Lecture # 6

Bio 347 Chapter #4: Antigens and Antibodies
I. Antigens
A. Factors influencing immunogenicity
1. Terminology: immunogenicity--immunogens, antigenicity--antigens, allerogenicity-allergens, tolerogenicity--tolerogens
2. Immunogen: Foreignness, Size, Chemical Composition, Degradability
3. Biological Systems: responders vs non-responders, dosage and route of
administration, adjuvants
B. Epitopes/antigenic determinants
1. B cell epitopes
a. usually hydrophilic surface amino acids (immunodominant)
b. topographical (native conformation)
c. multiple epitopes
2. T cell epitopes: recognize processed antigen, two interaction sites: MHC and TCR
C. Haptens
1. Hapten
2. Hapten-carrier conjugate (albumin or keyhole limpet hemocyanin (KLH)
3. Immune detection
II. Immunoglobulins: Structure and Function
A. Overview of antibody structure
1. Contributions from myeloma proteins
2. Contributions from inbred strains of mice
3. Variable versus constant regions
4. Phylogenetic trees
4. Mechanisms for explaining variable and constant regions
a. Allelic/mutation hypothesis
b. two genes/one polypeptide hypothesis
Typical Immunoglobulin (IgG): heavy and light chains, bispecific, variable versus
constant regions, domains, hinge region, F(ab)2 (pepsin); Fab & Fc (papain); heavy and light
C. Ig's: Classes (), Subclasses (), Types ()
D. allotype, idiotype, isotype
E. All antibodies:
1. are similar in overall structure
2. are composed of two identical heavy and two identical light chains
3. exhibit intra- and inter-chain disulfide bonding to give globular structure
4. possess immunoglobulin domains
5. belong to immunoglobulin superfamily
6. evolved from common ancestral gene
7. can be divided into distinct classes (isotypes) and subclasses
8. individuals express 1 x 107--- l x l09 different antibody molecules
F. Evolution of Ig’s
1. Ancestoral gene
2. How to establish evolutionary homologies: common functions, DNA & amino acid
homology, conserved regions, genetic alterations (deletions, duplications)
G. Immunoglobulin mediated effector functions
1. Opsonization--promotion of phagocytosis of antigens by macrophages
2. Activation of complement
3. Antibody-dependent cell-mediated cytotoxicity (ADCC)
H. Monoclonal antibodies: production and uses