Immunology Flashcards
1
Q
Define a pathogen
A
An organism that causes a disease, damaging the host
2
Q
Define infectious
A
A disease that may be passed or transmitted from one individual to another
3
Q
Define a carrier
A
A person who shows no symptoms when infected by a disease organism but can pass the disease to another individual
4
Q
Define a disease reservoir
A
Where a pathogen is normally found; this may be in humans or another animal and may be a source of infection
5
Q
Define an endemic
A
A disease which is always present at low levels in an area
6
Q
Define an epidemic
A
Where there is a significant increase in the usual number of cases of a disease often associated with rapid disease spread
7
Q
Define a pandemic
A
An epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people
8
Q
Define a vaccine
A
Uses non-pathogenic forms, products or antigens of micro-organisms to stimulate an immune response which confers protection against subsequent infection through memory cells
9
Q
Define antibiotics
A
Substances produced by microorganisms which affect the growth of bacteria
10
Q
Define antibiotic resistance
A
Where a microorganism which should be affected by an antibiotic is no longer susceptible to it
11
Q
Define a vector
A
A living organism which transfers a disease from one individual to another
12
Q
Define a toxin
A
A chemical produced by a pathogen which causes damage to cells and tissues of the host
13
Q
Define 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.
14
Q
Define an antigen
A
A molecule that causes the immune system to produce antibodies against it. These may be individual molecules or those on the surface of cells
15
Q
Define an antibody
A
A protein produced by immune cells (B cells) which binds to a specific antigen
16
Q
What is the name and type of the pathogen that causes cholera?
A
Vibrio cholerae, gram negative bacteria
17
Q
What is the name and type of the pathogen that causes tuberculosis?
A
Mycobacterium tuberculosis, bacterium
18
Q
What is the name and type of the pathogen that causes smallpox?
A
Virola major, virus
19
Q
What is the name and type of the pathogen that causes influenza?
A
Influenza viruses, virus
20
Q
What is the name and type of the pathogen that causes malaria?
A
Plasmodium parasites, parasite
21
Q
What is the site of infection and symptoms of cholera?
A
Toxins affect the gut lining causing a watery diarrhoea, severe dehydration and frequently death
22
Q
What is the site of infection and symptoms of tuberculosis?
A
Most commonly affects lung and neck lymph nodes. Symptoms include coughing, chest pain and coughing up blood
23
Q
What is the site of infection and symptoms of small pox?
A
Small blood vessels of the skin, mouth, throat and lungs causing a rash and blisters. 30-60% fatality rate
24
Q
What is the site of infection and symptoms of influenza?
A
Upper respiratory tract, causing a sore throat, coughing and fever
25
What is the site of infection and symptoms of malaria?
Liver and red blood cells, causing them to burst when more parasites are produced.
Symptoms include severe bouts of fever and flu-like illness, headache, muscle aches, and tiredness. Nausea, vomiting and muscle aches may also occur
26
What is the mode of transmission of cholera?
Humans act as carriers or reservoirs and can contaminate water supplies with the pathogen. The pathogen is transmitted by drinking contaminated water, although it only multiplies in the human host
27
What is the mode of transmission of tuberculosis?
Can be spread rapidly in overcrowded conditions and is transmitted through airborne droplets through coughing and sneezing of infected individuals in close proximity
28
What is the mode of transmission of smallpox?
Airborne droplets of infected individuals in close proximity
29
What is the mode of transmission of influenza?
Airborne droplets through coughing and sneezing of infected individuals in close proximity
30
What is the mode of transmission of malaria?
By a vector - a female mosquito from the genus Anopheles when feeding on the blood
31
How is cholera prevented and controlled?
Treatment of waste water, good hygiene and provision of clean drinking water. Vaccine may provide temporary protection
32
How is tuberculosis prevented and controlled?
BCG vaccine programme for children
33
How is smallpox prevented and controlled?
Now extinct due to immunisation programmes. This was possible due to low rates of antigenic variation/mutation. in addition, there was no animal reservoir and people were keen to be immunised because of devastating side effects
34
How is influenza prevented and controlled?
