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6.3.3 - Outline the role of skin & mucous membranes
6.3.4 - Outline how phagocytic leucocytes ingest
pathogens in the blood and in body tissues
6.3.5 - Distinguish between antigens & antibodies
6.3.6 - Explain antibody production
http://www.youtube.com/watch?v=IWMJIMzsEMg
The Body’s Defence
antibodies
actively made by
the body
physical and
chemical barriers,
e.g blood clotting
Specific vs. Non-Specific
Cure
Prevents pathogens that have entered
the body causing harm
Immune system/leucoytes
(phagocytotic & lymphocytes)
Prevention
Prevents pathogens entering the
body
Skin, mucus membranes, various
other ‘fluids’ & structures
Both can be artificially acquired
The body’s defence: Non-specific
• First line of defence:
skin
• Externally covered by
keratinised protein of the dead
cells - Tough and impervious
• Folds in skin with moisture can
lead to breaking barrier e.g.
athlete’s foot
• Diagram not required
Non-specific immunity: summary
• Complement system: 20 or so antimicrobial proteins in blood
• Localised damage – inflammation: increased number of leucocytes. Mast cells
secrete histamine which makes blood vessels ‘leaky’ – allowing complement to
reach damaged tissue.
• Blood clotting helps to seal off any wounds.
Phagocytes – Non-Specific Secondary Defence
Phagocytes are a type of leucocyte (white blood cell). They recognise the
pathogen after it has been coated by an antibody and destroy it
Phagocytes - Phagocytosis
http://www.youtube.com/watch?v=KxTYyNEbVU4 v
http://www.exploratorium.edu/imaging-station/gallery.php?Asset=Human+white+blood+cell+-
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Antibody
Production
What is the difference
between an antibody and an
antigen?
Antigens vs. Antibodies
FOREIGNERS
RESPONSES TO THEM
• Antigen (Ag)– molecule
• Antibodies (Ab) – a globular
recognised as foreign by the
protein that recognises Ag
immune system
• The outer surface of
microbes are covered in
antigens
• Antibodies are produced by special
white blood cells called B-cell (Blymphocytes)
• These are formed and matured in
• Phagocytotic leucocytes may the bone marrow but are stored in
present these on their outer
the lymph nodes, where they come
surface
into contact with Ag
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Identify the
antigen and
antibody
Structure of an antibody
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The blood contains two types of white blood
cell or Leukocyte
Phagocytes ingest bacteria by
endocytosis…
Lymphocytes produce antibodies…
•There are many types of lymphocyte, you do not need to
know them… but each has a very specific function within the
immune system
• CD4 lymphocyte deficiency is associated with AIDS and leads to
reduced antibody and ‘killer’ production as this cell helps the others
function
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Antibodies
•Proteins that recognise and bind to specific
antigens
• Lock and key system
• Antigens are foreign substances that stimulate
production of antibodies
•Many molecules on surface of viruses and
bacteria are antigens
SL •Antibodies are specific – they usually bind to only one specific antigen
• Millions of different lymphocytes in the body, all with unique
complement of antibodies to recognise the antigens
Antibodies
Antigen
Microbe
Est. a single humans is capable of generating ~10-billion different kinds of
antibodies. Each type of antibody defends the body against a specific type of
antigen.
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Production of Antibodies by Lymphocytes
A lymphocyte can produce only one type of
antibody so a huge number of different types are
needed
Each lymphocyte has some of its antibody on its
surface…
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The antigens of a pathogen bind to the antibodies
in the surface membrane of a lymphocyte…
…This activates the lymphocyte.
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The active lymphocyte divides by mitosis to
produce a clone of many identical cells
MITOSIS
The clone of cells
starts to produce large
quantities of the same
antibody…
… the same antibody
needed to defend
against the pathogen!
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Most microbes have more
than one antigen on their
surface, so…
…they stimulate more than
one type of lymphocyte…
…resulting in the production
of many different antibodies
which will act against it.
These are called
polyclonal antibodies.
