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TAS Infection And Immunity ✅ > Host Defence Mechanisms ✅ > Flashcards

Host Defence Mechanisms ✅ Flashcards

1
Q

What type of barriers are there that prevent infection before it comes into contact with the immune system?

A
  • Mechanical
  • Biochemical
  • Microbiological
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2
Q

Give a mechanical barrier to infection

A

Skin

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3
Q

Give a biochemical barrier to infection

A

Bile acid

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4
Q

Give a microbiological barrier to infection

A

Host flora

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5
Q

What is the main anatomical structure of the immune system?

A

The lymphoreticular system

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6
Q

What does the lymphoreticular system include?

A
  • Bone marrow
  • Lymph nodes
  • Tonsils
  • Thymus
  • Peyer’s patches
  • Appendix
  • Spleen
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7
Q

What is the function of the bone marrow in the immune system?

A

Produces all cells of the immune system

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8
Q

What is the function of the thymus in the immune system?

A

This is where T cells mature

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9
Q

What do the cells forming the immune system differentiate from?

A

Stem cells

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10
Q

Which cells differentiated from stem cells form part of the immune system?

A
  • Monocytes
  • Neutrophils
  • Thymus
  • Bone marrow
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11
Q

What do monocytes develop into?

A

Tissue macrophages

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12
Q

What functions do tissue macrophages carry out?

A
  • Phagocytosis

- Chemotaxis

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13
Q

What is attracted by chemotaxis caused by tissue macrophages?

A

Neutrophils

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14
Q

What is the function of neutrophils?

A

Phagocytosis

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15
Q

What can the immune system be divided into?

A
  • Innate

- Adaptive

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16
Q

What does the innate immune system include?

A
  • Antigen non-specific immune cells
  • Receptors
  • Soluble effector molecules
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17
Q

Give 2 soluble effector molecules in the innate immune systerm

A
  • Cytokines

- Complement

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18
Q

What is the purpose of the innate immune system?

A

It provides a rapid response to broad range of pathogens

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19
Q

What is the limitation of the innate immune system?

A

It may not completely eradicate pathogens

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20
Q

What kind of pathogens is it particularly difficult for the innate immune system to eradicate?

A

Intracellular pathogens

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21
Q

What recognises invading pathogens in the innate immune system?

A
  • Macrophages

- Dendritic cells

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22
Q

How do macrophages and dendritic cells recognise invading pathogens in the innate immune system?

A

Using receptors called pattern recognition receptors (PRRs)

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23
Q

What do pattern recognition receptors detect?

A

Classes of molecules common to groups of pathogens called pathogen-associated molecular patterns (PAMPs)

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24
Q

What pattern associated molecular patterns (PAMPs) do gram -ve bacteria have?

A

Lipopolysaccharide

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25
Q

What pattern recognition receptor detects lipopolysaccharide?

A

TLR4

TLR = toll-like receptor

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26
Q

What PAMPs do gram +ve bacteria have?

A

Peptidoglycan cell wall

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27
Q

What PRR detects the peptidoglycan cell wall?

A

TLR2

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28
Q

What PAMPs do viruses have?

A

Double-stranded RNA

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29
Q

What PRR recognises double stranded RNA?

A

TLR3

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30
Q

What PAMP do intracellular pathogens have?

A

Pathogen RNA

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31
Q

What PRRs recognise pathogen RNA?

A

NLRP3 (nucleotide-binding oligomerisation domain (NOD)-like receptor pyrin domain containing 3)

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32
Q

What PAMPs do fungi have?

A

Beta-glucan

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33
Q

What PRR recognises beta-glucan?

A

Dectin-1

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34
Q

What happens once macrophages and dendritic cells have detected PAMPs?

A

They become activated and take up the pathogen by phagocytosis

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35
Q

What do activated macrophages initiate?

A

An acute inflammatory response

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36
Q

What is the purpose of the initiation of an acute inflammatory response by activated macrophages?

A

To attract neutrophils and specific antigen-presenting cells

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37
Q

What does the inflammatory cascade initiated by activated macrophages consist of?

A
  • Pro-inflammatory cytokines
  • Chemokines
  • Lipids
  • Complement
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38
Q

Give 3 pro-inflammatory cytokines involved in the innate immune response?

A
  • IL-1ß
  • IL-6
  • TNF-⍺
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39
Q

Give a chemokine involved in the innate immune response

A

IL-8

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40
Q

Give 2 lipids involved in the innate immune response

A
  • Prostaglandins

- Leukotrienes

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41
Q

What is the effect of complement in the innate immune response?

A
  • Can lyse pathogens directly

- Can opsonise pathogens

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42
Q

What is the purpose of opsonisation of pathogens by complement in the innate immune response?

A

Assist phagocytosis by macrophages and neutrophils

43
Q

What does the adaptive immune system consist of?

A
  • T cells

- B cells

44
Q

What do B and T cells provide?

A

Cell-mediated and antibody-mediated immunity

45
Q

What produces T cells?

A

The thymus

46
Q

What can T cells be divided into?

A
  • T-helper cells

- T-cytotoxic cells

47
Q

What do antigen-presenting cells do?

A

Carry antigens to regional lymph nodes

48
Q

What do antigen-presenting cells do at regional lymph nodes?

A

Present antigen on major histocompatibility complex (MHC) class II receptors to T-cell receptors

49
Q

What does the presentation of antigen on MHC class II receptors to T-cell receptors lead to?

A

Activation and proliferation of T-helper cells

50
Q

What do activated T-helper cells do?

A

Secrete cytokines that activate T-cytotoxic cells and activate B cells

51
Q

What do activated T-cytotoxic cells do?

A

Recognise and kill altered host cells, such as virus infected cells

52
Q

What produces B cells?

