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8/6/2019 3rd Line of Defence
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The Immune Response
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� The main components of the bodys main
immune response are:
Lymphocytes: B cells
T cells
Antibodies
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� There are manydifferent types of
WBC
s� Lymphoctyes are non-
phagocytic whiteblood cells
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� All the differenttypes of bloodcells, including
lymphocytes, arisefrom stem cellsmade in the bonemarrow
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� The 2 different types of lymphocytes
responsible for the immune response in
humans are: B cells (humoral or antibody mediated response)
T cells (cell mediated response)
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� Each B cell has an antibody on its surface that
can bind with a particular chemical shape
� If a B cell collides with a molecule, an antigen,that binds its antibody it becomes activated
and goes to the lymph node to rapidlyreplicate
� This is called clonal expansion
� Most cloned cells specialise to become
plasma cells
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� A plasma cell will make and release aparticular antibody which exactly binds with
the antigen that triggered the response
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� Antibodies areproteins found in blood
plasma that can bindwith and help toneutralise an antigen
� Antibodies are highly
specific for the antigenthat stimulated theirsynthesis and release
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� An antibody can react with an antigen in anumber of ways: Combine with the antigen to cover the active site so it
has no effect on the body Dissolve parts of the cell walls of bacteria, destroying
them
Neutralise the toxins made by the antigen
Cause bacteria to clump together, making thebacteria less active and more easily taken up by the
lymph system
Make the antigen more susceptible to phagocytosis
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� Can live for many years in the body
� They carry the same antibody so that ever an
antigen (on a pathogen or foreign chemical)enters the body again, it will immediately be
recognised, and cloning and antibodyproduction can begin immediately
� The body can begin destroying the pathogenbefore it has time to cause an infection
� ie. You are immune to that pathogen!
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� Made in the bone marrow� Mature in the thymus gland, situated under the
sternum
� Constantly circulating through the blood to thelymph nodes and spleen and then back to theblood
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� One component of the 2nd line of defenceinvolves macrophages acting on pathogens
by engulfing and destroying them byphagocytosis� The macrophage will then display pieces of
antigen from the destroyed pathogen on its
surface on complex molecules called majorhistocompatibility complexes (MHCs)� B cells can also present antigens onMHCs on
their surface to T cells
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� T cells recognise theseantigens by interactingwith these macrophagesandB cells
� These lymphocytes canthen launch a
coordinated attack todestroy any remainingantigen
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� T cells can differentiate into different kinds of
cells, each with different roles:
Killer, or cytotoxic, T cells Memory T cells
Helper T cells
Suppressor T cells
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� Have a T cell receptor (TCR) on the surface of each cell
�
TC
Rs work with body fluid proteins calledmajor histocompatibility complexes (MHCs)� Each T cell searches the surfaces of cells
throughout the body for anMHC to match
with its TRC� If it finds a match, T cell cloning begins to
make killer cells that destroy those cells� Activated by interferons
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� Use TCRs to recogniseMHCs on B cells,macrophages, and other white blood cells,
and produce chemicals called cytokines inresponse
� Cytokines affect the recognised cell, helping
other lymphocytes to destroy it, as well as
stimulating the production of more B cellsand T cells and coordinating their response
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� Turn off the productionof other lymphocytes(bothB and T cells)when the antigenshave been removed
� Also play a role in
protecting the bodyfrom immune attackson itself
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� Retain the ability to recognise the original
invading antigen so that a subsequent
invasion can be dealt with quickly� Take no further part in the attack but remain
in the body ready to respond more quickly toany future antigenic molecules
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