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Antibody Structure and Function
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What are lymphocytes?
Lymphocytes are a type
of white blood cell
(leukocyte) found in the
blood and lymph nodes.
Lymphocytes recognise
antigen molecules on the
surface of pathogens, and
co-ordinate the immune
response against that
pathogen.
Collectively, lymphocytes can recognize millions of different
antigens, due to the large variation of lymphocytes produced.
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Humoral and Cellular Immune Responses
-
Involve lymphocytes
B-lymphocytes – mature in bone marrow
T-lymphocytes – mature in thymus
B-lymphocytes produce antibodies –
humoral response
- T-lymphocytes directly affect
cells – cellular response
Different types of lymphocytes
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Humoral immune response
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B-cells
B-cell binds to antigen.
B-cell divides by mitosis.
Some cells formed are plasma cells – secrete
antibodies.
Some cells formed are memory cells – remain
in blood for a period of time, providing
immunity.
B-cells
Cellular immune response
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T-cells
Phagocyte takes up pathogen.
Antigens presented on surface of phagocyte
(antigen-presenting cell).
T-cell binds to antigen on APC.
T-cell divides by mitosis.
Several types of T-cell produced, including
memory cells and cells that stimulate B-cells
to replicate.
T-cells
The graph below shows the levels of anti-Rubella (German Measles) in the blood
Concentration of anti-Rubella antibody
in the blood/arbitrary units
SecondaryBResponse
10000
1000
PrimaryAResponse
100
10
10
First exposure
X to antigen
 infection, or
 vaccination
20
30
Long interval
Time/days
Second
Y exposure to
antigen
Antibody Concentration – Primary and Secondary Response
Primary Response
1. Infection (Ag)
2. Antibodies produced
3. Antibody level rises to combat
infection
4. Ag dealt with
5. Ab level declines – short lived
Secondary Response
After the primary response, Ab’s do not stay in blood – the level declines
If the body is infected by the same Ag a second time Ab’s must be made again
Re-infection causes much more rapid and a stronger immune response – concentration of
Ab’s rises sooner- reaches a higher concentration – more plasma cells than in 1o
response – more cells to respond to Ag; less time to produce same number of plasma
cells –hence, a greater [Ab] compared to 1o response; increased affinity of Ab for Ag.
This is due to the presence of memory cells (made during the primary response) – no
need for antigen presentation and clonal selection
Long-lived; basis of vaccination
12
Primary – establishes immunological
memory
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Differences between humoral and cell
mediated immunity
Humoral Immunity
Main cells involved
Where do cells
develop?
Antibodies?
How are pathogens
identified?
How are pathogens
killed?
How do cells divide
once they are
stimulated?
Cell mediated immunity
Differences between humoral and cell
mediated immunity
Humoral Immunity
Cell mediated immunity
Main cells involved
B lymphocytes
T lymphocytes
Where do cells
develop?
Produced and mature in the Produced in the bone marrow,
bone marrow
mature in the thymus gland
Antibodies?
Involves production of
antibodies
Does not involve production of
antibodies
How are pathogens
identified?
Via antigens floating in the
blood
Via antigens on the surface of
infected cells.
How are pathogens
killed?
By antibodies
By specialised ‘killer T cells’
How do cells divide
once they are
stimulated?
cells divide into either
plasma cells or memory
cells
cells divide into different types
of specialist T cells
Plasma and memory cells
• Plasma cells
–
–
–
–
Involved in the primary immune response.
Secrete antibodies directly.
They only survive for a few days.
Response is slow and person will get ill before pathogen is
killed.
• Memory cells
– Involved in the secondary immune response
– They circulate in the blood and tissue fluid
– When they encounter the antigen from the primary
response they divide rapidly.
– Response is rapid and person will not get ill.