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Microbiology > the immune system > Flashcards

the immune system Flashcards

(105 cards)

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1
Q

what is immunology?

A

the study of the immune system

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2
Q

what is the immune system?

A

an integrated system of cells and molecules that defends against disease and reacts against infectious pathogens

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3
Q

how can the immune system be manipulated and how can it malfunction?

A

it can be manipulated to protect us against diseases using vaccines
it can malfunction leading to immunodeficiencies, allergies, autoimmune diseases and graft rejection

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4
Q

what are immunodeficiencies?

A

susceptibility to infections because the immune system is impaired

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5
Q

what are allergies?

A

an overreaction of the immune system

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6
Q

what are autoimmune diseases?

A

diseases caused by the immune system attacking its own cells

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7
Q

what is graft rejection?

A

when transplants are rejected because the immune system recognises the cells as non-self and attacks them

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8
Q

what are immunological techniques?

A

when antibodies are used in research, diagnostics and drugs

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9
Q

what are the 2 branches of the immune system?

A

the innate immune system that we are born with
the adaptive immune system that adapts over our lifetime to the pathogens we encounter

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10
Q

where are white blood cells derived and what are the 2 lineages?

A

derived from pluripotent cells in adult bone marrow
gives rise to one lineage for myeloid cells (innate) and one for lymphoid cells (adaptive)

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11
Q

what is the innate immune system and what cells and molecules are involved?

A

it has broad specificity in recognising pathogens and isn’t improved by repeat infection because it doesn’t have a memory, it responds quickly
uses phagocytes and natural killer cells
contains soluble factors, lysozymes, the complement system and interferon proteins

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12
Q

what is the adaptive immune system and what cells and molecules are involved?

A

it is very specific in recognising pathogens, improves with repeat infections because it has memory but is slower
it uses B and T lymphocytes and antibody proteins

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13
Q

how does the skin protect against infections?

A

it secretes sebum containing fatty acids, lactic acid and lysozymes which help destroy pathogens

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14
Q

how do mucous tracts help protect against infections?

A

the epithelial cells lining the tracts contain cilia that remove debris
they produce mucous that traps pathogens

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15
Q

how do stomach cells and bacteria protect against infections?

A

cells lining the stomach release hydrochloric acid lowering the pH to prevent growth of pathogens
the natural flora of bacteria protect against pathogens

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16
Q

what are phagocytes?

A

white blood cells present in blood that can enter tissues
they are short-lived but fast acting and they take up pathogens and use lysozymes to hydrolyse them

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17
Q

what are neutrophils?

A

the most common type of phagocyte
they have granules containing specialised lysozymes

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18
Q

what are the 2 types of mononuclear phagocytes and what do they do?

A

monocytes found in the blood and macrophages found in tissues
they live longer and help initiate adaptive immune responses

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19
Q

what are microbe-associated molecular patterns (MAMPs)?

A

molecules on the surface of microbes that are recognised by pathogen-recognition receptors

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20
Q

what are natural killer cells and what are they important for?

A

a type of lymphocyte that will only kill virally infected host cells
they recognise self and non-self cells and defend against cancer

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21
Q

what is the complement system and how do they destroy pathogens?

A

a group of 20 proteins found in the blood
when the body is infected they are activated and causes bacterial cell lysis of gram-negative bacteria

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22
Q

what are defensins and how do they destroy pathogens?

A

positively charged peptides made by neutrophils
they insert into bacterial membranes and disrupt them

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23
Q

what are interferons and how do they destroy pathogens?

A

proteins produced by virally-infected cells
they bind to receptors on the surface of infected cells activating antiviral genes
they also activate macrophages and NK cells

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24
Q

what are cytokines and how do they destroy pathogens?

