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A-Level EDUQUAS Biology > Component 3: Immunology and Disease > Flashcards

Component 3: Immunology and Disease Flashcards

1
Q

What does the innate immune system do?

A

reduces risk of infection of pathogens (prevents entry of pathogens)

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2
Q

Natural Barrier: Skin flora

A

Skin flora provides protection against pathogenic bacteria

  • compromises of bacteria and fungi
  • permanent residence, don’t cause disease
  • outcompete pathogenic strains
  • maintain low pH on the skin, preventing overgrowth of pathogens
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3
Q

Natural Barrier: Ciliated epithelial cells

A

Ciliated epithelial cells in the respiratory tract waft mucus (secreted by goblet cells that traps pathogens from inhaled air) to top of trachea, where it is swallowed into the stomach and stomach acid kills any microbes (very low pH)

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4
Q

Natural Barrier: tears, mucus and saliva

A

Tears, mucus and saliva all contain lysozymes, an enzyme that hydrolyses peptidoglycan in bacterial cell walls, killing the bacteria

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5
Q

Natural Barrier: Inflammation/Blood clotting

A

Blood clotting seals wounds and prevents entry of microbes (reducing infection)
- inflammation sets in: raising temperature so that’s unfavourable for microbe growth and increased blood flow to bring more phagocytic cells

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6
Q

Natural Barrier: Skin

A

The skin is made up of keratinised (epidermal cells) and collagen (connective tissue of dermis)
- vitamin C is essential for collagen biosynthesis, so skin is maintained by vitamin C = strong connective tissue

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7
Q

Natural Barrier: engulf and destroy

A

if microbes enter the blood phagocytes (including macrophages and neutrophils) ingest and destroy the invading microbes

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8
Q

Phagocytosis

A
  • Pathogens entering the body are phagocytosed (enter a phagocyte by endocytosis)
  • Lysosomes fuse with the vacuole containing the pathogen, releasing toxic compounds which destroy the ingested microbes - enzymes and hydrogen peroxide
  • Debris is released and antigens from the microbes are presented on the surface of the macrophage in antigen presentation which stimulates lymphocytes
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9
Q

What are B lymphocytes?

A

B lymphocytes are produced by stem cells in bone marrow and mature in the spleen and lymph nodes, have specialised receptors on the plasma membrane

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10
Q

What does the humoral response result in?

A

This response results in the production of antibodies

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11
Q

What is the process of the humoral response?

A
  • Antigen presentation causes B lymphocytes to respond with clonal selection taking place, every B lymphocyte has a unique shaped antigen receptor and whichever lymphocyte has a complementary receptor will bind to antigen, stimulating clonal expansion
  • The complementary B lymphocyte then undergoes clonal expansion, induces cloning of specific B lymphocyte by mitosis:
    · develops into plasma cells which produce antibodies with specific antigen receptors
    · also produces memory cells, divide again if same antigen returns (dormant until then)
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12
Q

Antibodies definition

A

An immunoglobulin produced by the body’s immune system in response to antigens

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13
Q

Antibody molecule

A
  • quaternary structure
  • each molecule is made up of 4 polypeptides (2 light and 2 heavy)
  • disulphide bonds
  • variable portions are specific to each antigen
  • each antibody molecule can bind to 2 antigen molecules
  • constant region binds to phagocytes
  • IgG in the most common (crosses placenta)
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14
Q

Antigens

A
  • substances that are recognised as foreign by the immune system
  • proteins, polysaccharide or glycoprotein molecules
  • stimulate an immune response
  • usually a specific shape
  • can be on the cell surface of foreign tissue such as organ transplants and transfused blood cells
  • each type of pathogen has its own unique antigens; these are genetically determined
  • can be free molecules such as toxins released by microbes
  • can be on the surface of bacteria or virus
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15
Q

What are the functions of antibodies?

A

Antibodies bind to microbes and “non-self cells”

  • Opsonisation
  • Agglutination
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16
Q

What is Opsonisation?

A

a process by which antibody molecules attached to the phagocyte makes an invading microbe more susceptible to phagocytosis

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17
Q

What is Agglutination?

A

the formation of clumps of cells as a result of the binding of specific antibodies to surface antigenic components

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18
Q

What does the cell-mediated response refer to?

A

The activation of phagocytic cells, B lymphocytes and T lymphocytes

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19
Q

What are T lymphocytes?

