15. Immune System Flashcards
1
Q
What is the immune system?
A
A versatile defence system that protects us from pathogenic microbes
2
Q
What are the layers of the defence strategy?
A
- First line - innate immunity
- Second line - innate immunity
- Third line - specific/adaptive immunity
3
Q
What is the first line of defence - innate immunity?
A
Physical barrier created by the skin and mucous membranes
4
Q
What is the second line of defence - innate immunity?
A
Non-specific immune response that includes some immune cells, proteins, fever and inflammation
5
Q
What is the third line of defence - specific/adaptive immunity?
A
Activated by the innate immune system, producing a response towards a specific pathogen
6
Q
What is a pathogen?
A
An infectious agent that can cause disease in a host
7
Q
How can pathogens enter the body?
A
Breaks in the skin Respiratory system Digestive system Reproductive system (male and female) Eyes
8
Q
What is an antigen?
A
A substance that can be recognised by leukocytes
9
Q
What are the two types of antigen?
A
- Foreign antigens
2. Self-antigens
10
Q
What are foreign antigens?
A
Microbes
Food
Drugs
11
Q
What are self-antigens?
A
Found on cell membranes
12
Q
What do antigens usually consist of?
A
Proteins (specific 3D shape)
13
Q
What are antibodies?
A
Proteins produced in response to a specific antigen
14
Q
What do antibodies and the specific antigens do?
A
Combine
15
Q
What makes the skin a first line of defence against pathogens?
A
Made up of layers of tightly packed epithelial cells
Outer epidermis - consists of dead epithelial cells which sheds every 40 days to remove microbes
Dermis - contains accessory structures such as sebaceous glands and sweat glands
16
Q
How does sweat perform an immune function?
A
Removes microbes from skin
Contains IgA
17
Q
How does sebum perform an immune function?
A
Contains fatty acids which inhibit microbial growth
18
Q
Where can mucous membranes be found?
A
Digestive tract
Respiratory tract
Urogenital tract
Conjunctiva
19
Q
What is the function of mucous membranes?
A
Prevent entry into the membrane
20
Q
How do the mucous membranes perform an immune function?
A
Mucous traps microbes and foreign particles
Saliva, tears and mucous secretions wash away the trapped microbes
They also contain anti-microbial substances
21
Q
How does the immune function work in the respiratory tract?
A
Mucocillary escalator
Cilia propel any foreign substances towards the pharynx where they are swallowed or coughed up
22
Q
How do tears and saliva perform an immune function?
A
Contain IgA and lyzozymes
Lyzozymes are enzymes that break down bacterial cell walls
23
Q
How does the nose perform an immune function?
A
Hairs in the nose filter air
24
Q
How does the vagina perform an immune function?
A
In menstruating women, vagina is acidic making it unfavourable for microbes
25
How does gastric acid perform an immune function?
Acidity destroys many bacteria
26
How do microflora perform an immune function?
Outcompete pathogens for attachment sites on epithelial cell surfaces (e.g. GALT)
27
How does the excretion of urine and faeces perform an immune function?
Both expel microbes
28
How does vomiting and diarrhoea perform an immune function?
Both rapid means of expelling pathogens
29
When does the second line of defence get activated?
When pathogens penetrate the physical and chemical barriers of the skin and mucous membranes
30
What does the second line of defence consist of?
```
Transferrins
Complement system
Phagocytes
Natural killer cells
Inflammation
Cytokines
Fever
```
31
What are transferrins?
Iron-binding proteins in blood
32
How do transferrins work?
Inhibit the growth of certain bacteria by reducing the amount of available iron
33
Why are transferrins necessary?
Without transferrins, bacteria would use the iron available for their growth
34
What is the complement system?
Secondary defence system made up of over 30 proteins produced by the liver
35
How are complement proteins identified?
By a letter (mostly C) and a number e.g. C3
36
How does a complement protein start out?
Inactive
| Only become active when split by enzymes into active fragments e.g. C3 = C3a and C3b
37
What happens when a complement protein is activated
Acts in a cascade
38
What is the most common mechanism through which complement proteins are activated?
