What are killer cells also called?

A

Cytotoxic cells

48
Q

What do killer T cells do?

3

A

They kill virus infected cells

They kill tumour cells

Apoptosis

49
Q

What do helper T cells do?

2

A

They secrete cytokines to react with other cells

They help B cells make antibodies

50
Q

What CD molecules are always expressed by T cells?

A

CD3

51
Q

What CD molecules are always expressed by helper T cells?

A

CD4

52
Q

What CD molecules are always expressed by killer T cells?

A

CD8

53
Q

What type of cell is needed to activate a killer T cell?

A

Any nucleated cell

MHC class 1

54
Q

What type of cell is needed to activate a helper T cell?

A

APC

MHC class 2

55
Q

What is an epitope?

A

A specific amino acid sequence from an antigen

56
Q

Can B cells activate without T cell help?

A

Yes

But their function is limited

57
Q

How exactly does a B cell activate without the help of a T cell?
(5)

A

If more than one antibody reacts with the epitopes on an antigen they will become cross linked

This cross linking activates the B cell

B cell then becomes a plasma cells

Plasma cell can now secrete antibodies

However, it will only make IgM antibodies (1/5 types)

58
Q

Explain how a helper T cell activates a B cell

4

A

A B cell has a peptide (its an APC) and its trying to find a T cell

If a Helper T cell recognise the peptide it can provide cytokines to the B cell

These cytokines help the B cell make antibodies

This also allows memory B cells to be made

59
Q

What are antibodies?

2

A

Soluble versions of the B cell receptor

Immune proteins synthesized and released by plasma cells

60
Q

What are antibodies also called?

2

A

Gamma globulins

Immunoglobulins (Igs)

61
Q

Describe the structure of an antibody.

4

A

4 protein chains - 2 identical light chains and 2 identical heavy chains

Chains held together by disulphide bridges

2 regions - fab region (fragment with antigen binding) and the Fc region (fragment that is crystallisable)

Two binding sites for antigens

62
Q

What are the two regions in an antibody?

A

Fab region

Fc region

63
Q

What is the fab region of an antibody?

A

Fragment with antigen binding

64
Q

What is the Fc region of an antibody?

A

Fragment that is crystallisable

65
Q

How many different types of antibodies are there?

A

Five

66
Q

What are the five different types of antibodies?

A

IgM

IgA

IgD

IgG

IgE

67
Q

What does each variable region of an antibody contain?

A

An antigen-binding site

68
Q

What are the four main ways antibodies deal with antigens?

A

Precipitation/agglutination

Lysis

Neutralization

Opsonisation

69
Q

Explain precipitation

A

Occurs when antibodies bind their soluble targets into clumps

70
Q

Explain agglutination.

A

Occurs when antibodies cause clumping of insoluble particles

Something insoluble is bound up by antibodies

71
Q

What is the function of precipitation/aglutination?

A

This sequesters the target and increases the likelihood of phagocytosis

Something soluble is bound up by antibodies

72
Q

Explain how antibodies use lysis.

5

A

Antibodies bind to a bacterium

The complement system is activated

Complement proteins form a MAC

This perforates the bacterial cell membrane

Cell lyses

73
Q

Explain how antibodies are involved in neutralisation of antigens.
(3)

A

Antibodies bind to their target and interfere with the pathogen function

Antibody interferes with viral entry into host cell

Antibody binds to toxins and renders them inactive

74
Q

How are antibodies involved in opsonisation?

2

A

Antibodies bind to pathogens

This marks out pathogens for phagocytes

75
Q

How long is the lag period after the initial encounter until antibody production?

A

It takes 5-7 days

76
Q

What happens ten days after an initial encounter?

A

Plasma antibody levels peak and begin to decline

77
Q

How is the memory response greater than the initial response?
(4)

A

A shorter lag time-

Plasma cells that last longer-

Higher Antibody levels achieved more quickly-

Higher efficiency of binding between Antigens & Antibodies

1. Immunology (9 decks)

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