Reminders

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Reminders

• Exam 3-
• Questions where mistake in key was corrected
• 10 answer AB is correct.
• 17 answer E is correct.
• Exam out of 98 points instead of 100.

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The humoral immune response

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Germinal center is an island of cell division.

• 90 B cells
• 10 T cells

• Centrocytes
• Cell division slows
• Increase expression of surface IgM IgD.

• Centroblasts
• divide every 6-8 hrs.
• Decrease expression of surface IgM IgD.

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• Proliferating centroblasts undergo somatic
  hypermutation.
• Mutation occurs every 2 divisions.
• Centrocytes undergo affinity maturation-
• Programmed to undergo apoptosis if they do not
• internalize process antigen
• engage a Th2 cell via CD40-CD40L interaction.

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FDC coat themselves in antigen

• Do not carry MHC class II.
• Do carry Fc receptors Complement Receptors (CR3)

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The follicular dendritic cells assists in helping
B cells find taste antigen.

• Iccosomes- Immune complex coated bodies

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Affinity maturation of centrocytes

• BclXL- death inhibiting protein prevents
  apoptosis.

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Following activation in the Germinal center, the
B cell may differentiate into a plasma cell or
memory cell
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Class Switching

• Th2 cells required
• CD40L interaction with CD40
• Cytokines

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Cytokines that drive class switching in mice

• Fig. 7.14, Parham (table)

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Antibodies with different constant regions have
different physical characteristics.
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The Effector Functions of Antibody
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Neutralization
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Opsonization
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Antibody Dependent Cell Mediated Cytotoxicity
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IgM

• Structure
• Each monomer is connected by disulfide bonds.
• J chain

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IgM Characteristics

• Produced by plasma cells in the LN, spleen,
  bone marrow
• Circulates in the blood (90) lymph (10)
• Large pentameric form impedes ability to move
  into extravascular sites.
• IgM is the first Ab to be produced.
• Low affinity, high avidity
• Produced prior to somatic hypermutation
  affinity maturation.
• Lacks of flexibility (no hinge).

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Fig 2-29

• IgM Immune Complex Formation

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IgG

• Most abundant Ab in blood, lymph, extracellular
  fluids in tissues.
• Produced in plasma cells located in LN, spleen,
  BM.
• Small size
• Easier access to extracellular spaces of tissue.
• Crosses the placenta.
• Flexible arm contributes towards IgG having more
  effector functions than IgM.

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• IgG is transported across the endothelium
• Brambell Receptor (FcRB) on endothelial cells.
• Placenta contains an FcRB receptor to transport
  IgG to the developing fetus.

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• IgG Immune Complex Formation

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IgA

• Monomer
• Plasma cells in the LN, spleen, BM secrete IgA
  into the blood.
• Dimer
• Plasma cells lining the mucosal associated
  lymphoid tissue.

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Characteristics of IgA

• Monomer IgA is found in the blood, lymph,
  extravascular spaces.
• Dimeric IgA is found on mucosal membranes in
  secretions
• Milk, saliva, tears, sweat, mucus
• 10-15 g of IgA is produced each day most is
  secreted.
• Transcytosis
• Epithelial cells carry receptor- poly Ig
  receptor.
• Binds IgA Fc

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Poly Ig Receptor bind the CH3 domain of the Fc
2.5X1010 plasma cells line the intestine
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The distribution of Ig
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The levels of Ig before after birth
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IgE

• Present in low amounts.
• Monomer form.
• Basophils, eosinophils Mast cells- Fc Receptors
  
• Mast cells
• Connective tissue
• along the blood vessels (dermis of the skin).
• of the gastrointestinal tracts respiratory
  tract.

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• Eosinophil attacking a schistosome larva

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IgD

• 0.2 of total Ig.
• Membrane bound
• Function?
• Activation of B cells?