Cells (Immunity) - Types of Immunity and Vaccination

Question 1

What is an antigen?

Answer 1

A molecule which is recognised as foreign by the immune system and goes on to trigger an immune response. Lymphocytes are activated that produce antibodies against the antigen.

Question 2

What is a lymphocyte?

Answer 2

Type of white blood cell responsible for the immune response. They become activated in the presence of antigens. There are two types: B lymphocytes and T lymphocytes.

Question 3

What is a phagocyte?

Answer 3

Type of white blood cell which carries out a non-specific immune response and ingests and breaks down pathogens by phagocytosis.

Question 4

What is phagocytosis?

Answer 4

Mechanism by which phagocytes engulf particles to form a vesicle or a vacuole.

Question 5

What is a lysosome?

Answer 5

Contain enzymes called lysozymes which they release into the phagosome which hydrolyse the bacterium.

Question 6

What is a phagosome?

Answer 6

A vesicle formed as the bacterium is engulfed by the phagocyte. The lysosome release their lysozymes into the phagosome.

Question 7

What is antigen-presentation?

Answer 7

When an antigen-presenting cell e.g. phagocyte displays foreign antigens on their own cell-surface membrane.

Question 8

What is cell-mediated immunity?

Answer 8

The type of response when T lymphocytes respond to antigens that are presented on a body cell.

Question 9

What are T-cells?

Answer 9

Cells which mature in the thymus and are associated with cell-mediated immunity.

Question 10

What is clonal selection?

Answer 10

As the receptor on a helper T cell attaches to the antigen this activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells. These cloned T cells stimulate B cells to divide and form a clone of identical B cells all of which produce the antibody that is specific to the foreign antigen.

Question 11

What are Th cells (helper T cells)?

Answer 11

Contain receptors which respond to a single antigen. Many different types of T cell, each one responds to a different antigen.

Question 12

What are Tc cells (cytotoxic T cells)?

Answer 12

Kill abnormal cells and body cells that are infected by pathogens by producing a protein called perforin which makes holes in the cell-surface membrane.

Question 13

What is humoral immunity?

Answer 13

The type of response which involves B lymphocytes and antibodies.

Question 14

What are B cells?

Answer 14

Each type of B cell produces a specific antibody that responds to one specific antigen.

Question 15

What are plasma B cells?

Answer 15

When the B cell is activated to divide by mitosis it gives a clone of plasma cells which produce and secrete the specific antibody that exactly fits the antigen on the pathogen’s surface.

Question 16

What is an antibody?

Answer 16

A protein with specific binding sites produced by B cells in response to the presence of appropriate antigen.

Question 17

What are memory B cells?

Answer 17

Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies as part of the secondary response.

Question 18

What are monoclonal antibodies?

Answer 18

Antibodies produced by a single clone of cells.

Question 19

What is a primary response?

Answer 19

Caused by initial response to the antigen which involves the production of antibodies and memory cells.

Question 20

What is a secondary response?

Answer 20

Caused by second exposure to the antigen. Memory cells are responsible for this response – they divide rapidly and develop into plasma cells (which secrete many antibodies quickly) and more memory cells.

Question 21

What is passive immunity?

Answer 21

Passive immunity is produced by the introduction of antibodies into individuals from an outside source. No direct contact with the pathogen or its antigen is necessary to induce immunity. Immunity is acquired immediately. As the antibodies are not being produced by the individuals themselves, the antibodies are not replaced when they are broken down, no memory cells are formed and so there is no lasting immunity.

Question 22

What is active immunity?

Answer 22

Active immunity is produced by stimulating the production of antibodies by the individuals’ own immune system. Direct contact with the pathogen or its antigen is necessary. Active immunity is due to memory B cells and antibodies which are typically long lasting. Immunity takes time to develop and is generally long lasting.

Question 23

What is natural immunity?

Answer 23

A type of active immunity resulting from an individual becoming infected with a disease under normal circumstances. The body produces its own antibodies and may continue to do so for many years.

When an organism is infected by a pathogen for the first time, the body mounts a primary immune response. This leads to the development of immunological memory.

Question 24

What is artificial immunity?

Answer 24

A type of active immunity that forms the basis of vaccination (immunisation). It involves inducing an immune response in an individual without them suffering symptoms of the disease.

Question 25

What is a vaccination?

Answer 25

Vaccination is the introduction of the appropriate disease antigens into the body, either by injection or by mouth. The intention is to stimulate an immune response against a particular disease. The material introduced is called a vaccine and, in whatever form, it contains one or more types of antigen from the pathogen. These antigens stimulate the immune response. The response is slight because only a small amount of antigen has been introduced. However, the crucial factor is that memory cells are produced. These remain in the blood and allow a greater, and more immediate, response to a future infection with the pathogen. The result is that there is a rapid production of antibodies and the new infection is rapidly overcome before it can cause any harm and with few, if any, symptoms.

Question 26

What is herd immunity?