A

The bone marrow

53
Q

What do B cells do when they encounter antigen?

A

Clonally expand and terminally differentiatiate into plasma cells

54
Q

What do plasma cells do?

A

Produce antibody

55
Q

What do activated T-helper cells develop into?

A
  • T-helper type 1 cells
  • T-helper type 2 cells
  • Th17
  • T-regulatory cells
56
Q

What do T-helper type 1 cells do?

A
  • Produce pro-inflammatory cytokines

- Activate T-cytotoxic cells, macrophages, and B cells

57
Q

What pro-inflammatory cytokines are produced by T-helper type 1 cells?

A
  • IL-2

- IFN-γ

58
Q

What do B cells activated by T-helper type 1 cells produce?

A

Oponising antibody (IgG)

59
Q

What do T-helper type 2 cells do?

A
  • Produce anti-inflammatory cytokines

- Favour humeral response

60
Q

What anti-inflammatory cytokines are produced by T-helper type 2 cells?

A
  • IL-4

- IL-15

61
Q

What molecules are involved in the humeral response favoured by T-helper type 2 cells?

A
  • IgM
  • IgA
  • IgE
62
Q

What do Th17 cells produce?

A
  • IL-17

- IL-22

63
Q

What is the role of Th17 cells?

A

Important role in tissue inflammation and mucosal/epithelial defences against fungal and bacterial infections

64
Q

What is the role of T-regulatory (Tregs) cells?

A
  • Shutting down immune responses in antigen-specific manner

- Preventing autoimmunity

65
Q

How do Tregs cells prevent autoimmunity?

A

Induce apoptosis of T-effector cells

66
Q

How is the ability of the adaptive immune response to distinguish between antigens achieved?

A

By the enormous diversity of T and B cell receptors

67
Q

How is the diversity of T and B cell receptors generated?

A

By random association of genes for the constant parts of the receptor chains with one of a large number of variable, diversity and joining (VDJ) region genes

68
Q

How many unique antigen receptors are produced by VDJ genes?

A

10^14 - 10^18

69
Q

What happens to the antigen-specific affinity of T-cell receptors throughout the immune response?

A

It stays high

70
Q

What happens to the antigen-specific affinity of B-cell receptors and antibodies over time?

A

They undergo affinity maturation

71
Q

What is affinity maturation?

A

The process whereby the immune system generates antibodies of higher affinities during a response to antigen

72
Q

Which type of antibody is produced early in the immune response?

A

IgM

73
Q

Why is IgM produced early in the immune response?

A

It has a high binding capacity

74
Q

What is the limitation of IgM?

A

It has a low antigen affinity and avidity

75
Q

What is produced later in the immune response?

A

IgG, IgE, or IgA

76
Q

Why does the immune response later switch to IgE, IgG, or IgM?

A

They have a higher affinity

77
Q

What do T-helper cells secrete?

A

Cytokines

78
Q

What is the effect of cytokines secreted by T-helper cells?

A

Coordinates local and systemic immune response

79
Q

What local immune responses do cytokines coordinate?

A

Recruitment and activation of macrophages

80
Q

What systemic immune response do cytokines cause?

A

Fever

81
Q

What immune cells are active against intracellular organisms?

A
  • Cytotoxic T cells

- NK cells

82
Q

How to cytotoxic T cells and NK cells kill intracellular organisms?

A

By inducing apoptosis

83
Q

How do cytotoxic T cells and NK cells induce apoptosis?

A

Through the performin-granzyme system

84
Q

What is the role of T-helper cells?

A

Amplifying and shutting down the immune response

85
Q

What adaptive immune response predominates in the early phase of the immune response?

A

Pro-inflammatory (Th1)

86
Q

What causes innate and adaptive immune responses to shut down?

A

An increase in the specificity of the humeral and cytotoxic response, shifting to a Th2-type response involving Tregs cells

87
Q

What happens to T and B cells after the immune response is complete?

A

A proportion form long-lived memory cells

88
Q

What is the purpose of memory cells?

A

Capable of mounting a faster and more efficient secondary response

89
Q

When do cells of the adaptive and innate immune system develop?

A

Early in fetal life

90
Q

Describe the immune state of a fetus?

A

Overall immunosuppressed state with Th2 bias and predominance of Tregs cells

91
Q

Why is the fetus in an overall immunosuppressed state?

A

Due to the high tolerance required for maternal antigens in utero

92
Q

To what extent are foetuses capable of mounting an immune response?

A

They can recognise foreign antigens and mount adaptive responses, but may be ineffective in clearing infections

93
Q

What can result from ineffective clearance of infection by the foetal immune system?

A

Congenital infection

94
Q

What protects the foetus from infection?

A

The placental barrier

95
Q

When does materno-fetal IgG transfer begin?

A

Around 17 weeks gestation

96
Q

When do fetal IgG levels reach half of the maternal level?

A

30 weeks

97
Q

When do fetal IgG levels reach full maternal levels?

A

Close to term

98
Q

What is the implication of fetal IgG levels not reaching maternal levels until near term?

A

Infants born prematurely are highly susceptible to infection

99
Q

What happens to transferred maternal IgG after birth?

A

It declines and virtually disappears by 6 months of age

100
Q

What happens to overall IgG levels after birth?

A

The infant’s own IgG increases, but there is a low point around 3-6 months

101
Q

What is the result of an infant being immunologically naive?

A

Symptomatic infections are more frequent and severe in the early years than at older ages

102
Q

When is there a further period of immunosuppression in a child?

A

In early adolescence

103
Q

Why is there a temporary period of immunosuppression in early adolesnce ?

A

Associated with the onset of sex hormone secretion

TAS Infection And Immunity ✅ (14 decks)

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