Classical pathway
39
What is the 'classical pathway'?
Where antigens and antibodies join together
40
What is the role of complement proteins?
1. Promoting phagocytosis
2. Contributing to inflammation
3. Causing cytolysis
41
How do complement proteins promote phagocytosis?
The fragment C3b coats a microbe in a process called opsonisation
This promotes the attachment of a phagocyte to a microbe
42
How do complement proteins contribute to inflammation?
C3a and C5a bind to mast cells and cause them to release histamine
43
How do complement proteins cause cytolysis?
The final complement proteins join together and create a hole in the foreign cell
The hole fills with tissue fluid and makes the cell swell and rupture
44
What are cytokines?
Small protein hormones that stimulate or inhibit normal cell functions
Mediate the connection between the innate immune system and the adaptive immune system
45
What are cytokines secreted by?
Leukocytes
46
What are the types of cytokines?
Interleukins
Interferons
Tumour necrosis factor
47
What are interleukins?
Mostly produced by T-helper cells
| Mediators between leukocytes
48
What are interferons?
Anti-viral proteins produced by cells that are infected by a virus
49
What is tumour necrosis factor?
Promotes the accumulation of neutrophils and macrophages to an area
Causes cell death
50
How do interferons work?
They diffuse to uninfected neighbouring cells and induce synthesis of anti-viral proteins that interfere with viral replication
51
Do interferons stop a virus attaching to it?
No but they prevent the virus from replicating
52
What do phagocytes do?
They perform phagocytosis - cell digestion - of anything they don't recognise
Non-selective
53
How do phagocytes work?
They attach to sites of inflammation by chemotaxis
54
What is chemotaxis?
Directed migration of a cell in response to a chemical stimulus
55
What are the two major types of phagocyte?
Neutrophils
| Macrophages
56
What do neutrophils do?
First to migrate to a scene of inflammation
Like neighbourhood watch
Try to mop up the day to day problems
57
What do macrophages do?
They follow the neutrophils and eat up the remnants of whatever needs to be broken down and digested
They engulf and digest the pathogen, excrete some of the waste and display the rest on the cell membrane to present to T-lymphocytes
Like the police coming to the scene of a crime
58
Where can macrophages be found?
In tissue
59
Where can monocytes be found?
In blood
60
What do monocytes do?
Migrate to the site of infection and enlarge to form wandering macrophages
61
What do fixed macrophages do?
Stand guard in specific tissues
62
In which tissues can fixed macrophages be found?
Histiocytes (connective tissue macrophages)
Kupffer cells - liver
Microglia - nervous tissue
Alveolar - lungs
Langerhans cells - skin
Tissue macrophages - spleen, bone marrow, lymph nodes
63
What are the stages of phagocytosis?
1. Chemotaxis - release of chemicals by leukocytes, damaged tissue and activated complement that attract phagocytes
2. Adherence - attachment of phagocyte to target - aided by complement
3. Ingestion - cell membrane extends to engulf the microbe
4. Digestion - ingested structure merges with lysozymes to be digested
5. Excretion - ingested material is excreted
64
What are natural killer cells?
Non-specific lymphocytes
65
What percentage of lymphocytes do natural killer cells make up?
5-10%
66
Where can natural killer cells be found?
Blood
Lymph nodes
Spleen
Bone marrow
67
How do natural killer cells work?
They attack anything that they don't recognise including abnormal body cells e.g. cancerous cells
They bind to a target cell and release granules containing the protein perforin
68
What does perforin do?
It inserts into the cell membrane and creates a channel for tissue fluid to flow into the cell - cytolysis
69
What is inflammation?
A non-specific defensive response to tissue damage
70
What can inflammation be caused by?
```
Pathogens
Abrasions
Chemicals
Cell distortion/disturbance
Extreme temperatures
```
71
What response does inflammation create?
Non-specific
72
What are the cardinal signs of inflammation?
```
Redness
Heat
Pain
Swelling
Loss of function
```
73
What are the stages of inflammation?
1. Vasodilation and increased permeability
2. Emigration of phagocytes
3. Tissue repair
74
How does vasodilation help inflammation?
