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Immune System Flashcards

1
Q

What is the immune system

A

A versatile defence system that protects us from pathogenic microbes
With 3 main lines of defence

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2
Q

First line of defence

A

“Innate immunity”

Physical barrier ie skin & mucous membranes

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3
Q

Second line of defence

A

“Innate immunity”
Non-specific response when pathogens pentrate first line of defence

includes:
Complement system
Transferrins
Phagocytes
NK cells
Inflammation
Cytokines (eg interferons)
Fever

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4
Q

Third line of defence

A

“Specific/adaptive immunity”

Activated by innate immune system, producing a response towards a specific pathogen

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5
Q

What is a pathogen

A

An infectious agent that can cause disease in a host

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6
Q

What aRe antigens

A

A protein (hence specific 3D shape) with an identifiable genetic code
That can be recognised by leukocytes

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7
Q

2 main types of antigens

A
  1. Foreign (eg microbes, food, drugs)
  2. Self-antigens (present on cell membranes) - transmembrane proteins
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8
Q

What are antibodies

A

Proteins produced in response to a specific antigen
Combine with specific antigens reading identifiable code

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9
Q

Where are IgA found

A

Saliva, sweat, tears, breast milk, mucous secretions

Immunoglobulin - aka antibody - first layer of defence on surface

Stress compromised

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10
Q

How does the skin act as a first line of defence

A

Physical barrier with tightly packed epithelial cells
Outer epidermis consists of dead epithelial cells & sheds which remove microbes

Dermis contains accessory structures sebaceous & sweat glands which have immune functions

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11
Q

Immune function of sebaceous glands

A

Contains fatty acids which inhibit microbial growth as well as waterproofing the skin

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12
Q

mucous membranes as first line of defence

A

Digestive, respiratory & urogenital, conjunctiva

Contain IgA & lysozomes

Saliva, tears, mucous Wash away microbes & are antimicrobial

Mucous traps microbes & foreign bodies eg mucociliary escalator take down to stomach to be swallowed

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13
Q

What are transferrins

A

Iron-binding proteins in blood

Act to inhibit growth of certain bacteria, by reducing the amount of available iron

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14
Q

Why is excess iron problematic

A

Feeds bacteria if pathogens present
Increases favourable environment

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15
Q

What is the complement system

A

A defensive system of proteins that help to destroy microbes

made of over 30 proteins produced by the LIVER

Proteins Identified by a letter with a number eg C3
Proteins are inactive & only become active when split by enzymes into active fragments eg C3 > C3a + C3b

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16
Q

What is the classical pathway

A

Most common mechanism through which complement system is activated
Whereby antigen-antibody complexes are formed

When activated they act in a cascade -amplified

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17
Q

What is opsonisation

A

Where complement fragment C3b ‘coats’ a microbe causing phagocyte to attach

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18
Q

What complement fragments contribute to inflammation

A

C3a & C5a bind to mast cells & cause release histamine

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19
Q

What complement fragments contribute to cytolysis of a microbe

A

C5, 6,7,8,9
Join & create hole in cell, which causes it to take in fluid & ultimately bursts microbe

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20
Q

What are cytokines

A

Protein hormones that act as chemical messengers, stimulating or inhibiting immunity cell functions

Group of non-antibody proteins secreted by leukocytes

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21
Q

What are interleukins

A

Group of cytokines
Act as mediators between leukocytes

Released by macrophages

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22
Q

What are interferons

A

Grouped under cytokines
Produced by cells that are infected by a virus

Involved in anti-viral responses
Messenger tells surrounding uninfected cells to stop dividing & induce synthesis of anti-viral proteins that prevent viral replication

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23
Q

What are Tumour Necrosis Factor (TNF)

A

Grouped under cytokines

Promote accumulation of neutrophils & macrophages to cause cell death

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24
Q

Two main types of phagocytes

A
  1. Neutrophils
  2. Macrophages

Non-selective in targets
‘Antigen presenting cells’

