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Immunoglobulin

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Immunoglobulin, Antibody, Fragment Antigen Binding, Immunoglobulin Fab Fragment, Fragment Crystallizable, Immunoglobulin Fc Fragment, Ligand, Humoral Immunity, Immunoglobulin Constant Region, Immunoglobulin Variable Region, Immunoglobulin Heavy Chain, Immunoglobulin Light Chain, Immunoglobulin J-Chain

  • Definitions
  1. Fragment Antigen Binding (Fab)
    1. Antibody region that recognizes and binds Antigens
  2. Fragment Crystallizable (Fc)
    1. Antibody region that interacts with Immune System components
    2. Endogenous Fc triggers Natural Killer Cells and complement cascade
    3. Synthetic monoclonal antibodies may bind Fc to toxins or radioisotopes in Chemotherapy
  3. Ligand
    1. Molecule that binds to a specific receptor
  4. Humoral Immunity
    1. Humoral Immunity (i.e. B-Cells and antibodies) targets extracellular pathogens
    2. Part of Adaptive Immunity (learned Immunity) in combination with cellular Immunity (T-Cell function)
  • Physiology
  • B-Cells
  1. Derivation
    1. Fetal Liver
    2. Bone Marrow Pluripotent Stem Cells
  2. Peripheral Migration to Secondary Lymphoid Tissue
    1. Spleen
    2. Lymph Nodes
    3. Peyer's Patches (Small Bowel)
  3. Activation
    1. Recognition
      1. Antigen binds B-Lymphocyte Surface Receptor (BCR)
      2. BCR binding activates B-Lymphocyte
        1. T-Cell Independent Antigen (e.g. inert Antigens) alone activate B-Cells
        2. T-Cell Dependent Antigen (e.g. microbes) require added stmulus (e.g. T Cells)
    2. B-Cell Proliferation
      1. Activated Lymphocytes proliferate
    3. B-Cell Differentiation
      1. Plasma Cells (Antibody producing cells)
        1. Survive for days to weeks producing antibodies, and without replicating
      2. Memory Cells
        1. Remain in B-Lymphocyte pool ready to respond to the same Antigen in future
        2. Future Antigen response is known as secondary immune response
  • Physiology
  • Immunoglobulin
  1. Images
    1. idAntibody.jpg
  2. Immunoglobulins (or antibodies) are Y-Shaped glycoproteins generated by Plasma Cells
  3. Immunoglobulin is composed of a 4 chain monomeric structure
    1. Two heavy chains (identical)
      1. Five heavy chain classes: M, D, E, A, and G1-4
    2. Two light chains (identical)
      1. Two light chain classes: kappa and lambda
  4. Immunoglobulin stem (Fc) is composed of 2 identical heavy chains
  5. Two Immunoglobulin Arms emanate from the stem
    1. Each arm is composed of 2 heavy chains and 2 light chains
    2. The end of each arm contains an Antigen binding site (Fab)
  6. Immunoglobulins have 2 forms
    1. Membrane bound Immunoglobulins (on surface of B-Cell)
    2. Secretory Immunoglobulin (unbound, free-floating)
      1. Monomeric antibodies exist as single Antibody molecules (IgE or IgG)
      2. Multimeric antibodies exist as multiple joined antibodies (IgA or IgM)
        1. Connected with J Chains
    3. Antibodies
      1. Immunoglobulin (Ig)
  • Types
  • Immunoglobulins
  1. Immunoglobulin G (IgG and subclasses IgG1-4)
    1. Monomer with Molecular weight 160,000 dalton
    2. Accounts for 75% of all Antibody
    3. Serum half-life of 23 days
    4. Responsible for long lasting Immunity (secondary immune response) and Type 2 Hypersensitivity
  2. Immunoglobulin A (IgA and subclasses IgA1, IgA2)
    1. Dimer (2 Antibody molecules) when secretory Ig with Molecular weight 350,000 dalton
    2. Accounts for 10-15% of all Antibody
    3. Serum half life of 6 days
    4. Present in body secretions (e.g. tears, Saliva, milk) and responsible for mucosal Immunity
  3. Immunoglobulin M (IgM)
    1. Pentamer (5 Antibody molecules) when secretory Ig with Molecular weight 900,000 dalton
    2. Responsible for early, primary Antibody response
  4. Immunoglobulin E (IgE)
    1. Long stem (Fc) monomeric Antibody with Molecular weight 180,000 dalton
    2. Serum half-life of 2.5 days
    3. Reacts to allergans (Type 1 Hypersensitivity) and Parasitic Infections
  5. Immunoglobulin D (IgD)
    1. Monomer with Molecular weight 160,000 dalton
    2. Serum half life of 3 days
    3. Membrane bound surface Antibody
  • References
  1. Bakerman (1984) ABCs of Interpretive Lab Data, p. 392
  2. Mahmoudi (2014) Immunology Made Ridiculously Simple, MedMaster, Miami, FL