4th hour

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4th hour

• By the end of the lesson, students should be able
  to
• describe and explain the primary and secondary
  immune responses to antigen
• explain the concept of self and non-self
  recognition and its application in organ
  transplant, grafting and blood transfusion

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IMMUNOLOGICAL MEMORY
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Primary and secondary response

• When a person is exposed to an antigen for the
  first time, there is a lag of several days before
  specific antibody becomes detectable. This
  antibody is IgM.
• After a short time, the antibody level declines.
  These are main characteristics of the primary
  response.

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• If, at a later date he or she is re-exposed to
  the same antigen, there is a far more rapid
  appearance of antibody, and in greater amount. It
  is of the IgG class and remains detectable for
  months or years. These are the features of the
  secondary response.
• If, at the same time that he is re-exposed to an
  antigen, he is exposed to a different antigen for
  the first time, the properties of the specific
  response to this antigen are those of the primary
  response.

Memory cell
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The Primary and secondary immune responses
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Putting the two together to explain graph
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• If a second dose of the same antigen is given
  days or even years later, an accelerated 20 or
  anamnestic immune response (IR) occurs. This lag
  phase is usually very short (e.g. 3 or 4 days)
  due to the presence of memory cells.

• Following the first exposure to a foreign
  antigen, a lag phase occurs in which no antibody
  is produced, but activated B cells are
  differentiating into plasma cells. The lag phase
  can be as short as 2-3 days, but often is longer,
  sometimes as long as weeks or months.

2. The amount of antibody produced is usually
relatively low.
2. The amount of antibody produced rises to a
high level.
3. Over time, antibody level declines to the
point where it may be undetectable.
3. Antibody level tends to remain high for longer.
4. The main type of antibody produced is IgG
(although small amounts of IgM are sometimes
produced).
4. The first antibody produced is mainly IgM
(although small amounts of IgG are usually also
produced).
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Example of vaccination for health (doses of
antigen)
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Doses of antigen
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Self and non-self recognition
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Major Histocompatibility Complex (MHC)

• The ability of the vertebrate immune system to
  distinguish self from non-self depends on a group
  of membrane protein known as Major
  Histocompatibility Complex (MHC)
• HLA system ( human leucocyte antigen system)
• - A series of four gene loci (A,B,CD) in humans
  that code for a group of glycoproteins, present
  on the surface of cell membranes that act as
  antigents and are important in determining the
  acceptance or rejection by the body of a tissue
  or organ transplant.

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• These antigents are one group of
  histocompatibility. Successful transplantation
  requires a minimum number of HLA differences
  between the donors and recipients tissues.
• These markers are present on the surface of most
  cells slightly different in each individual
• No two people (except identical twin) are likely
  to have the same MHC protein on their cells

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• The more closely related two individuals are,
  the more HLA antigens they have in common
• 3 group of MHC MHC class I, MHC class II MHC
  class III
• MHC class I antigens are found on most nucleated
  cells and are important in distinguishing between
  self and non-self

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• MHC class II antigens are found only on cells of
  the immune system, particularly B cells,
  macrophages, some T cells and dendritic cell
• MHC class III proteins include components of the
  complement system

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Tissue rejection

• Certain organs such as skin, the heart and
  kidney, could be transplanted easily from one
  person to another if the body did not attempt to
  reject them
• Rejection occurs because antibodies cytotoxic T
  cells bring about destruction of foreign tissue
  in the body
• When rejection occurs, the immune system is
  correctly distinguishing between self and
  non-self

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• This problem can be controlled by carefully
  selecting the organ to be transplanted and
  administering immunosuppressive drugs
• It is best if the transplanted organ has the same
  type of HLA antigens as those of the recipient
  because cytotoxic T cells recognize foreign HLA
  antigens

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ORGAN TRANSPLANT (liver)
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Application in Grafting

• Grafting an isolated portion of living tissue
  that is joined to another tissue, either in the
  same of a different organism (process of joining
  the tissues).
• Animal and human grafts are used to replace
  faulty or damaged parts of the body. Eg skin
  graft used for severe burns.

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Example

• Autograft - tissue grafted from one area to
  another on the same individual. Rejection is not
  a problem. Skin grafting.
• Isograft- a graft between two genetically
  identical individuals such as identical twins.
  Rejection nat a problem
• Allograft- a tissue grafted from one individual
  to genetically different individual of the same
  species
• Xenograft- a graft between individuals of
  different species such as from pig to human.

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This happens when there is graft rejection

• Tissue from donor transplanted into body of
  recipient ?Tc cells recognize MHC antigens on
  transplant cells as foreign? Tc cells launch
  immune response (graft rejection) ? Tc cells
  destroy transplant.

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Prevention

• Tissues matching- obvious and necessary
  precaution before any surgery.
• Exposure of bone marrow lymph tissues to
  radiation by X-rays tent to inhibit production
  white blood cell.
• Two well-known immunosuppressive drugs
  Cyclosporine and Tacrolimus. Both act by
  inhibiting the response of T cells to cytokines.

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Blood transfusion

• When a patient receives a blood transfusion it is
  vital that they receive blood that is compatible
  , a type of immune response occurs
• Two antigen exist, A and B
• The complementary antibodies a and b
• A person with specific antigen in the red cells
  does not possess the corresponding antibodies in
  the plasma

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• Eg anyone with antigen A in the red membranes
  has no antibody a in the plasma is called blood
  group A person
• If both antigen presence is known as blood group
  AB and if there is no antigen it is refer as
  blood group O

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