Download Topic guide 8.6: Defence mechanisms

Unit 8: Pharmacological principles of drug actions
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Defence mechanisms
The immune system is made up of special cells, proteins, tissues and organs
and defends people against microorganisms. In most cases, the immune
system does a great job of keeping people healthy and preventing infections.
But sometimes problems with the immune system can lead to illness and
infection. Through a series of steps called the immune response, the immune
system attacks organisms and substances that invade body systems and
cause disease. The cells involved are white blood cells, or leukocytes, which
come in two basic types that combine to seek out and destroy diseasecausing organisms or substances.
On successful completion of this topic you will:
•• understand the function of the immune system and how drugs may affect
it (LO4).
To achieve a Pass in this unit you need to show that you can:
•• explain functions of defence mechanisms (4.1).
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Unit 8: Pharmacological principles of drug actions
1 Non-specific immune response
Inflammation
The non-specific immune response occurs due to tissue damage – mast cells and
basophils release substances that cause inflammation. Inflammation is a response
to tissue damage causing redness and heat because of dilating blood vessels and
an increased blood flow to the area of damage.
Inflammation causes swelling because the extra blood pushes tissue fluid into
damaged tissue. This swelling puts pressure on nerves causing pain. White blood
cells (or leukocytes) are cells of the immune system involved in defending the body
against both infectious disease and foreign materials – they are attracted to the
inflamed area to remove dead cells by phagocytosis. The photograph in Figure 8.6.1
shows inflammation of the knee joint – look at the red nature of the inflammation.
Figure 8.6.1: A photograph showing
the effects of inflammation.
Phagocytosis
Key terms
Basophil: A type of white blood cell
that helps you fight infections.
Phagocytosis: The engulfing of
foreign particles.
Lytic enzymes: Enzymes that cause
lysis (breaking down).
8.6: Defence mechanisms
Phagocytes include white blood cells such as neutrophils and monocytes. They
engulf pathogens and digest them with lytic enzymes (see Figure 8.6.2). The
outer membrane of the neutrophil engulfs the bacteria, which results in the
bacteria being contained inside a vacuole. Lysosomes fuse to the vacuole to digest
the bacteria with their digestive enzymes. The vacuole breaks into fragments
containing parts of the digested bacteria and attaches to proteins of the major
histocompatibility complex (MHC).
The vacuole continues to fuse with the cell membrane and the fragments of the
bacteria along with the MHC stick out of the surface of the neutrophil. The antigen
of the bacteria ends up on the outside of the phagocyte so an immune response is
activated against the bacteria.
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Unit 8: Pharmacological principles of drug actions
Figure 8.6.2: Neutrophil
engulfing bacteria.
Wound site
Neutrophil
B
Histamines
C
A
Migrate to
infection site
Invading
pathogens
Neutrophil engulfs
invader
Blood
vessel
D
Destroys pathogen
using hypochlorous
acid or enzymes
2 Specific immune response
An antigen is a foreign molecule detected by the specific immune system. The
immune system responds to this detection by producing specific antibodies
(proteins released to the site of infection).
Lymphocytes are a type of white blood cell in the vertebrate immune system
(T and B cells). They are produced in the bone marrow and they migrate to the
lymph nodes.
The specific immune system responds in two ways that are closely linked –
antibody-mediated immune response and cell-mediated immune response.
Antibody-mediated immunity
This response does not directly involve cells; it works through chemicals called
antibodies. Antibodies are made by white blood cells called lymphocytes. B cells
attack any foreign objects such as bacteria and viruses when they get inside the body.
The primary immune response occurs when B cells are made on the detection
of a foreign antibody. One B cell is produced for every antigen detected; they
are specific to the particular antigen that has entered the body. Therefore many
identical cells are made – they do not directly attack the foreign matter but they
make Y-shaped proteins (antibodies) that interact with the antigen on the foreign
molecule and stop it being harmful.
Most of the newly synthesised B cells die once the infection is under control but
some are left in the body – these are called memory cells. If this particular antigen
is detected again the memory cells reproduce and many more are made, enabling
the body to defend itself against this foreign bacteria – this is known as the
secondary immune defence.