Answer 26

Herd immunity arises when a sufficiently large proportion of the population has been vaccinated which makes it difficult for a pathogen to spread within that population. The concept is based on the idea that pathogens are passed from individual to individual when in close contact. Where the vast majority of the population is immune, it is highly improbable that a susceptible individual will come in contact with an infected person. In this way, those individuals who are not immune to the disease are nevertheless protected.

Question 27

What is antigenic variability?

Answer 27

A vaccine stimulates the primary immune response, and produces memory cells against a specific antigen. It assumes that if there is a second infection, then the same antigen will be present on the pathogen.

However, pathogens may mutate frequently so that its antigens change suddenly rather than gradually which means vaccines become ineffective because the new antigens on the pathogen are no longer recognized by the immune system. This can be caused by mutations or horizontal transfer of plasmids containing new genes.

When these pathogens infect a second time, the memory cells are ineffective and a new primary immune response needs to be generated.

Question 28

What is the ELISA test?

Answer 28

Enzyme linked immunosorbent assay which uses antibodies to detect the presence and quantity of a protein in a sample.

Question 29

What is an antibiotic?

Answer 29

A substance produced by living organisms that can destroy or inhibit the growth of microorganisms.

Question 30

What are examples of passive immunity?

Answer 30

Anti-venom given to the victims of snake bites and the immunity acquired by the fetus when antibodies pass across the placenta from the mother.

Question 31

What are the features of a successful vaccination programme?

Answer 31

• A suitable vaccine must be economically available in sufficient quantities to immunise most of the vulnerable population.
• There must be few side-effects, if any, from vaccination. Unpleasant side-effects may discourage individuals in the population from being vaccinated.
• Means of producing, storing and transporting the vaccine must be available. This usually involves technologically advanced equipment, hygienic conditions and refrigerated transport.
• There must be the means of administering the vaccine properly at the appropriate time. This involves training staff with appropriate skills at different centres throughout the population.
• It must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity.

Question 32

What is the importance of herd immunity? How can it be achived?

Answer 32

Herd immunity is important because it is never possible to vaccinate everyone in a large population. For example, babies and very young children are not vaccinated because their immune system is not yet fully functional. It could also be dangerous to vaccine those who are ill or have compromised immune systems. The percentage of the population that must be vaccinated in order to achieve herd immunity is different for each disease. To achieve herd immunity, vaccination is best carried out at one time. This means that, for a certain period, there are very few individuals in the population with the disease and that transmission of the pathogen is interrupted.

Question 33

Why may vaccination not eliminate a disease?

Answer 33

• Vaccination fails to induce immunity in certain individuals, for example people with defective immune systems.
• Individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent it. These individuals may harbour the pathogen and reinfect others.
• The pathogen may mutate frequently, so that its antigens change suddenly rather than gradually. This means that vaccines suddenly become ineffective because the new antigens on the pathogen are no longer recognised by the immune system. As a result, the immune system does not produce the antibodies to destroy the pathogen. This antigenic variability happens with the influenza virus. which changes its antigens frequently. Immunity is therefore short-lived and individuals may develop repeated bouts of influenza during their lifetime.
• There may be so many varieties of a particular pathogen that it is almost impossible to develop a vaccine that is effective against them all. For example, there are over 100 varieties of the common cold virus and new ones are constantly evolving.
• Certain pathogens ‘hide’ from the body’s immune system, either by concealing themselves inside cells, or by living in places out of reach, such as within the intestines, for example, the cholera pathogen.
• Individuals may have objections to vaccination for religious, ethical or medical reasons. For example, unfounded concerns over the measles, mumps and rubella (MMR) triple vaccine has led a number of parents to opt for separate vaccinations for their children, or to avoid vaccination altogether.

Question 34

What are the ethics of using vaccines?

Answer 34

• The production of existing vaccines, and the development of new ones, often involves the use of animals. How acceptable is this?
• Vaccines have side-effects that may sometimes cause long-term harm. How can the risk of side effects be balanced against the risk of developing a disease that causes even greater harm?
• The vaccine must be tested on humans first to determine toxicity. On whom should vaccines be tested? How should such trials be carried out? To what extent should individuals be asked to accept risk in the interests of public health?
• Is it acceptable to trial a new vaccine with unknown health risks only in a country where the targeted disease is common, on the basis that the population there has more to gain if it proves successful?
• To be fully effective the majority, and preferably all, of the population should be vaccinated. Is it right, in the interests of everyone’s health, that vaccination should be compulsory? If so, should this be at any time, or just when there is a potential epidemic? Can people opt out? If so, on what grounds: religious belief, medical circumstances, personal belief?
• Should expensive vaccination programmes continue when a disease is almost eradicated, even though this might mean less money for the treatment of other diseases?
• How can any individual health risks from vaccination be balanced against the advantages of controlling a disease for the benefit of the population at large?

Question 35

How do vaccinations work?

Answer 35

Vaccinations introduce the antigen to the person’s body without causing the disease. The body will make memory cells against the antigen.

Question 36

What are the different types of vaccination?

Answer 36

A vaccination must contain the antigen but not cause the disease.

