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Specific Cellular Defence
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Range of white blood cells (WBCs) circulate
monitoring for damage, pathogens or
cancerous cells
In response to damage or infection some
WBCs produce cytokines which lead to
increased WBCs in the area.
These WBCs include Phagocytes, Lymphocytes
(Natural Killer Cells, T Cells and B Cells)
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The body has a huge number of different
lymphocytes each with a different membrane
receptor that is specific to for one particular
antigen
Stages in clonal selection;
◦ An antigen binds to its specific receptor on a
lymphocyte
◦ The lymphocyte undergoes repeated division,
resulting in several clones of identical lymphocytes
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T- Lymphocytes (T-Cells)
Produced in the bone marrow
Mature in Thymus Gland
Can be distinguished from other lymphocytes
by their cell surface receptors (TCRs)
Allow them to detect specific antigens that
enter the body
These proteins allow T Cells to distinguish
between self and non self
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Cytotoxic T-Cells (Killer T-Cells)(TC Cells)
Destroy cells which the immune system
regards as foreign (infected cells and tumour
cells)
Recognise antigens on foreign cells, bind to
the cells and destroy by apoptosis
Majority of TC Cells then undergo apoptosis
themselves
A few remain as memory cells
Killer T-cells:
Can attach themselves to cells with foreign
antigens on their surface and destroy them
1. Virus attaches
to and
enters
host cell
2. Viral DNA causes host cell to express viral
anitgens on its surface
3. Killer T-cell attaches
to viral
antigen on
infected cell
4. Killer T-cell induces
death of
infected cell
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Do not destroy infected cells
Secrete cytokines that activate B lymphocytes
and TC Cells
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When a tissue has been infected by a
particular pathogen, phagocytes are attracted
to the pathogens by chemicals and engulf
them in phagocytosis
Some phagocytes then move part of the
pathogen to their own surface
They are now antigen presenting cells
Can activate the production of a clone of T
Cells that move to the site of infection,
directed by cytokines.
SUMMARY SLIDE
specific defences
T lymphocytes
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One group of T lymphocytes destroy infected cells
by inducing apoptosis.
Another group of T lymphocytes secrete cytokines
that activate B lymphocytes and phagocytes.
When pathogens infect tissue, some phagocytes
capture the pathogen and display fragments of its
antigens on their surface.
These antigen presenting cells activate the
production of a clone of T lymphocytes that move
to the site of infection under the direction of
cytokines.
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B-Lymphocytes (B-cells)
Produced and mature in bone marrow
Activated by APCs and T cells produce a clone
of B-cells
Secrete antibodies into lymph and blood
systems
Clonal Selection Theory
Each antibody fits an antigen like a key fits a
lock
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Antibodies bind to the antigen to form an
antigen-antibody complex which can;
Inactivate the pathogen or toxin
Make it more susceptible to phagocytosis
Stimulate a response by T cells resulting in
cell lysis (cell destruction)
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Some T and B cells produced by clonal
selection survive long term as memory cells
They remain in the body and the same
antigen is encountered in a secondary
exposure a new clone of lymphocytes are
produced giving a response which is
◦ Quicker
◦ Greater
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Immunological memory is specific for a
particular antigen and is long lived
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When the body reacts to a small trace of a
harmless foreign substance
The antigen involved is called an allergen
Animal hair
Pollen
Moulds
Dust mites
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Some common diseases caused by allergic
reactions are;
Hay fever
Anaphylactic shock
Allergic asthma
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Animation: The Immune Response
Specific defences
Immune surveillance
•A range of white blood cells
constantly circulate monitoring the
tissues.
•If tissues become damaged or
invaded, cells release cytokines which
increase blood flow resulting in
specific white blood cells accumulating
at the site of infection or tissue
damage.
•Recognition of self and non self
through specific surface proteins
(antigens)
•Lymphocytes respond specifically to
antigens on foreign cells, cells infected
by pathogens and toxins released by
pathogens.
SUMMARY SLIDE
specific defences
B lymphocytes
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Each B lymphocyte clone produces a specific
antibody molecule that will recognise a specific
antigen surface molecule on a pathogen or a toxin.
Antigen-antibody complexes may inactivate a
pathogen or toxin or render it more susceptible to
phagocytosis.
In other cases the antigen-antibody complex
stimulates a response which results in cell lysis.
B lymphocytes activated by antigen presenting cells
and T lymphocytes produce a clone of B
lymphocytes that secrete antibodies into the lymph
and blood where they make their way to the
infected area.
Specific defences
Immunological memory cells
• Some T and B lymphocytes produced in
response to antigens by clonal selection
survive long term as memory cells.
• A secondary exposure to the same antigen
rapidly gives rise to a new clone of
lymphocytes producing a rapid and greater
immunological response.
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Failures of immune system
•Failure in regulation of the immune system
leads to a T lymphocyte immune response to
self cells (auto immune disease).
•Allergy is a hypersensitive B lymphocyte
response to an antigen that is normally
harmless.