A

T lymphocytes are produced by stem cells in the bone marrow, migrate to the thymus to mature/be selected and develop into:

  • T suppressor cells (Ts), switch off the immune system response
  • T killer cells (Tk), which kill pathogenic cells with antigens by lysing them
  • T helper cells (Th), activates antibody response, release chemicals including cytokines to activate macrophages, B lymphocytes and other T lymphocytes (important for a response)
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20
Q

Cytokines

A
  • chemical messengers involved in activation of immune cells
  • stimulate phagocytic cells, monocytes and neutrophils to engulf and digest pathogens
  • stimulate B and T lymphocytes to undergo clonal expansion (these lymphocytes generate the cell-mediated response; B lymphocytes generate the humoral response)
  • stimulate B lymphocytes to make antibodies
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21
Q

Cell-Mediated Response Process

A
  • Phagocytes engulf microbes, destroy them and present their antigens
  • Th cells which recognise these antigens activate B lymphocytes, other T lymphocytes and macrophages
  • They do this by releasing molecules called cytokines and other chemical messengers
  • These bind to the cell membrane and activate/de-activate cells
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22
Q

Primary Immune Response

A
  • In first exposure to an antigen there is a latent period in which the invading pathogen is engulfed and destroyed by a phagocyte and the pathogens antigens being presented to the Th cells
  • Th cells activate B cells, Tk cells and macrophages (B lymphocytes which have receptors complementary to the antigen are stimulated in clonal selection to divide many times in clonal expansion
  • this means that there is a latent period where there is no response
  • also means that the immune response is specific to that pathogen/antigen
  • some of these cells differentiate into antibody producing cells (plasma cells) as well as memory cells (population of memory cells are produced)
  • antibodies are produced which clear the infection within 2-3 weeks
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23
Q

Secondary immune response

A
  • as the immune system has already encountered the pathogen before there are many memory cells present
  • quicker (shorter latent period), produces more antibodies (10-100 times than initial response) and antibodies stay in the blood for longer (no symptoms develop as levels stay high)
  • stimulated by much smaller quantities of antigen
  • this is why we vaccinate people, it leads to a secondary response which is faster and means pathogens are destroyed before they can become established and cause symptoms
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24
Q

Definition: Pathogenic

A

an organism that causes damage to its host

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25
Q

Definition: Infectious

A

a disease that may be passed or transmitted from one individual to another

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26
Q

Definition: Carrier

A

a person who shows no symptoms when infected by a disease organism but can pass the disease on to another individual

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27
Q

Definition: Disease reservoir

A

where a pathogen is normally found; this may be in humans or another animal and may be a source of infection

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28
Q

Definition: endemic

A

a disease which is always present at low levels in an area

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29
Q

Definition: epidemic

A

where there is a significant increase in the usual number of cases of a disease often associated with rapid spread

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30
Q

Definition: pandemic

A

an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people

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31
Q

Definition: antibiotics

A

substances produced by microorganisms (fungus) which diminishes the growth of bacteria

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32
Q

Definition: antibiotic resistance

A

where a microorganism, which should be affected by an antibiotic, is no longer susceptible to it

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33
Q

Definition: vector

A

a living organism which transfers a disease from one individual to another

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34
Q

Definition: toxin

A

is a chemical produced by a microorganism which causes damage to its host

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35
Q

Definition: antigenic types

A
  • organisms with the same or very similar antigens on the surface
  • such types are sub groups or strains of a microbial species which may be used to trace infections
  • they are usually identified by using antibodies from serum
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36
Q

Key term: innate immunity

A

A group of natural barriers that resist infection in several ways

37
Q

Key term: Commensal skin flora

A

Comprises many microbiota including bacteria and fungus which colonise the skin

38
Q

Key term: inflammation

A

A localised physical condition in which part of the body becomes reddened, swollen, hot and often painful especially as a reaction to injury or infection

39
Q

Key term: Phagocyte

A

A cells (such as a macrophage or neutrophil) that engulfs and consumes foreign material (such as microbes) and debris (such as dead tissue cells)

40
Q

Key term: Lysozyme

A

An enzyme that hydrolyses peptidoglycan molecules in bacterial cell walls and kills them

41
Q

Key term: Active immunity/Adaptive immune system

A

Protection of a host organism from a pathogen or toxin. It is mediated by B cells and T cells, and is characterised by immunological memory. This response is highly specific to a given antigen and is highly adaptable

42
Q

Key term: Humoral

A

This response results in the production of antibodies

43
Q

Key term: Cell mediated response

A

Lymphocytes, which along with T cells, constitute the adaptive immune system, providing a specifically targeted response to infection by producing antibodies

