Principles of Immunology Antigens 2/9/06 “It is only when you give of yourself that you truly give.” K Gibran

Word List  Adjuvant  Antigen  Epitope  Hapten  Immunogen  Xenogeneic

Antigens  Antigen-Antibody-generating substance  Antigen-A substance that will bind to antibody  Immunogen-A substance that will elicit an immune response

Antigenic Macromolecules  Antigens are generally proteins or polysaccharides.  Lipids are not generally immunogenic (or antigenic) unless they are complexed with proteins or polysaccharides

Types of Antigens  Autoantigens-”self”  Alloantigens-”same species”  Heteroantigens-”different species”  T-cell dependent antigens-Requires T cell involvement; proteins  T-cell independent antigens-Does not require T cell involvement; polysaccharides

Properties of Immunogenicity  Degree of “foreignness”-Based on genetic relatedness  Molecular Size-Usually MW >100,000; <10,000 non immunogenic; 10, ,000 MW is imunogenetically variable

Properties of Immunogenicity  Chemical composition-Proteins; Primary, secondary, tertiary and quaternary structure all contribute. Haptens  Ability to be processed by APCs- Function of size

Biological Influences on Immunogenicity  Genotype of host-Expression of MHC genes  Dose of route of antigen presentation Immunological tolerance Vaccines Lymph or circulatory system

Biological Influences on Immunogenicity  Adjuvants-Enhance immunogenicity Potential mechanism  Ag persistence  Cell signaling or cytokine effect  Induction of inflammation  Lymphocyte stimulation Types  Alum  Freund’s incomplete adjuvant  Freund’s complete adjuvant

Epitopes  The active region of an immunogen (One antigen may have multiple epitopes)

Ag/Lymphocyte Interaction

Ag/T Lymphocyte Interaction  Ternary complex TCR MHC II molecule Antigen (peptide) Also includes Co-receptor - CD4