• attenuated pathogen: weakened live pathogen
• dead pathogen: whole cell
• subunit vaccine: mixture of correct antigens
• toxoid: altered toxin made harmless

Question 37

What is the difference between natural and artificial immunity?

Answer 37

• Natural active immunity arises from being exposed to an antigen/getting the disease whereas natural passive immunity is the result of crossing of mother’s antibodies through the placenta and their presence in breast milk.
• Active artificial immunity is acquired through vaccinations which stimulate the immune system and lead to production of antibodies whereas passive artificial immunity is where antibodies are injected into the body.

Question 38

What are vaccines?

Answer 38

Vaccines are a way of introducing a pathogen into the body in order to produce an immune response. The pathogen may be dead of inactivated, but the antigens on its surface will still produce an immune response. This is an example of active immunity and results in the creation of memory B cells which will be able trigger a rapid secondary immune response should the same pathogen ever be detected again.

Question 39

What is a weakness of active artificial immunity?

Answer 39

An individual may need to obtain booster vaccinations after a period of time to revitalise immunity. For some vaccines, the immunological memory fades after a certain amount of time.

Question 40

When is passive artificial immunity used?

Answer 40

When an individual needs immediate treatment. Once injected, the antibodies can quickly identify the pathogen to eliminate the infection.

Question 41

What is natural active immunity?

Answer 41

An individual develops a disease, and the immune system make antibodies and memory cells.

Question 42

What is natural passive immunity?

Answer 42

A mother passes on antibodies to a baby (e.g. through the placenta).

Question 43

What is artificial active immunity?

Answer 43

A vaccination injects an inactive pathogen to activate an immune response and antibody production.

Question 44

What is artificial passive immunity?

Answer 44

Injection of antibodies from another animal.

Question 45

What is the importance of vaccination?

Answer 45

• Upon infection, given enough time, our bodies can itself gain active immunity against a pathogen by developing an immune response.
• The process of mounting a successful primary immune response and gaining immunological memory usually takes around two weeks.
• Many pathogens act too quickly for our immune systems and can kill an individual in a matter of days.
• Vaccines enable the immune response to occur quickly.
• Data shows that vaccinations can allow the body to rapidly eliminate a live infection for the first time within seven days.
• The peak of the immune response occurs within the first three days.

Question 46

Why is strong herd immunity necessary?

Answer 46

• Many infants are too young to receive particular vaccines.
• Most vaccines are given to an individual over different stages of childhood to prevent certain risks.
• Strong herd immunity is necessary to protect infants and other individuals who cannot be vaccinated for various reasons.

Question 47

What are the ethics of herd immunity?

Answer 47

• Herd immunity can fall if people don’t get vaccines.
• Loss of herd immunity leads to a resurgence of disease.
• Near-eradicated diseases can return.
• Diseases were almost eradicated due to vaccines (e.g. whooping cough and MMR).
• Concerns over vaccinations lead to a big fall in vaccinations for these diseases.
• This led to a rapid resurgence of whooping cough and MMR, both of which can be fatal to infants and young children.

Question 48

What are the risks and counter-arguments of autism/vaccination?

Answer 48

Risks: There have been speculative reports of potential links between autism and vaccination.

Counter-Arguments: No scientific literature supports these claims, and more evidence shows there is no link between vaccination and autism.

Question 49

What are the risks and counter-arguments of the safety of vaccines?

Answer 49

Risks: There have been concerns over the safety of injecting pathogens into people.

Counter-Arguments: However, vaccine manufacturing is a tightly regulated process with many safeguards in place to prevent production of bad batches of vaccines.

Question 50

What are the risks and counter-arguments of animal testing?

Answer 50

Risks: Vaccines are often tested on animals, so people argue that there is violation of animal rights.

Counter-Arguments: But if the testing is done in an animal friendly and fair way then the overall benefit of vaccines is positive.

Question 51

What are the risks and counter-arguments of human volunteers?

Answer 51

Risks: When new vaccines are launched, the first humans tested are at risk.

Counter-Arguments: There is always a risk with new treatment. It is inevitable and overall more human lives are saved by vaccines.

Question 52

What are the negatives on animals?

Answer 52

• Animals may be given diseases to stimulate antibody production, and there are concerns over animal rights.
• Often mice are given induced cancer.

Question 53

What are the negatives on humans?

Answer 53

• Side effects may occur, i.e. allergic reactions.

- Monoclonal antibodies have been used to treat multiple sclerosis and have led to deaths.

Question 54

What are the positives of vaccinations?

Answer 54

• Used to treat many conditions.
• Can be used to detect early pregnancies to help mothers.
• Monoclonal antibodies as cancer treatment has less side effects than alternative therapy.
• They are specific so useful in diagnosing diseases quickly.

Question 55

What are the two types of antigenic variation?

Answer 55

• Antigenic Drift: Minor variations in antigenic structure. This results in the production of new strains of a particular virus.
• Antigenic Shift: Major variations in antigenic structure. This leads to the development of entirely new types of viruses.