Transcript preventing-disease-4

Protection Against Disease
15.12
Antibody Mediated Immunity- B
cells
Learning Objectives
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Explain how B lymphocytes are
responsible for antibody mediated
immunity
Describe and explain the role of
antibodys in the specific immune
response
Starter
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Crossword
B Lymphocyte formation
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B lymphocytes are derived from
stems cell in the bone marrow
(as are t cells) and they
undergo further differentiation
in the liver, spleen or lymph
nodes
The plasma membrane of each
B cell has protein molecules
that are specific for a particular
antigen
These proteins are called
antibodies and are released
into the lymph
Each B cell has a single
antibody type that it is able to
make and there are over
1000000 different types that
can be made
Competence
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When the antibody matches an antigen the B cell is
said to be competent
After infection a macrophage with an antigen
embedded in its membrane causes a competent
helper T cell to interact with the appropriate
competent B cell
The increased activity in lymph nodes during times of
infection results in the characteristic swelling of
lymphatic tissue near the site of infection
A viral or bacterial infection of the upper pharynx
often results in swollen tonsils because the lymph
nodes in the tonsils are where the B cells are
producing antibodies
Antibodies
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When the antigen is detected the B cell divides
repeatedly by mitosis to form a clone and because
they are all identical, the plasma cells synthesise
large quantities of antibodies of the same kind =
clonal proliferation
These plasma cells only live a few days but secrete
2000 antibody molecules/second
It takes a few days for enough B cells to be made to
make enough antibody for it to be detectable in the
blood therefore you may feel ill because in the
meanwhile the pathogen is reproducing
Antibodies eventually get the upperhand though and
the symptoms of the illness subside. This is the
primary response
Immunity
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If the antigen invades again a faster response occurs
when more antibody is made faster. This is because
some of the cells which didn’t divide by mitosis to
form the clone form memory cells and remain in the
body and can secrete antibody for a long time after=
immunity
The immune response is stimulated in the body by a
particular antigens which are foreign substances
A division of labour is caused by the development fo
2 types of lymphocytes T and B
Summary
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An antigen is detected by a B cell
The specific B cell will now clone itself by
mitosis
The plasma cells secrete specific antibodies
and form antibody – antigen complexes
Antibodies kill the pathogen by;
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Preventing pathogens attaching to cells
Changing the shape of toxin proteins
The memory cells continue to secrete small
amounts of antibodies for decades
Tasks
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Complete the flow chart to show how antibody
mediated immunity occurs
On the back of the flow chart describe and explain
the function of the plasma and memory B cells
Complete the past paper questions and then pass to
the group opposite to mark
Take the mark scheme and check the marking of the
group
Extension – page 74 application
Primary and Secondary
Response
Plenary
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Quick Quiz
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What stimulates the immune response by
B and T cells?
How do cytotoxic T cells destroy
pathogens?
What is the role of memory B cells in
immunity?
How do antibodies destroy pathogens?
Homework
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Hand in BYB7 and BYB678 papers
Hand in essays
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Homework for Wed next week
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BYB7 paper June 2004
BYB6,7,8 June 2004
The energy essay- use mark scheme to
help you write the essay