Antigens
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Antigens. Jennifer Nyland, PhD Office: Bldg#1, Room B10 Phone: 733-1586 Email: [email protected] Teaching objectives. To compare and contrast immunogen , antigen & hapten To describe the factors influencing immunogenicity To define the chemical nature of immunogens

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Antigens

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Antigens

Antigens

Jennifer Nyland, PhD

Office: Bldg#1, Room B10

Phone: 733-1586

Email: [email protected]


Teaching objectives

Teaching objectives

  • To compare and contrast immunogen, antigen & hapten

  • To describe the factors influencing immunogenicity

  • To define the chemical nature of immunogens

  • To compare the structures of T-independent and T-dependent antigens

  • To introduce the concept of hapten-carrier conjugates and their structure

  • To characterize antigenic determinants

  • To define superantigens


Overview of the immune system

Overview of the immune system


Vocabulary

Vocabulary

  • Immunogen

  • Antigen (Ag)

  • Hapten

  • Epitope or antigenic determinant

  • Antibody (Ab)


Factors influencing immunogenicity

Factors influencing immunogenicity


Immunogenicity contribution of immunogen

Immunogenicity: contribution of immunogen

  • Foreignness

  • Size

  • Chemical composition

    • Primary structure --- sequence determinants

    • Secondary structure

    • Tertiary structure

    • Quarternary structure

Conformational

determinants


Immunogenicity contribution of immunogen1

Immunogenicity: contribution of immunogen

  • Foreigness

  • Size

  • Chemical composition

  • Physical form

    • Particular > Soluble

    • Denature > Native


Immunogenicity contribution of immunogen2

Immunogenicity: contribution of immunogen

  • Foreigness

  • Size

  • Chemical composition

  • Physical form

  • Degradability

    • Ag processing by Ag-presenting cells (APC)


Immunogenicity contribution of biological system

Immunogenicity: contribution of biological system

  • Genetics

    • Species

    • Individual

      • Responders vs Non-responders

  • Age


Immunogenicity method of administration

Immunogenicity: method of administration

  • Dose

  • Route

    • Subcutaneous > Intravenous > Intragastric

  • Adjuvant

    • Substances that enhance immune response to Ag


Chemical nature of immunogen

Chemical nature of immunogen

  • Proteins

  • Polysaccharides

  • Nucleic acids

  • Lipids

    • Some glycolipids and phospholipids can be immunogenic for T cells and illicit a cell-mediated immune response


Antigens t independent

Antigens: T-independent

  • Activate B cells without MHC class II T help

  • Polysaccharides

  • Properties

    • Polymeric structure

    • Polyclonal B cell activation, but poor memory

    • Resistance to degradation

  • Examples

    • Pneumococcal polysaccharide, LPS

    • Flagella


Antigens t dependent

Antigens: T-dependent

  • Require T help to activate B cells

  • Proteins

  • Structure

  • Examples

    • Microbial proteins

    • Non-self or altered-self proteins


Hapten carrier conjugates

Hapten-carrier conjugates

  • Definition

    • Ag only if bound to carrier protein

  • Structure

    • Native determinants

    • Haptenic determinants


Antigenic determinants recognized by b cells and ab

Antigenic determinants recognized byB cells and Ab

  • Composition

    • Proteins, polysaccharides, nucleic acids, haptens

    • Sequence (linear) determinants

    • Conformational determinants

  • Size

    • 4-8 residues


Antigenic determinants recongized by b cells and ab

Antigenic determinants recongized byB cells and Ab

  • Composition

  • Size

  • Number

    • Limited (immunodominantepitopes)

    • Located on the external surface of the Ag (exposed)


Antigenic determinants recognized by t cells

Antigenic determinants recognized byT 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 MHC


Superantigens

Superantigens

Ag

T cell

T cell

  • Definition

    • Polyclonal T cell response

  • Examples

    • Staphlycoccal enterotoxins

    • Toxic shock toxin

TCR

TCR

SuperAg

MHC

MHC

APC

APC


Summary of immune response

Summary of immune response

  • Adaptive immune response

    • Discrete determinants

    • Reacts with specific pathogen

  • Innate immune response

    • Broad molecular patterns

    • Reacts with a variety of pathogens


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