Application of immunology

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Chapter 9

• Application of immunology

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Immunity

• Definition
• The acquired ability to defend against infection
  of disease-causing organisms.
• Acquired means to gain by or for oneself.

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Different types of immunity

• Immunity against particular pathogens is
  achieved in different ways it may be
• Naturally active
• Artificially active
• Naturally passive
• Artificially passive

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Natural active immunity

• This type of immunity occurs when a person is
  exposed to and survives a particular pathogen.
  This results in them producing memory cells that
  will prevent them from being infected again.
• For example if you have had chicken pox, you are
  unlikely to get it again.

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Artificial Active Immunity

• This type of immunity is achieved through
  vaccinations.
• This type of immunity still results in the body
  having to actively mount an immune response and
  therefore means that they make memory cells.

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Vaccines

• A small amount of weakened or dead
  micro-organism, or inactivated form of the toxins
  they release, is injected into the patient the
  vaccine.
• The presence of foreign antigens activates the
  immune response that results in memory cells
  specific for those antigens.
• So if the person becomes infected with the true
  form of that antigen, the body will respond more
  quickly and intensely meaning the person shows no
  symptoms of the disease.

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Vaccines cont.

• Attenuated vaccines these are a weakened form
  of the disease causing agent that is still able
  to reproduce, but which does not cause disease
  symptoms.
• Examples include polio, mumps, rubella
• Inactivated vaccines these have sufficient
  immunogenic capacity to provoke a response, but
  are unable to replicate.
• A example would be the foot-and-mouth vaccine.

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Natural Passive Immunity

• Passive means that the person does not produce
  their own antibodies against a pathogen. This
  means that they also dont produce any memory
  cells so they are not protected against further
  exposure to the antigen.
• This type of immunity occurs during pregnancy
  when the mothers antibodies can cross the
  placenta to aid the foetus and are also passed to
  the newborn baby in the breast milk.
• Passive immunity protects immunity protects
  babies for the first few months while their own
  immunes systems develop.

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Artificial Passive Immunity

• If you have already been exposed to a pathogen it
  is then to late to vaccinate you against it.
  What can be done to help your ability to fight
  the infection is to administer you with antibody
  serums that contain antibodies for that
  particular antigen.
• These antibodies destroy the invading cells like
  a natural immune response, often stopping the
  disease before it sets in, but because the
  antibodies werent produced by the patient, they
  produce no memory cells.
• Antivenoms are an example of this type of
  treatment.

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Antibody serums

• These antibodies destroy the invading cells like
  a natural immune response, often stopping the
  disease before it sets in, but because the
  antibodies werent produced by the patient, they
  produce no memory cells.
• Antivenoms are an example of this type of
  treatment.

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Disorders of the immune system

• There are several kinds of immunological
  disorders
• Hypersensitivity caused by excessive immune
  action as in the case of allergies and rhesus
  incompatibility.
• Autoimmunity caused by misdirected attack
  against self as in the cases of rheumatoid
  arthritis, MS and diabetes.

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• Immunodeficiency caused by reduced
  responsiveness of the immune system as in the
  case of AIDS and Bubble babies
• Persistent inflammation caused by absence of
  the normal dampening of the inflammatory response
  which causes problems with diseases like
  Alzheimer's and cancer

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Allergies

• First encounter with an allergen
• The allergen/antigen stimulates a B cell to
  produce IgE antibodies
• IgE antibodies travel through the blood and
  attach themselves to mast cells by their
  non-variable portion that are in epithelium and
  mucosal tissues.
• Second encounter with the allergen
• The allergen combines with the IgE antibodies on
  the mast cells surface and this stimulate the
  mast cells to release histamine (degranulate).

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The release of Histamine

• Histamine is released from mast cells as part of
  the normal second line of defence as part of the
  inflammation response.
• Also when a mast cell with IgE present causes the
  release of histamine on a small scale the blood
  vessels to dilate and the membranes to become
  leaky. This, in small amounts can be positive as
  leaky membranes will hopefully wash away the
  allergen or make the skin itchy so you will
  respond by brushing away the parasite.
• It becomes a problem when too much IgE is formed
  and the response becomes excessive.

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Annoying Vs Severe responses

• Having hay fever is annoying, but not life
  threatening. An allergy to something like a bee
  sting can result in anaphylactic shock and death.
  Why?
• Because the venom is injected into the
  bloodstream, the allergen travels around the body
  and can stimulate mast cells all around the body
  and this causes mass histamine release which can
  cause blood pressure to drop and this is what
  causes the problems
• This type or reaction needs to be treated with
  adrenaline, which counteracts the effects of
  histamine quickly.

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Rhesus blood groups

• People either have Rh antigen (rhesus positive)
  or dont (rhesus negative). A person who is
  rhesus negative recognises Rh positive antigens
  as foreign.
• Problems from this arise during pregnancy if the
  mother is rhesus negative and the baby is rhesus
  positive.
• During birth some of the babies blood will be
  spilled into the mother and her body will then
  make antibodies against the babies blood.
• This then becomes a problem if the mother then
  has another rhesus positive child because the
  mother has antibodies that will fight against the
  babies red blood cells and cause them to lyse
  (haemolytic disease)

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How can this be avoided?

• Mothers and babies blood groups are now routinely
  tested. If the mother is neg and the baby
  positive, straight after the birth the mother
  will be injected with antibody serum against the
  rhesus blood.
• This means that the artificial antibodies will
  attack the antigens before the body has a chance
  to make them so the mother wont have memory cells
  against the antigens.

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Autoimmunity

• During development of the T cells in the thymus
  have body cells presented to them so that they
  can learn to recognise self markers (not just
  MHC markers).
• In people with autoimmune diseases this screening
  process hasnt worked properly. This means they
  then have a T-cell that will work to destroy self
  tissue.
• This can be isolated and easily treated as in the
  case of diabetes.
• It can be difficult to treat if it affects large
  tissue types like Multiple Sclerosis.

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Immunodeficiency

• Two main types
• Primary immunodeficiency a child is born with a
  deficiency due to a genetic defect or
  developmental abnormality. As is the case of
  bubble babies.
• These children fail to develop either T or B
  cells and need to kept away from all forms of
  foreign antigens, hence they live in a bubble.

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Immunodeficiency cont.

• Secondary immunodeficiency is acquired as a
  result of severe stress or another disease as in
  AIDS
• The AIDS virus infects helper T cells which in
  effect renders the third line of defence useless.
• Death from AIDS is usually due to infections that
  the body cannot respond to.