Antigens

1
Antigens

• Jennifer Nyland, PhD
• Office Bldg1, Room B10
• Phone [phone]
• Email jnyland_at_uscmed.sc.edu

2
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

3
Overview of the immune system
4
Vocabulary

• Immunogen
• Antigen (Ag)
• Hapten
• Epitope or antigenic determinant
• Antibody (Ab)

5
Factors influencing immunogenicity
6
Immunogenicity contribution of immunogen

• Foreignness
• Size
• Chemical composition
• Primary structure --- sequence determinants
• Secondary structure
• Tertiary structure
• Quarternary structure

Conformational determinants
7
Immunogenicity contribution of immunogen

• Foreigness
• Size
• Chemical composition
• Physical form
• Particular gt Soluble
• Denature gt Native

8
Immunogenicity contribution of immunogen

• Foreigness
• Size
• Chemical composition
• Physical form
• Degradability
• Ag processing by Ag-presenting cells (APC)

9
Immunogenicity contribution of biological system

• Genetics
• Species
• Individual
• Responders vs Non-responders
• Age

10
Immunogenicity method of administration

• Dose
• Route
• Subcutaneous gt Intravenous gt Intragastric
• Adjuvant
• Substances that enhance immune response to Ag

11
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

12
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

13
Antigens T-dependent

• Require T help to activate B cells
• Proteins
• Structure
• Examples
• Microbial proteins
• Non-self or altered-self proteins

14
Hapten-carrier conjugates

• Definition
• Ag only if bound to carrier protein
• Structure
• Native determinants
• Haptenic determinants

15
Antigenic determinants recognized byB cells and
Ab

• Composition
• Proteins, polysaccharides, nucleic acids, haptens
• Sequence (linear) determinants
• Conformational determinants
• Size
• 4-8 residues

16
Antigenic determinants recongized byB cells and
Ab

• Composition
• Size
• Number
• Limited (immunodominant epitopes)
• Located on the external surface of the Ag
  (exposed)

17
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

18
Superantigens

• Definition
• Polyclonal T cell response
• Examples
• Staphlycoccal enterotoxins
• Toxic shock toxin

19
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