A

small proteins secreted from white blood cells and T cells
they bind to cells and regulate the immune system to alert the body to an infection
they cause changes in gene expression or cause cells to move to the site of an infection

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25
what is the role of inflammatory mediators and what are 2 examples?
they cause inflammation to recruit immune cells to the infected area e.g. histamine and prostaglandins
26
what is inflammation?
a localised response to infection that causes heat, redness, swelling and pain
27
what causes heat, redness and swelling when there is inflammation?
increased blood flow to the area causes heat and redness fluid leaking into the tissue causes swelling the blood vessels dilate causing redness and the capillaries become more permeable causing swelling
28
why does body temperature increase due to infection?
when the body is infected macrophages release cytokines which acts on the hypothalamus the hypothalamus increases body temperature which stimulates more phagocytosis and reduces the level of iron in the blood to slow bacterial growth
29
where do B cells originate from and where do they mature?
originate from a stem cell precursor in the bone marrow they mature in the bone marrow
30
where do T cells originate from and where do they mature?
originate from a stem cell precursor in the bone marrow mature in the thymus
31
what does it mean when a white blood cell matures?
they gain receptors that allow them to identify antigens
32
what receptors do B and T lymphocytes use?
B cells use antibodies T cells use T cell receptors
33
what is the primary and secondary (peripheral) lymphoid tissue?
primary lymphoid tissue is bone marrow and thymus secondary lymphoid tissue is lymph nodes and the spleen
34
what happens in primary and secondary (peripheral) lymphoid tissue?
primary lymphoid tissue is where lymphocytes mature secondary lymphoid tissue is where lymphocytes develop further if they encounter an antigen
35
how do B cells respond to a pathogen and which pathogens do they respond to?
they secrete antibodies into the blood they respond to extracellular bacterial and secondary viral infections
36
how do T cells respond to a pathogen and which pathogens do they respond to?
NK cells directly kill infected host cells they make cytokines they respond to intracellular bacterial and parasitic infections
37
what are antibodies?
proteins produced from B cells in response to an antigen found on the surface of a pathogen
38
what does the clonal selection theory state?
that a specific B cell recognises an antigen and when it binds to it the B cell is selected and divides to form many identical clones
39
what happens to the B cell clones?
some differentiate into plasma cells and the others stay in the body as memory cells
40
what are plasma cells?
B cells that no longer have a receptor on their surface but release soluble antibodies into the blood
41
what are memory cells?
B cells that survive in the body after infection and produce a faster immune response with a higher concentration of antibodies if they encounter the same pathogen again
42
how are plasma cells adapted to produce antibodies?
they have lots of endoplasmic reticulum
43
what is the structure of an antibody?
the 2 arms are called Fab and the tail is called Fc they are joined by a flexible region in the middle called the hinge they are made up of beta pleated sheet immunoglobulin domains
44
why is the hinge in an antibody important and what makes it flexible?
it allows the Fab arms to move relative to each other and bind to antigens far apart its immunoglobulin domains are less folded making them flexible
45
what are the 2 roles of antigens in the immune system?
antigen recognition which is where Fab regions recognise bind to lots of different types of antigens because they are variable antigen elimination which is where the Fc region binds to complement, NK cells and Fc receptors for immune response
46
what are the 4 polypeptide chains that make up antibodies and what are their molecular weights?
there are 2 light chains (25kD) and 2 heavy chains (50kD) each chain is made up of 4 immunoglobulin domains with a folded structure
47
what are the two regions of an antibody?
the variable region on the Fab arms where the antigen binds the constant region on the Fc tail
48
how are the variable and constant regions of antibodies different?
they are encoded for by separate exons
49
what happens to an antibody when it is treated with an enzyme?
it splits into 2 Fab fragments and one Fc fragment
50
what are the 5 immunoglobulin antibody classes and how are they different?
IgG, IgM, IgA, IgD and IgE the amino acids of their heavy chains are different
51
what is the role of IgG antibody?
it is the main class of antibody in serum and tissues it is involved in secondary immune response and memory it is the only class that can cross the placenta because it has a longer half life it has gamma heavy chains
52
what is the role of IgM antibody?
important in primary immune response it had micro heavy chains
53
what is the role of IgA antibody?
it is found in serum and secretions it protects mucosal surfaces it has alpha heavy chains
54
what is the role of IgD antibody?
it protects against respiratory infections it has delta heavy chains
55
what is the role of IgE antibodies?
