Specific Immunity

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Specific Immunity
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Who are the players?

• Antigens foreign proteins, usually part of
  virus or bacteria
• Antibodies Proteins made by immune cells that
  recognize or bind with particular antigens.
  Original diversity of antibody-producing cells
  depends on recombination of genetic sequences
  during cell development
• Macrophages phagocytic cells in blood)
• Cytotoxic T-cells killer white blood cells
• Helper T-cells present antigens so that good
  match can be found among antibody-making cells
• B-cells recognize antigens and make antibodies
• MHC Major Histocompatiblity Complexallows body
  to recognize own cells so that their proteins
  dont trigger immune response, also important in
  clonal selection
• Clonal selection process by which B and T-cells
  that make antibodies that recognize bodys own
  antigens (autoantigen) are eliminated during
  development.

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Antigens

• Proteins (or sometimes carbs) that are recognized
  (glom onto) specific antibody
• Exogenous antigens On outside or free of
  pathogen
• Endogenous antigens From pathogens that live
  and reproduce inside host cell. Immune cells can
  only see these antigens when they are presented
  on surface of host cell surface, incorporated
  into cell membrane
• Auto-antigens Bodys own antigens. Immune
  cells that recognize these antigens are
  eliminated during immune system development (by
  antibody editing or clonal selection/deletionmore
  below)

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Antibodies

• Each antibody has specific antigen binding site
  formed by variable regions of heavy and light
  amino acid chains. Variation among antibodies in
  these binding sites comes from random
  recombination from billions of possible DNA/gene
  combinations.
• Rest of heavy and light chains are constant
  giving antibodies their characteristic shape and
  function

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What do antibodies do?

• Disable pathogens by glomming (agglutinating)
  them together
• Neutralize toxins by glomming onto them on the
  surface of pathogens
• Stick to surface of pathogen so it can be
  recognized by phagocytic cells
• Immunoglobulins are classes of antibodieseach
  class has more specific immune function

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Macrophage on the attack!!
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Where do antibodies come from?

• Made by B-cell lymphocytes
• 1011 B-cells in body, each with specific
  antibody, present for life
• Each B-cell has 100,000s of copies of its
  antibody embedded in cell membrane, called B-Cell
  Receptors (BCR)
• When a BCR reacts or gloms onto an antigen that
  it recognizes, that cell iss timulated to produce
  free antibodies that are secreted into blood as
  immunoglobulin (Ig)

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Antibody editing by clonal selection or deletion

• Variety of B-cells produced by random
  recombination of genes for variable regions of
  antibody
• During B-cell development, certain clonal lines
  are eliminated because their antibodies glom onto
  the bodys own antigens
• B-cell production and clonal selection occurs in
  bone marrow during early years of life

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B-cell and antibody immune function simple,
right?

• Each B-cell make specific antibody which is
  present on cell surface as BCR (B cell receptor)
• When that cell recognizes an antigen (the
  antigen sticks to the BCR), then it begins
  producing free antibody (immunoglobulins or Igs)
  to secrete into the blood
• Those Igs work to eliminate the source and
  possible damage caused by this antigen via
  agglutination, neutralization and opsonization
• BUTusually B-cells cannot recognize antigens on
  their ownand the simple antibody response is
  usually sufficient to fight an infection.
• THUST-cells (oh, no).

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T-cell lymphocytes

• Also made in bone marrow, but mature in thymus
  (thus T)
• Have TCR (T-cell receptor), much like BCR), but
  dont produce Igs
• Also about 1011 T-cells, each with its own
  specific antigen recognition site, produced by
  random recombination of genetic sequence and
  edited via clonal selection in thymus
• 90 of lymphocytes in blood are T-cells. Also in
  lymph nodes, spleen, Peyers patches of
  intestines
• Three types of T-cells

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Cytotoxic T-cells (CD8)

• Recognize and kill other cells of the bodywhy?
• Those cells are infected by virus or other
  intra-cellular pathogen
• Cells process antigen from virus and present
  it on cell surface embedded in cell membrane so
  that TCRs or antibodies can recognize that
  non-self antigen

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Helper T-cells (CD4)

• Type 1stimulate cytotoxic T-cells
• Type 2stimulate B-cells
• Helper T-cells recognize antigens, but can do
  nothing about it on their own. They secrete
  cytokines (such as interleukin) to direct what
  kind of immune response should be activated.
• For most infections, Helper Ts are crucial for a
  robust response.
• Thus, in AIDS, these cells are killed, as they
  themselves present viral antigens and invite
  cytotoxic T-cells or macrophages to ingest them.
• Without the helper T-cells, good response to most
  infections cannot be mounted.

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Antigen processing and MHC

• Phagocytes that have ingested pathogens, as well
  as cells infected with virus can process and
  present antigens on their cell membrane
• MHC molecules aid in this process
• By presenting antigens, the immune response is
  greatly accelerated
• Especially important in stimulating early
  response to previous pathogens (immunological
  memorycoming next!)

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Antigen processing and MHC
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Review specific immune response

• From the molecules of HIV text
• http//www.mcld.co.uk/hiv/?qhelper20T20cells

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Nice graphics and animations
http//science.nhmccd.edu/biol/inflam.html
http//fajerpc.magnet.fsu.edu/Education/2010/2010_
INDEX.HTM