Immunogenetics

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Immunogenetics

• Genetic Changes that Provide for Homology and
  Diversity Among Immune System Proteins

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Immune System Cells and Receptors
Stimulate an immune response
Antibody
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Communication Among Immune System Cells
1. Macrophage engulfs invader
2. Macrophage displays processed antigen on MHC
molecule
7. Division gives rise to memory B cells and
plasma cells
6. Activated Helper T cell stimulates division of
selected B lymphocyte
4. Helper T Cell binds to Macrophage
3. Invader binds to B lymphocyte that carries
antibody matching the antigen
5. Macrophage releases cytokines to activate
Helper T cell
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Clonal Selection of B cells
Each B lymphocyte has a unique antibody on its
surface
B lymphocyte with antibody matching the antigen
is stimulated to divide
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(No Transcript)
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Applying Your Knowledge

• T cell receptor
• MHC Protein
• Antibody
• All of these are correct.
• None of these is correct.

• Which one is used to display antigen on the
  surface of a macrophage?
• Which one is secreted by plasma cells?
• Which one recognizes displayed antigen on the
  surface of a macrophage?

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Antibody Structure

• Antibody has 2 heavy chains and 2 light chains.
• Each chain has variable (V) and constant (C)
  region joined by a J region.
• Variable regions bind to antigen.
• Constant regions bind to cells or other
  antibodies.

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Structure and Expression of Light Chain Genes
30-50
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Somatic recombination brings one V and one J
segment together
RNA Processing leads to one VJC combination
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Structure and Expression of Heavy Chain Genes
27 D
6J
51 V
Somatic recombination brings one V, D and J
segment together near a C segment
RNA Processing leads to one VDJC combination
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Somatic Recombination
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Generating Antibody Diversity
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Applying Your Knowledge

• Junctional Diversity
• Germ Line Diversity
• Somatic Recombination
• Somatic Hypermutation

• Which choice best explains or causes
• The presence of multiple V, D and J segments in
  DNA of precursors to B cells?
• The increase in variability of V regions as the
  immune response progresses?
• The formation of unique VJC combinations for
  heavy and light chains?

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How did the arrangement of antibody genes arise?

• Changes in gene number and organization are due
  to
• Duplication
• Diversification
• Selection

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Levels of Duplication
Individual Genes
Multigene Families
Gene Superfamily
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Action of Natural Selection

• Natural selection acts on the genetic variability
  caused by mutation

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Three Multigene Families Encode Antibodies
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Immune System Receptors Belong to the
Immunoglobulin Gene Superfamily

• A Gene Superfamily is a large set of related
  genes that is divisible into smaller sets or
  families
• Genes in each family are more closely related to
  each other than to genes in other families
• Multigene families within this Superfamily
• Antibody Genes
• T cell receptor genes
• MHC protein genes

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Immunoglobulin Superfamily Genes Share a Common
Homology Unit
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Applying Your Knowledge

• Duplication
• Diversification
• Selection

• Which process would lead to different sequences
  for V regions of IgM and TcR?
• Which process causes an increase in the number of
  homology units?
• Which process would establish a new variant of
  the homology unit as part of the gene family?