44
Q

Key term: Antibodies

A

An immunoglobulin produced by the body’s immune system in response to antigens

45
Q

Key term: T lymphocytes

A

Immune cells, originating in the bone marrow and maturing in the thymus, which are programmed to be specific for one particular foreign particle (antigen)

46
Q

Key term: T helper

A

Cells which activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells

47
Q

Key term: T killer

A

These are capable of killing self-cells infected with foreign pathogens and also cancer cells

48
Q

Key term: T suppressor

A

a subpopulation of T cells that suppress the immune responses

49
Q

Key term: Antigen Presentation

A

The process by which protein is presented to lymphocytes by other cells of the immune system

50
Q

Key term: Clonal Expansion

A

Production of identical daughter cells which recognise one antigen all arising from a single cell

51
Q

Key term: Agglutination

A

The formation of clumps of cells as a result of the binding of specific antibodies to surface of antigenic components

52
Q

Key term: Opsonisation

A

A process whereby molecules attached to the pathogen make an invading microorganism more susceptible to phagocytosis

53
Q

Key term: Primary Response

A

Following first exposure to an antigen there is a short latent period where populations of antigen specific T cells and B cells are produced

54
Q

Key term: Secondary Response

A

This response relies on clonal expansion of antigenic specific memory T cells and B cells. Antibodies are produced much more quickly and up to 100 more times more concentrated

55
Q

Key term: Vaccine

A

A weakened or killed pathogen, or a toxin or antigen derived from it, which stimulates the immune system to produce an immune response against it without causing infection

56
Q

Key term: Natural Active

A

A form of immunity in which the body makes its own antibodies in response to either an infection or pathogen

57
Q

Key term: Natural Passive

A

A form of immunity where the individual receives antibodies produced by another individual (e.g. tp the baby in breast milk)

58
Q

Key term: Artificial Active

A

A weakened or killed pathogen, or toxin or antigen derived from it, which stimulates the immune system to produce an immune response

59
Q

Key term: antibiotic

A

Antibiotics are used to treat bacterial diseases. Antibiotics can either prevent growth or kill bacteria. Medically affect bacterial metabolism but don’t interfere with the host cell metabolism

60
Q

Key term: Broad Spectrum Antibiotics

A

Antibiotics that affect many different gram-positive and gram negative species

61
Q

Key term: Narrow Spectrum Antibiotics

A

Antibiotics that are much more selective (e.g. penicillin G kills gram positive bacteria only)

62
Q

Key term: bacteriocidal

A

Antibiotics that kill bacteria (e.g. penicillin which destroys the cell wall)

63
Q

Key term: bacteriostatic

A

Antibiotics that prevent bacterial multiplication, but do not cause cell death (e.g. sulphonamides which are competitive enzyme inhibitors)

64
Q

Key term: peptidoglycan

A

Also referred to as murein, this structure is the main constituent of the bacterial cell wall

65
Q

Key term: Tertracyclin

A

This broad-spectrum antibiotic inhibits protein synthesis by binding to the small 30s subunit of ribosomes and blocking tRNA attachment. It is a bacteriostatic antibiotic

66
Q

Key term: Penicillin

A

This antibiotic is produced from the fungus p.notatum. It prevents the formation of the cell wall by inhibiting the enzyme DD-transpeptidase

67
Q

Key term: Antibiotic Resistance

A

A situation in which a microorganism that has previously been susceptible to an antibiotic is no longer affected by it

68
Q

Memory cells v plasma cells (differences)

A

Memory cells…
- very little cytoplasm
- don’t produce antibodies
- long lived, allow the cell to respond to another infection from the same pathogen
- the basis for immunological memory and vaccination
Plasma cells…
- these cells have a large cytoplasm
- have lots of rough endoplasmic reticulum (RER)
- produce antibodies
- die after infection is over (soon)
- not involved in vaccination

69
Q

What is active immunity?

A

The body makes its own antibodies in active immunity, stimulated by either infection or vaccination
- individual produces antibodies
- long lasting because the response produces memory cells
Natural Active Immunity
- immunity received from previous infection with the same pathogen, for example chicken pox
- pathogens like influenza and malaria get over this by changing antigens regularly (antigen variation)
Artificial active Immunity
- immunity from vaccination which generates memory cells
- the immune system generates a primary response and memory cells
- antigens, dead or weakened (attenuated) pathogens are injected

70
Q

What is passive immunity?