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25
Two types of macrophages
Aka Monocytes in blood, macrophages in tissue Fixed = watch over specific tissues Wandering = migrate to sites of infection & enlarge Digests, excretes, sticks small amount onto its own cell membrane to then present to T-lymphocyte helper cells to learn specific antigens ‘Antigen presenting cells’
26
Two main antigen presenting cells
Macrophages & B-lymphocytes Present to T-lymphocytes
27
Main types of fixed macrophages & where they are found
• histiocytes - connective tissue • kupffer cells - liver & erythrocytosis • alveolar macrophages -lungs • microglia - nervous tissue • langerhans cells - skin • tissue macrophages - spleen, bone marrow & lymph nodes
28
What is a granuloma
Pathogens resistant to adherence in phagocytosis are instead surrounded by macrophages & immune cells to try & contain microbe Eg tuberculosis
29
What are NK cells
Non-specific lymphocytes Attack anything not recognised, including abnormal body cells Bind to a target cell & release granules containing protein ‘perforin’ Present in blood, lymph nodes, spleen & bone marrow
30
What is perforin
A protein released by NK granules when binding to a target cell Perforin inserts into target cell membrane & creates a channel for tissue fluid to flow into the cell = cytolysis
31
Main cardinal signs of inflammation
• redness • heat • pain • swelling • loss of function
32
How do histamine & heparin promote inflammation
Cause vasodilation & increased permeability Released by mast cells & basophils
33
Leukotrienes as inflammatory mediator
Attract phagocytes & increase vessel permeability Released by basophils & mast cells
34
Kinins as inflammation mediators
Proteins that induce vasodilation & increase permeability. They also attract phagocytes & induce ‘pain’
35
Prostaglandins as inflammatory mediators
Lipids released by damaged cells Enhance effects of histamine & kinins (& so intensify pain)
36
What does the cytokine interleukin-1 increase
A hormone protein that enters the blood & resets hypothalamus thermostat Increases body temp/induces a fever
37
Positives of elevated body temp
- makes interferons more effective - inhibits growth of some microbes - speeds up reactions that aid repair When reaching beyond 39 degrees becomes dangerous
38
Leukocytes are either
Granular or agranular
39
Most abundant leukocyte
Neutrophils 60% Phagocytic cell Release lysozomes that digest
40
What cells release histamine & heparin & roles
Basophils & mast cells Histamine = vasodilation/increase permeability Heparin = anticoagulant Involved in inflammation - easy flow to prevent stagnation Express receptors for IgE & hence involved in allergies & hypersensitivity
41
Main leukocyte involved in asthma
Eosinophils Also destroy parastitic worms via phagocytosis (less efficient cell)
42
Main antigen presenting cells
Macrophages Also b lymphocytes
43
What mediates the connection between ‘innate’ immune system & the ‘adaptive’
Cytokines & antigen presentation T & B lymphocytes are usually at rest unless activated for specific antigens
44
What is the MHC
Major Histocompatibility Complex Group of cell surface proteins that are required for recognising self-antigens vs non-self Formed of four polypeptide chains & display a protein produced by the cell (‘self’) on its binding groove Two types MHC-I MHC-II
45
Class I MHC role
Located on all body cells except erythrocytes Cell produces its own proteins that combine with MHC-I & are displayed on the cell membrane indicating whether ‘self-antigen’ If damaged/abnormal this shows in the proteins produced Allows leukocytes to differentiate between healthy body cells from abnormal/infected
46
Class II MHC role
Located only on membrane of ‘antigen presenting cells’ Eg B-lymphocytes & macrophages Displays the foreign antigen on its binding groove after ingestion to then present to T helper cells
47
What involved in cell-mediated immunity
T-cells / T-lymphocytes Each have a unique T-cell receptor CD4 receptor Produced in bone marrow but mature in thymus
48
What involved in antibody-mediated immunity
B-cells / B-lymphocytes
49
CD4 cells
CD4 protein present on surface T-helper cells & macrophages
50
CD8 cells