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Antigen
Antigen
Activate
Lymphocyte
(B-cell)
Clone
Memory
Cell
Activate
Lymphocyte
(Helper T-cell)
Antibody Production:
Summary
Plasma
Cell
Macrophage/
Phagocyte
Antibodies
Immunity PacMan!
• One PACMEN
(phagocyte)
You can eat things tagged
with antibodies
• Three + opposing
pacmen (bacteria)
You must be tagged –
only then you can be
destroyed
• Three + fruits
(lymphocytes)
•Can tag the bacteria,
making them recognisable
to pacmen
http://www.youtube.com/watch?v=ZbjTqkSuHeo
Immunity Questions
1.
2.
3.
4.
5.
6.
What is an antigen? [2]
What is an antibody? [2]
Where are leucocytes produced? [1]
How are antibodies produced? [2]
What is a memory cell? [2]
What is meant by the ‘specificity’ of the
immune response? [2]
7. How do antibodies kill antigens? [2]
Marks out of 13:
Immunity Answers
1.
2.
3.
4.
5.
6.
7.
An antigen is a protein on the outside of a foreign cell that can be recognised as
‘foreign’ and can evoke an immune response
A protein produced by certain leucocytes (B lymphocytes, plasma cells) in
response to a specific antigen
In the bone marrow
Antibodies are produced by lymphocytes once they have come into contact with a
complementary/specific antigen
Memory cells are a type of lymphocyte that is produced during the primary/first
immune response to an antigen (on a pathogen). They live for years and are
responsible for the ‘immunity’ we develop after we have had a disease.
Every WBC has a unique complement of antibodies. A specific antibodys only
bind to specific antigens, thus a lymphocyte with a complementary antibody
must come into contact with the antigen before an immune response happens
The complementary ‘arm’ of the antibody binds to an antigen on the surface of a
pathogen. Antibodies coat the pathogen, directly killing it or ‘tag’ it for
phagocytosis/ ingestion by a phagocyte.
Immunity
Immunity multiple choice:
1.
2.
3.
4.
5.
A
B
D
B
C
Whiteboard Quiz
http://www.cellsalive.com/quiz3.htm
Question & Answer
http://www.biology-questions-and-answers.com/the-immune-system.html
Crash course biology (15 mins)
http://www.youtube.com/watch?v=CeVtPDjJBPU
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Higher Level Details
Antibody Production: The Primary Response
Step 1: Antigen Presentation
Antigen
Macrophage
Macrophages take in antigen
by endocytosis
The macrophage processes the
antigen and attaches it to a
membrane protein called a
MHC protein
The MHC protein is moved to the
cell surface membrane by
exocytosis so that the antigen is
displayed on its surface.
MHC protein
Step 2: Activation of Helper T-cell
Helper T-cells have receptors on
their cell surface membranes which
can bind to antigens presented by
macrophages.
receptor
Helper T-cell
Helper T-cell binds to macrophage
presenting the antigen
Macrophage sends a signal to activate the helper T-cell
Step 3: Activation of B-lymphocytes
B-cells have antibodies in their cell surface
membranes
Antigens bind to the antibodies in the surface
membranes of B-cells
Antigen
Inactive B-cell
Antibody
An activated helper T-cell with
receptors for the same antigen
binds to the B-cell
SIGNAL
The helper T-cell sends a signal to the B-cell,
activating the B-cell.
Step 4: Proliferation
The activated B-cell starts to divide
by mitosis to form a clone of plasma
cells.
Plasma cells are activated B-cells
with a very extensive network of
rough endoplasmic reticulum.
Plasma cells synthesis large
amounts of antibody, which they
excrete by exocytosis.
The Secondary Response: Memory Cells
• If an antigen invades your body a second time, a
much faster response occurs which produces
much larger quantity of the required antibody.
•When activated B-cells are dividing during the
primary response, some cells stop dividing and
secreting antibody and become memory cells.
• Large numbers of memory cells remain in the
body for a long time…
• …they are capable of producing large amounts of
antibody very quickly when stimulated.
Antigen
Antigen
Activate
B-cell
Clone
Memory
Cell
Activate
Helper
T-cell
Antibody Production:
Summary
Plasma
Cell
Macrophage
Antibodies