exam 2

• Antigen


  Any substance that binds to a specific antibody or TCR
• Innate immunity


  • Responses occur within mins/hrs
  • Uses broad, limited patterns
  • Does not have a memory component
  • Employs phagocytes (Neutrophils, mast cells, dendritic cells, and natural killer cells)
• Types of epitopes B cells and T cells interact with

  • B-cells can bind to soluble antigens and do not require an APC to give them antigens (highly accessible). Conformational and Linear.
  • T-cells can only receive an antigen from an APC (enzyme by digestion). Linear only.
  • Both can be linear
• Epitopes


  Discrete portions of an antigen that react with an antibody or TCR (antigenic determinant)
• Both innate and adaptive immunity

  Can employ NK cells and T cells
• Immunogenicity


  Ability of an antigen to elicit an immune response
• Immunogen


  Substance capable of eliciting an immune response
• Large, foreign, and chemically complex molecules make the best immunogens
• General properties of immunogenicity

  • Foreignness
  • Tolerance
  • Molecular size
  • Complexity
  • Processing and presentation
• Membrane-bound antibody vs. soluble antibody

  Membrane-bound antibodies have FC regions that anchor them to the membrane. Soluble antibodies are not bound. RNA splicing causes variability
• Structure of an antibody

  • Immunoglobulin=antibody
  • Two heavy chains
  • Two light chains
  • Held together by intra/interchain bonds disulfide covalent bonds
• Antibody-mediated effector functions

  1. Neutralization: binding and blocking receptors that pathogen uses to enter a cell. This blocks the packaging of viral components and blocks membrane and virus fusion. It prevents the release of viral progeny.

  2. Opsonization: promotion of phagocytosis
• Classes of antibodies (immunoglobulins)


  • IgG: Most abundant (75-80%), main job opsonization, activates the complement system, crosses the placenta for fetal immunity
  • IgM: Pentamer, 1st class produced in response to an antigen, activates complement system
  • IgA: Dimer, predominant class in secretions, found in breast milk, saliva, mucous, and tears
  • IgE: Responsible for hypersensitivity reactions (allergies)
  • IgD: Major membrane-bound immunoglobulin expressed by mature B cells
• Antibody-mediated effector functions

  1. Neutralization: Binding and blocking receptors that pathogen uses to enter a cell, blocking the packaging of viral components and membrane and virus fusion, preventing the release of viral progeny

  2. Opsonization: Promotion of phagocytosis of antigens by macrophages and neutrophils through Fc receptors

  3. Activation and assistance of the complement system: Fixing complement by binding to pathogen and initiating the complement cascade, tagging as an altered self-cell

  4. ADCC (Antibody Dependent Cell Mediated Cytotoxicity): Antibody-antigen complexes bound by Fc receptors on NK cells and granulocytes, leading to the release of perforin, proteases, and granzymes inducing programmed cell death (apoptosis)
• Isotypes vary in the constant region with differences in the heavy chain (5 types)
• Idiotypes have an antigenic determinant that differs, with a unique binding site
• Allotypes are allelic differences
• Humoral immunity is host defenses mediated by antibodies present in plasma, lymph, and tissue fluids
• Cellular immunity is host defenses mediated by antigen-specific T cells and various nonspecific cells of the immune system
• There is a complex interaction between the T cell and target and/or APC during antigen presentation. What is the role of each of the following in this process? TCR? MHC + antigen? CD4/8? CD3? Are other molecules involved? What is the effect of this interaction? How is the effect different between helper T cells and cytotoxic T cells?

  TCR: Aids in binding to the antigen.

  MHC and antigen: holds and displays fragments of antigen so that approaching T cells can engage with T cell receptors

  CD8: cytotoxic function, class 1.

  CD4: helper function, class 2.

  CD3: involved in the signal transduction.