Cytotoxic T-cells
51
What traits are T-cells tested for in the thymus
1. Ability to recognise self-antigens 2. Not react to self-antigens “self tolerance” - loss leads to autoimmunity Tested against thymus epithelial cells Only 1-5% make through the process B-cells undergo similar screening process in bone marrow
52
Role of interleukin 2 in antigen presentation
When antigen fragment binds with T helper cell it secretes the cytokine interleukin2 This causes T-lymphocyte proliferation & stimulates “clonal selection” of B-lymphocytes This creates the active attack as well as immune memory
53
What does cell mediated clonal selection produce
1. Cytotoxic T-lymphocytes - protein digests via perforin & granzymes 2. Memory T-lymphocytes 3. Helper T-lymphocytes - release cytokines increasing immune cell activity Or suppresses when threat removed
54
Role of regulatory T-cells
De-activate immune cells when response no longer required Maintining immune system homeostasis & tolerance to self-antigens
55
Why lock and key analogy for antibodies
Because they only bind specifically with the antigen that stimulated their production “Antibody-antigen complexes” formed
56
What ways can antibodies inactivate antigens
1. Neutralising 2. Immobilising - binding 3. Agglutination & precipitating - both binding sites can cause clumping 4. Activating complement cascade 5. Enhance phagocytosis
57
Concept of a vaccine
Immunological memory is the basis Contain weakened, whole or partially dead portions of microbes - are immunogenic but not supposed to be pathogenic! B & T cells activated can take several day
58
Naturally acquired active immunity
Natural exposure to a disease
59
Naturally acquired passive immunity
Transfer of IgG antibodies across the placenta from mother to child Transfer of IgA from mother to child via breast milk
60
Artificially acquired active immunity
Vaccination Encourages bodies immune process
61
Artificially acquired passive immunity
Injection with immunoglobulins eg anti-venom for snake bite Immunity without body doing anything as remedy given
62
Hypersensitivity means
An excessive immune response produced by normal immune system
63
Hypersensitivity type I, II, III are mediated by
Antibody-mediated
64
Hypersensitivity type IIII mediated by
Cell-mediated T-cell aka cytotoxic
65
What is type 1 hypersensitivity
Aka allergy IgE antibody mediated (produced by plasma cells) that bind to mast cells causing degranulation Immediate onset/rapid Reactions eg hay fever, eczma, irritant contact dermatitis or serious reaction eg anaphylaxis & shock
66
What is type 2 hypersensitivity
As seen in blood transfusions & haemolytic disease of newborn IgG antibody mediated as can cross placenta Bind to antigens on cell surface activating complement system Rapid onset
67
What is type 3 hypersensitivity
As seens in glomerulonephritis, RA & SLE (lupus) Antibody-antigen complexes are formed and deposit in capillaries, skin, kidneys, joints which activates complement system triggering immune response eg inflammation IgG, IgM, IgA mediated Onset 4-8 hours
68
What is type 4 hypersensitivity
Involved in skin graft rejection, allergen contact dermatitis & MS Cell-mediated, over reaction of T-lymphocyte cells to an antigen Large number of CD8 (cytotoxic) & cytokines released, damagining normal tissues Delayed type, 48-72 hours
69
What is anaphylactic shock
Severe, systemic allergic response within 5-10 mins of antigen exposure IgE antibodies activate mast cells & basophils causing degranulation & histamine release Bronchoconstriction, vasodilation & oedema of tissue Danger because can occlude airways Epinephrine treatment aka adrenaline - Epipen reverses histamine
70
Structure of an antibody
Y shaped made up of 4 polypeptide chains Containing a variable region & a constant region & 2 binding grooves
71
What does antibody mediated clonal selection produce
Antigen binds to B cell where it is broken down and then expressed on the MHC-II Helper T cells recognise the antigen complex on B membrane & release interleukin 2 which triggers B-cell clonal selection Plasma cells (secrete antibodies) & Memory B cells are produced

Biomed2 (9 decks)

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