GM4085 Principles of Biomedical Science for Nursing

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GM4085 Principles of Biomedical Science for
Nursing

• Unit 4. Introduction to Immunology
• Lecture 7
• Antibodies and Antigens
• Click mouse to begin

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Specific and Non specific Immune Responses

• We can roughly divide our immune response into
• Non-specific responses pathogens are recognised
  as foreign and destroyed
• Specific responses pathogens are recognised by
  their species and a response specific to that
  pathogen is initiated

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Non specific Immune Responses

• Pathogens may enter the body via a portal or
  through breach of our defences
• Non-specific immune defences can very quickly
  deal with foreign invaders
• Inflammation is a non-specific response
• Can you remember some physical barriers to
  infection?

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Antigen

• Specific and Non specific Immune Responses both
  depend on the body recognising pathogens such as
  bacteria and viruses
• They do this by recognising the ANTIGEN on the
  pathogen

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What is Antigen?

• Glycoproteins found on the cell membrane that act
  as recognition markers for the immune system
• Antigens can be self so the immune system knows
  that the cell is one of ours
• Antigens can be non-self and the immune system
  recognises them as foreign and starts an immune
  response

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What is Antigen?
Membraneglycoproteinsact as antigen markers
Cell
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What is Antigen?
Macrophage checks the antigen on a cell
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What is Antigen?

• If the antigen is self then the immune system
  ignores it
• If the antigen is found on a non-self cell such
  as a bacterium then the immune system destroys
  the cell
• Can you think of a non-self cell that we would
  not want destroyed?
• Transplanted organs and tissue

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Specific Immune Responses

• Our specific immune system recognises and
  responds to specific antigen from specific types
  of pathogens
• T and B Lymphocytes (B cells and T cells) play a
  major role in our specific responses
• Produced in the bone marrow they mature either in
  the Bone marrow or Thymus
• Mature B and T cells live in the lymph nodes

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Specific Immune Responses

• When mature, T and B cells become IMMUNOCOMPETENT
• These lymphocytes recognise specific antigen
• They can recognise any pathogen that infects the
  body
• Antigen is brought to the lymph nodes by the
  lymphatic system

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B Lymphocytes

• A B cell has surface receptors that bind to a
  specific antigen
• Binding to an antigen activates the B cell
• The B cell will then multiply, forming an army of
  identical clones (plasma cells)
• These clones produce ANTIBODIES that target the
  activating antigen

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B Cells and Antibodies
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Antibodies (Immunoglobulins)

• Antibodies receptors bind to the same antigen
  that activated their parent B Cell
• These receptors are called antigen recognition
  sites, or antigen binding sites
• The binding of an antibody to an antigen creates
  an antigen-antibody complex
• This complex is a marker that identifies cells to
  be destroyed by other immune cells such as
  phagocytes

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Types of Antibody

• We have 5 different types of antibody, playing
  slightly different roles, but they all have a
  common structure.

The antigen binding site is located on a hinged
arm. The hinge makes it easier to bind to
multiple antigens
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Types of Antibody 2
Dimeric - IgA

• IgA
• Important role in respiratory infections.
  Secretions (mucus, saliva) contain large amounts
• IgD
• Possible role in regulating B cell activity?
• IgE
• Activate mast cells
• IgG
• The most abundant antibody. Very effective at
  binding to bacteria, viruses and toxins
• IgM
• Activates complement

Monomeric - IgD, IgE IgG
Pentameric - IgM
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What do antibodies do?

• Antibodies do not destroy the pathogens
  themselves
• Antibodies bind to bacteria, preventing them from
  moving or multiplying - agglutination
• Antibodies attract other leukocytes and stimulate
  phagocytosis - opsonisation
• Antibodies bind to bacterial flagella and
  immobilise them
• Antibodies neutralise viruses and toxins,

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Agglutination by Antibodies
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T Lymphocytes I

• T cells are particularly effective against
  viruses
• Viruses parasitise cells and T cells kill viruses
  by killing the cells they have infected
• There are different types of T cell
• CD4 T cells recognise antigen and activate CD8 T
  cells
• CD8 T cells destroy virally infected cells

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T Lymphocytes II

• Antigen presenting cells ingest antigen and
  present it to the CD4 T cells in the lymph nodes
• CD4 T cells recognise the antigen and activate
  CD8 T cells via interleukins
• CD8 T cells move into the blood stream and locate
  infected cells
• They kill infected cells by releasing perforins
  and other enzymes

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Action of T Lymphocytes
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Immunological Memory

• When exposed to antigens, the specific immune
  system creates MEMORY CELLS
• Both B and T Cells retain memory
• Should the antigen be encountered again in the
  future, they mount a very effective response
  system that targets the culprit
• This immune response is much larger and more
  effective than the first encounter

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Immunological Memory

• The process of B cell proliferation and the
  making of antibodies and memory cells may take
  several days
• This is described as the primary immune response
  .
• We may have symptoms for some days before the
  immune system develops sufficiently to overcome
  infection by the pathogen

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Immunological Memory

• Once the memory cells are created, they remain
  alert, ready to act when required.
• Any subsequent exposure to the same pathogen will
  result in a more rapid and more extensive immune
  response termed the secondary immune response
• The memory cells recognise the antigen and
  stimulates the production of new T cells and
  antibodies quickly - within hours

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Immunisation

• To protect against infectious diseases, the
  immune system is primed with an immunogen that
  stimulates a primary immune response.
• Vaccinations involve the administration of
  immunogens, in the form of weakened (attenuated)
  infectious agents - a vaccine
• The body is tricked into thinking it has been
  infected by the bacteria or virus represented by
  the immunogen.

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Immunisation

• B and T Cells memory cells are primed by the
  vaccine and are waiting for the next attack from
  the bacteria or virus
• When next we are infected by the bacteria or
  virus, the immune system mounts a rapid and
  devastating attack
• The pathogens are killed before they can multiply
  and cause infection

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Primary and Secondary Responses
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Booster vaccinations
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The ABO System

• There are 4 main blood groups

A
B
AB
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A persons blood group is determined by the
antigen that is expressed on the surface of their
erythrocytes.
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Erythrocyte antigens

• There are just 2 erythrocyte antigens
• A antigen
• B antigen
• It goes like this.
• Blood group A has A erythrocyte antigen
• Blood group B has B erythrocyte antigen
• Blood group AB has A B erythrocyte antigens
• Blood group O has no erythrocyte antigen

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Erythrocyte Antibodies

• Antibodies that recognise A and B antigens
  circulate in the blood
• It goes like this
• Blood group A has anti-B plasma antibody
• Blood group B has anti-A plasma antibody
• Blood group AB has no plasma antibody
• Blood group O has anti-A anti-B plasma antibody

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Summary of ABO antigens and antibodies
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Summary of ABO antigens and antibodies
A

B
A
B
none
AB
none
AB
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Blood transfusions

• When blood is transfused, it is essential that
  the donor and recipient are compatible
• If the donated blood contains antigen
  incompatible with the recipients antibody, an
  immune reaction will result.
• The antibodies will bind to the antigen, causing
  agglutination of the blood cells

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Agglutination of RBCs

• B blood group has been transfused into a person
  of blood group A

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Blood donors and recipients
A and AB
A and O
B and O
B and AB
A and B and AB and O
AB
A and B and AB and O
O
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Transfusion reactions

• Inappropriate transfusions not only cause
  agglutination of erythrocytes but also activate
  complement
• The donated erythrocytes will rupture due to this
  immune attack
• It is the donated erythrocyte antigens that must
  be compatible
• Any incompatible antibodies are so dilute they do
  not cause a reaction