Immunity and Vaccinations
Natural Active immunity
• If you survive an infection
with a pathogen e.g. Vibrio
cholerae you usually
acquire permanent immunity
against that organism.
• During primary response
one B cell is activated by a
specific antigen that has a
complementary shape to
that of the immunoglobulin
on the cell surface of the B
cell.
• The B cell divides
many times to form a
clone of cells which
can produce identical
antibodies against the
antigen. Some of the
B cells resulting from
mitosis become
memory cells.
Second Exposure
• If person is exposed
to same antigen
again, the secondary
response takes place.
• The memory cells
formed in the primary
response divide to
form a large
population of B cells.
• Each one of these can
produce clones that can
make antibodies to
destroy the antigen or
disease agent
• The secondary response
is faster and greater than
the primary response
because it starts with a
large number of memory
cells rather than one B
cell
Artificial active immunity
• This can reinforce
natural immunity e.g.
vaccination.
• Vaccination was first
used by Edward
Jenner –
http://www.bbc.co.uk/history/historic_fi
gures/jenner_edward.shtml
How vaccinations work
• Involve using
weakened pathogens
– called attenuation.
• It can be natural (as
in cowpox) or it may
be carried out
artificially by -
• Culturing the pathogen
repeatedly in high or low
temps, or without oxygen, until
suitable mutants occur (e.g.
the Sabin poliomyelitis
vaccine)
• Using viruses or bacteria that
have been killed so that they
still trigger the immune
response but cannot induce
the disease e.g. the Salk
poliomyelitis vaccine
• Use inactivated toxins called
toxoids that are harmless but
trigger the same type of
immune response e.g.
diphtheria and tetanus
vaccines.
Herd Immunity
• Ideally vaccinations for highly contagious diseases
should be given to a large number of people at the
same time. This gives a general immunity to the
population called herd immunity.
• Vaccinations are not equally effective on all people –
in fact some people will not respond at all. They may
have inherited a defective immune system or their
defences may already have been weakened by
disease or malnutrition.
• How does herd immunity offer these people some
protection?
Antigenic variation
• Some diseases are difficult to
vaccinate against e.g. the
influenza virus because they
mutate regularly and change
their surface antigens.
• Our immune systems can
recognise small changes
(known as antigenic drift) but
not large changes (antigenic
shift) such as the one that
caused Hong Kong ‘flu in 1997
http://www.sciencefriday.com/pages/19
97/Dec/hour1_121997.html
• The way the influenza
virus evades attack is
called Antigenic
Variation
• Antigenic concealment
– this is where pathogens
avoid the immune system
in another way. E.g.
Vibrio cholerae lives on
the wall of the intestine
bathed in intestinal juices.
• How does this mean it
avoids the immune
system?
• The vibrio cholerae
bacterium also
undergoes
considerable
antigenic variation
• This is why it spreads
so rapidly and is very
virulent
Passive immunity
• Active immunity, whether
natural or artificial is not
immediate. During the delay
between infection and full
immune response, some
disease causing agents, such
as the toxins from Clostridium
tetani can kill.
• A person infected with a lifethreatening disease such as
tetanus may be given readymade antibodies against the
toxin. This is called passive
immunity.
Natural Passive Immunity
• This occurs when a fetus is
still in the uterus. Maternal
antibodies cross the placenta
into fetal blood.
• They may protect the baby for
example against measles,
during the first few months
after birth. Infants also acquire
some passive immunity from
the antibodies in colostrum
(the first milk produced by a
lactating mother).
• Passive immunity is only
temporary – Why?
Now answer the following
1. Which type of immunity involves the body
making its own antibodies in response to an
antigen?
2. Why are influenza vaccines sometime not
effective?
3. Why is the secondary response to an infection
quicker than the primary response?
4. Explain why passive immunity is only
temporary.
• The antibodies are eventually broken
down by the spleen and liver
• There is no immunological memory
because the baby did not make the
antibodies for itself.