Quarantine and hygiene but difficult to control. Annual vaccination programmes but due to new types this is not always effective
35
How is malaria prevented and controlled?
Knowledge of life cycles. Nets, clothing and repellent
Vaccines difficult to develop
Drug treatment to reduce chances of infection
36
What is the treatment for cholera?
Antibiotic treatment is possible but oral rehydration is the main method
37
What is the treatment for tuberculosis?
A long course of antibiotics
38
What is the treatment for influenza?
Rest, keep warm, drink plenty of fluids and take painkillers
39
What is the treatment for malaria?
Drugs that affect Plasmodium outside cells are available but limited success and have side effects
40
Why are male mosquitos not vectors of the Plasmodium parasite?
Male mosquitos feed on the nectar of plants to get sugar. They do not feed off human blood like females.
41
Describe the stages of the malaria lifecycle
1. The infected mosquito takes a blood meal and the plasmodium parasite enters the blood stream
2. Plasmodium traves to and then invades liver cells, where the parasite matures
3. Liver cells rupture and release plasmodium parasites. They then invade red blood cells and multiply asexually. Red blood cells then also rupture, releasing more plasmodium parasites, which invade other red blood cells. The rupture of RBCs results in severe fever.
4. If a female mosquito feeds on the blood of an infected individual, the Plasmodium parasites infect the mosquito, which acts as a vector to pass the disease onto another host
42
Name and explain the malaria prevention methods that respond to mosquito behaviour
- **Sleep under nets**: mosquitos feed at night, prevents them biting
- **Nets are treated with the pyethroid insecticide**: pyethroid kills mosquitos
- **Spray indoor walls with insecticide**: kills mosquitos as they rest on walls after feeding
- **Drain or cover stagnant water**: removes femal mosquitos access to egg laying sites
- **Film of oil on the water**: prevents larvae piercing surface to obtain oxygen
43
Name and explain the malaria prevention methods that use biological control
- **Fish introduced into the water**: larvae are aquatic and fish eat them
- **Infecting mosquitos with bacterium**: bacteria infection blocks plasmodium development in mosquito
- **Male mosquitos sterilised with X-rays**: after they mate with females, no offspring are produced
44
Why have malaria vaccines been difficult to develop?
The plasmodium parasite has high mutation rates and there are many antigenic types
45
Describe the lytic cycle
Viruses immediately reproduce using the host's metabolism to copy their nucleic acid and synthesise new coat protein. Once new viral particles have been assembled in the host cell cytoplasm, they will leave the host cell in one of 2 ways:
**Lysis** of the host cell
**Budding** from the host cell surface
46
Describe the lysogenic cycle
Following penetration of the host cell and shedding of the capsid, the viral nucleic acid is **integrated** into the host cell genome and may remain there for many cell generations with no clinical effect. The virus then enters the lytic cycle at some time later which is when symptoms are produced
47
State the ways in which a virus can be pathogenic
1. **Cell lysis**: when viruses escape from cells to infect other cells
2. **Production of toxic substances**
3. **Cell transformation**: viral DNA can integrate into the host chromosome. If the DNA inserts into a proto-oncogene or tumor suppressor gene it can result in the cell undergoing rapid and uncontrolled cell division
4. **Immune suppression**
48
Define antibiotics
A substance produced by a fungus which diminishes the population growth of bacteria
49
What is the difference between bacteriostatic and bactericidal?
Bacteriostatic prevent the population growth of bacteria whereas bactericidal kill bacteria
50
What do broad spectrum antibiotics do?
Act against a wide range of disease-causing bacteria by targeting both gram poitive and gram negative bacterial groups
51
Whhat do narrow spectrum antibiotics do?
They are active against a selected group of bacterial types. They can act on either gram-positive or gram-negative but not both
52
Describe the bacterial cell wall structure
- Contains peptidoglycan consisting of molecules of polysacchharide cross-linked by amino acid side chains. This provides strength and prevents osmotic lysis.