it is present in low levels in serum protects against extracellular parasites involved in allergies it has epsilon heavy chains
56
what are the 2 different types of light chains in antibodies?
kappa and lambda they can be any class
57
what is a primary immune response and which antibodies are produced?
an immune response that is triggered when the antigen is first recognised it is slow and there is a lag phase IgG and IgM are produced
58
why is there a lag phase in the primary immune response?
it takes time for B cells to undergo clonal selection and differentiate into plasma cells
59
what is the secondary immune response and which antibodies are produced?
the immune response that is triggered when an antigen is recognised a second time it is faster more IgG antibodies are produced IgM antibodies are produced faster but in the same amount
60
why are antibodies described as being multivalent?
there are multiple binding sites for antigens because there are 2 Fab arms
61
what are the 4 ways that antibodies protect against infection?
1. neutralise toxins 2. clump microbes together to stop them moving around the body 3. surround viruses to prevent them attaching and infecting host cells 4. form complexes with bacteria so they can be engulfed by phagocytes easier
62
what are Fc effector functions?
functions carried out by the Fc regions of antibodies that evoke the innate immune systems and affect the destruction of pathogens
63
what are the Fc effector functions?
activate complement bind to Fc receptors on phagocytes, NK cells and mast cells labelling them
64
how do antibodies activate the complement system?
they trigger an enzyme cascade that causes serum proteins in the complement system to be produced
65
what are the 2 complement pathways?
the classical complement pathway where complement is activated by antibodies binding to antigens the alternative complement pathway where complement is activated by certain bacteria
66
what is the mechanism of the classical complement pathway?
each complement protein is activated individually and they act as proteases to activate the other proteins e.g. protein C3 is cleaved by C3 convertase to produce C3a and C3b peptides
67
what is needed for the classical complement pathway?
at least 1 antigen and 2 antibodies
68
how does the complement system affect phagocytosis?
it activates phagocytes to move into the tissue because C3a and C5a act as chemoattractants
69
how does the complement system induce inflammation?
C3a and C5a act as anaphylatoxins because they bind to mast cells causing a release of histamine
70
what is opsonisation and how is it carried out?
a process where opsins (e.g. C3b) bind to the surface of a pathogen labelling it allowing phagocytes to recognise the pathogen easier
71
how does the complement system cause bacterial cell lysis?
it causes the formation of the membrane attack complex which creates pores in the membrane of gram-negative bacteria
72
why are gram-positive bacteria not affected by the membrane attack complex?
they have a thick peptidoglycan layer that stops it creating pores in the membrane
73
what is the mechanism of phagocytosis?
1. the bacterium binds to the phagocyte 2. pseudopods extend from the phagocyte and fuse with the bacterium containing it in a phagosome 3. lysosomes fuse with the phagosome forming a phagolysosome 4. granules are released into the phagolysosome containing lysozymes, reactive oxygen species and competitors that destroy the bacterium
74
what is the mediate antibody dependent cell-mediated cytotoxicity (ADCC)?
a process where antibodies help natural killer cells deal with viral or intracellular bacterial infections
75
what is the mechanism of ADCC?
1. NK cells have Fc receptors on their surface that bind to the Fc region on IgG antibodies 2. the antibody binds to antigens on the host cell and secrete perforin 3. this makes pores in the host's membrane and enzymes move through the pore causing the cell to die by apoptosis
76
what is the role of mast cells?
defend against large parasites mediate allergies through anaphylaxis
77
what happens when someone with an allergy encounters the allergen?
1. they produce IgE antibodies against the allergen that bind to Fc receptors on mast cells under mucosal surfaces 2. the mast cells are sensitised but they are only activated when the person comes back into contact with the allergen 3. when this happens the Fc receptors crosslink triggering the mast cells to release granules by degranulation 4. degranulation releases inflammatory mediators such as histamine
78
what is antisera?
a serum containing antibodies usually from animals such as rabbits or sheep
79
how is antisera produced?
1. the protein of interest is purified and injected into the animal to produce a primary immune response 2. the immune response is boosted so the animal produced lots of IgG antibodies against the protein 3. a sample of blood is taken from the animal and left to clot to remove the serum containing the antibodies
80
what is conventional/polyclonal antisera?
antisera produced against a protein that could be recognised by different types of B cells and could produce many different antibodies from different plasma cells
81
what are the disadvantages of using antisera?
it lacks specificity and is difficult to standardise because the animal's response can vary
82
what are monoclonal antibodies?
