Host Defence Mechanisms ✅ Flashcards
(103 cards)
1
Q
What type of barriers are there that prevent infection before it comes into contact with the immune system?
A
- Mechanical
- Biochemical
- Microbiological
2
Q
Give a mechanical barrier to infection
A
Skin
3
Q
Give a biochemical barrier to infection
A
Bile acid
4
Q
Give a microbiological barrier to infection
A
Host flora
5
Q
What is the main anatomical structure of the immune system?
A
The lymphoreticular system
6
Q
What does the lymphoreticular system include?
A
- Bone marrow
- Lymph nodes
- Tonsils
- Thymus
- Peyer’s patches
- Appendix
- Spleen
7
Q
What is the function of the bone marrow in the immune system?
A
Produces all cells of the immune system
8
Q
What is the function of the thymus in the immune system?
A
This is where T cells mature
9
Q
What do the cells forming the immune system differentiate from?
A
Stem cells
10
Q
Which cells differentiated from stem cells form part of the immune system?
A
- Monocytes
- Neutrophils
- Thymus
- Bone marrow
11
Q
What do monocytes develop into?
A
Tissue macrophages
12
Q
What functions do tissue macrophages carry out?
A
- Phagocytosis
- Chemotaxis
13
Q
What is attracted by chemotaxis caused by tissue macrophages?
A
Neutrophils
14
Q
What is the function of neutrophils?
A
Phagocytosis
15
Q
What can the immune system be divided into?
A
- Innate
- Adaptive
16
Q
What does the innate immune system include?
A
- Antigen non-specific immune cells
- Receptors
- Soluble effector molecules
17
Q
Give 2 soluble effector molecules in the innate immune systerm
A
- Cytokines
- Complement
18
Q
What is the purpose of the innate immune system?
A
It provides a rapid response to broad range of pathogens
19
Q
What is the limitation of the innate immune system?
A
It may not completely eradicate pathogens
20
Q
What kind of pathogens is it particularly difficult for the innate immune system to eradicate?
A
Intracellular pathogens
21
Q
What recognises invading pathogens in the innate immune system?
A
- Macrophages
- Dendritic cells
22
Q
How do macrophages and dendritic cells recognise invading pathogens in the innate immune system?
A
Using receptors called pattern recognition receptors (PRRs)
23
Q
What do pattern recognition receptors detect?
A
Classes of molecules common to groups of pathogens called pathogen-associated molecular patterns (PAMPs)
24
Q
What pattern associated molecular patterns (PAMPs) do gram -ve bacteria have?
A
Lipopolysaccharide
25
What pattern recognition receptor detects lipopolysaccharide?
TLR4
TLR = toll-like receptor
26
What PAMPs do gram +ve bacteria have?
Peptidoglycan cell wall
27
What PRR detects the peptidoglycan cell wall?
TLR2
28
What PAMPs do viruses have?
Double-stranded RNA
29
What PRR recognises double stranded RNA?
TLR3
30
What PAMP do intracellular pathogens have?
Pathogen RNA
31
What PRRs recognise pathogen RNA?
NLRP3 (nucleotide-binding oligomerisation domain (NOD)-like receptor pyrin domain containing 3)
32
What PAMPs do fungi have?
Beta-glucan
33
What PRR recognises beta-glucan?
Dectin-1
34
What happens once macrophages and dendritic cells have detected PAMPs?
They become activated and take up the pathogen by phagocytosis
35
What do activated macrophages initiate?
An acute inflammatory response
36
What is the purpose of the initiation of an acute inflammatory response by activated macrophages?
To attract neutrophils and specific antigen-presenting cells
37
What does the inflammatory cascade initiated by activated macrophages consist of?
- Pro-inflammatory cytokines
- Chemokines
- Lipids
- Complement
38
Give 3 pro-inflammatory cytokines involved in the innate immune response?
- IL-1ß
- IL-6
- TNF-⍺
39
Give a chemokine involved in the innate immune response
IL-8
40
Give 2 lipids involved in the innate immune response
- Prostaglandins
| - Leukotrienes
41
What is the effect of complement in the innate immune response?
- Can lyse pathogens directly
| - Can opsonise pathogens
42
What is the purpose of opsonisation of pathogens by complement in the innate immune response?
Assist phagocytosis by macrophages and neutrophils
43
What does the adaptive immune system consist of?
- T cells
| - B cells
44
What do B and T cells provide?
Cell-mediated and antibody-mediated immunity
45
What produces T cells?
The thymus
46
What can T cells be divided into?
- T-helper cells
| - T-cytotoxic cells
47
What do antigen-presenting cells do?
Carry antigens to regional lymph nodes
48
What do antigen-presenting cells do at regional lymph nodes?
Present antigen on major histocompatibility complex (MHC) class II receptors to T-cell receptors
49
What does the presentation of antigen on MHC class II receptors to T-cell receptors lead to?
Activation and proliferation of T-helper cells
50
What do activated T-helper cells do?
Secrete cytokines that activate T-cytotoxic cells and activate B cells
51
What do activated T-cytotoxic cells do?