Allows additional blood, oxygen, nutrients, immune cells to get to the area
Toxins and dead cells are removed
75
How does increased permeability help inflammation?
Permits the movement of immune cells, defensive proteins (antibodies) and clotting factors into the tissue
76
How do vasodilation and increased permeability work together to help inflammation?
Together they create redness, swelling and heat
77
What is the pain of inflammation a result of?
Injury to neurons and toxic chemicals released by microbes
78
What happens when phagocytes migrate to an area?
1. Phagocytes migrate to the scene (via chemotaxis)
2. Neutrophils stick to the endothelium during vasodilation and squeeze through the vessel wall to reach the damaged area
3. Monocytes quickly follow and transform into wandering macrophages
4. Dead phagocytes accumulate pus
79
What are the types of inflammatory mediators?
Histamine
Leukotrienes
Kinins
Prostaglandins
80
What is histamine and its function?
Released by mast cells and basophils
| Causes vasodilation and increased permeability
81
What are leukotrienes and their function?
Released by basophils and mast cells
| They attract phagocytes and increase permeability
82
What are kinins and their function?
Proteins
Causes vasodilation and increased permeability
Also attract phagocytes and induce pain
83
What are prostaglandins and their function?
Lipids released by damaged cells
| Enhance effects of histamine and kinins (intensifying the pain)
84
What are the benefits of inflammation?
Promotes phagocytosis through increased temperature
Promotes immune response via vasodilation/permeability
Dilutes toxins
Fibrin formation - isolates affected area and helps bind wound edges
85
What are the harmful effects of inflammation?
Swelling - dangerous if in cranium
Pain - can become chronic
Adhesions and scar tissue
Atherosclerosis
86
What are the outcomes of inflammation?
Resolution
Chronic inflammation
Granuloma
Fibrosis
87
What is chronic inflammation?
If the injury-causing agent persists
Can cause chronic pain
Prevalence of macrophages, plasma cells and lymphocytes
88
What is granuloma?
Cellular attempt to contain a foreign body through aggregation of macrophages surrounded by lymphocytes
89
What is fibrosis?
Formation of scar tissue
Formed by the secretion of collagen by fibroblasts
Occurs as a result of chronic inflammation
90
What is a fever?
An abnormally high body temperature
91
Why does a fever occur?
Because the hypothalamus thermostat resets
92
When is a fever most likely to occur?
In infection and inflammation
93
What happens pathophysiologically during a fever?
Bacterial toxins elevate body temperature which triggers release of fever-causing cytokines e.g. interleukin-1
94
What is the key function of interleukin-1?
To induce fever
95
What does an elevated body temperature do?
Makes interferons more effective
Inhibits growth of some microbes
Speeds up the reactions that aid repair
96
What can be granular or agranular?
Leukocytes
97
Which leukocytes are classed as granular?
Basophils
Eosinophils
Neutrophils
98
Where can you find basophils?
In blood
99
Where can you find mast cells?
In tissue
100
What do basophils and mast cells do?
Release histamine and heparin
Release leukotrienes
Express receptors for IgE
101
What does histamine do?
Causes vasodilation
| Increases vessel permeability
102
What does heparin do?
Anti-coagulant
103
What do eosinophils do?
Destroy parasitic worms via phagocytosis
| Play a role in inflammation (central in asthma)
104
What do neutrophils do?
Phagocytic cell
| Granules release lysozymes that digest debris
105
Which is the most abundant leukocyte?
Neutrophils (60%)
106
Which leukocytes are classed as agranular?
Monocytes/macrophages
Natural killer cells
B and T lymphocytes
107
Where can you find monocytes?
In blood
108
Where can you find macrophages?
In tissue
109
What do monocytes/macrophages do?
Phagocytic
| Secrete cytokines e.g. IL-1 and TNF
110
What do natural killer cells do?
Target foreign cells
| Secrete perforin to induce cytosis
111
What are B and T lymphocytes?
Effector cells of the adaptive (specific) immunity
112
Which leukocytes are phagocytic?