A
  • Body receives antibodies made elsewhere
    Natural Passive Immunity
  • immunity from the transfer of antibodies from mother to child (either from mother to foetus across placenta ot to the baby in breast milk)
  • short term immunity
  • colostrum contains high levels of IgA which is absorbed into the blood
    Artificial Passive Immunity
  • when pre-synthesised antibodies are injected into an individual (e.g. tetanus antitoxin and rabies)
  • short lived as the antibodies are quickly destroyed by host immune system (recognised as foreign and no relevant memory cells made)
71
Q

Vaccination

A
  • The products or antigens of microorganisms to stimulate an immune response which confers protection against subsequent infection
  • development of protective immunity can be maintained through exposure to a vaccine
72
Q

Effectiveness of vaccination

A

Some pathogens show a lot of variation or mutate frequently (e.g. influenza and malaria)

  • memory cells made in first exposure may not be stimulated in next exposure if virus has mutated
  • these require repeated immunisation with different vaccines each year and even then the vaccination isn’t totally effective
  • The most successful vaccines (e.g. small pox) are for pathogens with no or low levels of antigenic variation/mutation and highly immunogenic (e.g. rubella)
73
Q

What are antibiotics?

A
  • they interfere with the biochemistry of bacteria (don’t interfere with host cell metabolism)
  • they can be used without harming human cells as they target metabolic reactions in the bacterium to humans (treat without harm to the patients)
  • can’t be used against viruses or eukaryotic cells
  • viruses don’t have cell walls or the metabolic pathways seen in bacteria (protein synthesis) - absence of metabolic pathways
74
Q

Types of antibiotics?

A

Compounds that inhibit growth of bacteria are called antimicrobials there are…

  • antiseptics used on living tissue
  • disinfectants used on non-living surfaces
  • antibiotics
  • broad-spectrum antibiotics kill many different Gram-positive and Gram-negative species
  • narrow-spectrum antibiotics will only kill certain types of bacteria
  • bacteriostatic antibiotics slow down or prevent bacteria growth but don’t kill bacteria (e.g. sulphonamides which are competitive enzyme inhibitors)
  • bactericidal antibiotics kill bacteria (e.g. penicillin which destroys bacterial cell walls)
75
Q

Bacterial Cell Wall: Gram Negative Bacteria

A
  • thin layer of murein surrounded by a thick outer layer of lipoprotein and lipopolysaccharide
  • they are resistant to penicillin as they have a more complex wall structure which aids in protection
  • during colonisation the stain leaks out of the cell (crystal violet) and is removed when rinsed with ethanol
  • appear red in colour when counter-stain is added
  • e.g. Salmonella sp. and E.coli
76
Q

Bacterial Cell Wall: Gram Positive Bacteria

A
  • Cell wall contains a thick layer of peptidoglycan (murein)
  • murein is accessible to molecules outside the cell, making it more susceptible to antibiotics and lysozyme enzyme (found in tears)
  • pore in murein close during decolourisation of Gram stain protocol, crystal violet dye is retained (stains violet)
  • dye isn’t washed out by ethanol
  • counter-stain safranin turns cells purple
77
Q

Bacterial Cell Wall

A
  • Gram reaction (stain) reflects the nature of the cell wall
  • Contains peptidoglycan consisting of molecules of polysaccharides cross linked by amino acid side chains. The cross linking provides strength and the wall protects against osmotic lysis
  • The presence of extra layers protects cells from the action of some antibacterial agents such as lysosome and penicillin
78
Q

Penicillin

A
  • Penicillin affects the formation of cross linkages in the cell walls of bacteria during bacterial cell division
  • Does this by binding to and inhibiting the enzyme responsible for the formation of the cross linkages between the molecules of peptidoglycan
  • The wall is weakened so when water enters due to osmosis the bacterial cell now bursts (lysis)
  • Penicillin is less effective against gram negative bacteria as these are protected from the action of the penicillin by outer layer of lipoprotein and lipopolysaccharide
  • Penicillin is narrow spectrum (only useful against some gram positive bacteria)
  • Penicillin is bactericidal as it kills bacteria
79
Q

Tetracycline

A
  • An antibiotic that affects protein synthesis - common to all bacteria so tetracycline is a broad spectrum antibiotic
  • Acts as a competitive inhibitor of the second anti-codon binding site on the 30s subunit of bacterial ribosomes where it prevents the binding of tRNA molecule to its complementary codon
  • So tetracycline inhibits translation stages of protein synthesis so the bacteria are unable to produce enzymes and other proteins
  • Tetracycline prevents growth of the bacteria so it’s bacteriostatic
80
Q

What actions may increase likelihood of resistant bacteria?

