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8/13/2019 02 Antigens
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Antigens
Jennifer Nyland, PhD
Office: Bldg#1, Room B10
Phone: 733-1586Email: [email protected]
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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
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Overview of the immune system
Immune system
Innate(nonspecific)
1stline of defense
Cellularcomponents
Humoralcomponents
Adaptive
(specific)
2ndline of defense
Cellularcomponents
Humoralcomponents
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Vocabulary
Immunogen
Antigen (Ag)
Hapten Epitope or antigenic determinant
Antibody (Ab)
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Factors influencing immunogenicity
Factors
Contribution
of
immunogen
Contribution
of biological
system
Method of
administration
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Immunogenicity: contribution of
immunogen
Foreignness
Size
Chemical composition Primary structure --- sequence determinants
Secondary structure
Tertiary structure
Quarternary structure
Conformational
determinants
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Immunogenicity: contribution of
immunogen
Foreigness
Size
Chemical composition Physical form
Particular > Soluble
Denature > Native
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Immunogenicity: contribution of
immunogen
Foreigness
Size
Chemical composition Physical form
Degradability
Ag processing by Ag-presenting cells (APC)
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Immunogenicity: contribution of
biological system
Genetics
Species
Individual
Responders vs Non-responders
Age
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Immunogenicity: method of
administration
Dose
Route
Subcutaneous > Intravenous > Intragastric
Adjuvant
Substances that enhance immune response to Ag
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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
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Antigens: T-independent
Activate B cells without MHC class IIT help
Polysaccharides
Properties
Polymeric structure
Polyclonal B cell activation, but poormemory
Resistance to degradation
Examples Pneumococcal polysaccharide, LPS
Flagella
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Antigens: T-dependent
Require T help to activate B
cells
Proteins
Structure
Examples
Microbial proteins
Non-self or altered-selfproteins
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Hapten-carrier conjugates
Definition
Ag only if bound to carrier protein
Structure
Native determinants
Haptenic determinants
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Antigenic determinants recognized by
B cells and Ab
Composition
Proteins, polysaccharides, nucleic acids, haptens
Sequence (linear) determinants
Conformational determinants
Size
4-8 residues
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Antigenic determinants recongized by
B cells and Ab
Composition
Size
Number Limited (immunodominant epitopes)
Located on the external surface of the Ag
(exposed)
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Antigenic determinants recognized 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 MHC
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T cell
TCR
T cell
TCR
APC
MHC
APC
MHC
Ag SuperAg
Superantigens
Definition
Polyclonal T cell
response
Examples
Staphlycoccal
enterotoxins
Toxic shock toxin
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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