Neutrophils
| Monocytes/macrophages
113
Name the different types of T-lymphocytes
Cytotoxic T-cells
Helper T-cells
Memory T-cells
Regulatory T-cells
114
What do helper T-cells do?
Co-ordinate the immune response (head office of FBI)
115
What do cytotoxic T-cells do?
Immune cells out in the field
116
What do memory T-cells do?
Create a memory of a pathogen after they've been exposed to it
117
What do regulatory T-cells do?
Turn off the immune response when it's finished to avoid excessive reactions
118
Where are T-cells produced/mature?
Produced in bone marrow
| Mature in the thymus
119
Name the different types of B-lymphocytes
Plasma cells
| Memory B-cells
120
Where are B-cells produced/mature?
In red bone marrow
121
Where do T-cells and B-cells function?
In the 3rd line of defence
| Adaptive (specific) immunity
122
How do T-cells and B-cells know how to respond to foreign antigens?
Through learning
| They usually can tell the difference between self and non-self antigens
123
Which sort of pathogens do T-cells and B-cells go after?
Specific ones
124
How do T-cells and B-cells know which antigens they've met before?
Through immune memory
125
What does immune memory allow T-cells and B-cells to do?
Produce a quicker and more effective attack next time they encounter the pathogen
126
When is the 3rd line of defence activated?
When the 1st and 2nd lines fail to destroy the pathogen
| Otherwise they are resting
127
What are major histocompatibility complexes?
Group of proteins on cell surface that are used by the immune system to recognise cells that are self cells vs non-self
128
What are MHCs formed from?
4 polypeptide chains
129
How do MHCs work?
They display a protein (a self-antigen) produced by the cell on its binding groove
130
How do MHCs help T-cells?
By presenting foreign antigens to T-cells
131
Name the two types of MHC
Class I Major Histocompatibility Complex (MHC-I)
| Class II Major Histocompatibility Complex (MHC-II)
132
Where can you find MHC-I?
On all body cells except erythrocytes
133
How do MHC-I work?
When body cell is cancerous or invaded by pathogen, the cell starts to produce abnormal proteins
These proteins are combined with MHC-I and displayed on the cell membrane
Flags up to (mostly) cytotoxic T-cells as a non-self antigen
134
Where can you find MHC-II?
Only on the cell membrane of 'antigen presenting cells' - macrophages and B-lymphocytes
135
How do MHC-II work?
The MHC-II displays the foreign antigen on its binding groove, having ingested the foreign cell
136
What are MHC-II specifically used for?
Communication between themselves and T-helper cells
| They present the antigen to the T-helper cells as part of antigen presentation
137
How does an antigen become associated with MHC-i or II
By the route it's trafficked through the cell
138
Which type of immunity do T-cells play a central part in?
Cell-mediated immunity
139
What is unique about T-cells?
Each has a unique T-cell receptor (TCR) that only recognises a specific antigen
140
What are T-helper cells also known as?
CD4 cells
| because they express the CD4 protein on their surface
141
What are cytotoxic T-cells also known as?
CD8 cells
142
To function properly, which traits should T-cells have?
Self-recognition - to recognise self antigens
| Self-tolerance - must lack reactivity to fragments of self antigens
143
What does a lack of self-tolerance lead to?
Autoimmunity
144
How are T-cells tested?
Against epithelial cells in thymus
| Should be able to recognise self antigens
145
What happens to T-cells if they don't recognise self antigens?
They undergo apoptosis
146
What percentage of T-cells make it through the maturing process?
1-5%
147
What is adaptive immunity?
Ability of the body to defend itself against specific foreign cells
148
What is adaptive immunity characterised by?
Specificity for particular foreign antigens
| Production of immune memory
149
What are the two types of adaptive immunity?
Cell-mediated
| Antibody-mediated
150
What is cell-mediated immunity?
Driven by T-cells
Cytotoxic T-cells directly attack specific invading antigens
Mostly against intracellular pathogens
151
What is antibody-mediated immunity?
Driven by B-cells
B-cells transform into plasma cells, which synthesise and secrete specific antibodies (Igs)
Mostly against extracellular pathogens
152
Which cells are antigen-presenting cells?