- In some bacteria this cell wall is surrounded by an outer layer of lipopolysaccharides
- The Gram stain reaction highlights cells with this additional layer (Gram negative) and they retain a counter stain and appear pink/red
- The presence of this extra layer provides Gram negative bacteria with protection from some antibacterial agents such as lyzozyme and Penicillin
53
Describe how tetracycline (a broad spectrum, bacteriostatic antibiotic) works
It affects protein synthesis. Both Gram+ve and Gram-ve carry out protein synthesis
It blocks the second tRNA binding site in the large subunit of bacterial ribosomes, preventing the binding of a tRNA molecule's anticodon to its complementary codon
54
Describe how penicillin (narrow-spectrum, bactericidal antibiotic) works
Affects the formation of cross-linkages in the peptidoglycan cell wall during growth and division of bacterial cells. It does this by binding to and inhibiting the enzyme responsible for the formation of these cross linkages (transpeptidase). Penicillin binds irreversibly to transpeptidase and it is not complementary to the active site of this enzyme.
55
What type of bacteria is most susceptible to penicillin?
Gram positive is more susceptible to penicillin due to their thick peptidoglycan cell wall
56
Which type of bacteria is least effected by penicillin?
Gram negative bacteria as they only have a thin peptidoglycan cell wall and contain the outer lipopolysaccharide layer
57
What are the 2 sources of antibiotic resistant alleles?
1. Bacteria divide under optimum conditions and have a **high mutation rate**. Naturally occuring mutations that confer resistance to antibiotics give these bacteria a selective advantage in the presence of antibiotics
2. **Plasmids** containing the antiobiotic resistance allele can be transferred from one bacterium to another via conjugation
58
Why do resistant bacteria only have a selective advantage when the antibiotic is present?
If there are no antibiotics in the environment then having this resistance will not provide the bacteria with a selective advantage over bacteria without resistance. The antibiotics select for the resistant bacteria and the frequency of the resistance allele increases
59
Name 2 bacteria that are resistant to several antibiotics
1. MRSA
2. Colstridium difficile
60
How do cilliated mucous membranes act as a natural barrier?
Inhaled air is a source of microorganisms. Mucus traps them and cilia on the cilliated epithelial cells waft to bring the mucus up and out of the trachea
61
How does localised inflammation act as a natural barrier?
To localise breaks in the barrier
62
How does the skin act as a natural barrier?
A tough barrier and vitamin C is required to maintain strong connective tissue containing keratin and collagen
63
How does the skin flora act as a natural barrier?
Bacteria and fungi found on our skin offer competition for pathogenic bacteria
64
How do the tear ducts, saliva and stomach act as a natural barrier?
Lysozyme in tears and saliva hydrolyse peptidoclycan cell walls to kill bacteria. Stomach acid kills many bacteria
65
How does blood clotting act as a natual barrier?
If capillaries are broken, blood prevents the entry of pathogens
66
What is the role of phagocytosis and antigen presenting cells in the non-specific immune response?
A phagocyte engulfs a bacterium, enclosing it within a vacuole. Lysosomes fuse with this vacuole releasing hydrolytic enzymes that destroy the bacteria. These can then add the antigens to their own membrane becoming an antigen presenting cell
67
Where do B-lymphocytes originate from and mature?
Originate: stem cells in bone marrow
Mature: spleen and lymph nodes
68
Describe the humoral response
When a foreign antigen enters the blood or lymph vessels, specific B-lymphocytes bind to the foreign antigens. The B cells become activated +, stimulating clonal expansion to form:
- **Plasma cells** which secrete antibodies specific to the foreign antigen
- **Memory B cells** which remain dormant in the blood circulation ready to rapidly divide by clonal expansion to form more B lymphocytes if the same antigen is encountered in the future
69
What are antibodies and the function of them?
- Y shaped globular proteins made from 4 polypeptide chains and has 2 antigen binding sites
- Each antibody is specific to the antigen to which they bind, forming an antigen-antibody complex
- When an antigen-antibody complex is formed, the antigen is rendered inactive by processes such as agglutination which allows phagocytes to locate and engulf the pathogens
- Antibodies can also bind to toxins and undergo agglutination of toxins, rendering the toxins inactive
70
Where to T-lymphocytes originate from and become activated?
