HL Human Physiology: 11.1 Antibody Production and Vaccination

Question 1

Outline how the immune system recognises body cells?

Answer 1

All nucleated cells of the body possess unique and distinctive surface molecules that identify it as self

These self markers are called major histocompatibility complex molecules (MHC class I) and function as identification tags
The immune system will not normally react to cells bearing these genetically determined markers (self-tolerance)

Question 2

Outline how the immune system recognises foreign cells?

Answer 2

Any substance that is recognised as foreign and is capable of triggering an immune response is called an antigen (non self)

Some glycolipids and glycoproteins on the cell surface membranes act as antigens

Question 3

Explain why red blood cells can be transferred between individuals without automatically causing immune rejection

Answer 3

Red blood cells are not nucleated and hence do not possess the same distinctive and unique self markers as all other body cells

Question 4

What do red blood cells possess which limit the capacity for transfusion?

Answer 4

However, red blood cells do possess basic antigenic markers which limit the capacity for transfusion (the ABO blood system)

Red blood cells may possess surface glycoproteins (A and B antigens) either independently (A or B) or in combination (AB)
Alternatively, red blood cells may possess neither surface glycoprotein (denoted as O)

Question 5

Explain the ABO blood group system as a consequence of the unique feature of red blood cells

Answer 5

As humans produce antibodies against foreign antigens, blood transfusions are not compatible between certain blood groups

AB blood groups can receive blood from any other type (as they already possess both antigenic variants on their cells)
A blood groups cannot receive B blood or AB blood (as the B isoantigen is foreign and will stimulate antibody production)
B blood groups cannot receive A blood or AB blood (as the A isoantigen is foreign and will stimulate antibody production)
O blood groups can only receive transfusions from other O blood donor (both antigenic variants are foreign)

Question 6

Define pathogen

Answer 6

A pathogen is an agent that causes disease – either a microorganism (bacteria, protist, fungi or parasite), virus or prion

Question 7

Define disease and illness

Answer 7

A disease is any condition that disturbs the normal functioning of the body (i.e. the body can no longer maintain homeostasis)
An illness is a deterioration in the normal state of health of an organism (a disease may cause an illness)

Question 8

What is the general nature of pathogens?

Answer 8

Pathogens are generally species-specific in that their capacity to cause disease (pathogenesis) is limited to a particular species

Polio, syphilis, measles and gonorrhoea are examples of diseases caused by pathogens that specifically affect human hosts

Question 9

What is the meaning of zoonotic diseases?

Answer 9

Certain pathogens may cross the species barrier and be able to infect and cause disease in a range of hosts

Diseases from animals that can be transmitted to humans are called zoonotic diseases (or zoonoses)
Examples of zoonotic diseases include rabies (dogs), certain strains of influenza (e.g. bird flu) and the bubonic plague (rats)

Question 10

Outline various ways of disease transmission

Answer 10

Direct contact – the transfer of pathogens via physical association or the exchange of body fluids
Contamination – ingestion of pathogens growing on, or in, edible food sources
Airborne – certain pathogens can be transferred in the air via coughing and sneezing
Vectors – intermediary organisms that transfer pathogens without developing disease symptoms themselves

Question 11

Explain the immune response against a pathogen mentioning clonal formation

Answer 11

When the body is challenged by a foreign pathogen it will respond with both a non-specific and a specific immune reaction

Non-specific immune cells called macrophages will engulf pathogens non-selectively and break them down internally
A proportion of macrophages (dendritic cells) will present the antigenic fragments of the pathogen to specific lymphocytes

The body contains millions of different T lymphocytes and B lymphocytes that each recognise a single, specific antigen

Antigenic fragments are presented to specific helper T lymphocytes (TH cells) that, when activated, releases cytokines
The cytokines stimulate a specific B cell that produces antibodies to the antigen to divide and form clones (clonal selection)
Most of the clones will develop into short-lived plasma cells that produce large quantities of specific antibody
A small proportion of clones will differentiate into long-lived memory cells that function to provide long-term immunity

Question 12

Why several types of a helper T and B lymphocytes are activated as immune response?

Answer 12

Pathogens typically contain multiple distinct antigenic fragments on their surface and hence a single pathogen is likely to stimulate several different T and B lymphocytes to produce a variety of specific antibodies (polyclonal activation)

Question 13

Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Agglutination

Answer 13

Agglutination
Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together (agglutination)
This reduces the chance that the pathogens will spread through the body or taken into cells, instead the clumps are removed by the lymphatic system and digested by phagocytes

Question 14

Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Opsonisation

Answer 14

Antibodies attach to bacteria making them readily identifiable to phagocytes, this is called opsonisation
Once identified, phagocytosis occurs

Question 15

Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Neutralisation

Answer 15

Neutralisation of viruses and bacteria

Antibodies can combine with viruses and toxins of pathogens (e.g. bacteria) to block them from entering or damaging cell

Question 16

Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Complement activation

Answer 16

Antibodies can trigger proteins, called complement proteins, which create holes in the cell walls of pathogens causing them to burst (cell lysis) when ions are absorbed and water moves in by osmosis