Macrophages
| B-cells
153
What happens during antigen presentation?
1. Antigen presenting cells break down the antigen into fragments (using lysozymes)
2. Some fragments are combined with MHC-II molecules on their cell membrane
3. They migrate into lymphatic tissue where they present the antigen to T-helper cells
4. Antigen fragment binds with the T-helper cell
5. T-helper cell secretes a cytokine called interleukin-2
6. Interleukin-2 causes the T-helper cell to undergo clonal selection
154
What happens during clonal selection of T-cells?
Division and proliferation of activated T-cells
155
What does the process of T-cell clonal selection produce?
1. Cytotoxic T-cells that bind to target cell and destroy it using granzymes and perforin
2. Memory T-cells - these are inactive but will recognise the antigen in the future if it appears again
3. Helper T-cells that release cytokines which increase the activity of immune cells such as T, B and NK cells
156
What do granzymes do during T-cell clonal selection?
Break down the foreign cell
157
What does perforin do during T-cell clonal selection?
Burst the foreign cell
158
Why are regulatory T-cells important?
Without them the body would continue to fight off a disease that no longer exists and could end up fighting its own cells
159
What happens during antibody mediated immunity?
1. Antigen binds to specific B-cell receptors
2. It's taken into the cell and broken down into fragments
3. Fragments are expressed on the MHC-II
4. Helper T-cells recognise the antigen complex on the B-cell membrane and stimulate it by releasing IL-2 which triggers B-cell clonal selection
160
What types of cell does B-cell clonal selection produce?
Plasma cells - secrete antibodies into blood, short lived
| Memory B-cells - remain inactive until next immune reaction, long lived
161
Which group of glycoproteins do antibodies belong to?
Globulins/immunoglobulins
162
How are antibodies structured?
4 polypeptide chains - 2 heavy, 2 light
Variable region for each type of antibody
2 antigen binding sites
163
What do antibodies combine with?
The antigen that triggered their production
164
What does the combining of an antibody with an antigen produce?
Antibody-antigen immune complex
165
How to antibodies inactivate antigens?
1. Neutralising
2. Immobilising
3. Agglutinating and precipitating
4. Activating complement
5. Enhancing phagocytosis
166
What happens when antibodies neutralise an antigen?
Neutralises bacterial toxins or prevent viral attachment to cells
167
What happens when antibodies immobilise an antigen?
Binds to it on bacterial cilia or flagellae
168
What happens when antibodies agglutinate and precipitate an antigen?
Antibodies use both of their binding sites to cause a dumping of cells
169
What happens when antibodies activate a complement?
Antigen-antibody complexes activate the complement cascade
170
What happens when antibodies enhance phagocytosis?
Antibody acts as a flag to attract phagocytes and aids phagocytosis via agglutination and complement
171
What are the 4 different types of antibodies?
IgG
IgA
IgM
IgE
172
IgG - location, how common, function?
```
Blood, lymph, intestines
Most abundant (80%)
Protects against bacteria
```
173
IgA - location, how common, function?
Sweat, tears, saliva, breast milk
10%
Localised protection of mucous membranes
Decreases with stress
174
IgM - location, how common, function?
Blood, lymph
10%
Early immune response
175
IgE - location, how common, function?
Blood
0.1%
Allergic reactions
Binds to mast cells
176
What happens during the primary response of immunological memory?
Slow response
Antibodies start to appear after several days
Slow rise in IgM, followed by IgE
177
What happens during the secondary response of immunological memory?
Faster response as a full immune response has been developed in the memory cells
Usually so quick, the pathogen is killed off before any signs and symptoms present
178
How do vaccinations help the immune system?
With immunological memory against the disease the vaccination covered
179
What do vaccinations contain?
Weakened, whole or partially-killed portions of microbes
180
What happens after a vaccination is given?
B and T-cells are activated in a primary response
| Can take several days
181
In what 4 ways can you acquire immunity?
