Immunity and Vaccinations

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Immunity and Vaccinations
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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.

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• 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.

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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.

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• 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

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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_figures/jenn
  er_edward.shtml

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How vaccinations work

• Involve using weakened pathogens called
  attenuation.
• It can be natural (as in cowpox) or it may be
  carried out artificially by -

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• 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.

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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?

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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.co
  m/pages/1997/Dec/hour1_121997.html

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• 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?

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• The vibrio cholerae bacterium also undergoes
  considerable antigenic variation
• This is why it spreads so rapidly and is very
  virulent

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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 life-threatening disease
  such as tetanus may be given ready-made
  antibodies against the toxin. This is called
  passive immunity.

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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?

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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.

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• 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.