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Immunogen and Antigen: Key Factors and Characteristics

Learn about the components, determinants, and factors influencing the immunogenicity of antigens and immunogens. Explore the types of antigens, antigenic determinants, and their recognition by the immune system. Understand the distinctions between T-independent and T-dependent antigens, as well as superantigens and determinants recognized by the innate immune system.

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Immunogen and Antigen: Key Factors and Characteristics

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  1. Overview of the Immune System

  2. Antigens

  3. Definitions • Immunogen • Antigen (Ag) • Hapten • Epitope or Antigenic Determinant • Antibody (Ab)

  4. Sequence determinants Conformational determinants Factors Influencing ImmunogenicityContribution of the Immunogen • Foreignness • Size • Chemical Composition • Primary Structure • Secondary Structure • Tertiary Structure • Quarternary Structure

  5. Factors Influencing ImmunogenicityContribution of the Immunogen • Foreigness • Size • Chemical Composition • Physical Form • Particulate > Soluble • Denatured > Native

  6. Factors Influencing ImmunogenicityContribution of the Immunogen • Foreigness • Size • Chemical Composition • Physical Form • Degradability • Ag processing by Ag Presenting Cells (APC)

  7. Factors Influencing ImmunogenicityContribution of the Biological System • Genetics • Species • Individual • Responders vs Non-responders • Age

  8. Factors Influencing ImmunogenicityMethod of Administration • Dose • Route • Subcutaneous > Intravenous > Intragastric • Adjuvant • Substances that enhance an immune response to an Ag

  9. Chemical Nature of Immunogens • Proteins • Polysaccharides • Nucleic Acids • Lipids • Some glycolipids and phosopholipids can be immunogenic for T cells and illicit a cell mediated immune response

  10. Types of AntigensT-independent • Polysaccharides • Properties • Polymeric structure • Polyclonal B cell activation • Yes -Type 1 (TI-1) • No - Type 2 (TI-2) • Resistance to degradation • Examples • Pneumococcal polysaccharide, lipopolysaccharide • Flagella

  11. Types of AntigensT-dependent • Proteins • Structure • Examples • Microbial proteins • Non-self or Altered-self proteins

  12. Haptenic determinants Native determinants Hapten-carrier conjugates • Definition • Structure • native determinants • haptenic determinants

  13. Antigenic Determinants Recognized by B cells and Ab • Composition • Proteins, polysaccharides, nucleic acids, haptens • Sequence (linear) determinants • Conformational determinants • Size • 4-8 residues

  14. Fe Antigenic Determinants Recognized by B cells and Ab • Composition • Size • Number • Limited (immunodominant epitopes) • Located on the external surfaces of the Ag

  15. Antigenic DeterminantsRecognized by T cells • Composition • Proteins (some lipids) • Sequence determinants • Processed • MHC presentation (lipid presentation by MHC-like CD1) • Size • 8 -15 residues • Number • Limited to those that can bind to MHC

  16. Superantigen Conventional Antigen Polyclonal T cell response 1:4 - 1:10 Superantigens • Definition Monoclonal/Oligoclonal T cell response 1:104 - 1:105

  17. Superantigens • Definition • Examples • Staphylococcal enterotoxins • Staphylococcal toxic shock toxin • Staphylococcal exfoliating toxin • Streptococcal pyrogenic exotoxins

  18. Determinants Recognized by the Innate Immune System • Adaptive Immune System – Discrete Determinants • Reacts with a specific pathogen • Innate Immune System – Broad Molecular Patterns • Reacts with a variety of pathogens

  19. Determinants Recognized by the Innate Immune System • PAMPs – Pathogen Associated Molecular Patterns • PRRs – Pattern Recognition Receptors

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