A
  1. Prescribing antibiotics for trivial infections or viral infections
  2. People don’t complete their prescribed course of antibiotics
  3. Antibiotics being routinely used by farmers
81
Q

Overuse of Antibiotics

A
  • The overuse of antibiotics has resulted in the spread of antibiotic resistance amongst pathogenic bacteria
  • Bacteria divide rapidly under optimum conditions and they have a high rate of mutation
  • Some mutations may give resistance to antibiotics
  • Naturally occurring mutations that give antibiotic resistance have given these bacteria a selective advantage in the presence of antibiotics
  • Not affected by drugs so divide rapidly to produce a colony of antibiotic resistance
  • For example MRSA and forms of TB
82
Q

What is the last resort antibiotic?

A
  • Vancomycin is an antibiotic of last resort, used t treat highly resistant infections (very resistant strains of bacteria), however now there is some resistance to this antibiotic
  • Linezolid is the new antibiotic, but must be used sparingly
83
Q

Tuberculosis (TB)

A
  • Caused by the Gram positive bacterium, Mycobacterium tuberculosis
  • Spreads rapidly in overcrowded conditions
  • On the increase partially due to the HIV epidemic (decrease immune efficiency)
  • Most forms of TB attack lungs and lymph nodes in the neck
  • Symptoms include coughing, chest pain, fever, loss of appetite and coughing up blood
  • Transmitted by airborne droplets from infected individuals coughing or sneezing
  • Treatment involves a long course of antibiotics (however bacterium is showing resistance)
  • TB is prevented by the BCG vaccination programme for children
84
Q

Cholera

A
  • Caused by the Gram negative bacterium called Vibrio Cholerae
  • Endemic in some areas of the world
  • V.cholerae produces a toxin that affects the gut lining (violent inflammation of the mucous membrane of the gut)
  • Leads to severe dehydration (from watery diarrhoea) and frequently death
  • Humans act as reservoirs and carriers of the bacteria and contaminate water supplies in which the organism is transmitted (however only multiplies in the human host)
  • Antibiotic treatment is possible but treatment is largely by rehydration (giving patients electrolytes orally or intravenously in severe cases)
  • Cholera is prevented by the treatment of water, good hygiene and the provision of clean drinking water
  • A vaccine only provides temporary protection (killed organism or genetically engineered)
85
Q

Smallpox

A
  • Caused by a DNA containing virus called variola major
  • Virus is inhaled or transmitted in saliva or from close contact
  • Enters blood vessels in skin, mouth and throat causing rash, fluid-filled blisters (some survivors suffer blindness and limb deformities)
  • Infected people have a 30-60% chance of dying (fatality rate)
  • The only organism that humans have intentionally made extinct (outside specialist labs)
86
Q

Immunisation of smallpox?

A
  • A successful immunisation programme was based on its low rate of antigenic variation/mutation and the highly immunogenic nature of its component antigens
  • This meant that vaccines were highly effective
  • Live virus used in vaccine
  • There was no animal reservoir and people were keen to be immunised against the devastating effects of the disease
87
Q

Influenza

A
  • Influenza is caused by a virus of which are 3 main sub-groups A, B and C
  • There are many different antigenic types within each subgroup (antigenic variation)
  • Virus attacks mucous membranes (cells lining) the upper respiratory tract causing sore throat, coughing and fever
  • Prevention includes quarantine and hygiene (i.e. regular hand washing and using tissues) however the spread of influenza is difficult to control
  • Spread by droplet infection from coughs and sneezes
  • Annual vaccination programmes are available but due to antigenic variation with emergence of new types they are not always effective
  • Antibiotics are useless against the virus and are only use to treat symptoms of secondary bacterial infection
88
Q

Malaria

A
  • Malaria is caused by a protoctistan parasite called plasmodium spp
  • Mainly caused by P.falciparum and P.vivax but both within have many different antigenic types
  • Endemic in some sub-tropical regions (can become epidemics during wet seasons)
  • Organisms initially invades liver cells and then multiplies in red blood cells which burst (lysis) releasing more parasites and causing severe bouts of fever
  • Female Anopheles mosquitoes act as vectors to transmit the parasite when taking a blood meal
  • Drug treatment is available but to mainly reduce the chances of infection
89
Q

Prevention of infection

A

Methods to prevent transmission: prevent biting by use of nets, long clothing and using insect repellents
Destroying populations of the vector:
- introducing fish to eat mosquito larvae
- kill larvae by draining breeding sites or spraying the surface will oil
- adults killed with insecticides, bacterial infections or sterilisation
Vaccines have proved difficult to develop as the parasite mutates and antigenic variation

A-Level EDUQUAS Biology (24 decks)

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