antibodies that are specific to a single epitope (the shape an antibody binds to) and derived from a single B cell clone
83
how are monoclonal antibodies collected?
1. an animal such as a mouse is immunised with an antigen 2. a tumour cell line (that can divide indefinitely) is fused with the B cell to form hybrid cells 3. the hybrid cell that produced the antibodies specific to the antigen are selected
84
what are the advantages of monoclonal antibodies?
they are easy to standardise and the cells can divide indefinitely so there is a constant supply
85
what are the 2 types of T cell?
T helper cells that are CD4 positive cytotoxic T cells that are CD8 positive
86
what are the roles of T helper cells?
help B cells make antibodies activate macrophages and NK cells help the development of cytotoxic T cells
87
what is the role of cytotoxic T cells?
recognise and kill infected host cells
88
what is the structure of T cell receptors (TCRs)?
it is the same for both T helper an cytotoxic T cells made up of an alpha chain and a beta chain they have a hydrophobic fatty acid chain at their C terminus that helps them stay in the membrane
89
what are the 2 domains in a T cell receptor?
the domain closest to the membrane is the constant domain the domain furthest from the membrane is the variable domain where the antigen binds
90
what is the difference between antigens recognised by B cells and antigens recognised by T cells?
B cells recognise soluble or free antigens that are native (haven't been processed) T cell recognise cell-associated antigens that have been broken down into smaller peptides
91
what is the role of major histocompatibility (MHC) proteins?
to bring molecules within a cell to the cell surface so they can be recognised by T cells
92
what are MHC proteins encoded by?
the major histocompatibility gene complex located on chromosome 6
93
how can major histocompatibility proteins cause the body to reject skin grafts?
they are polymorphic so there are many different alleles at each locus on the gene each person's MHC proteins are different so they can be rejected
94
what are the 2 types of MHC proteins?
MHC1 expressed by all nucleated cells and display antigens to cytotoxic T cells MHC2 expressed on macrophages, dendritic cells and B cells and display antigens to T helper cells
95
how are molecules moved to the cell surface using MHC protein 1?
1. cytotoxic T cells recognise a peptide bound to MHC 1 and bind to it 2. viral proteins within the infected host cell are broken down into peptides in the cytosol by proteosomes 3. the peptides exit the cytosol and are transported into the endoplasmic reticulum by MHC 1 4. the peptides are expressed on the cell surface as an antigen
96
what happens when cytotoxic T cells bind to peptides expressed on the surface of a cell?
the cytotoxic T cell binds to the peptide and is activated causing the infected host cell to die by by apoptosis
97
how are molecules moved to the cell surface by MHC protein 2?
1. helper T cells recognise a peptide bound to MHC 2 and bind to it 2. the macrophage/dendritic cell/B cell breaks down viral proteins in the cytosol into peptides by proteases 3. the peptides bind to MHC 2 and are carried to the cell surface in endosomes
98
what happens when helper T cells bind to peptides expressed on the surface of a cell?
the helper T cell binds to the antigen and is activated causing B cell to produce antibodies, cytokines to be created and leucocytes to be selected in the thymus
99
what happens during thymic selection?
a T cell enters the thymus and matures (gains its T cell receptor) it undergoes selection to ensure that the T cell only recognises self-MHC peptides and not self peptides the T cells that recognise self peptides die by apoptosis
100
what are cytokines?
small secretory proteins that act on other immune cells to change their behaviour they are involved in cell to cell communication during an immune response can be secreted by a wide range of cells
101
where are cytokines produced and where do they act and why is this important?
they are produced and act locally this is important because they cause inflammation which could harm other parts of the body
102
how do cytokines target cells?
they bind to specific cytokine receptors on the surface of target cells
103
what are the 5 main types of cytokine?
interleukins: act between leucocytes, made by T cells interferons: interfere with viral replication, respond to viral infections chemokines: cause white blood cells to move by chemotaxis tumour necrosis factor: promotes inflammation, can kill cancer cells colony stimulating factors: cause leucocyte production
104
how would the adaptive immune system respond to a cut in the skin?
1. dendritic cells or macrophages would recognise and take up the bacteria 2. they would induce inflammation to increase the flow of lymph to the infection 3. the dendritic cell/macrophage displaying the antigen would enter the secondary lymphoid tissue and T helper cells would bind to it 4. this would cause production of cytotoxic T cells and cause B cells to differentiate into plasma cells and produce antibodies
105
what are the 3 types of vaccine?
attenuated vaccine: live viruses that have been weakened killed pathogen vaccine: pathogen is killed by chemicals or heat subunit vaccine: a component of the virus is treated to weaken it

Microbiology (9 decks)

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