1. Naturally acquired active immunity
2. Naturally acquired passive immunity
3. Artificially acquired active immunity
4. Artificially acquired passive immunity
182
What is naturally acquired active immunity?
Natural exposure to a disease
183
What is naturally acquired passive immunity?
Transfer of IgG antibodies across the placenta from mother to child
Transfer of IgA antibodies from mother to child via breast milk
184
What is artificially acquired active immunity?
Vaccination
185
What is artificially acquired passive immunity?
Injection with immunoglobulins e.g. snake anti-venom
186
What cells can be found in GALT?
Macrophages
| B and T-cells
187
Where can GALT be found?
Tonsils
Oesophagus
Small intestine
Large intestine
188
What is a hypersensitivity reaction?
An excessive immune response produced by the normal immune system
189
What are the 4 types of hypersensitivity?
Type I, II and III - antibody mediated
| Type IV - cell mediated
190
What is Type I hypersensitivity?
An allergy
191
What is a Type I hypersensitivity mediated by?
IgE antibodies that bind to mast cells
| Causes degranulation
192
What are the 2 types of type I hypersensitivity reactions?
Systemic e.g. anaphylaxis
| Localised e.g. hay fever, eczema, irritant contact dermatitis
193
How soon is there a Type I hypersensitivity response?
Immediate - within minutes of exposure
194
What is Type II hypersensitivity?
Blood transfusion reactions
| Haemolytic disease of the newborn
195
What is a Type II hypersensitivity mediated by?
IgG antibodies which bind to antigen and activate the complement system
196
How soon is there a Type II hypersensitivity response?
Rapid onset
197
What is a Type III hypersensitivity mediated by?
IgG
IgA
IgM antibodies
198
How soon is there a Type III hypersensitivity response?
Within 4-8 hours
199
In which pathologies does a Type III hypersensitivity reaction occur?
RA
Systemic lupus erythematosus (SLE)
Glomerulonephritis
200
What happens in a Type III hypersensitivity reaction?
Antibody-antigen complexes form and deposit in capillaries, skin, kidneys, joints etc triggering an immune response
They activate the complement system
201
What is a Type IV hypersensitivity mediated by?
Cells
202
What happens in a Type IV hypersensitivity reaction?
Overreaction of T-cells to an antigen
| Large numbers of cytotoxic T-cells activated and cytokines released that can damage normal tissue
203
How soon is there a Type IV hypersensitivity response?
48-72 hours
204
What is an allergy?
A powerful immune response to an allergen
205
What is an allergen?
An antigen that generates allergy
| Usually harmless
206
How does an immune response towards an allergy develop?
1. Initial exposure causes sensitisation
Slow response as not many cells have learnt how to respond yet to that antigen
2. Subsequent exposure has a much quicker response
The full immune response has been developed and antibodies are readily available
207
How does the body prepare for an allergen response?
Body produces IgE specially for that antigen (B-cell):
1. Plasma cells activated
2. Antibodies produced targeting that specific antigen - one side binds to the antigen, the other side to the mast cell
208
What are the symptoms of an allergy?
Runny nose
Streaming eyes
Anaphylaxis
209
What percentage of adults are affected by a food allergy?
2%
210
What percentage of children are affected by a food allergy?
6%
211
What is a food allergy?
An IgE-mediated immune response
212
How is food intolerance different to an allergy?
Food intolerance doesn't have a defined immune response
213
What is a food intolerance?
Symptoms triggered by eating a quantity of food and lacking the enzymes/probiotics/bile/HCI and other digestive factors needed to deal with the food
214
What is missing if a person is lactose intolerant?
The enzyme lactase
215
What is anaphylactic shock?
Severe, systemic, allergic response to an allergen exposure
216
How soon can anaphylactic shock appear?
Within 5-10 mins
217
What happens in the body to create anaphylactic shock?
1. Exposure to allergen causes IgE to activate mast cells and basophils
2. Histamine is released
3. Causes bronchoconstriction, vasodilation and oedema of tissue
218
Why is anaphylactic shock dangerous?
Can cause occlusion of the airways
219
What is the treatment for anaphylactic shock?
EpiPen (Epinephrine)