Originate: stem cells in the bone marrow
Activated: thymus gland
71
Describe the cell mediated respone
When a T lymphocyte detects a specific specific antigen on an antigen presenting cell, it id stimulated to undergo clonal expansion to form:
- T helper cells
- T memory cells
- T killer cells
72
What is the function of T helper cells?
Produce chemicals called **cytokines** which:
- stimulate more phagocytic cells to migrate to the infected tissue, which then engulf more of the pathogens and digest them
- stimulate clonal expansion of plasma B cells to make and secrete antibodies specific to that particular antigen
73
What is the funcion of T memory cells?
Remain dormant in the circulation and then divide rapidly by clonal expansion to form more T lymphocytes if the same antigen is encountered in the future
74
What is the function of T killer cells?
Destroy infected body cells by lysing the cells
75
Explain why the latency period is much shorter and the antibody production much greater in the secondary immune response
- On re-exposure to the same antigen, after a very short latent period, memory cells undergo rapid clonal expansion
- A small amount of antigen stimulates rapid production of plasma B cells
- Antibodies are made much more quickly and more concentrated than in the primary response
- The antibodies remain at high concentrations for longer and no symptoms develop
76
Define passive immunity and give an example
The body may recieve antibodies that have been produced by another individual. Protection is short lived because the antibodies are recognised as non-self and are destroyed and no memory cells are produced
Eg when antibodies are transferred to the foetus via the placenta or to the baby in breast milk
artificial when pre-synthesised antibody is injected into an individual
77
Define active immunity and give an example
The individual produces their own antibodies. Protection is long-lasting due to the production of antigen specific memory cells
Eg natural production following infection
artificial production following vaccination
78
When would antibody injections be used?
In an emergency, antibodies can be injected to provide rapid protection against a pathogen. This allows time for a person's immune system to develop an active immune response. Injections of antibodies are also used with people who do not develop a strong immune response to a vaccination or who have a weakened immune system
79
Vaccinations can be:
1. Weakened or live "attenuated"
2. Inactive or killed pathogen
3. Inactivated toxin
4. Antigens (isolated form pathogen)
5. DNA and mRNA vaccines
80
Describe how vaccines work
- Often a weakened or inactive form of the pathogen is injected into an individual
- Specific antigens on the pathogen will be detected by specific B and T lymphocytes
- B and T cells will undergo clonal expansion, triggering an immune response
- The individual may show some symptoms as their body will undergo a normal immune response to the weakened pathogen
- As part of this response, memory cells will be produced
- If the same antigen is ever encountered in the future, memory cells will undergo rapid clonal expansion
- The pathogen will be destroyed before it can produce any symptoms so the person is said to be immune
81
What are the features of a successful vaccine?
- Safe / no side effects
- Effective / trigger an immune response
82
How effective are vaccination programmes?
Pathogens that exhibit no or low levels of antigenic variation are more likely to be protected by a single round of immunisations, however pathogens with many antigenic types and that mutate frequently are more difficult to protect against. Protection against these organisms require repeated immunisation against the most common antigens, however even this isn't always effective
83
How often are people offered flu vaccines?
Annually as there are many antigenic types of influenza and new types are always occuring due to high mutation rates. Annual vaccinations contain a few strains that are predicted to be most prevalent that year
84
What is the difference between antigenic drift and antigenic shift?
Antigenic drift is small mutations whereas antigenic shift is a whole new strain
85
What is herd immunity?
If enough people in a population are vaccinated, the spread of disease is controlled so even people who are not vaccinated have some protection
86
What are some ethical considerations for vaccination programmes?
- The rights of the individual when considering mandatory compared to voluntary programmes
- Cost vs effectiveness of the vaccine
- Side effects, whether real or percieved
- Protection of the individual compared to the protection of the community
87
What do clinical trials involve?
First testing a new drug on a small number of healthy people to find out a safe dosage and look for any side effects
The drug is then tested on a larger group of patients to see how well it works