Cell-mediated immunity
T cells are activated in the same way as B cells when an antigen invades body cells.
Activated T cells differentiate and have various roles in the immune response:
T helper cells, T killer cells, T suppressor cells and memory cells.
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Unit 8: Pharmacological principles of drug actions
T helper cells
These cells help the immune response to take place. They initiate B cells to divide
and produce antibodies, and they prepare the macrophages for phagocytosis to
digest the foreign pathogens.
T killer cells
These cells directly attack foreign cells – they punch holes into the membranes of
the foreign cells causing them to lose cytoplasm and die.
T suppressor cells
These cells help to return the immune system back to normal once the infection
has been eliminated. They are necessary so that the body reserves resources.
Memory cells
Some of the activated T cells become memory cells and remain in the body to
provide a secondary immune response if the pathogen invades the body again.
3 Immune system stimulation
Immune system stimulants encourage the body’s immune system to activate
an attack rather than fighting the pathogen themselves. Antiviral drugs and
interferons are used to stimulate the immune system to attack pathogens.
Interferons inhibit viral synthesis (production of new viruses) in infected cells. One
human interferon, interferon alpha, is the standard treatment for hepatitis B and C.
Vaccinations
Vaccinations help to speed up the immune response. A dead or inactive form
of the pathogen is injected into the body. The body detects the antigens and
produces memory cells that are stored in the body ready for a second invasion.
The memory cells will then be activated and reproduced in great numbers to
protect the body.
Passive immunity
Breast milk provides extra immunity to babies because the mother is able to pass
on antibodies that are stored in her body to the baby. Babies are able to absorb
these large proteins across their porous intestines straight into the bloodstream,
helping them to fight common pathogens.
4 Transfusions and transplants
Blood transfusions can be very dangerous because if the donor blood is a different
blood group from the recipient blood, the body’s immune system reacts. This
immune response can be fatal. Red blood cells have antigens attached to their
surface – the antigens present depend on the blood group.
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Unit 8: Pharmacological principles of drug actions
There are four blood groups: A, B, AB and O. Red blood cells in group O do not
contain any antigens, therefore no immune response will be activated if this blood
group is transfused into people with other blood groups.
Patients with blood group AB do not contain any antibodies so can receive blood
from any blood group. However, their red blood cells have both antigen A and
antigen B, so would cause a dangerous reaction if transfused into someone with a
different blood group.
People with blood group A contain antigen A on the surface of their red blood
cells, and anti B antibodies in their blood.
People with blood group B have antigen B present on the surface of the red blood
cells and anti A antibodies in their blood. If a person with blood group A received
blood group B during a blood transfusion, the anti B antibodies in their blood
would react with the B antigens on the surface of the red blood cells and cause an
immune response that could be fatal.
Transplantation involves the placing of tissues and organs into an individual from
a donor. However, the problem with transplants is the chance of rejection due to
the body’s immune system. Transplanted tissue surfaces are covered in antigens;
these foreign antigens activate a cell-mediated immune response. This can cause
destruction of transplanted cells and can lead to failure of an organ. The use of
drugs and tissue typing can help ensure that rejection does not take place.
5Immunosuppression
Immunosuppression is a reduction in activation of the immune system and may
happen because of a reaction to a medical treatment. If this did occur, immune
system stimulation drugs may be needed to enable the body to fight against
disease (see Case study on cancer treatment).
Immunosuppressant drugs are given to prevent the immune system from working.
For example, they may be necessary when carrying out an organ transplant – if
the recipient has a working immune system then the organ may be rejected.
Ciclosporine (cyclosporine, cyclosporin A), a common immunosuppressive drug, is
given to inhibit the activity of T cells and cell-mediated immunity.
6 Autoimmune diseases
Key terms
Immunosuppression: Suppression
of the immune system and its ability
to fight infection.
Myelin sheath: A layer insulating the
axons of nerve fibres.