Recognise and kill altered host cells, such as virus infected cells
52
What produces B cells?
The bone marrow
53
What do B cells do when they encounter antigen?
Clonally expand and terminally differentiatiate into plasma cells
54
What do plasma cells do?
Produce antibody
55
What do activated T-helper cells develop into?
- T-helper type 1 cells
- T-helper type 2 cells
- Th17
- T-regulatory cells
56
What do T-helper type 1 cells do?
- Produce pro-inflammatory cytokines
| - Activate T-cytotoxic cells, macrophages, and B cells
57
What pro-inflammatory cytokines are produced by T-helper type 1 cells?
- IL-2
| - IFN-γ
58
What do B cells activated by T-helper type 1 cells produce?
Oponising antibody (IgG)
59
What do T-helper type 2 cells do?
- Produce anti-inflammatory cytokines
| - Favour humeral response
60
What anti-inflammatory cytokines are produced by T-helper type 2 cells?
- IL-4
| - IL-15
61
What molecules are involved in the humeral response favoured by T-helper type 2 cells?
- IgM
- IgA
- IgE
62
What do Th17 cells produce?
- IL-17
| - IL-22
63
What is the role of Th17 cells?
Important role in tissue inflammation and mucosal/epithelial defences against fungal and bacterial infections
64
What is the role of T-regulatory (Tregs) cells?
- Shutting down immune responses in antigen-specific manner
| - Preventing autoimmunity
65
How do Tregs cells prevent autoimmunity?
Induce apoptosis of T-effector cells
66
How is the ability of the adaptive immune response to distinguish between antigens achieved?
By the enormous diversity of T and B cell receptors
67
How is the diversity of T and B cell receptors generated?
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
How many unique antigen receptors are produced by VDJ genes?
10^14 - 10^18
69
What happens to the antigen-specific affinity of T-cell receptors throughout the immune response?
It stays high
70
What happens to the antigen-specific affinity of B-cell receptors and antibodies over time?
They undergo affinity maturation
71
What is affinity maturation?
The process whereby the immune system generates antibodies of higher affinities during a response to antigen
72
Which type of antibody is produced early in the immune response?
IgM
73
Why is IgM produced early in the immune response?
It has a high binding capacity
74
What is the limitation of IgM?
It has a low antigen affinity and avidity
75
What is produced later in the immune response?
IgG, IgE, or IgA
76
Why does the immune response later switch to IgE, IgG, or IgM?
They have a higher affinity
77
What do T-helper cells secrete?
Cytokines
78
What is the effect of cytokines secreted by T-helper cells?
Coordinates local and systemic immune response
79
What local immune responses do cytokines coordinate?
Recruitment and activation of macrophages
80
What systemic immune response do cytokines cause?
Fever
81
What immune cells are active against intracellular organisms?
- Cytotoxic T cells
| - NK cells
82
How to cytotoxic T cells and NK cells kill intracellular organisms?
By inducing apoptosis
83
How do cytotoxic T cells and NK cells induce apoptosis?
Through the performin-granzyme system
84
What is the role of T-helper cells?
Amplifying and shutting down the immune response
85
What adaptive immune response predominates in the early phase of the immune response?
Pro-inflammatory (Th1)
86
What causes innate and adaptive immune responses to shut down?
An increase in the specificity of the humeral and cytotoxic response, shifting to a Th2-type response involving Tregs cells
87
What happens to T and B cells after the immune response is complete?
A proportion form long-lived memory cells
88
What is the purpose of memory cells?
Capable of mounting a faster and more efficient secondary response
89
When do cells of the adaptive and innate immune system develop?
Early in fetal life
90
Describe the immune state of a fetus?
Overall immunosuppressed state with Th2 bias and predominance of Tregs cells
91
Why is the fetus in an overall immunosuppressed state?
Due to the high tolerance required for maternal antigens in utero
92
To what extent are foetuses capable of mounting an immune response?
They can recognise foreign antigens and mount adaptive responses, but may be ineffective in clearing infections
93
What can result from ineffective clearance of infection by the foetal immune system?
Congenital infection
94
What protects the foetus from infection?
The placental barrier
95
When does materno-fetal IgG transfer begin?
Around 17 weeks gestation
96
When do fetal IgG levels reach half of the maternal level?
30 weeks
97
When do fetal IgG levels reach full maternal levels?
Close to term
98
What is the implication of fetal IgG levels not reaching maternal levels until near term?
Infants born prematurely are highly susceptible to infection
99
What happens to transferred maternal IgG after birth?
It declines and virtually disappears by 6 months of age
100
What happens to overall IgG levels after birth?
The infant's own IgG increases, but there is a low point around 3-6 months
101
What is the result of an infant being immunologically naive?
Symptomatic infections are more frequent and severe in the early years than at older ages
102
When is there a further period of immunosuppression in a child?
In early adolescence
103
Why is there a temporary period of immunosuppression in early adolesnce ?
Associated with the onset of sex hormone secretion