Question 17

Describe the function and mechanism of memory cells

Answer 17

Memory cells are produced to prevent this delay in subsequent exposures and hence prevent disease symptoms developing

When a B lymphocyte is activated and divides to form plasma cells, a small proportion will differentiate into memory cells
Memory cells are long living and will survive in the body for many years, producing low levels of circulating antibodies
If a second infection with the same pathogen occurs, memory cells will react more vigorously to produce antibodies faster
As antibodies are produced faster, the pathogen cannot reproduce in sufficient amounts to cause disease symptoms
Hence, because pathogen exposure no longer causes the disease to occur, the individual is said to be immune

Question 18

Define allergen and the kind of immune response that occurs

Answer 18

An allergen is an environmental substance that triggers an immune response despite not being intrinsically harmful

This immune response tends to be localised to the region of exposure (e.g. airways and throat) as an allergic reaction

Question 19

Outline the mechanism of an allergic reaction

Answer 19

An allergic reaction requires a pre-sensitised immune state (i.e. prior exposure to the allergen)

When a specific B cell first encounters the allergen, it differentiates into plasma cells and makes large quantities of antibody (IgE)
The IgE antibodies attach to mast cells, effectively ‘priming’ them towards the allergen
Upon re-exposure to the allergen, the IgE-primed mast cells release large amounts of histamine which causes inflammation

Question 20

What allergic symptoms are exhibited by histamine?

Answer 20

The release of histamine from IgE-primed mast cells causes an inflammatory response that results in allergic symptoms

Inflammation improves leukocytes mobility to infected regions by triggering vasodilation and increasing capillary permeability

Vasodilation is the widening of blood vessels to improve the circulation of blood to targeted regions

Vasodilation causes redness (as vessel expansion moves blood closer to the skin) and heat (which is transported in blood)

Capillary permeability describes the capacity for leukocytes to leave the bloodstream and migrate into the body tissue

Increased permeability leads to swelling (more fluid leaks from the blood) and pain (swelling causes compression of nerves)

Redness, heat, swelling and localised pain are all typical symptoms of an allergic response

Question 21

What is the function of vaccine?

Answer 21

Vaccinations induce long-term immunity to specific pathogenic infections by stimulating the production of memory cells

Question 21

What is the function of vaccine?

Answer 21

Vaccinations induce long-term immunity to specific pathogenic infections by stimulating the production of memory cells

Question 22

Explain the working of a vaccine

Answer 22

A vaccine is a weakened or attenuated form of the pathogen that contains antigens but is incapable of triggering disease
The body responds to an injected vaccine by initiating a primary immune response, which results in memory cells being made
When exposed to the actual pathogen, the memory cells trigger a more potent secondary immune response
As a consequence of this more potent immune response, disease symptoms do not develop (individual is immune to pathogen)

The length of time a person is immune to infection following a vaccination depends on how long the memory cells survive for

Memory cells may not survive a lifetime and individuals may subsequently require a booster shot to maintain immunity

Question 23

What is the benefit of vaccination in terms of population

Answer 23

Vaccination confers immunity to vaccinated individuals but also indirectly protects non-vaccinated individuals via herd immunity

Herd immunity is when individuals who are not immune to a pathogen are protected from exposure by the large amounts of immune individuals within the community

Question 24

What are monoclonal antibodies?

Answer 24

Monoclonal antibodies are antibodies artificially derived from a single B cell clone (i.e. identical specific antibodies)

Question 25

How are monoclonal antibodies made?

Answer 25

An animal (typically a mouse) is injected with an antigen and produces antigen-specific plasma cells
The plasma cells are removed and fused (hybridised) with tumor cells capable of endless divisions (immortal cell line)
The resulting hybridoma cell is capable of synthesising large quantities of monoclonal antibody

Question 26

Explain the treatment use of monoclonal antibodies

Answer 26

Monoclonal antibodies are commonly used to provide immune protection for individuals who contract harmful diseases

Because the rabies virus can potentially be fatal, injecting purified antibodies functions as an effective emergency treatment
Monoclonal antibodies can be used to target cancer cells that the body’s own immune cells fail to recognise as harmful

Question 27

Explain the application of monoclonal antibodies to test for pregnancy

Answer 27

Monoclonal antibodies can be used to test for pregnancy via the presence of human chorionic gonadotrophin (hCG) in urine

hCG is a hormone produced by women during foetal development and thus its presence in urine is indicative of pregnancy

Pregnancy tests use a process called ELISA (enzyme-linked immunosorbent assay) to identify a substance via a colour change

Free monoclonal antibodies specific to hCG are conjugated to an enzyme that changes the colour of a dye
A second set of monoclonal antibodies specific to hCG are immobilised to the dye substrate
If hCG is present in urine, it will interact with both sets of monoclonal antibody (forming an antibody ‘sandwich’)
When both sets of antibody are bound to hCG, the enzyme is brought into physicial proximity with the dye, changing its colour
A third set of monoclonal antibodies will bind any unattached enzyme-linked antibodies, functioning as a control