8.6: Defence mechanisms
Autoimmune diseases occur when an immune response is activated against
tissues normally in the body because the immune system mistakes some part of
the body for a pathogen and attacks its own cells. This is the cause of multiple
sclerosis – T cells attack the myelin sheath around neurones, limiting the
function of the nervous system. People with insulin-dependent diabetes make
antibodies that kill ß cells in the islets of Langerhans in the pancreas, inhibiting the
production of insulin and affecting blood glucose levels. Patients suffering with
myasthenia gravis make antibodies that attack specialised synapses that connect
motor nerves to effectors. This affects the ability of the muscle to contract.
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Unit 8: Pharmacological principles of drug actions
Corticosteroids
Corticosteroids are hormones used to relieve inflammation that occurs as part
of the immune response due to infection. Inflammation prevents the spread of
infection but, in some health conditions, the immune system causes inflammation
even though there is no infection. This is known as an autoimmune condition and
examples include rheumatoid arthritis and lupus.
Lupus can be treated with nonsteroidal anti-inflammatory drugs (NSAIDs),
cyclosporine and steroids. Corticosteroids are prescribed to people with lung
conditions, such as chronic obstructive pulmonary disease (COPD), where
inflammation occurs in the lungs or airways.
Checklist
In this topic you should be familiar with the following ideas about the immune system:
 the body has specific and non-specific immune responses
 parts of the non-specific immune response are the skin, membranes, inflammation and
phagocytosis
 the specific immune response includes antibody-mediated and cell-mediated responses
 antibody-mediated or humoral immunity uses antibodies from B cells to attack foreign
objects before they invade the body
 cell-mediated immunity activates T cells to attack infected body cells
 there are four types of T cells: T helper cells, T killer cells, T memory cells and T suppressor cells
 vaccinations are used to stimulate the immune system into producing memory cells to
protect the body
 blood transfusions and transplants can cause immune responses, which can be dangerous to health.
Immunosuppressant drugs are needed to stop any immune response that may be dangerous
 autoimmune diseases (such as MS) occur when the body attacks its own body cells
 cyclosporine (cyclosporine, cyclosporin A) is a common drug used to suppress the immune system
 antiviral drugs and interferons are used to stimulate the immune system.
Activity
1 Research hepatitis C and drugs
that can be used to stimulate the
immune system.
2 Research opioids and their
suppressive actions.
3 Summarise the body’s defence
mechanisms that provide
immunity.
Case study
In findings published in 2009 by the British Journal of Cancer, a study by scientists shows that two
existing cancer drugs are able to stimulate the body’s immune cells into attacking invading cancer cells.
Current cancer-fighting drugs are known as cytotoxics and they cure patients by killing cells
directly and stunting their growth. Experiments have shown that the drugs stimulate the immune
system in three stages: firstly, by hijacking the tumour and making it more visible to the body’s
immune system. This initiates a signal to the body’s defence system and encourages white blood
cells to attack the now visible cancer cells.
Further reading
Mak, T. and Saunders, M. (2005) The Immune Response: Basic and Clinical Principles, Elsevier Science
Publishing.
Schindler, L.W. (1991) Understanding the Immune System, Diane Publishing Co.
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Unit 8: Pharmacological principles of drug actions
Acknowledgements
The publisher would like to thank the following for their kind permission to reproduce their
photographs:
Shutterstock.com: Photostock 10; Science Photo Library Ltd: Pasieka 2
All other images © Pearson Education
We are grateful to the following for permission to reproduce copyright material:
Diagram of Neutrophil engulfing bacteria, produced by Puricore. Used with permission.
Every effort has been made to trace the copyright holders and we apologise in advance for any
unintentional omissions. We would be pleased to insert the appropriate acknowledgement in any
subsequent edition of this publication.
About the author
Joanne Hartley-Metcalfe studied Forensic Sciences at UCLAN and is currently Science Vocational
Coordinator, teaching KS3 and KS4 Science, level 3 Forensic and Medical Science and A level in
a Merseyside school. She has been a Standards Verifier for four years, quality assuring vocational
science courses across the country. Joanne has experience authoring and examining, and has
made contributions to a number of level 3 resources.
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